Do I need to change the irrigation for my Shamel Ash trees?

Question

I have three Shamel Ashes in my yard, all planted at roughly the same time and all irrigated in the same way. Despite professional care they haven't shown any substantial growth in over a year. If anything, they have thinned.

I live in Phoenix, Arizona (US). My research leads me to believe that the tree may struggle a bit in the hot weather but are still a viable choice for the region. I don't believe that they have been substantially under/over-watered though I could certainly be wrong. A small number (< 10%) of leaves have brown tips.

Each tree is currently watered with four drip lines located a short distance from the trunk. They are shown uncovered (normally they are buried) in the picture below.

The water has been on for an hour in this picture. Even if it soaks to an appropriate depth, it doesn't look like the water is well-distributed.

• Should I add more drip lines?
• Change the irrigation method entirely?
• Or should I be investigating other problems?

Answer 1

This does likely have something to do with watering, but there are several issues here. When watering, it is better to give the water all at one time, ideally over a period of ½ hour, and make sure it soaks in well. Then let it dry for a time before watering again. The time will depend on environmental factors, such as temperature, precipitation, and cloudiness. Making a shallow trench around the trees will keep the water where it should be, and help keep precipitation in place.

Mulch with a layer of organic matter to a depth of between 2 and 4 inches. This will conserve soil moisture, keep the soil temperature more even, and add organic matter as soil microbes work it in. Keep it away from the trunk, though, in a 6" diameter circle.

Those trees are on the larger end of those that are regularly transplanted. On trees this size, the first 2-3 years are often spent rebuilding the root system, which was severely damaged during transplanting. What you should do is make it as easy as possible for the tree, by watering properly, fertilizing very lightly, or with an organic fertilizer high in phosphorus, mulching, and even cutting back crowded top growth (which is possibly pulling more energy than is well sustainable.

From your picture, the trees look OK. Again, water more, in the style described above, fertilize, and mulch. Also, that wall will be very reflective, so that may have some affect on the leaves drying. If you can cover it with something less reflecting that will be beneficial. In any case, plan on at least a couple years before any major growth above ground.

Answer 2

From the picture it doesn't look like the drip irrigation extends beyond the root ball. It helps to not only give the tree what it needs in the root ball, but also to make conditions outside the root ball hospitable. If the soil outside the root ball is dry (or otherwise unfavorable), roots will tend to stay within the root ball - limiting growth potential. Also, if the soil outside the root ball is too compacted, the roots might not penetrate outside the hole. In such cases it can help to dig trenches away from the ball like spokes. Fill these trenches with high quality compost to serve as avenues for root growth outside the root ball.