Desert Horticulture Podcast: Dormant Oil, Repairing Limbs and Sunburn

Today I want to talk to you about dormant oil, why it’s important and how and when to put it on, borer damage to ornamental trees and repairing limb damage to apricots and damage from intense sunlight to trees and what to do about it. Join me now on these and many other topics In Today’s Desert Horticulture.

Bamboo Yellowing and Dead Shoots

Q. Several of my bamboo shoots died completely and now they are all starting to yellow and have a white film on them. Any suggestions?

White film on the culms or stems of bamboo probably a wax "bloom".

A. You didn’t say which bamboo it is, but I assume it’s one of the bamboo tolerant of our winter temperatures. The so-called “running bamboo” rather than the clumping types represent those that tolerate our climate better.

            The white film is sometimes called a “bloom” of wax on the outside of the stem and is normal. If these are instead white “fuzziness” in patches and appear to be a problem, then you might be looking at mealybugs. But I think this white “film” has more to do with the naturally occurring wax produced by many plants rather than a pest problem.

             Yellowing can be caused from water not draining from the soil around the roots and suffocating them because of poor drainage or watering too often. You may be thinking that this plant needs water all the time, which it doesn’t. The soil needs to be kept to moist for good growth but let the soil “breathe” so that the roots and rhizomes can get air.

            Invest $10 in a soil moisture meter for house plants. As long as the soil is somewhat soft, push the probe slowly into the soil and get a soil moisture reading at the 4 to 6 inch depth. I would not irrigate until the meter on this gauge reads approximately “6” at this depth in 3 different locations. On these gauges, “10” is sopping wet and the number 1 is totally dry.

            The yellowing could be a soil alkalinity problem but I think instead it is probably poor drainage. When planting bamboo, amend the soil with compost at the time of planting and cover the soil around the plant, out to a distance of  2 to 3 feet, with woodchips. If drainage is a big problem even after amending the soil, plant it on a mound.

Leaving Mature Citrus Fruit on Ground Not Good

Q. What are the best practices to use if I decide to leave calamondin fruits on the ground under the tree to decompose. Or is it better to put the fallen fruit in the trash from the git-go?

Immature calamondin (calamansi) fruit from the tree in the Philippines at MoCa Family Farm

A. Calamondin, called calamansi in the Filipino community, is a small citrus resembling a lime but is golden yellow inside. This citrus is native to the Philippines.

            Fruit can turn orange in color but is frequently harvested when green but the interior flesh is a golden yellow. We have about 8 calamondin on our farm in the Philippines where we have a tropical climate and they do very well there.

            Let’s be clear about growing citrus in the Las Vegas Valley. Many citrus, since they are semi tropical, share a risk of losing the fruit, or possibly the tree, during some cold winters and early spring freezing temperatures. There are parts of the Valley too cold most years for even the hardiest of citrus. Other areas with warmer winter microclimates can grow them. As long as you are comfortable with that possibility, have fun and grow them!

            In my opinion, all fruit trees should have the area under them free from rotting, mature fruit. Very young fruit is usually not a problem if it falls on the ground and decomposes. Immature fruit thinned from the trees can be dropped on the ground to decompose with no problems. Mature fruit dropped on the ground may present a different issue.

            If this were a peach, fig, apricot or plum tree we would most certainly cleanup the fallen mature fruit that dropped on the ground. There is a pest called the dried fruit beetle that becomes a problem infesting soft, mature fruit growing on the tree if fallen fruit is not picked up from the ground. With citrus, the only pests to worry about are rats and mice. To be on the safe side, I would pick up fallen fruit and dispose of them rather than leave them on the ground to rot and attract varmints.

            By the way, calamondin is easily grown from seed and does well on its own roots rather than purchasing it grafted like most commercial citrus trees.

Passionfruit Not Producing Fruit in Desert

Q. I have a 3 year old passion fruit tree in my garden which started bearing fruit that grew fine and was mature enough to eat in February. In spring I also had more flowers blooming on the same plant, but these flowers never had any fruit. The same thing again in this past summer, but the flowers are not fully developing and are stopping at just little buds.

Giant passionfruit with flowers growing in the Philippines.Giant passionfruit withstands even less cold than passionfruit and is more tropical.

A. Passionfruit is a semi tropical vine that can’t handle freezing temperatures very well. It also likes moderate temperatures so it will have difficulties during the hot summer months. It grows very nicely in the tropics and moderate temperatures of high elevations in Africa.

Intercropping passionfruit, strawberries and kale in Kenya.

            Unless you have a warm microclimate in your landscape, these plants will show serious damage or die from winter freezing temperatures. If you can grow oranges in your yard, you should be okay growing passion fruit vine. Passionfruit may have difficulty setting fruit during the summer months because of high temperatures and low humidity.

Flower of giant passionfruit

            Passionfruit definitely does not like soils with poor drainage. If this is the case, and you don’t do anything about it, the vine will always have problems and probably die. Make sure the soil is amended with compost at the time of planting and cover the area around the vine to a distance of about 3 feet with woodchips so that a decomposes into the soil.

Giant passionfruit trellised above fish nursery in Philippines

            Passionfruit flowers are beautiful but they need help sometimes to produce fruit or to produce larger fruit. You may need to hand pollinate the flowers, transferring the pollen from one flower to the next, a job normally done by a variety of different bees.

            You may need to grow 2 different vines and transfer the pollen from the flower of one vine to the flower of another vine. This helps prevent what’s called “self incompatibility” and failure of fruit to develop. Passionfruit germinates easily from fresh seed and does well on its own roots. Passionfruit propagated by cuttings has “self incompatibility” between flowers and will not set fruit.

            Also, prune the vine by removing side shoots after fruit is removed. This helps the new growth growing from the older wood of the vine where flowers are produced and keeps the vine renewed for more production.

            Besides trellising this vine and pruning it back occasionally after fruiting, apply wood chip mulch at its base to preserve soil moisture and keep the fruit from being dropped if the soil gets to dry. Fertilize the plant lightly after it flowers by applying a “tomato fertilizer” to the soil around the plant and water it in.

Propagating Prickly Pear Cactus from Pads

Q. I want to propagate my prickly pear and bunny ear cactus. Should I place the cuttings immediately in the ground or in a pot and plant them in the ground later?

A. You can plant cuttings from them directly into the ground. Forget the pot. It’s not necessary. Wait until it gets warmer like around March or April. Remove a pad from whatever plant you are propagating and let the pad with the cut end heal in the shade for about a week.

The pad can be removed by cutting at the suture with a sharp, sanitized knife.  

          T

o do this, take a sharp, sterilized knife and bend the pad over without breaking it. Touch the sharpened edge of the knife to the suture where the pad joins the mother plant. The pad should pop right off at the suture. If not, gently push the sharp edge of the knife into the suture and slice through it smoothly.

If you lay the pads horizontally they will begin to curve in a couple of days.

            If you really want to guard against infections in the pad, dust the cuts and of the pad with a fungicide such as Thriam, copper sulfate or Bordeaux. When you put the pad in the shade to heal, lean it against something so it is upright or the pad will begin curving if you lay it flat.

Plant them in amended soil so that the pads flat surfaces faced East and West. This way they get sun on both sides of the pad.

            Mix the soil where you are planting with compost and add water. Stick the pad so the flat sides of the pad faces East and West. Sink the pad about one third of its length into the soil and water it once. After that, water it about every 3 weeks and it will begin rooting into the soil where it is stuck.

Whaaat? Zuchinni Failure!

Q. For the second year, I am experience a repeat of last year losing my zucchini before they mature. This is not to say I have a total failure but my yield is slim at best. I have two zucchini locations of two plants each, which allow me to monitor the better location for growing. I have changed my watering schedule to 20 minutes at 4:00 am. which has been helpful for most other herbs and vegetables but I am suspicious of possible over watering the zucchini as the immature zucchini begin to develop, then gradually turn yellow, the blossom drops off and the zucchini withers. Any suggestions?

Summer squash fruit can yellow and drop off the plant for a variety of reasons. But don't let a poor selection or variety cause it for you. That's a lot of work on your part to invest in inexpensive seed. Good vegetable seed is worth the price.

A. This probably wont make you feel very good but actually summer squash is one of the easier vegetables to grow here. Just make sure you amend your garden soil with compost, starter fertilizer for vegetables and start them from seed. You can buy transplants but you don't need to. Probably the biggest problem with summer squash or any squash are the squash bugs and controlling them.

Male and female flowers of zucchini. Both flowers are necessary, as well as be activity and the right temperatures, to produce zucchini fruit. Male and female flowers must be open at the same time for the transfer of pollen and the making of fruit. You can transfer the pollen yourself with a Q-tip or soft paintbrush or let the bees do it for you.

Zucchini produce both female and male flowers on the same plant. The male flowers produce pollen which the female flower needs to produce a fruit from the female flower. Female flowers have a small zucchini like swelling at the bottom of the flower. The male flowers do not.

The transfer of the pollen from the male flower to the female flower is done usually by bees. If there are no bees around then the pollen does not get transferred and there is no fruit production.

Don't let your fruits become baseball sized. Pick them when they are small, about 16 inches long, and pick them often.

You can do the work of the bees by taking a soft horsehair brush and touching the inside of the male flower where the pollen is and transferring this pollen to the female flower. However, if there are very high temperatures then this might also not result in producing zucchini fruits.

If temperatures are too hot then the pollen from the male flower has a real hard time getting the female flower pregnant even if the bees transfer the pollen successfully. And in our climate that can be a problem.

You should have some production during days when the temperatures are cooler. If not, then try a different variety next year.

Don't buy your seed from the hardware store. Buy it online from a good seed supplier for hot and warm climates such as Park Seed Company, Harris Seeds, Grow Organic, Territorial Seeds and many others. Look for seed companies that have offerings for hot desert climates.

My Apple is Weeping!

Q. I noticed my Anna apple tree is seeping fluid and a white patsy substance from a previous cut done last year. What shall I do to help it?

A. Smell the fluid. Take your finger and wipe it against this wetness and judge your nose whether the smell is “yeasty” or not. If there is a strong yeasty smell, there might be a bacterial infection going on. If it does not smell “yeasty”, then there is probably no infection.

Slime flux or more commonly called wetwood is a bacterial disease that invades the wood of trees and lingers. It is not life threatening for the tree but it is an eyesore.

            I would not do anything to the tree regardless. The yeasty smell is caused by a non-lethal infection.

            The inside of a tree has a central core of dead wood. The living part of the tree is an outer cylinder of living wood that enlarges year-to-year. The inside of the living cylinder increases the diameter of this dead, central core each year.

            Growth in the length of branches is called primary growth. Growth in width or diameter is called secondary growth.

            Secondary growth is responsible for “rolling over” pruning cuts and they can no longer be seen. When this secondary growth rolls over a wound, it surrounds or engulfs the wound, covering it, but the wound doesn’t “heal” like it does in animals.

Anna apple is a good early apple for the desert but I still like Dorsett Golden a little better. Get them on M111 rootstock for the desert.

            The central core of the tree is dead. This dead wood can “rot” due to different microorganisms. This rotting caused by microorganisms can cause the “seeping fluid” you are seeing.

            I would do nothing to the tree at this time unless you see other problems developing in its overall health. Judging from the picture you sent, the old wound seems to be healing and rolling over the pruned cut very nicely.

            I would not disturb it in any way but let the tree heal on its own. It should stop weeping when tree growth begins in earnest in the next few weeks.

Foam Weeping from My African Sumac

I have not had time to confirm this but it appears to be slime flux or wetwood disease. I have seen this disease on other trees for many years but this is a good picture of this disease symptom.

It is usually non-life-threatening for the tree but in warm weather it can attract flies and sap beetles, insects attracted to the smell of yeast and alcohol.

Read more about slime flux or wet wood by following this link
And this one as well.

Whenever you make any kind of cut into a tree or plant, make sure your knife or pruner has been sanitized and preferably sterilized before you make the cut. I prefer to use alcohol or an open flame but household cleansers such as 409 and others will provide some measure of sanitation.

I have not had time to confirm this because the picture was sent to me, but this appears to be slime flux or wetwood disease on African sumac. Great picture forwarded to me by Joy Mandekic.

Some other pictures of mine of this same disease.

I took this picture of wetwood a long time ago and digitized it from a slide.

From Jim Falcone

Also from Jim Falcone

Proposed Changes to USDA List of Allowed and Prohibited Substances (Organic Standards)

Proposed Rule to Amend the National List for Crops and Handling

On February 15, 2019, the U.S. Department of Agriculture will publish a proposed rule in the Federal Register to amend the National List of Allowed and Prohibited Substances for crops and handling based on April 2018 recommendations from the National Organic Standards Board.

This proposed rule would allow:

• Elemental sulfur to be used as a slug or snail bait to reduce crop losses.
• Polyoxin D zinc salt to control fungal diseases when other organic fungicides have been found to be less effective.
• Magnesium chloride to be reclassified from a synthetic to a non-synthetic substance, requiring handlers to ensure that the product complies with the non-synthetic classification by obtaining details about the source of the magnesium chloride and its full manufacturing process.

The USDA welcomes comments on the proposed amendments. The 60-day comment period will close on April 16, 2019.

About the National List

More information on the National List, including how and why substances are added or removed from it, is available on The National List page.

Desert Horticulture Podcast: Spring Freeze Damage to Plants

Late spring freezes can have devastating effects on plants that would otherwise sail through these problems. Find out why and what you can do about it on this Desert Horticulture Podcast.

Pit Composting Is Much Easier Than Using Tumblers

Q. I only have a small container for composting so I mix it twice a week on the ground and put it back in the container. It’s about 2 months old and I’m wondering if I can use this compost now for my plants?

Composting is nothing more than getting stuff that you don't use to rot. Remember, garbage in and garbage out. If you want a high quality compost use good quality waste.

A. What you’re doing sounds like a lot of work! To judge if a compost is “finished” or not, look at its color, consistency and smell it. It should be rotten through and through, all the same color and have a good smell. Composting is controlled “rotting” of the ingredients.

A finished compost should be the same color through and through, and the smell should be earthy and not like rotten eggs or ammonia.

            I like to divide composting into 2 categories; “hot” composting and “cold” composting. Hot composting relies on developing high temperatures to “sterilize” the contents from human pathogens while cold composting doesn’t. They both rot the ingredients but hot composting is much faster than cold composting.

Compost can be soaked in water to extract nutrients and good microorganisms that can prevent disease and improve the microbiology of the soil. This discoloration of the water is a good thing and called "leachate".Sometimes it's referred to as a "compost tea".

            Your compost size is small so it will probably never become “hot” compost. Whenever handling any compost, always wear gloves and wash your hands afterwards. Your composting will be slow. You can speeded up by making the ingredients of your compost as small as possible.

Compost is a good thing around plants and here it's added to wine grapes. Just keep compost away from the trunk of plants or it may damage it.

            Compost is best used when it is mixed with the soil at the time of planting. Compost added to the top of the soil will improve the soil on the surface but not much below the surface. Because this surface soil is improved, roots will grow towards the surface in or near this composted area. Yes, you can apply it but I would cover the compost with a layer of woodchips if you can’t mix it into the soil.

            Try a composting technique called “pit composting”. It’s much easier to do than what you are doing if you have an open space where you can dig a hole in the soil and let the ingredients rot inside the pit.

Follow an Irrigation Schedule for Your Landscape Or...

Q. I had new landscaping installed last June and had to guess the proper watering schedule for my plants. I really don't know what I'm doing or why I'm doing it so I’m asking you to please suggest a proper watering schedule for my landscape during the four seasons of the year.

Homeowners irrigation controller with the watering schedule released by the local water purveyor. Now you just have to learn how to operate the controller

A. I suggest you follow the irrigation schedule sent by your local water purveyor. How the irrigation system was installed is anybody’s guess. Most landscapes have a mishmash of plants with varying root depths and watering needs so it’s difficult to give a blanket recommendation that fits everyone’s situation.

Research like ours clearly shows water use of plants varies with the seasons. This shows monthly water use of plants in general starting in January (1) through December (12). The trick is figuring out how to apply this schedule with an irrigation controller.

            You are already ahead of many people because you recognize your irrigation schedule should be adjusted seasonally. This adjustment to your watering schedule is primarily the number of days per week that you water. Once the number of minutes is established, or the amount of water plants receive, it doesn’t vary seasonally. The amount of water plants receive is adjusted by increasing or decreasing the number of drip emitters delivering water to each plant.

            There are four seasons in our desert but for someone who uses snow to recognize that it’s winter, they will be lost here. People might argue this point but the four seasons we have start approximately in February with Spring, May for summer, October for Fall and December for Winter. These months are the approximate times when irrigation controllers are adjusted to more or fewer irrigation frequencies each week.

            If you want more precision about how much water to apply, grab a three foot long piece of “skinny” rebar. If you push this rebar into the soil after an irrigation, it will slide into wet soil easily.

A piece of rebar about 2 to 3 feet long helps you to estimate how deep water from your irrigation system has penetrated into the soil. This can easily be translated into how many minutes you should use on your irrigation controller for that valve.

            Push it deeper until it’s hard to push any more. It’s difficult to push when it reaches dry soil. This is the depth of the irrigation water. Repeat this in 3 spots around the plant to get an average “wet soil depth” reading. If you hit rocks when you do this, keep poking the soil in different places until you find a place where you can push it in and get a measurement.

            Small plants, approximately a foot tall, should be watered a foot deep. Medium-sized plants, up to about 8 feet tall should be watered 18 inches deep. Water small trees and large shrubs 24 inches deep. Large trees require deeper irrigations so water them about three feet deep. Adjust the amount of water these trees get individually by adding or subtracting emitters.

Roofing Tar Probably Toxic to Trees

Q. I have a Mimosa tree that is about 15 – 20 years old with four main branches forming the trunk of the tree. These four branches form a "well" about 8 inches deep which catches rainwater and remains wet for about a week or so after a rain. Someone recommended filling this "well" with roofing tar so that the tree doesn't rot at the point where the main branches come together.

Not the readers picture but a silk tree that started to yellow. It could be poor drainage but it also could be the beginning of a disease called Mimosa wilt.

A. Mimosa, or silk tree, is not a long-lived tree due to disease problems. At 15 – 20 years of age it's getting close to the end of its life. Its short life is because of a disease problem called Mimosa wilt disease that invades some of the limbs and causes limb or stem dieback. The tree usually dies in a matter of months once it gets the disease.

            The reason I’m mentioning this is because you should realize this tree may die regardless of what you do so prepare yourself for that eventuality. It may die because of nothing you did or didn’t do. You don’t see a lot of old silk trees around for a good reason.

            I think filling that well with roofing tar is a bad idea and will damage the tree. Rainfall is so infrequent in our desert climate that I don’t think it’s worth the effort or concern. If this catchment is filling with water because of frequent irrigations by sprinklers, then this situation is different.

            Secondly, any compound made from petroleum is potentially damaging to plants. Petroleum products are normally not applied to plants because of their toxicity. You run the risk of damaging parts of the trunk in contact with the roofing tar.

            I appreciate the concern you have, but in my opinion if that tree has survived this long, then leave it alone.

Another Freeze Went through the Valley

            Another freeze went through the valley this past week along with some unusually cold weather. Freezing temperatures are more damaging to plants as we enter the spring months because plants are starting to “wake up” from their winter dormant period. These same plants might have no problems with these temperatures in December and January.

Spring recovery of oleander from a freeze that did a small amount of damage

            During these low temperatures, honeybees were not flying during the day so pollination of flowers would be light. They fly when temperatures are warmer, the sun is shining and wind is light. Put in some plants that flower during the winter that attract honeybees and it will help bring the few that are out there scavenging into your yard. One example is rosemary but there are many others.

Freeze damage to American agave. You can reduce freezing damage to potentially tender plants somewhat by not fertilizing plants with high nitrogen fertilizers a couple of months before anticipated freeze.

            In many places this was a “hard” freeze. Some landscapes were colder than others and this may affect fruit production in trees that were flowering or had small fruit on them. Electronic thermometers that record the previous days lowest temperature are not very expensive and may be worth having this time of year. By having one you will know the temperatures your landscape experienced. The extent of damage to plants relates to the lowest temperature, how long it lasted and the susceptibility of the plant to freezing temperatures.

An older Taylor digital thermometer that remembers the last 10 days of low temperatures. It doesn't give you a date but it gives you a sequence of days up to 10 days historically.Now they have wireless versions for less than $20.

            If you applied fertilizer to your landscape plants already, or plan to soon, then all that the damaged plants need is water for recovery. If fruit is lost due to a hard freeze, there’s nothing you can do about it. If you plan to apply fertilizer soon, save some money and apply it when temperatures begin to warm.