Regional Gardening Reports :: National Gardening Association

In the Garden:
Southwestern Deserts
June, 2010
Regional Report

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Low branches protect trunks from sunburn. Double berms protect the trunk from standing water while allowing water to soak in at canopy's edge where roots can absorb it.

Summer Citrus Tree Care

Citrus trees thrive grown outdoors across much of the Southwest's low desert elevations. However, they need special care to survive hot summers.

Prevent Sunburn
Citrus bark is very susceptible to sunburn, especially on southern or western exposures in summer. Sunburned bark turns black or discolored and often cracks and peels, opening up your tree to pests and diseases that will kill it. There are several options to prevent sunburn. The most common is to paint exposed trunks with white latex paint specifically designed for trees. Another option is to loosely wrap the trunk with tree tape, burlap, cloth or even layers of newspaper. Remove the wrap at the end of summer.

A more natural appearing option is to follow the preferred method of commercial orchard owners and leave as many low branches on the tree as possible. Not only does foliage protect the trunk, but you'll also spend less time pruning, painting or wrapping. Fruit is much easier to pick from low branches, making a fun little treat for kids and grandkids!

Don't Prune
Pruning in summer creates gaps in the tree's foliage, which allows the sun's rays to burn exposed tissue. Prune only to remove diseased or storm-damaged branches.

Provide a Wide, Deep Drink

One of the most common questions that University of Arizona Maricopa County Cooperative Extension Master Gardener volunteers answer is "Why are my citrus rinds cracking?" This question lights up the phone hotlines in fall if trees didn't receive adequate water in summer. Without sufficient water, rinds can't expand as they grow, so they crack.

However you apply water (hose, drippers, bubblers or flood irrigation), as your tree matures, expand the watering zone to keep up with the growing canopy. Applying water near the trunk of a mature tree is a waste, because there are no roots there to absorb it. Feeder roots, which take up water and nutrients, are found in the ground past the canopy edge.

Watering near the trunk is also bad news because it encourages Phytophthora, a fungus that moves with the aid of water. If water stands near the trunk, 

 the disease can kill the bark and the tree itself within a year. Prevent Phytophthora by building one berm of soil around the trunk to prevent irrigation water from standing against bark tissue. 
Then build a second berm at the outer edges of the canopy, creating a large basin to hold irrigation water so that it soaks into the root zone.

Your goal is to water deeply, but as infrequently as possible. With each irrigation, water should soak 3 feet deep for mature citrus (those that have been planted 3 years or more). For new transplants, water can soak from about 1.5 to 2.5 feet deep, depending on the size of the original rootball or container. Deep watering promotes root establishment and leaches harmful salts beyond the root zone.

How often to water depends on many factors, such as weather, soil type, elevation, wind exposure and your micro-climate. As a general guideline in June, July and August, irrigate mature trees (3 years or older) every 10 to 14 days. Water trees 1 year or young every 5 to 7 days and 2-year-old trees every 7 to 10 days. Remember this is a guideline only! It's important to look at your plants, feel the soil and get used to your micro-climate's conditions.

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