How often – and how much – a tree or shrub should be watered is a key question. In the first year or two after being planted, these plants need frequent watering. A steady supply of moisture helps them establish strong root systems that reach out and down through the soil. But once trees and shrubs are established, they can go for increasingly longer periods without supplemental watering, as their own roots gather moisture from the surrounding area. In fact, once most trees and shrubs have been in the ground for a few years, they can withstand occasional periods of drought without damage.

Mulching around your trees and shrubs and using a slow-application soaker hose to water new plants helps soil retain moisture and prevents hillside runoff.

Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

Mulching around your trees and shrubs and using a slow-application soaker hose to water new plants helps soil retain moisture and prevents hillside runoff.

Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

Plant trees and shrubs upright on sloped sites in terraces protected on the uphill side with a barrier wall to keep soil from sliding onto the trunk.

Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

But the first couple of years are vital to these plants. The amount of water that newly planted trees or shrubs require depends on your plants and the type of soil in which they’re growing. (Soils have varying water-storage capacities, with clay soils typically requiring less irrigation than sandy soils.) Generally, trees and shrubs need about 1 inch of water per week during their first growing season.

Once settled in, most trees and shrubs do best with infrequent, deep waterings that soak the soil at least 1 foot deep. Avoid frequent, shallow waterings – such irrigation encourages root growth near the surface, making the plants more vulnerable during periods of drought. In some cases, these surface roots can also cause nearby patios or walkways to crack.

Watering at the correct time of day also helps keep plants healthy. The guiding principle is to minimize the length of time that the leaves stay wet, since wet foliage is often an invitation to disease. Watering in the morning before 10 a.m. is usually best.

Determining when to water is fairly easy: With a shovel or soil-sampling tube, dig down into the soil about 8 inches. If the soil at that depth is dry, it’s time to water. If you find the soil is moist near the surface but dry below, that’s a sign that you need to irrigate more deeply – really let the water run and check how deeply it penetrates.

Deep watering conserves irrigation water, prompts trees to develop deep roots, helps prevent fungal spores from splashing from the soil onto foliage, and avoids runoff and erosion. If you had installed a deep-watering tube when you planted your tree or shrub – or if you install one when you dig your planting hole for your next landscape addition, you can automate your watering by installing a battery-powered irrigation-control valve and plastic drip line with emitters at the tube. Just take the steps shown in the following pictures and described in their captions.

No matter how you water your plants, get your newly planted trees and shrubs off to a good start by watering them regularly – and deeply – whenever natural precipitation falls short or drought conditions occur. Then back off on irrigation a bit once they’re established – and you should have well-rooted, sustainable, thriving plants.