Science in Action: Encouragement of Plant and Mycorrhizal Relationships

                     Two of the most important relationships between microorganisms and domesticated plants are the relationships between the nitrogen-fixing bacteria called Rhizobia and the mycorrhizal fungi called VAM fungi with vascular plants. The relationship between Rhizobia and the so called nitrogen fixing plants such as the mesquite and acacia can be appreciated mostly from the research done on Rhizobia and leguminous crop plants like the peas and beans.  If a soil contains the Rhizobial bacteria, then legumes planted into that soil can benefit from this bacteria’s ability to take inert nitrogen gas from the air and oxidize it, or fix it, into nitrate, a form of nitrogen usable by the plant. Soil devoid of Rhizobial bacteria need to be inoculated with a “starter” population so that legumes planted in it can take full advantage of this symbiotic relationship and the “free” nitrogen it provides to the plant. Of course in return the bacteria in this relationship receive nutrients and other benefits from the plant.

                     But the discovery of mycorrhizal fungi is relatively new to researchers when compared to the time when nitrogen fixing bacteria were discovered and explored. Unlike Rhizobial bacteria which live in close association with legumes, VAM type of fungi infect almost all higher plants. Also unlike Rhizobia, VAM fungi penetrate the living cells of plants and form the organs called vesicles and arbuscles in the root. By doing so, the fungi link the plant to the soil, assisting in the transport of mineral nutrients, particularly phosphorus, to the plant. In return, carbon compounds from the plant are released into the soil where soil microorganisms rely on these compounds as an energy source. The plants in both cases become home to these invading microorganisms and a relatively safe and necessary place for them to live.

                     It is a widely held belief among researchers that VAM mycorrhizae can play an important role in poor or eroded soils. Researchers believe that VAM fungi can play a major role in increased agricultural production particularly when soil nutrients have been depleted. For this reason we might be able to imply their importance when establishing landscape plants in poor soils. The known roles of VAM fungi are the increased absorption of minerals, stimulation of growth, increased production, enhancement of resistance to environmental stresses and soil diseases.

                     Although VAM fungi stimulate phosphorus uptake of plants from the soil, over application of phosphorus to the soil actually inhibits VAM growth. Concentrations of phosphate phosphorus over 50 ppm in the soil have been reported to severely inhibit VAM colonization. However, the application of what we would consider normally insoluble phosphates, such as rock phosphate and bone meal, are effective to maintain VAM fungi. VAM fungi aid in making the application of this type of phosphorus, normally mostly unavailable to plants, available to the plant as a slow release source. An additional advantage of insoluble phosphate with VAM then is the long- term availability of phosphorus, compared to more soluble phosphates.

                     Besides increasing the availability of phosphorus to plants, VAM fungi-infected plants have high a potential for resistance to soil and environmental stresses. According to fossil records, VAM fungi infected roots of Early Devonian land plants over 400 million years ago. The Early Devonian period is recognized as a time when plants invaded the land from the oceans. Researchers have speculated that VAM mycorrhizae may have played an essential role in assisting ocean inhabiting plants in their advance toward terrestrial living by helping them to adapt to a new stressful and continuously changing environment. 

                     Poor soils include soils naturally devoid of organic matter either naturally or through erosion, and those intensively cultivated or subjected to excessive use of fertilizers and agrochemicals. In the past to maintain economic levels of productivity, farmers were forced to increase the use of inputs such as agrochemicals. With the use of VAM mycorrhizae, agricultural production inputs such as fertilizers and agrochemicals could be reduced. In landscapes, decreased use of chemicals such as fertilizers and pesticides would probably be standard practice. Instead, more concentration on enhancing the soil environment to promote soil microorganisms would be recommended.

                     In general, the population of VAM spores in poor soils, such as the soils damaged by severe dryness or erosion, is very low. VAM has been known to develop well in close association with grasses. Grasses are very effective for the revival of soil with low a density of VAM fungi. VAM develop well in orchards where grass is used for a sod. However, some growers believe that a clean culture, bare soil, is best for high quality. This is true among growers of landscape plants as well. Thus our soil management system must be re-evaluated in light of this information.

                     When concentrating on enhancing the soil environment for VAM development it was mentioned above that the amount of agrochemicals and applied chemical fertilizers be reduced. Other agrochemical inputs would have to be addressed as well. The application of several kinds of fungicides, such as copper fungicides, iprodione, iprodione-like compounds, benomyl and benomyl-like compounds, have been shown to severely inhibit VAM growth. The application of herbicides may also inhibit the intensity of VAM infection by decreasing the population of specific so called weeds which strengthen the activity of VAM fungi.

                     Although several kinds of VAM fungi have been known to have the resistance to adverse pH conditions, most of the VAM fungi are vulnerable to high pH soils, preferring pH ranges less than 7.5. The growth of VAM fungi also is poor in anaerobic soils. Although VAM fungi infect the roots of aerenchima-developing plants such as mangrove and paddy rice plants the percentage of VAM infection is generally low

                     The application of uncomposted organic matter severely inhibits VAM development. Applications of composted organic matter, however, stimulates VAM formation and the growth of plants. One of the VAM stimulators is low concentrations of ethylene. Ethylene evolves from composting organic matter and, at very low concentrations, may be effective for VAM growth. About 0.5 ppm ethylene gas stimulates VAM hyphal growth and VAM development in association with plants. But ethylene at concentrations above 0.5 ppm can depress hyphal growth and mycorrhizal formation. In soils with poor aeration where uncomposted organic matter has been applied, ethylene is often detected at concentrations high enough to inhibit VAM growth.

                     Activated charcoal incorporated into soils has been shown to be very effective in VAM development. But excess applications of charcoal may inhibit plant growth. The reason for this inhibition is not known but is thought to be associated with changes in the soil chemistry. Therefore, an appropriate amount of charcoal to be applied is less than eight tons per acre which works out to be somewhere around one third of a pound per thousand square feet. Zeolite is a mineral soil amendment which shows some promise in assisting with the development of mycorrhizae without the problems of that are associated with charcoal. It absorbs antagonists which inhibit VAM growth without the problems associated with charcoal.

Mycorrhizae - Some Background

Q. What are your thoughts on mychorizae?  I bought some a while back from T&J Enterprises out of Washington state, and the chiles seemed to do really well.  Is it an aid or just my imagination?

A. I have had some experience with mycrorrhizae in the past and if the soil is void of these critters then plants will definitely improve if some is added. But if the soil already contains the right kind of mycrorrhizae then it won’t do much.

Mycorrhizae should not cost so much and they go a long way in your soil since they multiply under good growing conditions. These are fungi that live in and around plant roots. In the past they were normally associated with better uptake of phosphorus but now they have had many other things attributed to them as well.

I always like to take a little bit of soil from where a plant was growing just for the mycorrhiza content. That little bit of soil will have enough mycrorrhizae to inoculate your soil.

Purple Lantana Dying Out



yellow or gold lantana

Q. Am having trouble with purple Lantana. They are dying out. The gold Lantana is still doing well. Am watering 3 days a week at 20 minutes and 4 days a week at 7 minutes. I have noticed that my neighbors are having the same type of trouble. Hope you have a solution.

A. The lantanas in general flower on new wood so as they get older the flowers will get further and further from the center of the plant provided it does not freeze back. This tends to make the center kind of bare and most of the foliage and flowers at the ends.

Trailing or purple lantana

            If it freezes back and does not die out due to very low temperatures then the plant will stay more compact and will need to be trimmed back to a few inches each early spring. But this plant, if it is in a place where it stays warm and does not freeze back, will tend to get leggy and not have much foliage on the inside.

            So make sure you cut it back to keep renewing new growth close to the center of the plant. You can do that now to some degree. Cut back one third of the stems to a couple inches in length. Stagger the cuts so that they are random on older wood through the canopy

            It will require watering fairly often if the soil drains of water easily. Fertilize lightly in the spring and fall. To maintain bushiness irrigate frequently like any normal shrub. If you decide at some time to replace it make sure you add compost to the soil at the time of planting.

Figs Won't Make it Before it Freezes

Q. We have a Black Mission fig tree with about one hundred well-formed but still very green fruit. This will be the second crop for 2012. It is now the first week of November. We are afraid that the frost will come before these fruit mature. Do you have any suggestions on maximizing our yield from these trees? This is becoming an annual problem.

Two different crops of figs on the same branch: early figs
(briba) on the older, darker wood and the second crop
(main crop) on the green new growth.

 

A. In our Las Vegas Valley climate it is very common to have two crops of figs each year. In fact, if we could maintain warm temperatures through November we would actually get a third crop of figs.

            The first crop of figs in the summer comes from growth or wood that grew the previous year. In other words, the first crop of figs you should be getting the summer of 2013 will come from wood that grew in 2012. It is easy to see the difference between wood produced in 2012 from older wood because of the color difference.

            The second crop of figs, as well as the late third crop which you are seeing now, comes from the current season wood. So this coming year the second and third crop will grow on wood produced in 2013.

            There are the two things that you will most likely have to do this coming winter and the subsequent growing season. When you prune your fig tree this winter, leave some wood on the tree that grew this past season.

Fig along fence after winter pruning at The Orchard

            If you want an early crop, the first crop, you must leave some of last year’s wood on the tree. If you remove this wood by cutting everything back you will remove the early crop of figs. If this wood is excessively long, you can cut some of it back and it will still produce fruit. I would leave 2 to 3 feet of this wood remaining.

            If this wood, last year's wood, is not very long it means your tree is not getting enough water. Normally the wood produced last year could range from 2 to 6 feet or more in length. It varies with how much light it is getting, position on the tree, if it is upright or not, etc.

            Two things that will give you more growth is water and surface mulch. Fig trees do very well with organic surface mulch or wood mulch on the surface of the soil. 3 to 4 inches or more would be great.

            You would water a fig tree just like any other landscape tree that is not a desert plant. Figs are not really desert adapted. They are typical of more Mediterranean climates and they do like water for the production. I hope this helps. Watch my blog for this question and I will post pictures.

Cottonwoods (Poplars) Not a Good Choice for the Desert

Poplar or cottonwood growing in desert
landscape. It is difficult to water these
types of trees in our climate due to their high
water demand and our irrigation systems not
intended for very large, high water-demand trees.

Bob, I have 2 cottonwood trees that are about 15yrs old. They were doing very well until about 2 years ago. At that time I noticed a limb here and there dying. Now more and more are dying off. I cut off a limb that broke in the wind recently that was partially dead at the top. I saw bugs in the area that was dying. The bark turns brown and peels off the limbs that are dying. Also when I cut off limbs that are dead or dying the wood under the bark is turning a dark brown at the center. I found info on the internet that recommended using a pesticide applied to the soil along with a 10-10-10 fertilizer mix. I just did this last week so I don’t know if this will help. What do you recommend? What do you think is the problem? Am I doing the right thing? What do you suggest?

I really appreciate your help. It would be a shame to lose these beautiful trees.

Jim

Jim

Cottonwood trees require lots and lots of water. I hope these are not growing in a rock or desert landscape or you will have problems. If you will be successful they should be growing in a large turfgrass area with you supplying supplemental water to them deeply twice a month. This means not only are they receiving water from the lawn, but you would be watering them with extra water down to a depth of 18 to 24 inches twice a month during the growing season. The area that you are watering under the tree should be approximately the same area that is under the canopy or spread of the tree.

It is hard to judge but my guess would be that you are getting branch dieback from a lack of total water applied to the tree. These trees will not survive for any length of time if they are in drip irrigation. I would highly recommend that these trees be watered with a bubbler that releases large amounts of water quickly into a basin beneath the tree. This basin should be the size I mentioned above.

I don't believe that there is anything wrong with this tree that lots of water applied under the canopy would not cure. Watering schedule during the summer months would be every 2 to 3 days. The frequency of applied water decreases in the cooler months but the volume of water applied remains the same... that water needs to travel in the soil to a depth of 18 to 24 inches beneath the tree.

Pruned Newly Planted Peach and Got Only One New Shoot

Dear Bob

I purchased this nectarine at the orchard in either Jan/Feb of this year.  Since I planted it on a slope, I cut the trunk to 30" versus the 24" recommended by the gardener.  Unfortunately, as you can see from the picture, it only put out one scaffold branch?

I know you get hundreds of pruning questions, I read all of them on your blog, but I was wondering if, since it is still a young tree, if I should lower it another 6" in the hope that it will put out  more than one scaffold branch.  Or, if I should just live with the existing scaffold and hope that others will develop?

Any suggestions you could offer would be greatly appreciated.

Sincerely,

Scotty.

Sotty

That also happened to me on a peach once. These things do happen. When we make these dramatic cuts we sometimes don’t get pretty results. Peaches and nectarines both sometimes, depending on the variety and the size of the trunk, may respond by making one new shoot or several.

However, the larger the trunk on peach or nectarine we cut the more chances we will have of getting fewer new shoots. Smaller trunks will give you more shoot development… typically. There are three things you could do. This might depend on what you want the tree to look like. For production purposes you are fine where you are…. A bit higher than I would have liked to see but you will get fruit. But it does look a bit odd when it is young. This will disappear over time and you can enjoy the fruit soon.

You can recut the trunk (gulp). This is risky but what the heck. You will learn something one way or another. It might again send up one shoot. It might send up more than one shoot. It might not send up any new shoots. I can’t tell you what is going to happen but if I truly did not like the look of it I would recut the trunk and take a chance. If I don’t care about the looks so much then I would let it go.

Next time, pick a younger tree with smaller diameter trunk and cut it at knee height to start your scaffold branches. In one season you will not have any difference in size between the two.

Internal Browning of Pear May Be Due to Late Harvesting

Hi Bob:  I understand you are in Afghanistan.  Stay Safe over there!  If you have time to address my rather insignificant problem compared to where you are right now I would appreciate it.    If not ...no sweat! I have a large 12-15 year old Keiffer Pear Tree that always has literally hundreds of large pears on it each year. 

            I am just harvesting them and this year the pears look fantastic and are especially large but when one cuts them open all of them have rotten areas within the pear.   Perfect on the outside but ruined on the inside.   Last year they were perfect both inside and out…no problems but not so this year. I am sending a picture…hope you get this.   Any clue as to what’s going on with these pears?  

            The only issue I had with the tree early In the summer was a severe iron deficiency that I treated with an iron solution.  Don’t know if this caused the pear problem or not. I would appreciate any info you can give me. 

Billy

Keiffer pear at The Orchard

Billy. This is a tough one but I do not believe your applications of iron had anything to do with it. From the picture I believe this is called brown core or pithy brown core. I could be wrong. But the brown area would be pithy, not wet or watery. If this is in fact what it is I do not have good news because no one seems to know what causes it.

Let's run down a list of possibilities. One suggestion is cool weather. Some suspect that unusually cool weather can cause this problem in fruit. Another suggests that if you leave the fruit on the tree too long the fruit can develop this problem. Another suggests if you harvest the fruit and do not cool it down soon after harvesting this problem can develop.

Whatever caused it, from your description, it happened to all of the fruit this year. Look and see if the fruit on the South and West sides are harder hit than the ones on the North or North East side. Let's rule out over heating of the fruit. If you don't have good leaf cover on the tree this might be a problem because the fruit may not get enough for shade and cooling.

Corky spot on Comice pear at The Orchard

When harvesting the fruit, try harvesting the fruit a little earlier, maybe mid-October, and let them ripen a little bit off of the tree but inside the house. Make sure when they are harvested they do not sit in the sun for any length of time.

There is another disorder called corky spot that cause the flesh to be brown and pithy just under the skin. This is due to a calcium deficiency and calcium sprays are recommended five times during the growing season to alleviate this problem. But this does not appear to be corky spot.

That's about all I have to offer. If it does not happen again next year and you have not done much different perhaps we can conclude it was due to weather.

Science in Action: What Does Sulfur Do In Desert Soils?



Granular sulfur remaining on the surface of a desert soil three
years after its application.

Arid soils and irrigation water in the desert southwest present numerous problems to nondesert plants that are brought in from other parts of the country and the world. These problems include high pH and high levels of sodium and bicarbonates. Sulfur, in one of its many forms, is commonly used to reclaim these soils and water and improve their quality so that a broader range of plants may be used in landscapes. Sulfur, in the form of sulfuric acid, is used for injection into irrigation water to combat pH and high bicarbonates.

 

In some parts of the country granulated or micronized sulfur is used as part of the fertilizer program when it has been found to be deficient through soil or tissue samples or when a lowering of soil pH is needed. The purpose of using sulfur in a maintenance plan, and which form to use, is often confusing to a landscape manager. This can lead to disappointment when the results from the use of sulfur containing materials don’t live up to the expectations of the landscape manager.

In horticulture and agriculture, sulfur is used for two primary purposes: as a nutrient for plants growing in sulfur poor soils and to reclaim poor quality soils and irrigation waters. It should be noted here that all sulfurs and sulfur products are not the same. The form of sulfur that would be picked as a fertilizer is not necessarily the same form that would be picked for reclaiming poor quality soil and water.

Sulfur is an essential plant nutrient. Fortunately it is plentiful in most soils and shortages are not common but they do occur. Plants take up sulfur from the soil in the form of sulfates. Fertilizers that contain sulfur usually contain it in the form of elemental sulfur (soil sulfur) or in the sulfate form such as ammonium sulfate. Sulfur is converted to sulfates through a process called oxidation. When applied to aerated, moist soils, elemental sulfur is oxidized by soil microorganisms to form sulfuric acid. This sulfuric acid in turn supplies the sulfate ion that is taken up by the plants. During this conversion from elemental sulfur to sulfates is when sulfur releases its acidifying power. When elemental sulfur is incorporated into soils the oxidation of sulfur to sulfates is what helps to temporarily lower soil pH.

Sulfur containing fertilizers should be applied to soils when sulfur deficiency has been clearly established through soil tests or tissue analysis. The preferred sulfate fertilizer is ammonium sulfate due to its price, solubility in water and availability. Since the sulfur contained in sulfates has already been oxidized, the acidifying power possessed by sulfur has already been lost. The sulfates contained in fertilizers have little affect on the pH of a soil or water when added to it and so may not be a good choice if lowering the soil pH is desired.

Elemental sulfur, sometimes called soil sulfur, is not a good choice to quickly correct a sulfur deficiency or quickly lower soil pH. To become available to plants and release its acidifying power it must be first converted to the sulfate form by microorganisms. Like all microorganisms they are most active and efficient under environmental conditions that promote their activity. The size of the sulfur particles, soil temperatures, moisture and oxygen levels must be in a range favoring their growth and activity. Peak oxidation levels, provided soils are well aerated, occur at soil temperatures of about 85 degrees F. This conversion from sulfur to sulfates in soil is a relatively slow process even under the best of conditions. Even though acidification around the sulfur particle may be relatively quick, the diffusion of sulfuric acid to the surrounding soil volume is generally slow.

Generally speaking, given warm soil temperatures and good soil aeration, the smaller the sulfur particles the faster the release of acid and the formation of sulfates. This is why elemental sulfur is sometimes combined with bentonite clay to help in the physical breakdown of the sulfur particle. In water, a bentonite-sulfur particle swells, breaking it up into very fine particles. Once broken into small particles, the increased surface area allows soil bacteria to transform the sulfur to sulfate more quickly. However, even in the presence of small particles, transformation of sulfur to sulfate is a slow process often taking months.

Elemental sulfur may be a good choice on a long-term management program provided the economics justify its use. Reasons for continued application to soils include the temporary, but long term lowering of soil pH and the reclamation of soils containing excess sodium. Elemental sulfur is often chosen to lower soil pH, but it must be used carefully since it can have a high potential to burn plant tissue under certain conditions.

The amount of sulfur needed to decrease soil pH is determined from a soil test by the amount of lime contained in the soil. Each 10 pounds of elemental sulfur generates enough acidity to neutralize 30 pounds of lime. Applications are best made when temperatures are warm enough for the bacteria to oxidize the sulfur but not hot enough to burn leaf tissue. Since sulfur does not generally move in soil, surface applications may be tied up in the thatch layer and not move into plant root zones. Generally temperatures above 90 degrees F would be the upper limit for applications.

Incorporation of sulfur into the soil just after coring is a good method for reducing burn, reducing contact with plant foliage, improving aeration and moisture conditions for the oxidation of sulfur and treating a greater volume of soil than just applying it to the surface. Published rates of application for turfgrass are less than 5 pounds of actual sulfur per thousand square feet for bermuda and less than 0.5 pounds for bentgrass per application. Reapplication would depend on soil pH tests.

Sulfur is also used for reclaiming sodic soils (soils high enough in exchangeable sodium to cause plant damage and decrease soil permeability). For sulfur to work there must be enough calcium present in the soil for sodium to be precipitated out and good drainage. When calcium levels are low (rarely in arid soils of the western United States) gypsum may be used if a quick response is needed. In arid soils already plagued with salinity problems it is recommended that a degree of caution should be used when applying gypsum to correct sodic soils. Since using gypsum will add about five times the amount of salt to a soil as using sulfur, the addition of gypsum should be avoided when managing landscapes with salt sensitive plants.

Sulfuric acid injection into irrigation systems is sometimes chosen for lowering soil and water pH and correcting high bicarbonate levels in irrigation water. High bicarbonate levels in irrigation water exacerbate potential plant damage due to high sodium (measured as SAR). Bicarbonates will combine with calcium and magnesium and precipitate them out. This is a problem because calcium and magnesium help to "buffer" problems due to high sodium. As these calcium and magnesium ions drop out of the irrigation water solution, the relative sodium levels may rise to dangerous levels (measured as adjusted SAR). The addition of sulfuric acid to irrigation water helps to lower bicarbonate levels and keep calcium and magnesium in solution.

Directly injecting concentrated sulfuric acid into the irrigation system through an injector or using a device such as a sulfur burner will accomplish the same thing. Sulfuric acid can be made from sulfur by burning sulfur, also an oxidation process, in a combustion chamber. In the case of burning sulfur, the oxidized end products are sulfur gases; sulfur dioxide and sulfur trioxide. When these gases are mixed with water they produce sulfuric acid. Sulfuric acid is produced and can be injected directly into the irrigation system. This is the basic idea behind sulfur burners used for acid injection into irrigation systems. Sulfur burners have become more popular recently due to safety considerations when handling concentrated sulfuric acid.

Sulfur may be a good choice in managing arid soils provided the reasons for its application warrant it and the economics of its use justify it.

This article was originally printed in Southwest Trees and Turf

Did We Mess Up Planting a Maple in This Climate?





Autumn Maple in rock landscape.
Bad idea.

Q. We have a young Maple tree in our yard that we planted last October. We may have messed up when we planted it to replace a shrub that was dead when we moved in. The tree is in full sun all day. Last year toward the end of summer it lost most of it's leaves - they looked burned. However it re-leafed itself before going dormant, and survived the winter. So we figured it was because it was a young tree and might be okay this year.  Again this year it has done the same thing and is at present in it's second bloom of leaves.



            My question is, would it be better to move this young tree to a part of the yard that is not in full sun all day, and if so am I right in believing it would be better to wait until it goes dormant for the winter before doing so? Any advice will be much appreciated.

A. Oh boy Bill. This is not going to be an easy tree to take care of. Maples is a huge category of trees. They range from the ornamental and shade trees common to the northern and eastern states to the highly ornamental Japanese maples and even our native maples. But unfortunately all of them will struggle.



Autumn Blaze maple in desert landscape
in Summerlin Nevada

            I have seen two instances of Japanese maples successfully grown in Las Vegas. They were in sheltered, shady parts of the landscape. The soil was highly modified with compost and other sources of organic matter. In one case many years ago it was growing in a lawn situation.

The other was in a shrub border with lots of organic mulch. Another possible Maple you could play with are native maples such as Bigtooth Maple. If this is a Red Maple, Sugar Maple Or Silver Maple you will have some big problems down the road if you can get it to grow. I like to encourage people to try new things but if these are maples used for shade trees I would get a replacement and check it off as part of your education.

I have one entry in my blog concerning maples that you might find interesting concerning Autumn Blaze Maple in Las Vegas.

http://xtremehorticulture.blogspot.com/2011/10/autumn-blaze-maple-not-good-choice-for.html

Yes, you should move it now so it has the remainder of the fault to reestablish the root system and a spring for more growth before it gets hot. Pick the North side or shadiest part of the yard. Dig the hole 3 feet wide. Amend this volume of soil with about 75% compost. Plant it at the same depth. Stake it solidly in the soil so the root system cannot move. It is okay for the top to move but the roots should be totally immobilized. Cover the surface of the soil with 4 to 6 inches of wood mulch, keeping the mulch away from the trunk 6 to 12 inches. The mulch should totally cover the surface of the soil and the hole that was dug. I hope this helps. Try to find out or remember the type of Maple it is. This makes a huge difference.

How Long Can You Keep a Rose Bush?

Even though this rose is not that old it probably
should be replace and planted further from the house

Q. Tried to find list of roses which will do well in Southern Nevada and unable to do so.  Also, what would be the lifespan of  a rosebush (HT or Floribunda) in Southern Nevada.   We have some which are 30 plus years old.  Thanks for your help.

A. I just published some information on my blog this week on this subject and gave you a link to get the most recent recommendations from Weeks Roses. Please go there. Follow the link to Weeks Roses and their publications. Download their adobe acrobat (pdf) file on Recommended Varieties for Hot Dry Climates. This is an excellent publication.

http://www.weeksroses.com/resources.htm

            The life a rose depends on who is growing it. Rosarians (gardeners who belong to the American Rose Society or its affiliates such as the Las Vegas Valley Rose Society or the South Valley Rose Society). Rosarians may keep roses for a couple of years and pull them if they don’t like it or they may keep one that is their favorite for decades.

            On the other hand, homeowners may keep roses as long as they are vigorous and may keep them for 8 to 10 years and replace them. I am not a Rosarian so I generally tell people that ten years is long enough. They will get fairly woody and start developing problems with age as we all do.

            Besides, unless you have a real favorite it is nice to see a change after a few years. As far as their life expectancy, it could be decades but usually homeowners keep them far longer than they should.

Blood Orange Fruit Splitting

Readers blood orange

Q. My blood orange tree is looking healthy but my oranges are splitting as evidenced by the attached photo.  What if anything can I do to stop this?



A. To begin with we have to mention a couple facts about citrus in general and Pigmented (Blood) Oranges in particular . . !. Citrus set fruits right after blooming and the small fruits grow to a certain size and stay at that size all summer before beginning their 'sizing' phase in September  . . . All summer the small fruits have to hang on the branches exposed to the sun, wind, low humidity and heat potentially causing the rind on the more exposed fuits to get sun scalded . . .Then during the sizing phase the sun scalded areas of the rind have lost much of the suppleness and elasticity to expand and they often split . .. One early symptom can be the area that is sun scalded will color up earlier. . . (As can be seen by the yellowing around the split.)

Of all the oranges, the Pigmented are notorious for having the least densely foliaged canopy; and of the Pigmented Oranges the Moro variety is the most notorious for sporting the least dense canopy . . That said the fruits during the summer may be more vulnerable to sun scald simply from the fewer leaves . . .With maturity the tree gets fuller and fuller and the sun scald drops off appreciable . . .

So, this is sunscald from earlier in the summer expressing itself during the sizing phase . . . Now I know some will want to lay a guilt trip on you about poor watering or poor fertilizing or something else but that is rarely the case . . And with your description of the tree looking healthy that probably isn't the case at all and just the sunscald showing up . .

If, however you are into self blame and want to feel bad then: 'It's all your fault." . .Just kidding .

It will happen once in a while and the best thing you can do is keep the tree as healthy and well foliaged as possible to help shade and  thus mitigating the potential for sun scald . . .

Terry Mikel

Planting Garlic Now for May/June Harvest

Garlic Polish White at the Orchard

Garlic is easy to grow in southern Nevada. Both hardneck and softneck (the braiding types) will grow here. It is not difficult but you must have soil that is well prepared with plenty of compost and fertilized with a phosphorus fertilizer to a depth of 12 inches prior to planting. Some very good varieties to try include Polish White, Tuscan, Morado Gigante, Susanville, Red Janice, Kettle River Giant, Chesnok Red. I have never had a garlic failure with any variety. If you just want to try your luck the first year, buy some from the store (some people tell you not to because of disease but most gardeners do anyway) and plant them in a large container. The garlic will grow from the clove and stay frozen in time through the winter and resume growth and bulb up next spring.

Separate the cloves from the bulb and keep them in the house overnight. This gives the small damaged area created when separating them heal a short time before planting. It is actually best to wait a week but actually 24 hours is enough. I like to soak the cloves in fresh, cool water for several hours before planting. This should cut off a day or two in the emergence time.

Young garlic for grilling

Plant them in a row, in a bed equally spaced or container three inches apart (if you want to harvest some early for grilling) or six inches apart if you want to give them enough room to reach their full potential size and dont want garlic for grilling. Garlic for grilling is usually harvested as the garlic is just starting to bulb or swell up underground. This will be like March or early April. Plant them with the pointy end up and about four inches deep, covering them with soil of course.

Decide on your irrigation method. I like drip with inline emitters six inches apart. You could use soaker hose I guess or laser tubing but these will plug up and not last long. Acutally I like to use drip tape but I have to order it online from places like dripirrigation.com If planting in a bed, I like the drip tubing 12 inches apart. This way you can plant the entire bed with the cloves the same distance apart and not waste any space. You can plant three inches on either side of the drip tubing. In a container you will have to hand water or use a drip spray emitter probably.

Garlic scape

I usually sidedress nitrogen once a month during the growing season. (Sidedress just means you sprinkle some high nitrogen fertilizer six inches away from the bulbs and let the irrigation water move it toward the roots. Do not broadcast the fertilizer over the tops of the plants or you could damage them). Here are the basic procedures. Or you can install an inexpensive fertilizer injector that works by venturi system.

Once planted and feritlized water them in deeply and mulch with straw or paper mulch. This helps to keep the soil moist and aids in even emergence. I would water about twice a week until you see emergence then you can probably water once a week at the most. Keep the bed free of weeds.

Freshly harvested garlic at the Orchard. Morado Gigante.

The first thing you can harvest is your garlic for grilling. I will usually stick my fingers down into the soil and feel if the bulb is starting to swell in early March. When it does and if you planted three inches apart, harvest every other one for grilling. If you planted six inches apart then wait for the next thing to harvest.... scapes. Scapes are the flower stalks that emerge from the plant in spring. This growth comes from the center of the growing top of hardneck garlics and will produce a flower. We usually harvest it before the flower opens and the scape has made nearly a complete circle.

The last thing you harvest is the bulb itself. Watch the tops of the garlic plants. When the tops have died down about 1/3 (2/3 of the top is still green) lift the garlic plant with a spading fork or irrigate so the soil is very wet and pull the plants out of the ground.

Should I Prune My Modesto Ash Tree?

Q. This is a Modesto or Texas ash tree that was planted 7 or 8 years ago in my lawn.  Do you think if I prune it back this winter that it would grow in to be fuller?  if so, how much should i prune off?

A. For some reason I could not download your pictures but I have a pretty good idea what ash trees look like. In the early years of ash tree I would let them go and not prune them unless these were branches that were crossing, going down, too close together and the like... problem branches. Otherwise let them go and let it grow into its natural form.

Basic limb structure of ash tree in summer and winter.
These are not the readers trees but a much older trees.

Once you start pruning a shade tree and changing its form it can create future pruning problems for you. If you begin to cut them back it may do what you want, create a fuller tree, but at the expense of faster growth. I hope this helps.

When and How Do You Prune Pine Trees?

Q. I know you prune fruit trees when they're dormant, but what about pine trees and other conifers? Mine get a couple of growth spurts a year and I didn't know if there was a "better" time for pruning.

Pine tree candles.

A. Normally the decision to prune involves two pieces of information; when does it start growing for the season and if it has flowers or fruit that we value, we would normally prune after it finishes flowering or fruiting.

            In the case of pine trees that grow well in the temperate climates (those climates which have distinctive four seasons) we always default to the winter season for major pruning. So the normal time to prune nearly everything is during the winter months.

            In the case of pine trees that grow in temperate climates this is also the case. If we were talking about tropical pine trees (not in Las Vegas) then we would time or pruning to its normal season for dormancy which is the dry season.



Pine tree thinning to reduce blowover from high winds
and the subsequent loss of branch taper or caliper.
This practice can lead to branch breakage which it did
(see my other post on this blog). It is best to selectively
remove entire branches rather than lateral branches along
a major branch.

            An exception to this is a technique of pruning pine trees that encourages dwarfing and increased density of the canopy. This is a technique called “candling”. Candling is done when the new growth coming from the ends of the branches is about 4 to 6 inches long. This new growth as it is emerging resembles a candle.

            Candling is done with your fingers and simply breaks the new growth as it is emerging in the spring. Usually we break the candle in half, we never cut the candle. Cutting the candle with a pruning shears causes the tips of the needles, which are cut in the process, to turn brown. This is unsightly.

            By breaking the candle in half we cause the buds at the base of the candle to grow and instead of getting one branch to continue growing we may get three or four. These three or four new shoots will not grow as long as the single shoot we removed.



Pine tree thinned to reduce "sail" on the canopy resulting
several years later in caliper loss in branch and subsequent
limb breakage (bottom center).

            This new growth remains more compact. Having three or four new shoots instead of a single shoot increases the canopy density.

A recent problem has developed in pine tree pruning. This is the idea of "thinning" the pine tree canopy to prevent blowover. In some cases on shallow soils with shallow, frequent irrigations, pine trees might not have enough root structure to support the tree in heavy winds. With gale force winds these trees blowover damaging property.

One recent practice by arborists has been to offer "thinning" of the canopy by removal of branches thus reducing the "sail" effect of the canopy during high winds. This sounds good but you have to be careful WHICH branches are removed in the pruning process. If lateral or side branches are removed along a stem or branch, this might cause a decrease in the strength of this branch due to a future loss of branch "taper" or caliper. This decrease in strength due to a loss of branch taper can lead to breakage and dropping of these weak branches.

Citrus and Grape Leaves Distorted, Suspected Weed Killer



Leaves of citrus cupped and
distorted.

Q. Please see the attached photos of curly leaves. The one branch is from a citrus tree (lemon vs. tangerine) and the other is my grape.  The citrus has several small, green fruit, looks healthy otherwise.  The grape had many grapes which we have eaten, and doesn't appear to be problematic, but I just want to be sure.  Are either of these concerning? Are they related?  I looked at your blog, and hate to admit it, but I do not know how to ask a question on that venue.

 

A. The leaves of your citrus look like they are cupped, twisted and distorted. The kind of distortion helps to identify what the cause might be. In the case of twisted or "stretched" leaves this can be because of damage from herbicides or weed killers that were sprayed a week or more before you saw the damage. This is typical of what we call phenoxy type herbicides. An example of a phenoxy type herbicide is 2,4-D, the dandelion killer commonly used for weed control in lawns.

Usually the leaf has to be subjected to some sort of damage and then the leaf GROWS in a distorted fashion so it usually means the damage appears several days or a week or more after the damage occurs. In your case, I dont know but they leaves still look healthy but distorted. I would just continue to monitor it and hopefully the leaves will be distorted just for this year.

Grape leaf distorted

The plant SHOULD grow out of it and symptoms will probably be gone next year. The fruit is safe to eat next year.

Sap From Apricot Trunk MIght Not Be Borers

Orange sap oozing from readers apricot trunk

Q. Our apricot tree has orange sap oozing out of the trunk in several places (see pictures attached).  The tree appears to be healthy and produce a good crop of tasty apricots this past season.  In some places, the sap appears to be coming out of the crevasses in the trunk bark.  In other areas, it appears to be coming out of holes in the bark (borers?).  What can I do to save this tree?  Is there an insecticide or fungicide that I can use?  For the areas where the sap is coming out of the crevasses, should I scrape the sap off and paint the tree again?  For the couple of areas where it appears that the sap is coming out of holes in the bark, can I insert a thin strong wire to kill the borer?  Any suggestions would be appreciated.

A. This is a little bit more unusual in apricot than it is in peach or nectarine. It is most likely in this case a boring insect, the same type that attacks many of our other fruit trees and landscape trees and in particular peach and nectarine the hardest.

Readers apricot tree in very good condition except for
the orange sap from the trunk.

Of all the places for sap to emerge this is probably the worst. If the damage to the majority of the trunk you could lose the tree. If this were me I would take a sharpened and sterilized knife (alcohol is good enough or heat) and cut under the sap and examine the wood directly under it.

If the wood appears healthy (you see some green or it appears fresh and wet) I would stop and not do any more. If it is not fresh and damp with a healthy appearance but instead dead, then I would cut these bubbles of sap from the tree trunk and remove all dead areas until you find fresh wood again.

Make the border of this dead area as smooth as you can so it heals as quickly as possible. If the dead area of the trunk (if it is there) extends more than half way around the trunk the tree is in big trouble. Hopefully the sap is coming from the trunk as a sign of stress and not extensive damage to the trunk.

If you can find something to put between the tree trunk damage and the sun (I am assuming these sap bubbles are on the south, west or east side) and create a bit of shade on the trunk it would be good. Try not to put anything tight against the trunk so it does not trap heat on that spot.

This is kind of unusual to see damage like this on apricot in that location. I am wondering of you have another problem going on. You have a basin around the tree and some mulch right up to the trunk. I also see you still have your support stakes on the tree. This is an older tree and these should have been removed a long time ago if there was nothing wrong with the tree.

The tree looks very healthy and is vigorously growing. I would pull any mulch away from the trunk perhaps 12 inches if it is in fact touching the trunk. I would also make sure that you are watering so that even in summer you are not watering daily but there are several days between irrigations when the soil around the tree begins to dry. This kind of damage can also indicate the beginning of crown or root rot as well. So be very careful of your watering.

How Do I Protect My Bougainvillea From Freezing?

Q. How do I protect my bougainvillea in the winter here in Las Vegas? I've read posts that say to water a lot and others that say don't water at all.  Some say to drape frost cloth or burlap directly over the plant and others say to put stakes in the ground and don't let the cloth/burlap touch the plant.  Last winter 3 of our 4 plants (small ones) survived, but it took a long time for them to come back.  Right now they are beautifully pink and very healthy.

 

A. This is a question I get asked frequently so I will post it on my blog very soon. So you are the lucky winner and I will soon post your question and the answer I provide below! Bougainvillea will not tolerate temperatures below freezing without some damage. The degree of damage will depend on how much below freezing the temperature dropped and for how many hours and if there was wind to go along with those low temperatures.

In order to answer this I want to explain a few things about winter tender plants and how to manage them in general first before I speak directly about bougainvillea. Winter tender plants should be "hardened off" prior to freezing weather. This is by not fertilizing this plant with nitrogen fertilizers a couple of months prior to freezing temperatures and reducing the frequency of watering. In the Las Vegas valley freezing could be as soon as December 15 and, rarely, even soon than this. So generally speaking do not fertilize ANY cold sensitive, aka winter tender, freeze sensitive, frost sensitive, etc. plants after mid September. Secondly, begin giving these plants less water to improve their winter hardiness.

 

Those are the textbook answers. Actually holding back on water is very difficult to do with automatic irrigation systems. You SHOULD be cutting back on watering on all your plants in your landscape anyway at that time of year. The easiest thing to do and most realistic is to stop applying fertilizer in late summer. When you fertilize these plants and encourage growth late in the year they could push new succulent growth which will be more easily damaged in freezes.

Cover the plant with something if you hear it might freeze that night and remove the covering in the morning a couple hours after the sun comes up. If you use plastic, this plastic must also cover something that releases heat back under the plastic. This can be a warm, south facing wall, the soil beneath the plant, big jugs of water that was warmed during the day, rabbits with their long warmth emitting ears, etc. Do not just wrap the plant in plastic or it will freeze AND it may possibly get even colder inside the plastic than the outside. Blame it on physics.

The other problem is wind. Cold and wind together are more damaging than either alone. Try to keep the winter wind from the plant so an enclosed courtyard, patio or other protected area of the yard is a good idea for location for planting.

As the plant gets older and larger it will withstand a few extra degrees. Its root system will also be larger and capable of storing more food. When freezing weather kills the top to the ground, the roots and collar region will regenerate the top very quickly. Just give it lots of water (bougainvillea likes deep watering) and fertilizer so it recovers quickly. If temperatures drop to the teens it is possible you could lose the entire plant so make sure the soil is mulched with several inches of wood or rock mulch to insulate the roots and collar as much as possible and give it some extra protection.

Tulip Bed Attacked Probably by Ground Squirrels

Readers tulip bed attacked by probably ground squirrels.

Q. I am attaching a photo showing damage to my tulip bed. Yesterday I found three deep very round holes dug about 6” apart at the edge of my raised garden where I have had tulips planted for years. Dirt was kicked out and baby tulip bulbs were scattered.  Not one large bulb was there and no pieces of large bulbs present.  These were very mature bulbs and bloomed well. We have an over abundance of rabbits (near the golf course) and huge “flocks” of quail, but don’t know of other critters here. Do you think rabbits have done this damage? 

A. You have an interesting story to tell. To my knowledge, rabbits typically focus on foliage. I have not heard of them digging for tulip bulbs.

ground squirrel

 

We have both jackrabbits and the desert cottontail. The Jackrabbit will stand on its hind legs and eat fruit tree limbs and stems up to nearly an inch in diameter. Damage to fruit trees can extend to nearly 3 feet above ground from jackrabbits. I have never had them go after root crops in the Orchard, only the leafy greens including garlic and onions.

 

Our biggest pest problems for underground crops have been ground squirrels and gophers. As you know golfers attack from the ground but the ground squirrels can do damage similar to what you have observed.

 

Jackrabbit

My guess would be this is due to ground squirrels. There are only two options for you. You can put screening around these areas or you can use poison bait. If you choose screening you must not use chicken wire as the holes are too large. You must use wire mesh or wire cloth with very small diameter holes. I hope this helps.