The rule of thumb says established fruit trees or berry bushes will need an inch of water a week. How do you measure that? More importantly how do you know your plants are getting that?
Of course, rainfall is the natural source. Typically, ball park figures assume light rainfall is less than 0.10 inches of rain per hour. Moderate rainfall will provide between 0.10 to 0.30 inches of rain per hour. Heavy rainfall is considered over 0.30 inches of rain per hour. A rain gauge is calibrated to accurately tell you how much water accumulated during a rain shower.
When rain falls short of providing for your plants, you will need to supplement the natural rainfall to the extent of the shortfall. In many areas, summer may bring weeks of no rainfall; in which case you will have to provide all the needed water.
An inch of rain is precisely that, water that covers a given area to the depth of 1 inch. One square yard requires 4.7 or roughly 5 gallons of water to be covered 1 inch deep. The surface area covered by a small blueberry or currant bush could be roughly a square yard — 3 feet by 3 feet. A dwarf fruit tree might occupy more area, say 5 feet by 5 feet; 25 square feet or roughly 3 square yards. So, figure that your tree would need 3 times as much or 15 gallons of water.
One way to supply the necessary amount of water to your fruit would be via bucket; gently pouring the equivalent of one or more 5 gallon buckets gently around the root area and allowing it to drain into the soil. This method can require lots of heavy lifting and get old in a hurry if your fruit garden is extensive.
An alternative is to provide water from a gently trickling hose. To measure what your hose is providing:
- Turn your hose on to a gentle trickle. Make a note of the rate of flow of your hose. Did you give the faucet a half turn, a full turn or whatever creates a gentle trickle?
- Using the hose and nozzle setting that you will use for watering, fill a 5 gallon bucket, timing how long it takes to fill the bucket.
- Now the math is simple. If it took 2 minutes to fill the bucket, it will take 2 minutes at the same setting to provide 5 gallons of water to a small bush. Watering your fruit tree will take 3 times that — 6 minutes — to provide 15 gallons.
You can provide the water in several doses over the week or all in one dose. For deeper rooted trees and shrubs, one good deep soaking is better. It will encourage growth of a deep root system that is more able to find moisture when the soil surface becomes dry. Naturally shallow rooted bushes, such as blueberries, may do better with split applications of water that stay closer to the surface.
In extreme heat or drought, if may be appropriate to double the amount of water given to your garden since the plants may transpire more.
©2013. Adapted from the Backyard Orchardist: A complete guide to growing fruit trees in the home garden by Stella Otto.