Watering Trees: Do's and Dont's
Whether it's a row of trees dotting an urban street or several trees planted in a suburban backyard, you can't ignore their benefits. A group of 100 trees can help to remove 53 tons of carbon dioxide from the air each year. Trees also make people happier, increase property values and lower energy bills.
But for many homeowners or renters, figuring out the best way to water trees can stand in the way of enjoying the many benefits the plants can offer. When it comes to watering trees, the right amount can mean the difference between a thriving, healthy specimen and one that withers and dies.
Watering trees is all about balance. You don't want to deny the tree the moisture it needs, but you also want to avoid drowning it. Here's what you need to know to ensure the trees on your property enjoy a long and healthy life.
How Much Water Does My Tree Need?
Like people and everything else on our planet, trees are mostly made of water — more than 50 percent of a tree is water. Over the course of a growing season, a tree that's 100 feet tall can pull as much as 11,000 gallons of water from the soil.
That water needs to come from somewhere, and if there's not an adequate amount of rain in an area for a prolonged amount of time, usually that "somewhere" will be from your garden hose. Although the exact amount of water your tree will need depends on a few factors, a standard recommendation is to give the tree one to one and a half gallons of water for every inch of the trunk's diameter.
Another recommendation is to give your tree enough water to duplicate about two inches of rainfall per week. One easy way to tell if you’re watering enough is to place a two-inch-deep cup on the lawn or ground near the tree. Turn on the sprinklers, then turn them off when the container is full of water.
Do You Need to Water Trees?
Whether or not a tree needs to be watered depends on a few factors. For example, gardeners typically recommend you water newly planted trees more often than older or more established trees.
The amount of rainfall your area receives also determines how much effort you should put into watering your trees. If you live in an area that gets a lot of rain, giving your trees — even newly planted ones — an additional drink could lead to over-watering.
But if you're in an area that's experiencing a drought or that doesn't usually get a lot of rainfall, you'll most likely need to water your trees. The following do's and don'ts can help you determine if and when your tree needs a good soaking.
- Do: Water trees when you plant them.
- Do: Water trees daily during the first two weeks after planting.
- Do: Water the soil around the tree deeply.
- Don't: Water the tree's trunk — doing so encourages rot.
- Don't: Water the tree if the soil around it is soggy.
- Don't: Water the tree when it's not actively growing — e.g., in the winter.
What Kinds of Trees Need Water
More than 23,000 different types of trees exist, and each species needs water. Trees use water, along with light, carbon dioxide and nutrients from the soil to produce food, which it then uses to grow. When you cut down a tree and inspect the rings in its wood, you can tell the years when water was excessive or lacking by looking at the size of each ring.
That said, different types of trees have different water requirements. Some trees are drought-tolerant, which means they come from areas that don't get much rainfall. Drought-tolerant trees can tolerate periods of dryness better than other tree species. Once these trees are established in the ground, they will usually do fine without much water from you. A few examples of drought-tolerant trees include:
- Kentucky coffeetree
- White fir
- Thornless honeylocust
- Arizona cypress
On the other hand, some trees come from areas that experience either a lot of rainfall or that have naturally moist soils — such as the banks of rivers or streams. These trees are adapted to high-moisture areas and won't thrive if you don't give them an adequate amount of water each week. Examples of trees that tolerate or thrive in high-moisture soil include:
- Weeping willow
- Red maple
- Paper birch
- Silver maple
- River birch
It's also worth noting that the variety of tree affects its water needs. For example, you can usually take a break from watering deciduous trees in the fall, when they lose their leaves. You'll want to keep watering evergreen trees, or conifers, until the ground freezes.
How Does Climate Affect a Tree's Water Needs?
Climate and weather both have a direct effect on the water needs of trees. At the same time, trees can play a role in affecting the climate of an area.
Three aspects of climate influence or determine how much water a tree needs. Those aspects are:
Trees are adapted to a range of temperatures and how hot or cold it is in an area at particular times of year influence whether or not a tree is suited for that part of the world.
Temperature also influences a tree's water needs. If you plant a tree that's adapted to live in an area with moderate temperatures in part of the world with higher-than-average temperatures, that tree will need more water than the same species planted in its native habitat. That's because higher temperatures tend to speed up the rate at which moisture evaporates from the soil and from the air around the tree. If the tree doesn't get supplemental water from you, it's likely to experience stunted growth.
Wind also affects how much water a tree needs. If you plant a tree that's not adapted to wind in a windy part of the world, or if your area expects stronger and more frequent winds than usual, your tree will likely suffer and need more water than usual.
When it's windy, moisture evaporates from the air and soil more quickly than during calm conditions. The effect worsens when it's both breezy and hot. During a heated, windy summer, your trees might experience something similar to what you do when you use a blow dryer to style your hair. The heat and air pressure zap any moisture away.
Wind doesn't just affect the amount of water your trees need. It also impacts their overall appearance. For example, multiple days of strong winds can cause a deciduous tree to lose its leaves prematurely.
The amount of rain, snow or other forms of moisture in the area has a direct effect on the amount of water a tree needs. If you're growing a tree species that's native to your area, and your area usually gets X amount of rain during the growing season, you shouldn't have to water it once the tree is established, provided your area gets the standard amount of rain.
In times of drought, you are likely to find your tree needs a little help from you, even after it's grown for several years.
On the other side of the coin, if you plant a tree that thrives in areas that get X amount of rain in an area that gets twice that, it's likely the tree will get too much water and will show signs of being waterlogged. Since you can't stop a rainy area from getting a lot of rain, the best option in that case is to make sure you choose a tree that's designed to thrive where you live.
What Are the Best Ways to Water a Tree?
There are right ways and not-so-right ways to water a tree. While making sure your tree gets adequate moisture is important, so is making sure you use techniques that maximize the amount of water your tree receives. When it comes to helping your trees thrive, it's not just about knowing how much water do trees need, but what the best ways are to give them that water.
- Timing: As with everything, getting the timing right can be the difference between a happy and healthy tree and one that's dried out or over-watered. Usually, the best time to water your tree is at after the sun has set or in the early morning, before the sun is high in the sky. Watering your tree between sunset and sunrise will help it replace any moisture it lost during the heat of the day and minimize that amount of water that evaporates.
- Location: The roots of your tree are in the soil, and the roots are the part of the tree that take up the water and other nutrients. For that reason, you want to make sure you water the tree's roots, not its trunk or leaves. Aiming the water at the tree's leaves or trunk will just make it more likely to rot. Whether your tree is new or established, you want to measure the area known as the drip zone, which is the circle around the tree shaded by its canopy.
- Methods: One of the best ways to water a tree is called deep root watering. Trees take up water through their roots, so directing the water to those roots is going to make them healthiest and happiest. Deep root watering involves soaking the soil in the drip zone to a depth of about 12 inches — deep enough that the tree's roots have an adequate amount of water to take up. Trees won't be able to make efficient use of the moisture provided by shallower soakings.
- Tools: Not every tool available for watering is ideal for watering your trees. For example, if you use a watering can, you'll end up making trips back and forth and will tire out before the tree gets the water it needs. Usually, a soaker hose, which you can wind around the drip zone, is going to be your best bet. Soaker hoses have small holes along their length, so water seeps from the hose into the soil.
- Add Mulch: Adding mulch isn't exactly a way to water your trees, but it is a way to ensure your trees get the most out of the water you provide them. Mulch, which can be a layer of wood chips or other chopped-up natural materials, helps your trees in a few ways. First, it helps lower the temperature of the soil, which reduces evaporation. It can also provide insulation in colder temperatures, keeping your tree from freezing. A layer of mulch provides a buffer that helps keep the soil moist, so the roots don't dry out. Finally, it also helps suppress weeds, which prevents the need to pull them and keeps them from competing with your tree for water and nutrients.
Watering Established vs. Newly Planted Trees
Finally, it's important to understand the difference between watering newly planted trees and watering established trees. New trees usually need more care, attention and water than established trees, but that doesn't mean you can completely ignore trees that have been in the ground for longer.
Watering Newly Planted Trees
Usually, you'll want to water newly planted trees very frequently, then taper off the frequency of watering the longer the tree is in the ground. For example, arborists usually recommend you water trees daily during the first two weeks they are in the soil.
After the first two weeks, you can decrease watering to a few times a week, or about every other day. Maintain that schedule for the first three months of the tree's life in your soil. After 12 weeks, and until the tree is established, you can water weekly.
Watering Established Trees
How long it takes a tree to become established in the soil depends in large part on the size of the tree at planting. Usually, the smaller the tree, the less time it needs to acclimate and become established.
For example, a tree with a trunk that measures one inch in diameter at planting time will most likely become established within a year and a half. A tree with a six-inch-thick trunk at planting time will most likely need up to nine years before it's fully established.
Although you can ease up on watering established trees, you don't want to neglect them altogether. If your area isn't getting as much rain as it usually does, it's a good idea to check in on your trees to see if they could do with some water.
Trees that need water usually show signs of stress, such as droopy or limp leaves. Left on their own, these trees might begin to develop brown or curled leaves, two signs the specimen is very dehydrated.
Another way to gauge whether a tree needs water is to measure the moisture level of the soil. If the top nine inches of soil are dry, it's time to water the tree, especially if no rain is forecast for the next couple of days.
Making sure your tree gets enough water is just one part of taking good care of the trees on your property. For more helpful tips and tree care guidance, check out our additional resources.
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