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University of Minnesota Extension

Watering established trees and shrubs

Quick facts

  • Water established trees and shrubs with overhead sprinklers.
  • Apply a deep watering over the entire root zone area until the top 6 to 9 inches of soil are moist.
  • Avoid light watering as this promotes shallow root systems that are susceptible to summer heat and drought stress.
  • Water early in the morning to minimize water loss due to evaporation and wind drift.
  • Mulching around the base of trees and shrubs helps them take in water and stay healthy.

During periods of consistent rainfall, a well-sited and well-established tree or shrub will need little additional water. But during long periods without rainfall, established trees and shrubs can suffer or die without timely irrigation.

During periods of drought, you may need to water your trees and shrubs more often to ensure the health and survival of these long-lived plants.

How woody plants use water

As you stand in your garden or landscape, you are surrounded by water on the move within plants. This is due to a solar-powered process called transpiration.

  • Water is absorbed from the soil into the roots of plants.
  • Transpiration pulls streams of water molecules up into the plant through inter-connected tissues within roots, stems and leaves.
  • Water moves from the leaves into the atmosphere as an air-cooling vapor through tiny openings called stomata found primarily on the bottom surface of leaves.
  • Transpiration lifts enormous quantities of water against gravity to the tops of trees.
  • Transpiration is the main path of water loss in plants.
    • At least 90% of the water in plants is lost from leaves through transpiration.
    • The remaining portion of water is lost through other plant parts or is used during the processes of plant growth and development.

Water is vital to plant growth and development.

  • Comprises 80-90% of actively growing tissues (leaves, root tips).
  • Makes up about 50% of the woody portions (trunks, stems, large roots) of trees and shrubs.
  • Fuels photosynthesis and other processes involved in plant growth, flowering and seed production.
  • Helps defend against pests and stresses.
  • Transports nutrient minerals and other solutions throughout the plant.
  • Gives firmness and form to leaves, buds, flowers and new succulent stem tips.
  • Cools the plant as water vapor is lost during transpiration.

How, when and how much to water

Figuring out how far a tree's roots spread helps to determine the area you need to water and how much water is needed for an individual tree. 



Mulching trees and shrubs maximizes water uptake and tree health.

When trees and shrubs are grown in turf, competition for nutrients, water and space occurs below ground between turf roots and woody plant roots. Turf wins because its dense fibrous root system prevents woody plants from producing water-absorbing roots in the top few inches of soil. As a result, woody plants grow more slowly in turf areas than in mulched or bare soil areas.


Reviewed in 2022

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