This Watering Guide is posted here by permission of the Desert Botanical Garden, Phoenix, Arizona. You may visit their web site for more information on desert plants, just click on the following link. www.dbg.org.


WATERING DESERT TREES AND SHRUBS
Although desert plants have developed mechanisms for conserving and storing water, none have given up the need for water entirely. There are many variables that determine how much and how often plants need supplemental water. Soils with a high clay content hold moisture well, too well for some desert plants, and should be amended with organic matter, coarse sand or both. Rocky soils hold little moisture so plants growing in them may require more frequent watering.

The time of year which plants are put in can determine watering needs. Planting in the fall requires watering with less frequency, after the first two weeks, than planting in the spring. Watch plants carefully, especially the first month or when the weather changes dramatically. If the plant wilts often, or is languishing, check that water is being delivered properly and is draining properly. 

How you water can be as important as how often you water. Trees and shrubs (woody perennial) require regular, deep watering. Constant, shallow watering will result in shallow roots which increase the danger of toppling or heaving. In addition, shallow watering enhances the natural salt build up found in desert region soils. 

Using drip irrigation can dramatically aid in maintaining a proper amount of water for your plants, as well as use water more efficiently. Water is delivered directly to the roots with very little of it exposed to air evaporation. Drip emitters of at least 2g/hour should be used for trees and large woody shrubs. Smaller perennial, annuals and vegetables will be adequately watered by lg/hr emitters. Place at least two emitters on a tree that is planted, and up to 6 if the tree is in a 15 gallon container or larger. Drip irrigation helps establish a tree, and if the line is dedicated to trees, will provide ample water for the first 2-3 years it is in the ground. After that laying a hose on the ground and letting it run slowly and deeply overnight or longer is an even more effective system. This method is greatly enhanced by the use of a basin. Basins should be sized to extend at least to the edge of canopy, further if possible. For large shrubs two emitters will be adequate when originally planted and up to 4 later if the plant is particularly large. Smaller perennial rarely need more than one throughout their life. 

SCHEDULE 
For trees or large woody shrubs planted in the spring 
First week -- every day 
Through June or when temperatures are over 108 degrees -- 2 times/week 
July-September -- one watering/week 
October-November -- twice/month 
December-February -- one/month 
March-April -- twice/month 
If planted in the fall there is no need to water every day, twice a week will suffice unless the weather is unusually warm. 
For the next 3-5 years, or until the tree is about 4 inches in diameter 
April-September -- twice/month 
October-March - once/month 
For next 2-3 years or until a tree is about 12 feet tall 
May-September -- once/month 
October-April -- once/60 days 
After that time desert trees and large woody shrubs need watering only during the hottest time of the year - May through July a very long soak once a month. 
Smaller perennial planted in the spring or early summer 
First two weeks -- every day 
July-September -- twice a week 
October-November -- once/week 
December-February -- every 10 days to once a week depending on the weather 
March-April -- once a week 
May-July -- twice a week 
 

Remember these are general guidelines only and your particular soil and site conditions will have a great effect on how much and how often you water your plants. Watch them, adjust schedules when necessary, and be sure that only similar plants are being watered by one station or valve on the line.