Spring/Summer 2016

Plant Care

Watering Trees and Shrubs In Summer

Over-watering, as well as under-watering, can damage or even kill plants. Plants draw moisture and nutrients from the “root zone,” the soil surrounding the roots — which can be 2-4 times as wide as the plant’s canopy. The end of a plant’s canopy or branching is also known as the “drip line” because the tree or shrub drips rainwater there. This area and beyond has the most active water absorption and is where you or your irrigation should concentrate your supplement of natural rainfall.

If trees are placed within a lawn, ideally they would be watered separately from the turf and have a well-defined circle of mulch. Shrub and perennial beds as well have different requirements than lawns that typically require less water and should be on a separate zone or hand watered differently. This rarely seems to be the case in most landscapes.

Before watering, insert a “soil probe” or a thin, smooth rod into the ground. It will easily slide through the wet soil and become more difficult to push when it reaches dry soil.

A good rule of thumb is to water when the soil probe will not penetrate the ground more than 3-4 inches. Mature trees and shrubs should only require a thorough watering once a week based upon rainfall while younger and newer plants often require twice a week during the growing season. If the soil is shallow, compacted or sandy, water more often but for less time. Clay soil holds water more tightly so you should water less often but for more time.  The important rule of thumb is a little longer and less frequent in well-draining soils.

Signs of under-watering include dry soil, and wilted or curled, leaves. Over-watering may lead to constantly damp soil and the growth of algae and mushrooms, especially in compacted soils.  The signs of over-watering can be similar to under-watering and include wilted and/or yellow leaves.

Our arborists can work with you and your irrigation specialists to formulate the best management practices for your landscape.