It’s getting hot out there. Don’t forget to water your trees!
Temperatures are rising in the Midwest and Kansas City is creeping into 90 degree days. You may be feeling sluggish at work, dreading the evening walk with Fido or more commonly, craving a cool glass of water. Well, you wouldn’t be the only thing feeling the effects of the heat, your trees are too!
How much should I water my tree?
Check soil moisture before you water
There is no “one size fits all” approach to tree watering because it varies depending on tree species, soil type, drainage and climate.
Your watering schedule is highly dependent on the soil, which can vary greatly. Clay soils, which we typically have in our area, hold onto moisture. The best method is to use your fingers and feel the soil. Use a hand trowel or screwdriver to dig down below the mulch. Recent rainfall could also be a good indicator that it is time to check your trees. Check the National Weather Service or Johnson County StormWatch websites to gather local information about recent rainfall.
It is possible to over water your trees. When a tree starts to wilt and look thirsty, it could actually mean it might be too wet! This is why it is best to check soil moisture first.
Understand your tree species
Right tree, right place. Hopefully if you planted the tree, you learned about your planting site and the species beforehand so you could choose a tree species that thrives in the moisture content of that area. If the tree prefers the site’s conditions, it requires less of your support.
Some trees can’t handle wet feet. There are high water use and low water use species. Low water use species typically have smaller, thicker leaves and lose less water through foliage. Research your species and its natural habitat. Is it an upland or lowland species? Is it native to our area and our temperatures? Some trees surprise you, like bald cypress, which can tolerate extremely wet but also drier conditions. Some species names are misleading, like swamp white oak, which actually doesn’t prefer soils all that wet. Since almost all evergreens are nonnative to our area, they usually require extra care. Missouri Botanical Garden has an index of most species with water requirements and native habitats.
If you really want to understand water movement, soil and its relationship with trees, check out this presentation from the Illinois Arborist Association.
How to water your trees
Generally we advise about one inch or 20 gallons each week for young trees between 1-3 years after planting. (Note: Read above why this is only a general rule of thumb because watering needs vary depending on many factors.) Trees obviously require water their entire lifespan, but extra watering support is helpful for the first seven years after planting at least during dry months. Trees even need water in winter sometimes, too.
There are several options for watering trees, but all you really need is a garden hose. Turn the spigot for the hose about a quarter of a turn and place the nozzle approximately one foot from the trunk of the tree. Periodically, move the hose around the tree. You want to water the tree deeply, giving it a good soak, approximately 20 gallons for young trees. The majority of tree roots are typically in the top 18 inches of soil.
Don’t forget mulch!
Proper mulching reduces moisture loss through evaporation. Apply mulch only 2-4 inches deep in a donut shape around the tree. Leave six inches of space between the trunk and where mulch begins. Applying too much mulch (more than four inches) may result in mulch matting and actually wicking moisture away from roots.
Again, know your soil and site. If it’s wet, applying more than two inches of mulch may reduce soil drying to the point where your tree’s roots rot.
Tree watering systems
If you want to invest some money, there are a few other options for watering. You could install a soaker hose in a spiral in the area under the tree from the tip of the branches to the trunk, called the dripline.
Watering bags are also an option. These bags zip around the tree holding 20 gallons of water. They are filled with a garden hose then slowly leak out over an 8-hour time period.
If you have turf irrigation, consider installing a separate head/zone or drip system around your trees to make sure they receive adequate water. Healthy turf roots compete for the same moisture and are shallower. Watering on a timed cycle could mean you are watering shorter roots but it isn’t enough to saturate deeper where the tree roots are found.
Should I water my trees in the winter?
Water in winter? Yes. If it has not rained an inch or snowed a foot for a few weeks, your tree may need watered. Check your soil moisture. Colder temps mean less transpiration and drying out of soils, so you certainly do not need to water as much. Consider storing your bag away for the winter and just letting a hose trickle onto the root ball. Evergreens keep their needles throughout the winter, so they are still transpiring. They need more water than deciduous trees which drop their leaves.
Don’t just keep yourself hydrated, think of your trees as well!
Read more from K-State Research and Extension: Tree Watering for Summer Survival