Answer: It can be confusing when the same species growing in supposedly the same conditions perform differently. Here are some other possibilities to consider: One may have good drainage and the others have poor drainage. One could be getting more water than the other. The soil could be compacted where one is located. There could be construction debris under one, inhibiting root growth. One could have been root bound when planted so the roots continue wrapping around themselves, inhibiting growth. Did the roots dry out before transplanting? Was there any damage to the roots? Has there been any construction activity near the plant? Heavy equipment compacts the soil and can damage roots. Have you applied any weed killer near the tree? Any chemical drift from the neighborhood? Transplant shock is another possibility. Having said that, the most common cause of plant problems in the Southwest is inefficient watering, whether too much, not enough, or applied in the wrong spot and the wrong depth. I've included some detail on watering below. You might also want to contact your County Cooperative Extension office to see if they are aware of any problems affecting mugo pines in your area.
It's important to allow water to soak deeply through the entire root zone. 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. If you ?sprinkle? plants lightly and frequently with a hose or watering can or run drip irrigation for short periods, salts will build up in the top layers of soil and damage or kill your plant. Salt burn shows up as yellowing and browning, and then leaf or needle drop. Deep watering?or leaching?prevents this by flushing the salts past the root zone.
Roots also need oxygen to survive and soil that is continually wet doesn?t provide it. 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. For shrubs, water should reach 2 feet deep, for trees 3 feet deep. It's essential that you allow your system to run long enough for water to penetrate the appropriate depth. Depending on the size emitters, soil type, etc. this might take several hours. The majority of people do not let the water run long enough. 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. After a thorough soaking, allow the top 3 inches of soil to dry out before watering again. I would not recommend fertilizing during the summer, as the heat is stressful enough and adding fertilizer "forces" the plant to grow at a time when it is better off just maintaining. Fertilizer burn resembles salt burn. I hope this info helps.
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