Why Irrigation for Trees is Important

drought-resistant-plantsDuring a period of abundant rain, mature trees should not require supplemental watering. However, according to the University of Minnesota Extension, water comprises 80-90% of the leaves and root tips and up to 50% of trunks, stems, and roots. Water is also a vital requirement to:

  • Activate photosynthesis which results in growth, flowering, and seed production
  • Move nutrients through the entire tree for growth and survival
  • Cool the plant

Tree owners should also note that much of the water absorbed by tree roots ends up being lost through evaporation, both from the soil and even after entering the tree.

When water is absorbed by the tree’s roots, it travels by a process known as transpiration through an interconnected route of roots, stems, and leaves. Much of the water then evaporates through the stomata on the underside of the leaves.

Since so much of the moisture disappears, some moisture must be present in the soil at all times to keep the tree healthy.

Watering Mature Trees

As a tree grows, the roots tend to spread out in a circular pattern from the trunk below the surface. The roots nearer the top are the ones that typically absorb the most water. These smaller feeder roots spread approximately 12 to 18 inches below the surface for mature trees.

To determine if a tree needs water, dig a small hole near the base with a trowel. If the soil is dry at approximately 9 to 12 inches down, it is necessary to replenish the tree’s moisture.

You may also notice the beginning signs of wilting as the soil dries. Wilting means a lack of moisture, and watering is essential to revive the tree or shrub.

Watering New Trees

Gardening Knowhow suggests watering new trees depends on the amount of existing moisture and drainage characteristics of the soil. Irrigation for trees applies to transplants, as well as very young plants. A newly planted tree should be watered once per day for two weeks and then weekly for the first year. The soil, however, should always be kept moist, but not soaked.

Value of Mulching

One way to enhance the health of trees or shrubs is to add mulch around the base of the tree. The mulch should be spread at least 12 to 18 inches from the trunk. Adding mulch minimizes evaporation and keeps down moisture stealing weeds and grass.


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