|I have two sissoo trees in their 3rd year. I am told they have salt burn according to the laef appearance. I have asked several nuserymen what to do and often the answers conflict. Baiscly the consensus is to leach the soil with deep watering. However, the frequency of deep watering is confusing. a 24 hour slow drip around the base of the tree? How often should I deep water and for how long?? And is their siol amending with what?
|Desert soil and water both contain lots of salts, which can accumulate in the root zone over time. Salt burn shows up as yellowing and browning along leaf edges, and leaf drop. Deep watering?or leaching?prevents this by flushing the salts past the root zone. Here's what's happening. Salts dissolve in water. Salt buildup forms where the water stops penetrating. For example, if over time water soaks 6 inches deep, the salts will be deposited where the water stops at the 6-inch mark. If you water plants lightly and frequently, salts will build up in the top layers of soil and damage or kill your plant over time. We see this happen alot with drip irrigation because it doesn't supply sufficient water for deep watering. For example, an emitter that puts out one gallon per hour would only put a quart of water on the ground in 15 minutes. Think about dumping a Big Gulp on a tree, and you can visualize how ineffective this would be. For trees, water should soak 3 feet deep, as this is where most of the roots are located. It's essential that you allow your drip system (or hose or bubblers) to run long enough for water to penetrate the appropriate depth. Depending on the size and number of emitters, soil type, etc. this might take several hours or 10 hours or many more. You can reduce the time you run the system by putting on extra emitters or changing to emitters with higher gallon/hour flow rates. Use a soil probe (any long, pointed piece of metal, such as sharpened rebar or wood to poke into the soil) to check how far water has penetrated. The probe moves easily through moist soil, but stops when it hits hard dry soil. When the water has penetrated past 3 feet deep, you can stop the irrigation. Time the system so you'll know how long to run it. There are numerous variables involved for watering schedules, such as type of soil, how fast or slow it drains, sun and wind exposure at your site, temperature, age and condition of the plants and much more. Use the information above to determine how moist the soil is before automatically applying more water.
As a tree grows, its new roots tips, where nutrients and water are being absorbed, spread out laterally. Expand your watering zone out PAST the tree's canopy edge, or dripline, as it grows. As the tree grows, continue expanding that water zone. If you have an irrigation system, you need to move the emitters out. If you use a hose, just drag it out further. Watering as the base of the trunk is basically a waste of time and water as there are no feeder roots there to absorb it. I hope this info is helpful.
With any plant in the desert, your goal is to water slowly, deeply and as infrequently as possible for that plant's needs. Leaching is the only effective treatment to prevent salt burn. Finally, note that similar symptoms to salt burn will appear with overfertilization.