New plantings should be kept moist for the first three weeks after planting unless otherwise directed. This means that you should water long enough and often enough so that the soil is consistently moist (but not muddy) to a depth of about six to eight inches.
When planting in hot weather you may have to water more often to help establish the plants. If you notice wilting plants, water them immediately.
You can use a sprinkler or water by hand. Make sure that you water long enough for the water to penetrate to the appropriate depth. The trick is to water at a rate your soil can keep up with. If water puddles or runs off you should reduce your rate of watering or stop watering until the soil absorbs the excess water and start again. Watering in hour or half hour increments is a good practice to start until you know how fast and how deeply water is absorbed.
Be careful not to overwater. Too much ground moisture can suffocate your plants, so overwatering can be just as harmful as not watering enough.
The best time to water plants is early in the morning. The day’s heat will dry the water on the plants, keeping mildew from forming. Also, early morning watering reduces evaporation. Watering in the late afternoon or early evening is the next best time. You should avoid watering during the hottest part of the day, unless you live in a very mild climate.
Note: A good alternative to hose-end sprinklers and expensive sprinkler systems is drip irrigation. Drip irrigation reduces surface evaporation by watering plants at the ground level. This conserves water and promotes deeper root growth.
You can purchase drip irrigation systems that regulate and distribute water evenly. Many nurseries and home centers carry do-it-yourself drip irrigation kits that are relatively easy to install and maintain. The kits can get expensive, but they can also be worth the investment.
There are two styles to choose from: one has customizable water emitters for each plant, and the other has emitters spaced at regular intervals.