Watering-in-Shade Calculator
Get a realistic weekly watering estimate for a shaded bed or container, adjusted for your plant's water need, your shade level, your soil, and recent rainfall.
Watering plan
Water once or twice this week.
How the estimate is built
The calculator starts from a full-sun reference need for your plant's water-use category, then derates it for how much shade cuts evapotranspiration, and adjusts again for how well your soil holds onto moisture. Recent rainfall is subtracted directly, since rain and irrigation both go toward the same weekly total.
Treat the result as a starting point rather than a fixed rule — always check the top two inches of soil by hand before watering, since containers and very sandy soils can dry out faster than any formula expects.
Frequently Asked Questions
Why do shaded plants need less water than the same plant in sun?
Evapotranspiration — the combined loss of water from soil evaporation and leaf transpiration — is driven mainly by sunlight and heat. A shaded bed stays cooler and the soil surface dries more slowly, so the same species typically needs meaningfully less supplemental water in shade than it would in full sun.
How does soil type change the answer?
Sandy soil drains fast and holds little water between waterings, so it needs topping up more often. Clay holds water much longer, so the same plant in clay can go longer between waterings — sometimes to the point of risking waterlogged roots if you don't account for it. Loam sits in between and is treated as the baseline here.
Does this account for the rain I've already had?
Yes — enter your rainfall for the past week and the calculator subtracts it from the derated need. If recent rain already covers what the plant needs, it will tell you to skip watering rather than adding more on top.
How is the container watering amount calculated?
Once the net weekly need in inches is known, it's converted to a volume using the container's surface area and the standard conversion of 7.48 gallons per cubic foot of water — the same conversion irrigation professionals use to turn an inches-of-water figure into gallons.
Educational tool only. Results are estimates from standard reference rates — always check the soil directly before watering, especially in containers or after unusual weather.