Garden Watering Schedule Calculator

How it is calculated

Each plant type has a fixed weekly water target in inches: vegetables 1.5, lawn 1.0, flowers 1.0, shrubs 0.75 (an unrecognised plant type is treated as 1.0). The tool subtracts the rain already received, never going below zero, then converts depth to volume: apply = max(0, need − rain) in inches, and gallons = apply × area × 0.623, with area in square feet and gallons being US gallons per week. It also shows the inches still to apply and the rainfall credit. Area must be above zero, rainfall cannot be negative, and both fields must be filled in, with 0 entered for a dry week; otherwise there is no result. Real needs vary with soil, heat and wind, so treat the target as a starting point.

Common mistakes

• Entering the area in square metres or square yards. The formula assumes square feet, so the volume comes out wrong by a factor of about 10.8 or 9.
• Typing rainfall in millimetres: 10 mm of rain is about 0.39 in, not 10, and entering 10 wipes out the whole requirement.
• Leaving rainfall empty for a dry week. The field is required, so enter 0 to get a result.
• Choosing lawn for a vegetable bed, or the reverse. The weekly target changes from 1.0 to 1.5 in, which changes the gallons by 50%.
• Pouring the weekly total in one session when you water several times a week; the result is per week, so split it across your watering days.