A regular watering program is essential to establish your new planting. The key to successful watering is remembering that the roots of your new plant are in very contained areas. Water needs to be applied directly to the root area.
Container-grown shrubs should be watered by holding a hose directly over the center of the shrub. Count to ten then move to the next plant. Repeat this several times until each plant is thoroughly watered. Larger containers will require more applications of water than small containers to wet the soil down through the entire root zone.
Allow the root area to dry out somewhat before the next watering. Natural rainfall and temperatures will determine the frequency of water. In hot weather you may have to water daily immediately after planting. If temperatures are cooler, you may only need to water every 3-5 days. The goal is to gradually reduce the frequency of watering until you are on a once-a-week schedule. You should anticipate watering regularly for the first two years. Once shrubs are established, it should be necessary to water only during periods of heat or drought.
Balled trees should be watered thoroughly every 7 to 10 days. Lay a hose directly over the root ball and allow the water to slowly trickle for 30-60 minutes. Move the hose around the ball 2 or 3 times, or as needed to wet the entire root area. Water trees regularly for the first 2 years. Again, adjust watering frequency to the amount of rainfall. One way to test the moisture content of the root ball is to push a metal stake into the ball. If it inserts easily there is still moisture in the soil.
Perennial plants, annual flowers, and groundcover require shallow and frequent watering during their establishment. Most of these plants are supplied in small containers and have a proportionately sized root system. Water these plants regularly for the first few weeks. As feeder roots develop, reduce the frequency of watering until you are on a once-a-week schedule.
Plants can die from drought, but they can also drown in wet soil. Check your soil regularly and adjust your watering accordingly.