Meeting the Watering Needs of a Newly Planted Tree

Tree stewards often have more work to do than they can accomplish each week. Board members should prioritize tasks to stay motivated in their stewardship roles. Ensuring enough supplemental water for new trees is crucial, especially when water is limited. Lack of water is the number one reason newly planted trees do not survive. This article shares practical tree-watering recommendations.

Water is Critical to all Living Plants:

• Water is the main component in actively growing tissues such as leaves and root tips.
• Water accounts for about half the weight of live woody parts, such as trunks and roots.
• Water molecules supply the material for photosynthesis and other processes involved in plant growth, flowering, and seed production.
• Water helps defend against pests and stress.
• Water transports nutrient minerals and other solutions throughout the plant.
• Water gives firmness and form to leaves, buds, flowers, and new succulent stem tips.
• Water cools the plant as water vapor escapes through leaf pores called stomata, a process called transpiration. At least 90% of the water in plants is lost from leaves through transpiration.

Where should Water be Applied?

The soil surrounding the plant's roots, called the root zone, serves as the water storage area. Fine absorbing roots draw moisture and nutrients from the pore space between soil particles.

Newly planted roots remain within the planting hole for weeks, often the entire season. Water the entire root zone consistently to protect fragile roots. Dry soil causes roots to cease functioning, and recovery is delayed even after moisture returns.

When to Water

Newly planted trees or shrubs require more frequent watering than established ones. They should be watered when you plant them and at these intervals:

• 1-2 weeks after planting, water daily.
• 3-12 weeks after planting, water every 2-3 days.
• After 12 weeks, water weekly until the first frost.
• If planting in the autumn, follow the above guidance until the first frost, then resume weekly watering in the spring and continue through the end of the growing season.
• After the first year, continue to water weekly until the tree is established.

To keep it simple, you can stick to the above guidance, regardless of most weather conditions. More often than not, your newly planted trees will need regular watering while they are still establishing their roots. Do not assume rainfall is enough to skip watering. Only skip watering during the interval listed above if there is substantial rainfall over many hours (e.g., one inch or more over 24 hours). Keep in mind, when a storm brings a lot of rain quickly (e.g. one inch or more in less than an hour), most of that water will run off the surface and not benefit your trees.

You can monitor water needs by testing soil moisture in the rooting zone at 6 to 9 inches with a probe. If the soil is moist there, more water is not needed immediately; however, you will need to keep checking every day or two. The probe can be as simple as a metal rod. Moist soil is easier to penetrate than dry soil. Porous soil is easier to penetrate than dense or compacted soil. Given typical temperature and rainfall patterns, you can expect you will still be watering frequently until your new tree is established, and monitoring may not be worth the effort.

How long does it take for Tree and Shrub Roots to Establish?

Newly planted trees and shrubs usually undergo a period of transplant shock, during which they grow more slowly than before moving. Such plants can be considered established when their roots have grown into the surrounding soil and their growth rate remains consistent from year to year. In USDA Hardiness Zones 2 to 6, this can take a year for each inch of trunk diameter. For a standard balled and burlap landscape tree with a 2-inch trunk diameter, this means the tree will take two years (growing seasons) to be fully established. In moist climates, the plant roots are normally able to supply enough moisture to keep them alive by then if other growing needs are met.

Establishment times for trees increase with tree size. The trunk diameter at planting time can be used to estimate the time it takes for roots to resume functioning and growing as they did before they were disturbed. For trees with trunks smaller than four inches in diameter, measure six inches above ground level and the root flare. For larger trees, measure at 12 inches.

How much Water do Newly Planted Trees Need?

At a minimum, apply 1 to 1.5 gallons per inch of trunk diameter each time, watering throughout the root zone, not solely at the trunk.

Each watering method has advantages and disadvantages. Use the method you have the tools for. Your tools might be:

• Buckets from a tank. This is most laborious. Keep your water tank nearby.
• A watering bag, such as a Treegator. This provides a slow trickle of 15 gallons of water over 5-9 hours, but it needs tending over the growing season and should be removed over the winter.
• A soaker hose may clog or water unevenly. Arrange the hose into coils around the plant to evenly cover the watering zone.
• A sprinkler. Be careful not to concentrate water on the foliage and trunk to avoid sunburn or fungal troubles.

For best results, water over the entire root zone area until the top 6 to 9 inches of soil is moist. Use a soil probe or soil knife to evaluate soil moisture at depth. Moist soil penetrates more easily than dry soil. If it is difficult to probe or dig, delicate plant roots will also have difficulty absorbing water.

Some other tips:

• Avoid shallow watering. Deep watering encourages strong roots and improves heat and drought resilience.
• Water early in the morning to reduce evaporation and wind loss.
• It is important to manage weeds and unwanted plants to meet landscape goals.
• Do not cover the soil with plastic sheeting.
• Mulch around the bases of trees and shrubs to retain water and promote health. Keep mulch three inches from trunks and no deeper than three inches.

Under-watering and Over-watering

Applying the proper amount of water is important to tree and shrub health.

• Underwatering causes a decline in the growth and health of trees and shrubs.
• Over-watering is wasteful and can be just as harmful as under-watering, particularly in clay and compacted soils.
• Pore spaces between soil particles are shared by water and oxygen.
• Over-watering causes pore spaces normally occupied by oxygen to become filled with water.
• Plant roots need oxygen to function. Pores filled with water or crushed for more than a day may cause root suffocation and eventual death.

Symptoms of under-watering:

• The soil at 6 to 9 inches deep is dry.
• Older leaves turn yellow or brown and may drop off.
• Leaves are wilted or curled.
• Bark on young shoots may appear shriveled.

Symptoms of over-watering:

• The soil is constantly damp.
• Young leaves become light green or yellow.
• Young pliable shoots are wilted.
• Leaves are green yet brittle.
• Algae and mushrooms are growing.

When we can provide water for newly planted landscape trees and shrubs it improves their survival rates until they can resume normal function. Such efforts can make the difference in landscape success and community quality.