University of Maryland Extension

Watering Trees and Shrubs

man using a hose
Photo:Pixabay

Key Points

When to Water

  • Learn the specific water requirements of your plants and water accordingly.  Watering depends on the type of plant, soil texture, if it is an established or a newly installed plant, and weather conditions. 

  • Evergreens (tree or shrub having needles or leaves that remain green on the plant through the winter and into the next growing season) should be deeply watered in the fall before the ground freezes. Evergreens continue to lose water during the winter, especially when the temperature is above 40°F. and on sunny, windy days. If the soil is dry, the plants may become desiccated, turn brown, and die.

  • Newly installed plants require regular watering, especially when the weather is warm and dry.

  • Observe how quickly your soil dries out after a rain or watering. Clay soil drains slowly, porous sandy soil quickly. Adding organic matter to the soil will improve drainage in clay soil and increase water retention in sandy soil.

  • Check your soil 4-6 inches deep with a trowel or a screwdriver and water when soil is dry at that depth.

  • Water in the morning. Watering during the heat of the day increases the amount of water last to evaporation by as much as 40%. Late day, over-head watering increases the chances of some plants being infected by diseases.

Watering Priorities

  • Extended periods of drought can negatively affect most plants. Water trees, then shrubs, then herbaceous (plants with soft stems) plants. Large, mature shade trees and shrubs can be left alone unless the drought is severe or the trees begin to wilt or the root systems have been recently disturbed.

  • Water newly installed plants immediately after planting. For the next 2 weeks check the soil moisture daily and water deeply as needed. Direct the water to the roots and not the leaves of the plant. 

  • Water newly planted trees and shrubs until the roots become established. Typically, this is a 2 year period. 

  • During the hottest, driest part of the summer water new plants at least once a week or as needed.

How to Water Plants

  • Water deeply so the water penetrates the top 4-6 inches of soil.

  • Deep and infrequent watering encourages a deep root system and makes plants more tolerant of future droughts. Frequent, light watering encourages shallow root growth and thirstier plants. 

  • Apply enough water to thoroughly wet the root zone. The larger the plant the larger the root zone. The root zones of trees and shrubs extend out from the trunk a distance at least equal to the height of the plant. 

  • Apply water overhead with sprinklers or hoses, or apply water directly to the soil (the most efficient way to water) with soaker hoses, running a hose at a slow trickle around the roots, or drip irrigation.

  • Overhead sprinklers apply water rapidly to a patterned area. However, overhead watering can increase disease problems especially if water sits on the leaves for a prolonged period of time. For example, overhead watering promotes black spot on roses. 

  • Sprinklers can be portable and moved around the landscape as needed or they can be permanently installed systems. Uniformity of watering depends on the type of sprinklers used, water pressure, and wind conditions. Closely monitor watering patterns to make sure targeted plants receive adequate water and to check the water is not running-off especially near hard surfaces. 

  • Trickle or drip irrigation is one of the most effective and water-efficient methods of watering. The system discharges small quantities of water on a regular basis directly to the root zone under a tree or shrub. Very little water is lost to the air through evaporation. 
  • After watering, check the moisture level 4-6 inches deep by probing the soil in several locations using a hand trowel, screwdriver, or spade. 

  • Mulch plantings (no deeper than 3 inches) to reduce the need for watering during dry spells. Mulches keep soils cool and reduce water loss through evaporation.

  • Treegator® bags placed at the base of newly planted trees and shrubs provide a slow method of delivering water to root balls. They are often used by commercial landscapers but are available to retail customers.

How Much Water

  • To wet the soil at least 6-inches deep requires 1- to 2-inches of surface water (65-130 gallons water per 100 square feet). The amount of water depends on soil type, weather, and types of plants growing. 

  • Check the amount of water a sprinkler is providing to a group of plants by placing a tin can in the range of the sprinkler. When 1-inch of water accumulates in the can, 1-inch of water has been distributed in the soil. This is enough to penetrate 6- inches of soil.

Back to top

Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2020. Web Accessibility