The Q&A Archives: Watering Young Trees

Question: I planted two dogwood trees a couple of weeks ago--they've both started dying. I have been watering them daily, sometimes twice a day--I used plant food with them. Is it possible that I am overwatering them?

Answer: It shouldn't be necessary to water twice daily, so you may indeed be overwatering them. Plant roots need oxygen to thrive and saturated soil doesn't provide it. However, it's just as likely that the trees are not receiving sufficient water through the entire depth of the root system. Often, people "sprinkle" a bit with the hose, or run drip irrigation for 20 minutes, but don't realize that isn't applying enough water to moisten the roots.

For example, an emitter that puts out one gallon per hour would only put a quart of water on the ground in 15 minutes. For mature trees, water should soak 3 feet deep; for newly planted trees, about 2 to 2.5, depending on the size/depth of the rootball when it was planted.

Use a soil probe (any long, pointed piece of metal 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. 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. It's essential that you allow your drip system to run long enough for water to penetrate the appropriate depth. Depending on the size emitters, soil type, etc. this might take several or many hours.

Use the 1-2-3 Rule as an easy method to remember how much water to apply. Small plants with shallow root systems, such as perennials, veggies, herbs, cacti, succulents have roots that reach about 1 foot deep, so water needs to penetrate that far. When the top 1 inch of soil dries out, it's usually time to water again. Shrubs have root systems that are 2 feet deep so water needs to soak 2 feet deep. When the top 2 inches of soil dries out, it's time to water. Trees are 3 feet deep. As plants establish root systems, the time between waterings can be lengthened, but it is always essential to water to the same depth. So you are applying the same amount of water with each irrigation regardless of the time of year, but the frequency changes. As warm weather arrives, you need to water more frequently than during winter.

Desert soil and water both contain salts, which can accumulate in the root zone over time. This salt buildup forms where the water stops penetrating. Short periods of watering cause salts to build up in the top layers of soil and damage or kill your plant. Salt burn shows up as yellowing, browning along leaf edges, and leaf drop. Deep watering?or leaching?prevents this by flushing the salts past the root zone. Always water slowly, deeply and as infrequently as possible.

Here are some watering guidelines for establishing desert-adapted plants from Desert Landscaping for Beginners, published by Arizona Master Gardener Press. Weeks Since Planting 1-2, water every 1-2 days; Weeks 3-4, water every 3-4 days; weeks 5-6, water every 4-6 days; weeks 7-8, water every 7 days. Gradually extend the watering as plants establish. Note these are guidelines, which will vary depending on your soil type, microclimate, etc. and they apply to desert-adapted plants.

Without knowing the symptoms, some other possibilities include fertilizer burn or transplant shock. All plants experience some setback after transplant and usually recover. Fertilizer burn is more serious. I'd suggest stop fertilizing until the roots can establish. I hope this info helps!

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