No simple guide exists to tell us exactly how much water a tree will need to thrive, however, there are many common sense techniques to help you determine testing much water your tree needs and when. The goal in watering trees is to apply the least amount of water needed to keep your tree growing and healthy.
The top 3 things you can do to keep your tree properly and efficiently watered are:
- Install a drip irrigation system (with programmable timer) making adjustments to watering times and amounts seasonally
- Buffer your tree’s trunk with a mulch-filled watering basin
- Evaluate your tree’s watering needs as part of a landscape with variety
Watering Newly Planted Trees
A newly planted tree should have a raised rim of dirt surrounding the edge of a tree’s root ball. This “tree watering basin” should have a raised rim about 4 inches tall. The goal is to keep the root ball and the soil that surrounds the root ball moist but not soaked. Too much water will prevent air from reaching the tree’s roots and result in rot.
Soil type and weather conditions may warrant adjustments to how much water a tree needs, but in general, filling the watering basin three times per week is a good starting place for trees living here in the Truckee Meadows. Allow the soil to dry between waterings. If a drip irrigation system is in place, set four, 2-gallon emitters to run for one hour, three times per week.
The majority of a tree’s absorbing roots are located at the drip line of the tree, or just inside the edge of the canopy. A mature tree with a large canopy therefore has a wide radius of absorbing roots. It is usually impractical to install a watering basin on large trees. Instead we can use a drip system or soaker hoses to properly water mature trees.
Watering Mature Trees
As a tree matures, it needs more water at its roots. A drip system is ideal for tree watering because it can be modified as the tree grows, increasing the amount of water and applying it in the proper location. Adding emitters to a drip system is quick and easy. The goal in watering mature trees is to provide adequate water in a complete circle around the drip line. This will encourage the roots to grow evenly away from the tree, making it strong and healthy.
Checking Soil Moisture
Checking the soil for moisture content is an easy and accurate way to tell if you are watering too much, too little, or just right. Take a handful of dirt in your hand and try to roll it into a ball. If the soil doesn’t mold into a ball, it is too dry to provide water to plants. If the ball of soil won’t crumble when rubbed, it is too wet. An ideally moist soil can be molded into a ball and then will crumble when rubbed. Remember that sandy soils will crumble even when wet.
Watering Trees & Turf Together
When trees are planted in turf areas, applying the proper amount of water to meet the health needs of both plant types can be difficult. Trees generally require twice as much water as turf (due to their different ET rates).
Evapotranspiration & Other Environmental Considerations
When water is applied to soil around a tree (or any plant), the roots absorb some of the water leaving the rest to evaporate. This water loss is called evapotranspiration (commonly called ET) and is measured as a rate. Trees living in heavily urbanized areas typically have higher ET rates than trees living in suburban areas. For example, a mature tree living in a 6-foot-by-6-foot tree well in a parking lot surrounded by asphalt would have a higher ET rate than the same size tree living in a large park surrounded by turf and other trees. Higher ET rates mean more water is lost to the atmosphere, therefore more water will need to be applied to the tree to make sure its watering needs are met.
ET is just one of the environmental factors that influence a tree’s watering requirements. Other elements, such as amount of exposure to direct sunlight, outdoor temperatures, humidity, and wind will alter the rate at which trees require water. In addition, a tree’s size, species, and surroundings influence its watering needs.
How to Tell if Your Tree isn’t Getting Enough Water
Check your tree for water stress by looking at its leaves. If you notice wilting, your tree needs water. Leaves that are normally shiny when healthy will take on a dull appearance when thirsty. Bright leaves may also turn gray, indicating a need for water. Signs of stress due to lack of watering include
- Early fall color
- Leaves falling prematurely
- Death of young, new leaves
Over-watering
Although water is vital to plant health, too much water can damage and even kill trees. Watering a tree that doesn’t have good drainage can cause the tree to suffocate or get a disease. Over watering can also cause the salinity problems due to increased salt content in the soil.
When Does the Summer Irrigation Season Begin?
It is sometimes difficult to determine when to begin watering trees after the winter season. It is best to begin occasional watering using a garden hose until the weather is warm enough that irrigation systems are no longer in danger of freezing.
Some plants may wilt before others so should be used as an indication that soil moisture content is low and it’s time to start watering.
Winter Watering
Winter watering is important to our region’s community forest. As temperatures cool, lessen outdoor watering but remember that fall and winter in the Truckee Meadows are often characterized by dry air, little precipitation, a lack of moisture in the soil, and wide outdoor temperature swings. The need for winter watering may not be obvious but trees and plants need water during dry spells to stay healthy.
Dry periods can injure or kill tree root systems. Injured root systems are difficult to notice. It can take several seasons before the signs of distress appear on the tree itself. A struggling tree may put on very little new growth or lose its resistance to disease.
Newly planted trees are the most vulnerable to injuries caused by winter drought so take extra care during the first year or two of your tree’s life to make sure it is adequately watered during non-summer months.
Follow these helpful winter watering tips:
- Give your trees supplemental water every 2 to 4 weeks if Mother Nature isn’t watering. A healthy, watered tree can withstand strong wind and freezing temperatures far better than one that is dry and stressed.
- Use a soaker hose to encircle the tree midway between its trunk and midline. Apply some water and then move the hose outward toward the drip line. Wet the soil to a depth of 12 inches
- Irrigate when temperatures are above 40 degrees and early enough in the day that the water won’t freeze overnight.
- Avoid spraying trunks as it can increase the risk of frost injuries.
- To help retain moisture in the soil and regulate soil temperature, put a thick layer (three to four inches deep) of organic mulch such as wood chips, pine needles, or straw, around the tree, leaving a buffer between it and the trunk. Organic mulches will provide nutrients to the soil as it decomposes.
- Remove snow from trees to avoid breakage.
- Keep roofs clear of snow to prevent damage from falling ice and snow to trees located adjacent to homes or sheds.
- Avoid piling snow around trees as snow suffocation can occur.
- Pruning before winter sets in is a good way to keep trees healthy and resistant to damage from snow and ice. Consider hiring a certified arborist to ensure best pruning practices are followed.