The Q&A Archives: Watering in Phoenix, AZ

Question: I moved to Phoenix from Fort Worth, TX so I was used to humidity and lots of 'green'. I now have a 'rock yard' I did plant some lantanas but find I must water them everyday is this soil that is like cement when dry. I did use good soil, dug the holes twice the size of the container ... put circle guards around them to hold extra mulch (and keep the birds/quail/bunnies from eating or sleeping in them) but it appears I can not go more than 24 hours without giving them a thorough watering. I also have an old scotch pine tree in my yard that has lost most of it's needles. I do allow the water to run slowly at it's base once a month for several hours to ensure it gets a deep watering and have pounded in fertilizer stakes at it's drip line, but it still looks pretty bad. What should I be doing differently?

Answer: Welcome to desert gardening! There are many beautiful plant choices and here's a great resource: contact the Phoenix City Water Conservation Department for a free copy of Landscape Plants for the Arizona Desert. It is a color guide listing more than 200 low-water-use plants, along with growing and special characteristics (e.g., hummingbirds, etc.)

As for watering the lantana, you didn't say when you planted it, but if recently, just about any plant will require frequent watering to establish in this heat. 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. Non-desert, high-water-use plants would be more.

Use the 1-2-3 Rule for watering. Small plants with shallow root systems, such as perennials, veggies, herbs, cacti, succulents, groundcovers (like your lantana) 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, etc. 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. You need to water more frequently in summer than during winter. For veggies and small plants, it may be necessary to water daily.

A soil probe will help you determine how far water has soaked. It moves easily through wet soil but stops when it hits hard soil. Let your water run in timed increments, then wait several hours (for the water to continue penetrating), then use a soil probe to determine how far the water penetrated in your soil. For most areas, it's necessary to run irrigation much longer than people would think. The majority of the plant problems we see are because drip isn't running long enough. In improved soil garden beds, such as for veggies, it will soak more readily through the soil than it will in landscape settings.

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.

Your pine tree may not be receiving sufficient water even with the hose running for several hours. Apply water at the outer edges of the canopy, all around the tree, and use the soil probe to make sure it's penetrating deeply. Most pine trees in the Valley are Aleppo pine and they've been experiencing Aleppo pine blight for the last couple years, with needle dieback, most likely caused by a variety of cultural and weather factors. I hope this info helps!

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