Please note: This article was originally published on 8/13/2020 and was republished on 8/1/2023.
Last Fall I planted a Nikko maple (Acer maximowiczianum) for one of my neighbors. Somewhat uncommon, Nikko maple is a small statured, 20 - 30’ at maturity, trifoliate, hardy tree with nice fall color. It has good urban tolerance and was a good fit for its location with overhead utilities. I have been watering this tree somewhat regularly with a large watering can that I can easily carry across the street and have been pleased with the healthy appearance and good amount of new growth that has emerged this year. As far as I could tell the tree looked great so you can imagine my surprise when I came home recently from a long weekend getaway and discovered that the top half of the tree’s canopy had turned brown.
I approached the tree expecting to see an insect infestation, disease presence, or mechanical damage from my neighbor getting to close with his string trimmer. I could find none of these things. Upon closer inspection I noticed that the soil around the base of the tree was cracked, hard and dry and that I simply had allowed the root system to dry out. I felt like such a greenhorn. I immediately watered the tree with a slow deep soaking and will continue to do so through the end of October.
An arborist is not supposed to make this mistake but I share this story to show you how it can happen to anyone and to illustrate that there is a better way to water, and that watering is the single most important maintenance factor in the care of newly planted trees.
Many of the calls that come through our office are a result of improper tree watering, both directly and indirectly. Some are regarding trees that were planted and simply never watered, others are regarding trees that have experienced significant drought stress and now have been impacted by pest and/or disease problems targeting a vulnerable host.
Drought stress develops in trees when available soil water becomes limited. Newly planted trees are at the highest risk of drought stress because they do not have an extensive root system. As the soil dries it becomes harder and more compact reducing oxygen availability. When this happens young feeder roots can be killed outright further reducing the trees ability to absorb sufficient water even after it may return to the soil.
Why is water important to trees? Trees require water for two important functions: (1) Photosynthesis: the process by which plants synthesize food and (2) Transpiration: a process where water evaporates from the leaves and is drawn up from the roots helping to move nutrients up the tree.
No water in the soil means no nutrient transfer and no photosynthesis. This generally equates to tree death.
Knowing the best way to deliver water is the single most important maintenance factor in the care of newly planted trees so here are some basic guidelines and tips to follow to make sure you are getting the most out of your watering efforts:
When to water
Newly planted trees should be watered one to two times per week during the growing season. The best time to water is early in the morning or at night. This allows trees the opportunity to replenish their moisture during these hours when they are not as stressed by hot temperatures. Watering at night allows more effective use of water and less loss to evaporation. Side note: If watering at night, a system that directs water into the ground and away from the foliage is recommended. Some foliar fungal diseases like apple scab or needle cast can thrive on foliage that remains wet through the cool nighttime hours.
How to Water
The best way to water newly planted trees is slowly, deeply and for a long time so that roots have more time to absorb moisture from the soil. A deep soaking will encourage roots to grow deeper as opposed to frequent shallow watering which can lead to a shallow root system more vulnerable to drying out (like my Nikko maple).
I like to water trees slowly two different ways. Around my house I use a garden hose with the pressure turned low so that water is coming out at a slow trickle. I place the end of the hose on the root ball a few inches away from the main stem and leave it in place 30 - 60 minutes depending on the size of the tree. This should be done at least once a week during the growing season. Verify that water is coming out slowly and seeping into the soil rather than just running off into the lawn. For trees that are outside the range of my hose, I like to use 5-gallon buckets with two small holes poked in the bottom of one side. These can be filled up quickly with the hose but will drain slowly, ideal for a slow soaking. Two 5-gallon buckets once a week should suffice for most newly planted trees, depending on the size.
Where to water
It is important to understand that for the first growing season after planting, most newly planted tree's roots are still within the original root ball. This is where watering efforts should be focused. The root ball and the surrounding soil should be kept evenly moist to encourage healthy root growth. It can take two or more growing seasons for a tree to become established and for its roots to venture into the soil beyond the original root ball.
Trees under stress from disease or insect predation and trees in restricted root zones (trees surrounded by pavement) could take longer to establish.
Other important tips
Avoid fertilizing during drought conditions - synthetic fertilizers can cause root injury when soil moisture is low. Fertilizing in the summer could also cause additional new growth requiring additional moisture to support it.
A 1 - 2” layer of organic mulch over the root zone of the tree will help to conserve water.
The goal of watering is to keep roots moist but not wet. Excessively saturated conditions can also damage tree roots.
A “good rain” or even an irrigation system is not sufficient for most new tree plantings
During extended periods of drought all trees (including established ones) benefit from supplemental watering.
TJ Nagel & José Fernández posing for a photo for this article! Happy watering, everyone!
Remember, proper watering is the single most important maintenance factor in the care of newly planted trees. I am intentionally redundant on this point because it cannot be overstated. Air temperatures, precipitation, tree health, tree size, soil texture, etc. can all influence a tree's need for water. This article is intended to be a basis for proper tree watering procedures and cannot address every tree watering scenario. Happy watering and may your rain barrels always be full.
TJ Nagel | Scheduling Production Manager, Russell Tree Experts
ISA Certified Arborist® OH-6298A // Graduated from The Ohio State University in 2012, Earned B.S. in Agriculture with a major in Landscape Horticulture and minor in Entomology // Tree Risk Assessment Qualified (TRAQ) // Russell Tree Experts Arborist Since 2010