Trees especially need very large amounts of water the larger they become. For trees, the recommendation is 5 gallons of water per week for each inch of diameter. For example a 6″ diameter tree needs 30 gallons of water per week. Obviously, very large trees need inordinate amounts of water. Shrubs also need correct and consistent irrigation.
We have preached for years that you only need to deep water 1x per week to maintain your landscape. This will generally get your plants through the worst droughts but every yard is different. You may need to water less or you may need to water more. The key is to never allow your soil to become excessively dry. Trees require 5 gallons of water per each inch of trunk diameter per week. For example, a 5″ diameter tree would need 25 gallons of water per week. Your shrubs require at least 1″ of water per week. Measure your irrigation output with a rain gauge. Use 5 gallon buckets or Treegator® to water you trees.
During excessively hot and dry conditions you may need to water deeply two times per week to counteract increased evaporation and increased plant transpiration (water loss through the leaves). Again, if the soil is dry then WATER!
If you have allowed the soil to become dry, do an initial heavy watering to ensure the soil is adequately hydrated then you can move to the 1 time per week/1 inch per week regimen.
The key to proper watering and plant health is deep and consistent watering. Be sure you keep the soil moist, to a depth of at least 6″ into the root zone. Applying 1″ of water per week is usually sufficient to keep plants stable even during dry periods. Of course, since you are monitoring rainfall with your rain gauge, you know when you need to augment with irrigation.
Consistency is the other key to a healthy plant. You can’t make up for the lack of water by watering excessively AFTER you haven’t watered for weeks at a time when you were dry.
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