Watering and mulching
Tomatoes absorb water only through their roots and don't like moisture on their leaves. Proper watering and mulch protect against diseases and save water.
When and how much to water
Watering frequency depends on growing conditions, system, climate, and mulch. During dry, warm periods outdoors or in a greenhouse, you may need to water every two to three days, in pots – daily.
Ensure that a 20–25 cm layer of soil is moistened – this is especially important at the beginning of the season when roots are developing. Roots grow towards the moister layer.
It's best to water early in the morning or in the evening. Watering at midday causes a lot of water to evaporate, and drops on the leaves can cause burns.
Source: pomidorai.eu