Water behaves differently in different soils and climates—so the more you know, the better you can decide how and when to do it.

The time of day to water is controversial, with vociferous champions for both morning and evening watering. We like to take a more situation-specific approach.

Thumb spinach monoppa brighterWatering will cool the soil, not just because the water is cooler, but by evaporation. So, in the spring, when nights are cold, and it is important to let the soil warm up as much as possible, we like to water early in the day. That gives the soil all day to warm in the sun, and allows it to start the night as warm as possible. 

Thumb backlit cornLater, when the sun's heat is a threat as well as a boon, we switch to evening watering, giving the plants the water they need to grow during the night when they are not heat-stressed. If the weather is brutally hot, we will water during the hottest part of the day. Some water will be lost to evaporation, but by evaporating, it forms as little pocket of cooler, moister air to refresh the plants. And it cools and moistens the tender roots.

We do not generally water the plants themselves, but the soil underneath. Water can be a cooling, cleansing, and refreshing shower for plants—they are used to rain, after all. But there are situations where it is best to keep water off of the leaves:

  • When the sun is high and hot, water on the leaves—especially smooth leaves, like pepper plants--can act like a lens and actually cook areas underneath the droplets.
  • If you live in an area affected by fungal diseases such as rust, or late blight, avoid wetting the leaves, which can spread fungal disease
  • If temperatures are right for powdery mildew, avoid evening watering; water in the mornings instead so the leaves and soil have all day to dry.

Thumb scarecrowWe recommend mulch as well. Not only does it retain moisture in the soil, and add organic matter, it prevents disease. It works like this: Studies (and our experience) show that fungal diseases, and even some pests, arrive on the plant with soil splashed up from the surface by water droplets. Even with a good watering wand, the drops of water from your hose have a lot of force: they compact the soil after constant impact, and they also cause drops to splash up on the bottom leaves. Commercial tomato growers sometimes remove the bottom leaves to avoid this. Mulch cushions the impact and holds the soil particles, so you get less compaction, less erosion, and less disease from splashback.

For our July tipsheet on hot-weather gardening, please click here.

This is the first part of a longer article on watering. To read the entire piece, which goes on to talk about soil types and drip irrigation, Click HERE.

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