Monday, March 5, 2012
Q. My Texas Mountain Laurel has yellow leaves and they continue to get more yellow as time goes by. It faces southwest, has 2 adjustable emitters turned down low, in the winter watering once a week for one hour. In early August I fed it with a fertilizer for acid-loving plants. I have looked very closely for bugs, and see none. There are some brown spots that have been appearing on the leaves.
Want to see what this plant looks like?
A. This plant is native to the Chihuahuan desert and so is accustomed to very low rainfall, particularly during the summer months. This doesn't mean you should not water it in the summer but it does tell me that it would prefer deep but less frequent irrigations at the time of the year.
It is also not accustomed to high amounts of fertilizer and does not need fertilizers blended for acid loving plants. This plant grows easily in alkaline soils. It is a legume so go lightly with the fertilizers.
Generally speaking, deep irrigations to a depth of 12 to 18 inches, once a week should be fine during the summer months. You should be able to water less often in the winter. They are found on rocky soils in the desert but I am sure that they would prefer improved soils as long as they drain water.
In the spring this plant tends to get a caterpillar, the larva of the Genista moth, in it that feeds on the leaves. Sprays containing Bt, like Dipel or Thuricide or even Spinosad, should control it with one or two applications when you start to see them.
Genista moth on Texas Mountain Laurel
Genista moth on Texas Mountain Laurel
Q. My daughter has just moved into a house that has old growth lilacs and we need to know how to prune them without causing too much stress on the plants. Do you have any ideas?
A. By the way, Persian lilacs grow and bloom better here than the common lilac and are very showy. However, the lilac variety “Lavender Lady” requires less chilling and blooms very well here. These are not plants for rock landscapes but should be in the high water use zones and the soil should be amended well at planting and covered with organic mulch.
For good-looking lilacs always start pruning at the bottom of the shrub. At the bottom, identify the two or three largest stems coming from the base. Remove them with clean cuts close to the ground. I can't see the shrub but several smaller stems should remain that supports flowering for next year.
What you are trying to accomplish with many woody shrubs is to renew the shrub with new growth on a constant basis. You do this by removal of the largest stems close to the ground. This should cause smaller and newer growth to originate from the base keeping the shrub green, juvenile and full of flowers and leaves from top to bottom.
Every couple of years, repeat this type of pruning; remove the largest stems at the base. If done correctly, this will keep the shrubs renewed and looking good. This is all you need to do unless you have some crossed or broken branches at the top that you need to remove.
Don't forget to fertilize the with a good quality fertilizer made for woody plants. Fertilize plants whenever you take anything from them (pruning) or they give you something (flowering). So when you’re pruning or they bloom for you, you need to give back to them lightly in the form of a fertilizer. You can use fertilizer stakes. Put fertilizers close to the emitters or their source of water. Do this in late January through March and make light applications right after they finish blooming. I hope this helps.
|Orchard with wood mulch in the Mojave Desert|
A. I have never noticed this with the organic wood mulch that we use at the Orchard. It is very important that air gets to the roots. If this is a problem, then break up the crust with a rake.
Very fine mulches can compact or lay flatly on the surface of the soil over time. This can happen with sawdust, finely shredded newspapers and even very fine rock mulch such as 1/4 inch minus. Salts that are pulled up from the soil from surface evaporation can accumulate and cause crusts to form.
Coarse mulches seldom if ever have this problem because they cannot lay flat. Air moves through the coarse mulch where it supplies oxygen to microorganisms that help break down the mulch at the soil surface.
This constant breaking down of wood mulch adds organic matter to the soil which further aids in getting air into the soil. With time, the breakdown of wood mulch loosens the soil even further and causes the soil to allow even more air to the roots, particularly at the soil surface.
Hopefully you added compost to the soil at the time of planting. The wood mulch even adds more nutrients to the soil as it breaks down. It is important to have a wide diversity of different types of wood in the wood mulch; the more the better.
If you want a measurement of the activity, pull the wood mulch back where the soil is irrigated. After just a few months the soil will become much darker indicating its enrichment and biological activity which continuously improves the soil. Wood mulch also helps to keep the soil cooler aiding in decomposition as well.
Q. I want to replace my acacia-like tree because it does not lose its leaves during winter and thus persists in shading our house from the sun at a time we actually need the solar heat. I want a deciduous peach, apricot, plum or apple tree which would be a fast-grower, provide shade during summer, give little shade during winter, and bear some flowers and some good fruits on the side.
A. If you want some shade on your home to help reduce cooling costs in the summer you should focus on shading the South and West facing walls of your home. Since the walls typically have less insulation in them, they are the worst offenders for heat gain in the summer.
It is not as important to shade the roof as it is to shade the west and south walls. If you do focus on the walls, then some of the smaller fruit trees such as peach, apricot and plum and semi-dwarf apple will work just fine. All of these fruit trees are deciduous so they will not create shade from December through February or March.
I would recommend planting them about 5 to 7 feet from the wall and that far apart so that you can work all sides of the trees. Another possibility is to trellis them along the wall to create shade. The trellis should be a stand-alone trellis, not attached to the wall. You can also achieve the same thing by putting an arbor on that side of the house and using grapes to shade the walls from the overhead sun.
My recommended varieties can be found on my blog which is called Xtremehorticulture of the Desert and can be found at http://xtremehorticulture.blogspot.com