EMERGENCY: Aug 2, 2011. Since writing this article in mid July, the drought (heat/wind/dryness) has become much worse. And it promises to go on for an extended time. I have discussed this topic with many, and one thing seems clear. Gardeners are NOT checking their soil to actually feel the moisture. I strongly recommend: Dig down at least 8 inches into the soil (for garden, shrubs and trees). At that depth, a handful of that soil should be wet enough to not fall apart when squeezed and dropped. Tree tops are turning brown in our native forests --a sure sign of severe stress.
Here in Northwest AR, the hot/dry/windy weather that we are currently experiencing, is ow taking its toll on our shrubs and trees. The low humidity and wind has depleted the soil water to an extent that I have not seen in the past decade. If you have not watered your trees and shrubs, do it now. You could lose them.
How Much Water to Apply? First, here are some facts. A one-inch rain supplies 62 gallons for each 100 square feet. A tree can easily use one to two (or more) inches of rain per week. Consider the watering area for a tree to be at least as large as the the area under the crown. (Just get the average distance in feet across the whole crown and square it). A small tree (5-inch diameter stem) can easily have a crown area of 200 square feet and a mature tree can easily have a crown area of over 600 square feet.
For each 100 square feet, add roughly 90 gallons of water per week. For most small trees (200 hundred square feet of area under the crown), I simply turn on the faucet so that I am getting 1 gallon of water per minute, and let it run for 5 hours. A soaker hose is ideal for getting good distribution. For a large, mature tree (600 square feet of area under the crown), I let the water run for about 15 hours. If you have not watered in the past 8 weeks (with essentially no rain), you should start by doubling these amounts. The soil is gun-powder dry and this amount of water is needed.
I know this may sound excessive, and I understand if you have concerns. However, consider the costs associated with tree removal, replacement, energy savings from shade on a house, and/or losses from fruit or nut production. It will quickly add up, so don’t wait and don’t skimp on the water. Use this as a guide and adjust on the methods that fit your situation. Water at night if possible.
Water Costs will vary by where you live. At Washington Water, without city sewage costs, I pay about $12.00 per each 1,000 gallons. I have 15 trees, averaging about 300 square feet of crown area per tree. At the rate of adding 90 gallons per 100 square feet, that means I need about 4,050 gallons of water per week, at a cost of about $50.00. Even if I have to do that for 6 weeks, i.e. $300.00, that is a real bargain compared with loss of shade, future pecan production, and tree removal and replacement.
Water Conservation. Anything you can do to help the soil hold more water is beneficial. I use a 6-inch layer of mulch of wood chips and leaves around my trees. As the trees grow I make the mulch circle larger each year, up to 8 feet in diameter. As the mulch decomposes, it gets incorporated into the soil, which increases the soil water holding capacity. Through transpiration, trees use a lot of water and there is not much you can do to change that water consumption.
Priorities. You may feel that you cannot water all your trees. If so, select those for watering on the basis of value. Water those Of the trees you plan to save, water those in the driest places (shallow soils) first.