Some plants, like fuchsias and tuberous begonias, wilt when dry, but geraniums and succulents are not so sensitive to neglect. On the other hand, it is good to let soil dry out a little between waterings. This prevents the soil from turning sour.
Since unglazed containers dry out quickest, watch them more closely. Wooden tubs, window boxes, and planters dry out more slowly; metal is the slowest of all. Groups of plants in large containers keep moist longer than single specimens. Groupings of plants, arranged close together, shade one another and help prevent excessive moisture loss.
Ways to Water
There are several methods of watering. If you have many containers or large ones, depend on the hose, allowing water to flow through slowly and gently. Water small pots with a watering can that has a long spout. When plants are grouped closely, set up a sprinkler or hose with a fine spray nearby, allowing it to run for a long while, until soil is soaked. In California, where large containers are common and where summers are dry, a permanent apparatus is often set up for watering trees and shrubs and flowering plants with just the turn of a faucet. With geraniums and petunias, avoid sprinklers which spot blossoms.
One thing is certain; you must not depend on rain. Even heavy showers deposit a surprisingly small amount of moisture, and unless rains are frequent and lengthy, you must do your own watering. Window boxes and other containers near houses or under trees can stay dry in spite of an all-day downpour.
Though it is essential to give enough water, it is equally important not to overwater and so cause root rot. Over-watering also prevents aeration of the soil, and causes it to turn sour.
One good method is to set containers, if not too large,
in a basin or pail of water for several hours, or until the surface of the soil feels moist. Or immerse the pot in a tub or large barrel of water and leave it there until air is eliminated and the bubbling stops.
The best general rule is to soak soil thoroughly when you water and then allow it to go just a bit dry before you water again.