Desert Horticulture Podcast: When to Prune Flowering Trees and Shrubs

 It's very simple. Prune flowering trees and shrubs after they finish flowering. Now learn why and how to prune these plants in the desert.

Texas Ranger on the right was pruned with a hedge shears in June.

Looking for Sabadilla?

One reader looking for sabadilla and having no luck finding it. Sabadilla was very popular maybe 40 or 50 years ago as a "natural" pest control product. You can read more about other natural products including sabadilla by clicking here. Since that time other products (insecticidal soaps, Neem, spinosad products, pyrethrum, Bt and others) have grown in popularity. At one time sabadilla could not be found for sale in the US. It is back and growing in popularity. 

 It might have some potential against the leaf footed plant bug since it has been very effective in the past on squash bugs. But like any label for an insecticide, the crop you are spraying MUST be on the label in some way (even if it says vegetables or fruit trees!) and preferably the insect you are trying to kill as well.

Leaf footed plant bug

 

Squash bug on the underside of a squash leaf. About the same size as the leaf footed plant bug.

Q. I have a small amount of sabadilla dust leftover from about 30 years ago. It was the only thing I found that was very effective on squash bugs. I am having trouble finding it. Do you know where I can get more?

A. Sabadilla was made from the ground seeds of the sabadilla plant (S. officinalle). Sabadilla was not available in the US for a couple of decades but it is back. I remember it from my past but I had never used it. Now it is sold mostly for homeopathic treatments for allergies and runny nose. 

I did find one source (I think it might be the only one) online here available from MGK as a "USDA organic" insecticide. It is now a wettable powder (WP) and not a dust (D) anymore (dusts for the most part went by-by years ago and now you can find a few available to homeowners) so it must be mixed with water and applied as a suspension (some sort of agitation of the WP solution is required to apply it evenly). Suspension can sometimes be achieved if you stop and shake a hand sprayer regularly (keep the solution in motion) when you apply it.

Remember, "dose makes the poison" so anything considered "natural" or organic can be lethal if used the wrong way. I figure that if something can kill bugs, then it can kill me. That's true of anything including soapy water and table salt! So use any so-called "natural" or organic product with the same caution you would use with anything that can kill. Wash your clothes and take a shower right after you apply it. That is true of your dust product as well. And wear gloves at least! Always apply insecticides on a still, warm day.

Desert Horticulture Podcast: Confused About Pomegranates?

 There are over 600 varieties of pomegranates with all sorts of flavors and colors that make this a unique and hardy fruit tree for desert climates. 

Yellow pomegranate near northern Tajikistan

Protecting Orange Fruit from Freezing Weather

Q. My oranges haven’t ripened on my two-year-old tree. Some are green and others yellowish with very hard skin and last year’s fruit wasn’t very sweet or soft.  Should I cover them tonight? It will be freezing.

Its possible to get oranges in Las Vegas if the weather cooperates, you have a warm microclimate in your landscape and we dont get a hard freeze.

A. The fruit of many oranges attached to the tree are damaged at temperatures of 30°F or a few degrees lower.  The type or variety of sweet orange is highly variable to freezing temperatures. If you think winter temperatures will drop low enough for damage, then throw a sheet or blanket over the tree to protect it from cold and wind.

Go outside at night and look at the sky. Clear skies are more likely to contribute to lower temperatures than cloudy skies. If there is wind combined with freezing temperatures, fruit damage is worse.

Even though these oranges are ripe they are green. Thats because they are in the Philippines, a tropical country.

Your oranges may not be ripe yet. Ripeness depends on the variety and when it’s supposed to be harvested. Cold weather will get them to turn orange as they ripen. Oranges grown in tropical climates never turn orange when they are ripe. Consumers know this and their green color is acceptable. If they are ripe enough, put them in a paper bag with a few ripe bananas for a day and they will soon turn orange.

My guess from their color is they should stay on the tree longer. If they are sweet, they may handle some temperatures down to about 28F or so. Citrus grown in US commercially are found in in Yuma, Arizona, Rio Grande Valley in Texas, mid to south Florida and southern California. These places seldom freeze.

            Ripe fruit handles temperatures a couple of degrees lower than unripe fruit because of their natural anti-freeze; higher sugar content. The sweeter the orange, lower temperatures by a few degrees are needed to freeze them. If you want to measure the sugar content, follow my blog and type in the word “refractometer” in the search line.

            Our desert climate creates winter temperatures too low for growing and producing citrus. You might have a couple of warm winters in a row followed by low winter temperatures that may wipe out the citrus.

Will citrus grow in Las Vegas? Some years, depending on where they are planted and your choice in citrus. Will they produce fruit here? Sometimes, depending on when they flower and the temperatures just before and after flowering. 

Talk to your neighbors and look around your neighborhood. If your neighbors were lucky at growing oranges, you might have the same luck. Be suspicious of neighborhoods that have no citrus growing in them at all. There might be a weather and climate related reason for that or you might be the pioneer who starts something.

Pay attention to the type or variety of orange you have. You call yours an “orange”. This orange has a name or variety besides just “orange”. These different varieties of oranges flower and are harvested at different times. Some perform better here than others.

The “University of Arizona” published a fact sheet that you can retrieve online called, “Low Desert Citrus Varieties”. If this link is broken, use your favorite search engine and type in these words in quotations and look at the last two pages. This fact sheet tells you the harvest time for different varieties of citrus. Avoid varieties that are ready to harvest in the middle of December or later in the season.

 

 

Tree-Like Photinia Damage after Landscape Conversion

Q. We did a landscape conversion, removed the lawn and now our tree-sized specimen, multi-trunked photinia, is declining. The trunk has cracks, it’s gray and looks ugly. We bought Tree Secret fertilizer and applied water per the directions and it seems to be better. We added more lines around the basin to increase the amount of water and have mulched around the tree. When is the right time to trim it?

Tree-like photinia after landscape conversion

Grey and cracked trunk of photinia due to sunburn and possibly borer damage.

A. The photos you sent regarding the photinia were eye opening. I will post them on my blog as well, Xtremehorticulture of the Desert. These cracks in the trunk and gray color are from intense desert sunlight shining on the tender trunk. This might also include borer damage under that grey, cracked area of the trunk. The grey cracked bark is covering the dead side of the trunk so go ahead and remove the bark and see.

This is sun damage (advanced sunburn) to the trunk of a locust tree and the tree is surrounded by rock. Very similar to the damage on your photinia trunk.

In my opinion, you would have improved the plant by just applying water to a larger area under the canopy and not an expensive fertilizer. Applying a quality compost to that area gives the same benefit as any well-balanced fertilizer. In fact, a well-balanced fertilizer is formulated to substitute for what a compost does naturally. There are no “secret ingredients” when growing plants, just marketing and “time savers” similar to “Hamburger Helper” used in some kitchens.

This intense sunlight shining on a tender trunk results in sunburn, then death to the part of trunk that faces this intense sunlight. This damage is oftentimes followed by attacks by boring insects starting the same year as the damage. Sunburn is known to attract boring insects which has been the consequence of sunburned plants over and over for eons. Desert plants like palo verde and mesquite do the same thing if their tender trunks are exposed like your photinia.

What does photinia look like in a milder climate?

There are two problems going on. Photinia, native to Japan, is not a desert plant and its trunk sunburns easily when exposed to intense sunlight. The other is the landscape microclimate, i.e.,  where it is planted in the yard.

What to do? Obviously, this plant can’t be moved to a cooler microclimate in the yard. And it appears to have done well in that spot before the landscape conversion. I would expand the area irrigated to as much of the area under its canopy as possible. Ideally, irrigating the entire area under the canopy is best. 

Secondly, root prune the plant to the edge of its canopy by slicing into the wet soil at the canopy edge with a sharp shovel. The photinia has this fall, winter and spring to grow new roots just inside its canopy before it gets hot again. These new roots will find the water.

The direct harsh sunlight caused significant damage to the exposed trunk. Microclimate. I think exposing the tender trunks to direct sunlight may have burned them. Not much you can do that looks nice. You could paint the trunks with a very light coat of paint (light colored latex diluted half and half with water) but that might look kind of weird considering. If there are suckers that are growing from that area then leave enough to shade the trunk until it heals. Plant other plants in that area to shade the trunk. 

The trunk will heal in a year or two if this problem hasn’t already strangled the trunks.  You might consider planting something tolerant of the heat to shade the trunk and give it a chance to heal. You might consider lightly draping some burlap between the sun and the trunk to shade it until it can provide its own shade. But whatever shade you can create to keep the sun from damaging the trunk will help.

How to Make Larger Pomegranate Fruit

 Q. What should I do to increase the size of my pomegranate fruit next year? My soil has a red color.

Pomegranate flower

Pomegranate small fruit developing next to each other. Leave only one when they are small. Some varieties are more prone to this than others.

A. Red soil tells me you are probably not from around here and secondly, your soil has a lot of iron in it. This type of iron is not available to most plants because it is low in organics and the acidity is wrong. 

I also assume you are a backyard producer and not a farmer. My recommendations might be different if you had 50 or more pomegranate trees and were local.

Right now, since it is late Fall and it is getting colder and there are still leaves on the trees, there is nothing to do. To increase the size of fruit, focus on pruning, a fertilizer application, and don’t let the plant get droughty. You will see some smaller benefits by removing a flower for small fruit growing right next to another, some thinning and pest control.

First, don’t forget to sanitize your pruning equipment. 

Sanitizing loppers with 70% ethyl alcohol.

About a month before new growth begins in the spring, prune the pomegranate to 5 or fewer (yes, as few as one) larger stems coming from the ground. Remove all the remaining growth to the ground as well. From the remaining larger stems remove all side branches up to your knees. After this is done, spray the plant and the soil directly at its base twice with dormant oil before it begins flowering.

            When flowering first starts, apply fertilizer to the tree 12 to 18 inches from the stems and where the soil is wet. Use vegetable or rose fertilizer if you do not have a fruit tree fertilizer available. Because your soil is red and not brown, consider applying compost instead of mineral fertilizer. If you apply compost, apply one cubic foot of it in a circle 18 inches from these large stems.

Apply compost to fruit trees, not pomegranate but you get the idea.

You might see a smaller benefit by removing flowers during the first couple of months which are produced very close to each other (if your variety does this alot) and controlling pests when you spot problems. If you are an organic gardener, consider using a Dust Buster for removing larger pests instead of insecticidal sprays.

Asparagus Failure in Las Vegas and How to Prevent It

Q. As an avid killer of plants I can't seem to get anything to grow outstanding well.  My asparagus attempt is especially disappointing.  I did as you suggested, mostly, and dug down as deep as my tiller would dig about 13".  For better drainage I 2" drilled holes another 12" and filled them with gravel.  I feel that should be pretty good drainage. I ordered Jersey Knight asparagus and planted as per instructions. I had a very mixed bag.  Out of 10 crowns 5 have died.  1 shot up like a cannon but has since slowed its velocity.  The other 4 are in some stage of growing but not heartily. How do I figure out what I did wrong 9 times and right once?

Jersey Knight? This is a Rutgers release as are all the "Jersey" types. In my opinion it has lower tolerance to desert heat than UC151 types which were bred in Riverside for the Coachella Valley. Eastern US, use Jersey types. Hot western areas of US, use UC151 types. They hold their spears longer.

These should be very vigorous if the soil is amended properly and watered like they are growing in an irrigation ditch.

Put asparagus crowns on their own valve OR put them on a tree valve but not a valve used for growing vegetables in vegetable beds.

Planting depth for asparagus crowns is anywhere from 8 to 12 inches deep. The reason for this is because the crowns get bigger over time and planting them deeper helps them to last longer, over 25 years.

A. Usually the reason for losing asparagus is watering them too often or bad drainage. The gravel was not a good idea. It did nothing for drainage and made it difficult to get straight spears if it improves drainage. If the soil has bad drainage then plant them on a mound about 12 inches high and 24 inches across. Plant them about 8 inches deep. 

Planting asparagus at the University Orchard in North Las Vegas.

Water and don’t water them again until the soil dries out in the area of the roots. How to know that? Use a soil moisture meter like you use for houseplants Buy them for $10 at Lowes or Home Depot. 

Make sure it works. Those made in China sometimes work and sometimes don’t. That's been my experience experience with well over a hundred of them. If the needle moves when you grab the tip it is probably okay. Otherwise stick the tip in a glass of water. Measure the soil moisture about 4 inches deep and water again ONLY if the needle gets to 5. Water them by hand if you have to and don’t hook them up to a valve that waters something else. They are always wrong for asparagus.

 'Purple Passion' asparagus spear straight as an arrow and long because the soil was sandy and not full of rocks.

Pomello Flowering in October in Las Vegas

Q. My little pummelo which came bare root in March has profuse flowering now in November.  The tree is small -5'- and would not support any pummelo sized fruit. Should I wrap it up for the winter and disregard the flowers?

Pomello is a distant relative of grapefruit and enjoyed in many SE Asia countries like on our farm in the Philippines. Its tolerance to freezing temperatures is better than most limes but not as good as some oranges. Its chilling injury (refrigerator temps, think banana) is not well known but suggests it may exhibit chilling injury. Pomello grown in the Las Vegas area.

A. In this particular case I don’t think any of the flowers would have set fruit anyway. Pomello that I know takes about six years to bear fruit. It may flower earlier than this but the fruit have to be pollinated and not abort the fruit.

 

Yes, protect the tree this winter if there are threatening temps below freezing. 

I don’t know about chilling injury (temperatures not freezing but refrigerator like) to this fruit tree but there are some suggestions that it exists.

More information on chilling injury of pomello

https://allfruits.blogspot.com/search?q=pomello  

More discussion on freezing injury of pomello

http://tropicalfruitforum.com/index.php?topic=24319.0

Pomello growing in the Philippines.

A. 

 

What To Do with Ash Trees That Have Scorched Leaves

 Q. I think you addressed this not too long ago but I give your Saturday articles to my neighbor so I’m not sure what you said. The attached photos show two trees the builder put in my front yard two years ago.  I think they are Texas Ash?

 Ash trees with leaf scorch. Most likely this microclimate in the landscape is too hot for this tree.

Aha. This is a hot location if it is south or west facing. The irrigated area under this ash canopy is too small. Expand the area and apply water to a wider area.

I have three yellow emitters and now water these trees twice per week for 15 minutes.  (I can’t remember how many gallons the yellow ones due in an hour)!

A. Ash trees don’t like the heat all that much. All of them including Arizona ash. So surrounded by rock (even though it is five feet away from the trunk) is not the best thing for it. The roots of this tree can't keep up with the demand by this tree for more water. The main reason you are seeing the leaves burning on the outside (leaf scorch) is either because the soil needs improvement or the soil is staying too wet or both.

If you can make that basin covered in wood chips about three feet wider from the trunk it will help. Rake the rock back, get more scalloped pavers and make it bigger.  Also, the wood chips should be about four inches deep. Keep the wood chips from the tree trunk about six inches.

It helps to put a thin layer of compost on the soil surface under the wood chips. If this is a burden then sprinkle it on the top of the wood chips and water it in with a hose. Mixing it into the hole at planting time should have been done at planting time but some of the less expensive plantings (I have heard rumors of this happening with some “special deals” from nurseries) don’t use much amendment at planting time or not much mixed in the soil or the holes are dug too small or all of the above.

I am not sure how you are watering that tree (one of the ash). There needs to be AT LEAST four drip emitters to that tree at planting time about 12 inches from the trunk and enough water applied to wet the soil 18 inches deep each time you water. After the first couple of days the watering should NEVER be daily. The first couple of days daily watering is okay to get the soil wet and get rid of air bubbles. The soil needs to dry out between irrigations. 

A long piece of rebar or any thin piece of steel can be used to judge how deep the water gets after an irrigation. Shrubs less than 3 feet tall irrigate to 12 inches deep, medium sized shrubs and trees to 10 feet tall irrigate to 18 inches deep, if 20 feet tall then water to 24 inches deep and big trees water 36 inches deep.

Use a four foot piece of rebar from Lowes or Home Depot to judge if watering is deep enough. If not, water more minutes or add drip emitters or get some that deliver more water until it gets that deep.

In mid summer three times a week is plenty if they are all alone and no other plants for the ash tree roots to get water from. Right now once or maybe twice a week is plenty. In about two or three years you better add more drip emitters in another ring out past these emitters about 18 inches away.