Charleston, SC · 29401
Lawn watering need this week
Set your controller to
0.00 - 0.00inches this week
- 0.00in
- Keeps it alive. UC ANR is blunt about this level: expect “many brown areas, considerable thinning out, and little growth” under stress.
- 0.00in
- Full replacement. Keeps good quality turf green and growing through the week.
Total for the week, split across the days you already water. 1.89 in of rain fell here in the last 7 days and has already been deducted.
The working
How that number is built.
Step 1
0.670in ET0
Water lost from a reference lawn, last 7 days
Measured for Charleston, SC from heat, wind, humidity, and sunlight combined, using the FAO-56 Penman-Monteith equations.
Step 2
0.40in
What your grass actually uses
0.670 × 0.6, the crop coefficient for warm-season turf published by the UC ANR Center for Landscape & Urban Horticulture. This is what the plant transpires. It is not a controller setting.
Step 3
0.00 - 0.00in
What you have to apply to deliver that
Rain first: 1.89 in fell in those 7 days and counts toward what the plant needed. What is left is divided by 70% system efficiency, because no sprinkler puts every drop where the grass can use it. Colorado State Extension puts spray heads at 50%, small rotors at 65%, and large rotors at 70%, and notes most untuned home systems run 30% to 40%.
The low end uses 0.4 and the high end 0.6, UC ANR’s minimal and good-quality coefficients for warm-season turf.
Is this a normal week?
27.0% below normal
0.670 in ET0 this week against 0.918 in for the same seven calendar days averaged over the past 5 years here. Both sides are ET0, so this comparison holds no matter what grass you have or how good your sprinklers are.
Already have a weekly number you trust? Move it down 10% and check again in a few days, rather than jumping the whole way. Colorado State describes this as the Percent Key on most controllers, adjusted “in 10% increments.”
The week behind this number
| Day | Lost to weather | Rain |
|---|---|---|
| Thu | 0.14 in | 0.00 in |
| Fri | 0.14 in | 0.00 in |
| Sat | 0.05 in | 0.24 in |
| Sun | 0.09 in | 1.35 in |
| Mon | 0.03 in | 0.30 in |
| Tue | 0.09 in | 0.00 in |
| Wed | 0.14 in | 0.00 in |
Reference evapotranspiration and rainfall for Charleston, SC, from Open-Meteo, over the seven completed days ending Wed. Rain counts toward the week's need, so it is subtracted from what you have to put down.
Check another ZIP
Why estimates differ
Two sources can give Charleston, SC different numbers.
Weekly watering figures move with how the number was measured, which days it covers, and whether rain was subtracted.
How this number is worked out →Soil temperature for Charleston, SC
Nearby
Watering needs near Charleston
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