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Take a trowel and dig down gently close to the plants and if the soil is not damp at root depth then you need to water. Often the soil surface can look dry but where the roots are still has enough moisture. With newly planted plants it can make a difference whether they were bare-root or planted from containers with a soilless media rootball intact. In the latter case it is best to water the pot well a little while before planting. Basically watering is as needed, if it doesn't rain sufficiently. The frequency can vary depending on temperature, humidity, rainfall, soil type etc.