This is a correction to some mathematical errors in the Irrigation post of a year ago. In some of the calculations I used gallons rather than inches. And I did not adjust the figures for sandy soil. So here are the corrected tables:
Duration of irrigation (in minutes) for plants in sandy soil
grass perennial shrub tree
sprinkler 18 37 73 116
rotor 36 72 144 228
bubbler 0.3 0.6 1.2 1.9
soaker hose 18 36 72 114
1/2" dripline 30 60 120 190
1/4" dripline 36 72 144 228
This table assumes there are enough sprinklers, bubblers, emitters, etc. to cover the area that needs to be watered. If not, multiply the figure by the number of square feet each bubbler, emitter, etc. needs to cover.
For soil that is loam, multiple each figure by 1.5.
For soil that is clay, multiply each figure by 3.
Frequency of irrigation (times per month) for plants in sandy soil.
grass perennial shrub tree
cold 10.5 5.3 3 1.5
mild 26.4 13.5 6.6 4.2
hot 36 18 9 5.7
For soil that is loam, divide each figure by 1.5.
For soil that is clay, divide each figure by 3.
Note -- These tables are for plants that need normal amounts amounts of water (called "regular" in the Sunset Western Garden Book). The frequency of watering will need to be adjusted for plants needing "little", "moderate", or "abundant" amounts of water.
