Garden Watering Need Calculator

Many regional weather networks, irrigation districts, and agricultural extension services publish daily and weekly reference ET by weather station or ZIP code. In the western US, the CIMIS (California Irrigation Management Information System) and similar state networks provide this data. The FAO also provides global reference ET maps. Always use a local station's value - ET0 varies enormously with local climate, humidity, wind, and sun.

Generally yes for established plants. Deep, less frequent irrigation wets the full root zone and drives roots downward, dramatically improving drought resilience. Daily light sprinkling encourages shallow, vulnerable roots that suffer quickly when watering stops. The exception is newly seeded or transplanted beds, which need frequent light moisture at the surface until roots establish.

Significantly. Mulch cuts bare-soil evaporation, lowering the actual ET the soil layer contributes. A well-mulched bed often needs 20-40% less irrigation than the open-soil calculation suggests. If you mulch heavily, reduce your effective ET0 estimate or simply observe soil moisture directly to calibrate your schedule. Mulch is one of the highest-return investments in water efficiency for a home garden.

It converts inches of water depth over an area in square feet to US gallons. One inch of water depth over one square foot = 144 cubic inches of water (12 × 12 × 1). One US gallon = 231 cubic inches. So 144 ÷ 231 ≈ 0.623 gallons per square foot per inch. For a 200 sq ft bed needing 1.1 inches of irrigation: 1.1 × 200 × 0.623 ≈ 137 gallons.