Water from the monsoon season has been especially abundant this year, so why are some of our trees and shrubs acting water-starved?
In the low desert, we think that any time a plant doesn’t look well, it must need water. We actually need to step back and examine the situation.
- Is the soil moist under the surface? If so, it probably has enough water and something else is happening.
- If it is soggy or foul smelling, it is getting too much water.
- If the leaves are brown on the tips but soft, it’s also a sign of too much water.
- If the burned parts of the leaf are crisp, it is probably starving for water, but sometimes not because you haven’t given it enough. Its roots simply can’t take in the water.
Our low-desert summer months often cause the latter crispy leaf symptom because we increase our watering schedules to compensate for the heat.
When we combine drought with irrigation, often the crispy leaves appear in the middle of the growing season. The most frequent cause is salt burn.
WATER IS THE PROBLEM & THE CURE
Our soil is very alkaline, which means that it has a lot of sodium in it. Our irrigation systems also have quite a bit of salt content, which only adds to the alkaline presence in our soil.
When salt enters the ground through water, it can harden our clay soil around the tree roots if the water doesn’t carry the salt past the root system. Slowly, the hardened clay cuts off nutrients and water to the tree roots. If you don’t intervene, slowly the limbs will die and then the whole tree.
Generally, just applying more water to an already affected tree won’t save it because irrigation water is the biggest culprit. The clay soil has probably already bound up the roots and prevented water and nutrients from entering in.
When the symptoms are light, I recommend about six inches of fine compost around the tree and mulch on top of that. Then give the tree a long, slow, deep watering. The compost puts more nutrients into the soil slowly and the mulch will lessen evaporation so that salt doesn’t gather on the surface of the soil. The deep watering will flush the salt away from the roots and below the root line.
When symptoms are more serious (many leaves affected or limbs are brittle), gypsum along with the compost and mulch may be needed.
Generic gypsum is very inexpensive. You can get a 40-pound bag for about $4 at any gardening center. Make sure you purchase it from a garden department so that you know you are getting the non-toxic variety, not the construction version. You can pay much more for some that claim to be fast-acting, but I haven’t seen a major difference that would warrant the additional cost.
Pull back any current mulch and compost you have around the tree. If you didn’t create a well around the tree when you planted it, then build up a berm to hold in water. It should extend out to the canopy in a small tree, or at least 4-5 feet out from the trunk of a large tree. Dust the top of the soil within the well or the berm with gypsum. It should coat the top of the soil so you can’t see much soil beneath but you don’t want a thick layer. It should look like a dusting of snow. Now water very deeply to push the gypsum into the soil. It will begin to break up and aerate the clay around the roots. You may have to water very slowly for a couple of hours, let the water seep in for an hour or two, then water again for a couple of hours. Your goal is to get the water down at least 18 inches.
Once you are done, top the soil with about 6 inches of compost and then a layer of mulch. Pull the compost and mulch back about six inches away from the trunk.
If the tree doesn’t show signs of recovery within two weeks, repeat the process. Never apply fertilizers or other additives when you are treating salt burn. It will only cause more problems.
To prevent salt burn in the future, all shrubs and trees should get a monthly deep watering, especially in our warm months.
Salt burn can also affect potted plants and in-ground gardens. Rarely does it happen in raised beds because the soil is porous enough to flush it down. Treat pots and in-ground gardens the same as described for trees and shrubs.
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