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Thursday, January 31, 2013

Keys to Healthy Landscape Plants in the Desert

Q. We have several shrubs with an eastern exposure that appear to be very distressed or dying. The first three photos show the entire shrubs. Photos 4 and 5 are close ups of the distressed area. Photo 6 is a very healthy plant in the same area but with a southern exposure. Irrigation is excellent; enough that water is standing in the bed upon completion of the water cycle which is five minutes and four times a week in the hot summer.

Japanese euonymus in question
A. Thank you for the pictures.  There are several things that might be going on at the same time with these shrubs.  They appear to be variegated mock orange and Japanese euonymus.  Many of the leaves are yellowing and scorching or turning brown and dying from the tips back. 

            Most people will look at these pictures and say they are not getting enough water.  Another person might look at the same pictures and say they need iron. Another person may look at the same thing and say they are getting too much water. And even another person may look at that and say it is salt damage. The problem is they could all be correct just based on the pictures.

Leaf damage closeup of Japanese euonymus
            Many of these things, and even more, are interrelated.  Just giving more or less water or even iron may not solve the problem alone.  Let me just give you a rundown of the problems that I see as possibilities: plants planted in the wrong spot in the yard, improper pruning, lack of additions to the soil to improve it, wrong type of fertilizer and improper watering. 

            From these pictures, any of these could be a possibility and there could be combinations of things going on.  Let me handle each, one at a time and perhaps you can make the best decision.

First of all plant location.  If this is a very hot location, facing south or west with lots of reflected heat and light, then they will not do well in this spot. This does not mean that they cannot survive there; it just means it will require more effort to keep them looking good if they are placed in spots that are extreme for their best health. 

Variegated mock orange with scorching and dieback
            By finding the best location for plant in a yard means that they will require less time, energy and money to keep them looking good.  A very hot location will be even more difficult if there is no air movement and they just sit there and bake.

Pruning. These shrubs appear to be pruned with a hedge shears into the shape of a gumball.  This type of pruning may work for a few years but eventually this type of pruning makes the plants look ugly and contribute to their poor health. 

            Pruning with a hedge shears should be reserved for hedges, not shrubs.  This type of pruning forces older wood out closer and closer to the perimeter of the shrub.  Young or juvenile wood is the only wood that is removed. 
Closeup of variegated mock orange leaf scorch

            My guess is that you have a landscape maintenance company doing the maintenance.  This is how they prune. They don’t know any better. Very few, if any, prune shrubs properly. The proper way is to remove ¼ to 1/3 of the shrub each time it is pruned, forcing new growth to come from old wood deeper inside the canopy of the shrub.  This rejuvenates the shrub, adds more juvenile wood to the canopy and keeps it young and vigorous.

Soil amendments.  I could not tell from the picture but these shrubs will perform better if they were growing in organic mulch or wood mulch.  Not bark mulch.  The chipped wood decomposes into the nutrient poor soil and adds vital nutrients for the shrubs. 

            Rock mulch also breaks down but adds only minerals to the soil.  The shrubs will perform better if compost is added to the base of the plants and watered in with a hose.  Compost should be added to the list of fertilizers and soil improvements for these plants each year. 

            The first year I would add about 4 cubic feet of compost per plant along with its fertilizer applications.  After two or three years of this I would probably only add about 2 cubic feet per year.  Then of course the wood mulch is an added on top of the compost.  You should start to see improvements after one full season of growth after the additions.

 Fertilizers. The same type of fertilizer used for lawns will do a good job on most shrubs as well.  This is usually a fertilizer with a ratio on the bag of 3-1-2 or 4-1-2.  An example of a 3-1-2 fertilizer would be something like 12-4-8 and a 4-1-2 might be 16-4-8.  You will not find these numbers on fertilizer bags exactly but at least you can get the idea of how the numbers should go up and down in sequence. 

            The next fertilizer you need is an iron chelate such as iron EDDHA.  It is expensive but can go a long way since of the small amount is needed each year.  My apologies to other nurseries and outlets but I know that Plant World Nursery carries this iron chelate.  If others do, let me know please. Fertilizers are added to shrubs in February of each year.

Watering. The frequency of watering will vary during the year but during the heat they will probably need water about three times each week.  As it gets cooler, decrease that to twice a week, cooler yet, than once a week, etc. In the winter it should be no more frequently than once a week.

            The gallons of water to apply is going to be difficult for you to judge because you operate an irrigation clock in minutes. Somehow you need to get a handle on the relationship between the minutes on your clock and the gallons delivered to the plants. 

            These plants would probably be adequately watered if they were to receive somewhere around 5 gallons for the smaller shrubs to 10 gallons for the larger shrubs at each irrigation.

            All of these things are interrelated and so doing just one of them may or may not be enough. 

            The three top things I would investigate more closely are your watering, soil improvement and fertilizers.  If you can get the plants healthy, then they can handle higher temperatures provided they are pruned correctly.  Hope this helps.

1 comment:

  1. Another great post to forward - you hit all the points that need to be hit. Eventually, the word will get out to maintenance people, but especially the people who hire them no matter the scale of their project.

    Not to mention designers, who often don't consider the space a plant is forced into...