The short answer
If 5 mm or more of rain is forecast in the next day or two, hold off watering. A light shower of a millimetre or two barely wets the top of the soil and doesn't replace a watering.
How much rain is enough?
One millimetre of rain is one litre of water on every square metre of ground. That makes it easy to picture.
A few millimetres only soaks the surface. Around 5 mm in a day, or 20 mm across a week, leaves most garden soil moist below the surface, where the roots are.
Why not water anyway?
Watering soil that is about to be soaked wastes water. It can also do harm. Waterlogged soil starves roots of air, which can lead to root rot. Heavy watering followed by heavy rain also washes nutrients out of the soil, down past the roots.
When to water anyway
Rain doesn't reach every plant equally. Water as normal if:
- You are growing in pots or containers, which hold little soil and dry out fast.
- A bed sits under eaves, a veranda or a tree canopy that keeps the rain off.
- You have newly planted seedlings in a hot, dry spell and the rain is still a day or two away.
- The forecast is light or uncertain. Forecasts miss, and a "chance of showers" may bring nothing.
The most reliable check is the soil itself. Push a finger a few centimetres into the soil. If it is dry at that depth, the plants need water, whatever the forecast says.
What Agent Aqua does
Each morning Agent Aqua reads the rain from the last 24 hours, the last 7 days, and the forecast for the next 2 days. The forecast comes from Open-Meteo for your garden's location. Rain that has already fallen comes from Open-Meteo too, and from your own EcoWitt weather station if you have connected one.
It skips every zone that day if any of these is true:
- 5 mm or more fell in the last 24 hours.
- 20 mm or more fell over the last 7 days.
- 5 mm or more is forecast over the next 2 days.
The morning report tells you how many millimetres decided it. Rain below those amounts never causes a skip on its own. You can always water by hand if your soil tells you otherwise.
To see the full picture, read how the daily check works.