Frost Blanket, Crop Cover, Floating Crop Cover

Q. You wrote about some kind of blanket to wrap your plants with when it gets cold in winter to keep frost harming them.  Can you tell me where I can buy them?

 

When these covers are used to protect from freezing weather, they're called frost blankets.

A. Frost blankets don't produce any heat. They capture heat radiated from the soil or other surfaces that are warmed by the sun and also protects plants from wind. Wind is a partner in winter damage because warmth radiated from the ground, a nearby wall or even from the trunk of the plant itself, is lost quickly if there is air movement pushing it away from its source.

Sometimes crop covers are stretched over hoops to make low tunnels.

            Depending on their use, sometimes they are called floating row crop covers, crop covers, row crop covers. They are pretty much the same but another tool in the “toolbox” for gardeners. These fabric covers permit air and moisture to move through them but trap heat and disperse high light intensities.

            Some people use plastic sheeting or blankets to protect the plants from frost damage. They act like wind barriers and insulation. But frost blankets trap enough heat to keep crops 4 to 5°F warmer during light freezes. Frost blankets are lightweight, don’t have to be washed and are reusable.

A difference in germination and seedling growth when a crop cover is used on the right versus no crop cover used on the left.

            I have used frost blankets to cover broccoli, cauliflower and cabbage during cold winter months if I thought the temperatures were going to drop dropped really low. These blankets are rolled on top of plants, stretched over hoops and pinned to the soil so they don't blow away. If left on during cool, overcast days they push growth more than leaving plants exposed to the elements. Use them during cool weather, not when temperatures are hot.

            They work really well if a few degrees of protection is needed. But if temperatures get too low. they won't provide enough protection.

            Use I use them for insurance against moderately low temperatures that might cause damaged plants or when you want to push a little bit of growth during cold weather. They are available at local nurseries and garden centers as well as online stores. Two manufacturers of these frost blankets that come to mind are DeWitt and Agribon.

Try GrowOrganic.com, Johnny's Seeds, Greenhouse Megastore, Amazon, Park Seed Company, Harris Seeds and other online vendors. Please also check your local nursery. Many of them carry it.

Pomegranate Fruit Splitting Usually Water Problem

Q. I have grown Utah Sweet pomegranates in Summerlin for several years and only had a few fruit split open near the Fall harvest time. Mid July this year 40 green fruits split open. I assumed it was from high temperatures but more kept splitting open through the rest of the year. At least 80% of the fruit have split open and the birds cleaned out all the edible seeds. 

Split Utah Sweet pomegranates do to watering problems.

A. Harvest times for pomegranates are at different times depending on the variety of pomegranate. The earliest varieties start ripening in September and other varieties extend the harvest season past Halloween.

            The usual reason for early fruit splitting is irregular applications of water: soils alternating between wet and dry. Pomegranates handle high temperatures easily but they don’t produce well if water in the soil is limited during its fruiting cycle. 

Split Utah Sweet pomegranates most likely from irregular soil moisture. This can be a particular problem when trees are on drip irrigation and surrounded by dry soil. Don't turn off the irrigation system when it rains when growing in the desert. The amount of water the plant received is hard to calculate.

            Fruit splitting is a watering issue, not a temperature issue but the two could be related. If water is not available when the fruit is increasing in size, even for a day or two, fruit will be smaller because they begin maturing too early. Their outer “skin” begins to harden early.

            Now it rains heavily. This abundance of water available to the roots is “pushed into the fruit causing the fruit to expand and split. Unusually high temperature, combined with wind and an unprotected soil surface, can cause drought at times that are unexpected. Irrigation water is supplied according to a clock but it is too late. The damage is done.

            Put a surface layer of mulch 3 to 4 inches deep on top of the soil to slow water evaporation from the soil surrounding the roots. This surface layer of mulch helps to reduce wildly fluctuating amounts of water in the soil when it is hot and windy.

Pomegranate before winter pruning and surrounded by wood chip mulch in the desert

            Use woodchips from trees pruned by local arborists. Extend this surface layer of mulch so that it completely covers the soil under the tree canopy to a depth of four inches. Make sure these trees receive enough by adding emitters as it gets bigger and checking the soil moisture during hot weather.

Round hole in the side of pomegranate with inside totally cleaned out is a pretty good indicator of a rat problem.

            Birds eat pomegranate seed after the fruit has split open. They can’t open pomegranate fruit by themselves. Rats gnaw on the outer “rind” of the fruit leaving a large, somewhat round gaping hole in the side of the fruit with the inside totally cleaned out. One of the pictures you sent to me looks more like rat feeding than bird damage.

            Because rain in the desert happens so infrequently, never use the rain shut off on the controller. Irrigate plants even though it rained because estimating the amount of rain plants receive is very difficult to do accurately.

Decreasing Irrigation in Summer Can Create Problems

Q. A landscaper told us we were watering too much and re-programmed our "box" to water less. This was a disaster to a tall pine tree I have. It now looks like HELL with lots of dead needles from top to bottom. 

A. That was a mistake in judgment by your landscaper. Homeowner irrigation systems are notorious for watering plants unevenly; plants on the same valve not receiving enough water force us to overwater other plants on the same valve. The overwatered plants are easy to see. The plants receiving just enough water are not. It’s easy to make a snap judgment and assume that everything is being over watered when it’s not.

This is drought in an established pine tree. Notice how the crown is  round before it reaches its maximum height.The canopy is rather open and you can see through it which means it doesn't have a lot of new growth to fill the voids.

            Decreasing the number of minutes on an irrigation clock when all plants were “happy” is dangerous, particularly during the summer months. Plants react quickly to a lack of water during summer months. When decreasing minutes on a clock, do it during the cooler months. Then observe how the plants react to this new irrigation schedule. Plants have a few extra days before they are damaged by a lack of water during the cooler months.

This Siberian elm tree had massive limb die back as the result of a conversion to desert/rock landscaping, the elimination of grass and a substantial decrease in the applied water.

            For a short-term fix, buy two or three hose end sprinklers, attach them to short hoses with a splitter that feeds all the sprinklers at once from a main hose. This can be done for about $25. Connect the main hose to an inexpensive, dial-type mechanical timer at the hose bib and connect the other end to the splitter.

Hose end sprinkler.

            Water at the base of the pine tree for a total of about one hour. This should give the water a chance to soak deep into the soil where the roots are located. If water soaks into the ground easily, apply the water all at once. 

Mechanical timer for shutting off the water automatically when turning the dial.

            If it begins to run off the surface after several minutes, sprinkle irrigate water several times with a long pause between irrigations. But the total irrigation time should be about one hour. Water the tree like this once a week for the next month. This should thoroughly wet the roots growing deeper in the soil.

Hose splitter

            When you want to make some changes to the irrigation system, make sure your larger trees receive more water in accordance to the amount of time on the irrigation clock.

Miniature or Genetic Dwarf Peach and Disabilities

Q. Due to my bad shoulders I would like to have a peach tree that does not grow so high and I would like for it to be a freestone. Is there one which you would recommend?

Miniature or genetic dwarf peach is a good choice for container planting. It will also stay small with a minimum amount of pruning whereas keeping full-size trees small is a lot of work.The peach is produced on this tree are full-sized but the selection of good tasting varieties is much smaller.

A. The type of tree you're talking about is going to be a genetic dwarf peach sometimes called a miniature peach tree. They produce a full-sized peach fruit but stay small. The fruit is okay but it is not going to be as good, consistently, as some of the other larger peach trees. Look for names such as Bonanza or El Dorado or Pix Zee.

This is a genetic dwarf a.k.a. miniature peach in full production during the winter after all the leaves have fallen off. Notice its structure. It was pruned this way, it did not naturally occur like this. Plenty of space is left for fruit production and collection of energy from the sun.

Know the Difference between Fire Blight and Transplant Shock

Q. I live in Denver, CO, and just planted a Spring Snow Crabapple tree last week. Since 3 days ago, the tips of the leaves turned a darker green, and overnight turned brown. I am really hoping this isn't fire blight. I don't see any shepard’s hooks or oozing on trunk. Could it be lack of water? Transplant shock?

This Asian Pear came down with fireblight which was obvious by September. Asian Pear is very susceptible to fireblight in general. This tree came from the production nursery already infected. Doesn't happen very often, very small percentage, but it does happen even with the best orchards.

A. In your climate late summer and fall is a nice time to plant trees. Temperatures are in the upper 70’s during the day and dipping into the upper 40’s at night. So soil temperatures are probably in the low 60’s; warm enough for good root growth and establishment yet air temperatures are cool enough to slow the loss of water from the leaves.

This is a classic picture of fireblight I took showing the shepherds hook, small dead fruit and dieback in the limb. You can't see it but there is even the bacterial ooze there that you could see glistening off sunlight. This happens 3 or 4 months into the season and when the disease is spreading fullbore.

            Fireblight would infect trees in the spring and the symptoms usually appear in early summer. It is possible to transport this disease to a healthy tree through pruning a sick tree and then pruning a healthy tree without sanitizing the shears. But I doubt that is what is happening.

Even though most infection occurs at the time plants are in flower, the disease doesn't usually appear until a couple of months later occurring in the new growth or collapse of the flowers that were infected. It is very very possible to spread this disease through pruning from tree to tree and within the same tree.

            It is most likely how it was planted. Maybe the roots got too dry before it received water or it was planted with dry soil surrounding the roots. Always soak the soil around the roots with water from a hose a few times before turning it it over to an automatic irrigation system.

Some basic rules to follow:

1. Make sure the hole is at least three times the diameter of the container. If the soil is really bad, make it 5 times.

2. Make sure water can drain from the hole in half a day or less

3. Get the hole sopping wet before planting

4. Amend the soil put back in the hole with compost or other good soil amendment

5. Make sure this soil is wet immediately after you shovel it into the planting hole. Put water in the hole with a hose at the same time you are planting

5. Stake the tree after planting so roots don’t move during strong winds

6. Build a basin or moat around the tree to capture water from a hose

7. Water the plant twice, immediately after you plant it

8. Water it with a hose every other day for the first week to settle the soil around the roots.

9. Water once a week after planting with enough water to thoroughly wet the soil around the roots to a depth of 18 to 24 inches.

Aphids a Problem for Desert Artichokes

Q. I asked you before about tiny black bugs on my artichoke plant. After consulting you and the PC, I found a solution of Neem Oil extract from Garden Safe and sprayed it, hosed it down a couple times and cut off the top few inches. No pests since then. The main plant is dying and there are several suckers growing from the sides.  I have been looking online for care of the plant.

Aphids are a big problem on artichokes wherever you live but those and whiteflies almost make you pull your hair out. They cause the lower leaves, the older ones to turn yellow and collapse/die. Remove them. The plant doesn't need the lower leaves. They're always in the dark anyway and they are impossible to spray.

A. I never found Neem Oil very effective for insect control. Others have. I am glad you found a name brand that works for you, e.g. Garden Safe. Neem Oil is a “natural” pesticide, sometimes labeled organic, that has had some problems with quality control.

Not the same Neem Oil mentioned by the reader and making sure you select the right Neem Oil is critical. Different processes are used to extract Neem Oil and quality control is a problem.

            The effectiveness of Neem Oil apparently is dependent on how it is extracted or “manufactured”. Some brands of Neem Oil work well while others seemingly do not. It sounds like Garden Safe brand may be a good one for you. Let’s hope it stays that way.

 Fact sheet on Neem Oil from the National Pesticide Information Center

            Artichokes, like sunflowers, are aphid magnets. Those little black bugs were probably aphids, commonly found on the underside of artichoke leaves. Aphids are easy to control when they first appear. If left alone, they are not. Once populations build to epidemic numbers, they are difficult to get under control with “natural” or organic sprays.

            Neem Oil must contact the pest to be effective. It requires frequent, repeat applications when populations are small to keep levels of these pests manageable.

            Aphids don't like hot temperatures. Their populations build fastest in the cooler, darker, more humid areas near the soil. This is also where they are more difficult to see. Removing infested leaves helps reduce aphid populations.

            Artichokes produce okay in our hot desert climate during the cooler months but suffer during the heat of the summer. ‘Chokes here tend to be smaller and a little tougher; not the same quality as those produced in cooler, more humid climates.

            Artichokes love the cooler spring and fall months. They grow back quite nicely in the Fall after suffering during the heat of our very hot summers. Fertilize them just before new growth begins.

Remove Lower Leaves of Artichokes

Q. I cut the lower leaves off my artichoke plant a couple months ago per your suggestion.  In fact, my son who is a pretty good gardener asked why I cut them off. He comes over and helps me with the vegetables and asked me why I did that.

Don't let anyone tell you that you can't grow artichokes in desert heat and irrigating with drip. You can. You just manage them differently because "it ain't Omaha".

 How to Grow Artichokes in the Mojave Desert

A. Educate your son and tell him that not all leaves contribute back to the plant. If the leaves are in too much shade they pull nutrients and energy from the plant and it's best if they are removed.    This can be the reason lower leaves turn yellow and die. We see this frequently when plants are grown too close together. Over time, shading causes the lower, shaded leaves to become weak, die and drop.

Aphids feeding on the undersides of artichoke leaves causing yellowing. Remove these leaves at the main trunk. They are growing under other leaves so they are in nearly total darkness and are a drain on the energy supply of the plant. Besides that, it is impossible to spray the undersides of the leaves where the aphids are feeding.

            Removing lower leaves also helps control pests. Very often the highest concentration of plant pests is on the undersides of leaves closest to the soil where there is higher humidity, cooler and more protection from predators.

'Violetto' Artichoke being evaluated at the University Orchard in North Las Vegas In the Eastern Mojave Desert

 As vegetables get bigger, cut the lower leaves off the plant with a scissors while still young. If spraying a pesticide is necessary to control some insects, it's much easier to spray the undersides of leaves with lower leaves removed.

            When using organic sprays such as Neem Oil or soap and water, they must be applied when plant pest populations are small and building, with fewer adults and mostly immature pests. Frequent applications of organic sprays are often necessary to keep plant pests in check.

Pines Remain Staked After Five Years, No No No

Q. We have Mondel pines that are 5 ½ years old which are still staked.  I'm afraid these bindings will strangle the trees soon.  But we also have a lot of wind that could blow the trees over.  Can I safely remove the braces now?

The reason for staking trees is to prevent the roots from moving too much after planting. Wind blowing through the canopy of the tree can act as a lever and move the roots in the soil which damages them and delays their growth into the surrounding soil. The trunk should move, but not the roots.

A. Yes, remove the stakes.  Tree stakes, or as you call them bindings, should be removed after the first growing season.  If the planting holes are prepared correctly, these trees should be firmly anchored in the soil after one growing season.

These trees were properly staked at the time of planting if those largest stakes were pounded into the solid soil beneath the planting hole. If they were only pounded into the loose soil surrounding the tree, the stake moves with the roots and the wind.

            I understand your concern about the trees possibly blown over by wind.  As trees get taller with a full canopy, strong winds can uproot them easily if they are not firmly anchored in the soil.

           

This tree trunk lacks what is called "taper" or a wider trunk at the bottom and narrower trunk higher. This is because the tree was not grown properly at the nursery where it was produced. Trees like this require staking for several years because wind can snap or break the trunk easily. In fact, the trunk may never be strong enough to support the canopy of the tree. Trunks with good taper bend without snapping and require less staking time.This tree was secured to the stakes in the wrong place. The trunk is not given any chance to move and increase its taper.

Leaving the stakes tied to the trunk can result in those ties strangling the trunk. Eventually if these ties are not removed the trunk may snap in a strong wind or prevent water and nutrients from moving up and down the trunk.

 Solutions to this problem are twofold. First, prune these trees so that wind can flow more easily through the canopy. A method I don’t like, but used quite frequently, is to “rat tail” the limbs.  This technique removes all side branches along the limbs so that only a cluster remains at the ends.

            It’s true, it allows more wind through the canopy but unfortunately results in limbs that become weak and break easily during strong winds.  Don’t use this method.

Removing the inner branches so that air can move through the canopy works for a couple of years. But eventually the new growth at the ends of these branches becomes so heavy and the lack of taper that results from this type of pruning causes these branches to snap in strong winds. Some arborists refer to this method of pruning as "rattailing".

            A better method is to selectively remove entire branches from the trunk.  This method also allows wind to move through the canopy but without weakening and eventually breaking the remaining limbs.

            Secondly, increase the area irrigated under the tree as the tree gets larger and water them deeply.  This increases the size and depth of the root system thus improving its anchorage in the soil.  

Most Asparagus Varieties Grow Well in the Desert

Asparagus used to be marketed only if the spirit diameter was pencil -sized or larger. Now smaller diameter asparagus is popular.

Q. Do you have a recommended type or brand of asparagus that does well here in Southern Nevada?  I read your blog and you noted the purple varieties are "sweeter”, but do they grow as well as other types?

 

Asparagus is allowed to grow to its full height after harvest season is over

A. Yes, I do have recommendations on varieties of asparagus for the Las Vegas Valley climate. I grew 17 different varieties of asparagus for many years at the University research and demonstration orchard in North Las Vegas. The varieties included a few older European types, some old heritage types, varieties released from Rutgers University, University of California releases and a couple of commercial purple varieties.

Purple asparagus called Purple Passion

            All varieties grew well but some produced higher yields, some produced longer, good quality spears for a longer time when it started getting hot. Chefs who evaluated these varieties said different varieties had slightly different flavor profiles and could be paired with different foods.

Asparagus in emerging from seed the 2nd year after planting

            Generally speaking, University of California releases such as UC 157 give higher yields and produce quality spears for a longer period of time when it got hot than varieties such as Jersey Supreme and Jersey Knight, heirloom types such as Mary Washington and European varieties.

Female asparagus plants can be rolled out or eliminated because they drop seeds in the growing beds.

            Asparagus harvest can begin as early as mid-January in Las Vegas Valley and harvesting stops about 8 to 10+ weeks later when new spears are smaller than pencil diameter. The remainder of the year asparagus is not harvested but grown to its full height, between 5 and 6 feet, to rebuild itself for next year’s spring production. This is when fertilizer is applied, plants are inspected for insects and diseases and low yielding, female plants are removed.

Asparagus bundled in the cooler post harvest

            Purple varieties, such as Purple Passion, are unique and grow well in the desert but don’t yield as well as green improved varieties like UC 157. Purple spears are sweeter. The purple color disappears when they are cooked. In my experience, purple varieties are not as productive for the same number of years as green varieties.

            Any of the green varieties can be used to produce “white asparagus”.

            Asparagus plants are either male or female. Male asparagus plants produce more spears than female asparagus plants. Asparagus can be started from seed, not just from crowns, but the female plants should be “rogued out”or eliminated during the first couple of years if your focus is on higher yields.

            I have written an asparagus production guide for Southern Nevada and will post it on my blog in the next couple of weeks.