Trees in the Colorado Front Range need water to survive. The key is to give them the right amount of water. Too much AND too little water can result in decline and early death for both new and established trees. In this article, you’ll learn:
- how much water your landscape trees need,
- signs that a tree has too little – or too much – water,
- when and how to water them, and
- the factors that influence the amount of water required to keep trees healthy.
How Much Water Do Trees Need?
Alas, there’s no one answer to this question. There are a lot of factors that decide how much you need to water your trees.
Below, we explain some of the factors that affect trees’ water needs.
Different species of trees need different amounts of water and take up water at different rates. Native trees are generally the most water-thrifty, as these tree species have evolved to grow in their surrounding conditions.
If you have ornamental or “exotic” trees from other climates, you’ll probably be giving them more water than you would a native tree.
Tree Age and Maturity
Established trees need less frequent watering than newly planted or young trees. This is because older trees have developed large root systems that spread out and down into the surrounding soil.
Young trees have smaller root systems that can’t yet reach as far down into the soil. As a result, they can become water-stressed faster.
How long your tree has been planted
Newly planted trees need more water, especially in periods of drought.
Transplant shock can cause a new tree to drop leaves or stop making new leaves. To limit transplant shock, you’ll want to give new trees consistent, deep watering.
Whatever the size of your trees, their overall health will affect how much water they need.
If your trees have been disturbed by construction work, their roots are probably damaged. This means they’re stressed, and you should water them regularly.
A stressed tree is also more susceptible to insects and diseases.
Tree pruning, particularly extensive pruning, is another stressor for trees. Making new leaves and sealing off pruning wounds uses energy stores, so give your trees some extra water.
As you might expect, the larger a tree is, the more water it needs. A tree’s root system provides water to every leaf.
Watering your trees correctly when they’re young will help their root systems grow deep and wide, improving their drought resistance.
When it comes to how much water your trees need, where you plant your trees is important.
- A windy spot increases a tree’s transpiration rate, which means the tree needs more water to keep balanced.
- A steep slope will lose water faster as gravity pulls the water downslope, taking it away from tree roots.
- A low spot benefits from gravity and loses water more slowly than one on top of a mound.
- A tree in part shade will benefit from slower water evaporation than one in full sun.
Your Soil Type
The kind of soil you have influences how much water your tree will need.
Sandy soil drains water very quickly, sometimes too quick for tree roots to use it.
- You’ll need to water more often, and for longer, to get enough water to your trees’ root zone.
Clay soil absorbs water slowly and holds water longer. This is good, as long as the soil doesn’t become waterlogged.
- Waterlogged soil and overwatering can be as damaging to trees as drought (more about overwatering below).
Your soil depth affects how much water your trees need.
- Shallow soil can’t hold as much water as deep soil can, so trees need more frequent watering.
Use of Mulch
Mulching your trees is vital. A three-inch layer of organic mulch around your trees helps by:
- Insulating the soil and regulating its temperature
- Slowing water evaporation
- Suppressing weeds that compete for water
- Improving your soil’s water-holding ability over time
Competition for Water
What you have growing around your trees affects how much you water. All plants, small or large, are competing with your trees for available water.
This is another reason to water your trees deeply. As water soaks in, shallow-rooted annuals and perennials will take it. When you water for a longer period, it will infiltrate beyond the reach of smaller plants to reach deep tree roots.
Weather and Temperature
We mentioned wind, but temperature and sun are also critical.
This is because the hotter the weather, the more water tree roots take up and leaves expel.
Long summer days mean your trees will be photosynthesizing and transpiring water for many hours. Prevent water stress during periods of hot, dry weather by regular, deep watering.
Time of Year
Hot summer weather is when your trees need the most water, but they also need water in winter. Your dormant trees may look like they’re not doing anything, but their roots never stop working; trees need water even in winter.
The amount of soil around a tree’s roots affects how much water it needs. For example, trees in tight urban spaces and along sidewalks have less soil surrounding them, which means less water is available for tree roots. These trees will need more frequent irrigation.
Small planting areas surrounded by impervious surfaces (such as concrete and asphalt) compound the problem. The limited soil in these spots is hotter, as these materials absorb and hold heat.
If you can’t increase the size of your tree’s planting area, you can help out by watering your tree more often.
How to Tell if Your Tree is Underwatered … or Overwatered
Overwatered trees and underwatered trees can look very similar. This is because it’s generally the leaves that show the first symptoms of both.
But there are some signs that can help you tell if a tree is stressed from too little water and or from too much.
Signs of an Overwatered Tree
- Visibly wet soil
- Thriving weeds and surrounding plants
- Drooping leaves (or needles) that are yellowing and may have brown tips and margins but are not dried out
- Green leaves that are stunted or disintegrating
- Dying leaves on lower branches and inside the tree’s crown
Overwatering suffocates tree roots by filling up air spaces in soil that should hold oxygen. Leaves on overwatered trees are generally still flexible because they’re not lacking water, but oxygen.
Signs of an Underwatered or Drought-stressed Tree
- Visibly dry soil or soil that’s dry if you dig down several inches
- Dried up leaves with brown tips and margins
- Scorched, curling, and/or yellowing leaves
- Early or poor fall color
- Twig and branch dieback
- Dying leaves on branch tips and top of the crown
Pro tip: If your trees are showing signs of drought stress, water them as soon as possible, but don’t overdo it. You’ll add insult to injury by overwatering a drought-stressed tree and drowning its roots.
How to Water Trees
An up-to-date irrigation system is the most efficient way to water your trees.
Irrigation systems that include soil moisture meters and temperature sensors can automatically adjust watering cycles as weather conditions change.
For best results, follow these watering guidelines:
- Water very early in the morning – Watering in the evening is less efficient as trees are not actively photosynthesizing and need less water. Excess water will drain down and away from tree roots overnight, and won’t help your trees.
- Water consistently – Irregular or uneven watering stresses trees and can stunt growth or worsen drought stress.
- Water slowly, leaving the hose at a trickle – If the flow of water exceeds the soil’s ability to absorb it, water will run off and wash away soil.
- Water deeply – Ensure that water reaches at least a depth of 12” – that’s where the tree roots are.
- Water the entire root zone – There’s no point watering right up against the tree trunk; a tree’s roots spread out to (and, often, well beyond) the edge of the tree canopy. Make you cover this entire area when watering a tree.
How Much Water to Give Your Trees
There’s no one answer to how much to water trees, but there are some general guidelines that are beneficial for almost all trees.
For Small, Medium, and Newly Planted Trees
Small trees are those with a trunk diameter of 1 to 3 inches.
Medium trees have a trunk diameter of 4 to 8 inches.
You’ll want to irrigate these trees with about 10 gallons of water per inch of trunk diameter. Here’s how to calculate how much water you’ll need.
- Measure the circumference of the tree’s trunk at about chest height.
- Divide that number by pi, or roughly 3.14. You’ll often hear this number referred to as DBH, or diameter at breast height.
- Multiply that number by 10 to find the number of gallons you need.
- If there’s been recent rain, subtract that amount from your total.
- Water small trees weekly. Newly planted trees may need watering every 3 to 5 days. Medium size trees generally need to be watered only three times a month.
- In hot weather or periods of drought, increase frequency (but don’t reduce the amount of water provided each time you water).
- Don’t forget to continue watering trees in winter, especially during drought conditions!
And don’t forget to follow other best practices for keeping new trees healthy.
Use the handy calculator below to see how much water your young, mid-sized, or recently planted tree will need each time you water it.
Watering Calculator - Small TreesCalculates the number of gallons needed to irrigate with 10 gallons per inch of trunk diameter.
"*" indicates required fields
You should also measure how long it will take to produce that amount of water with whatever irrigation method you’re using. The gallons per minute emitted by different watering devices can vary dramatically!
For Large, Mature Trees
Large, mature trees are priceless so it’s important to make sure they have enough water to survive even the worst weather. Given a choice between watering a mature tree versus shrubs, lawns, or landscape plantings, we recommend focusing your irrigation efforts on the larger trees if they’re showing signs of drought stress.
Mature trees have a slower growth rate, but their roots still have to find water. In extended drought, there may not be enough soil moisture readily available to keep big, old trees hydrated.
- Large or specimen trees that decline or die from drought become fuel for wildfires, as big crowns of dead or dying leaves can explode into flame and spread fire faster.
- Tree removal costs more the bigger the tree is (and dead trees can be even more costly to cut down if they’ve become unsafe).
- Big trees provide food, nesting sites, and shelter for birds and wildlife that can’t be replaced.
With the many benefits mature trees provide in the Front Range area, they’re well worth protecting. Plus, if a large tree dies it will be 20 years or more before a replacement tree can even begin to take its place in the landscape.
Unlike smaller trees, large trees (those with a diameter of 10 inches or more) will need 15 gallons of water per inch of trunk diameter.
Deep Root Watering to Prevent Drought Death
Large trees benefit from deep root watering (and often benefit from fertilization and the addition of soil conditioners), where water is injected into the soil throughout the root zone. This places it where it can most easily be absorbed by the roots. And, because large trees need a lot of water (more than you might expect!), it helps prevent problems with water runoff.
For example, one inch of rainfall over 100 square feet (a 10×10 area) is equal to 62.34 gallons. In a deep watering we’re simulating a 1/2 inch of rain in the specified area. The water is injected into the soil in a grid pattern on 18″ centers: 4.5 holes over a 10 square foot area, 45 holes over a 100 square foot area, 445 holes over a 1000 square foot area. We inject two quarts per hole to give the tree consistent moisture throughout the entire root zone.
If you’d like to irrigate your mature trees yourself, be sure to keep the water flow low (to avoid runoff) and leave it on for a long time. The calculator below will show you how many gallons of water your tree will need to give it ½ inch of water over the whole root zone.
We Can Help
If you’re worried about your trees, drought, or fire danger, or if you’re not sure how much water your trees need, give us a call. We’re experts in tree care, firewise landscaping, and keeping trees healthy through all seasons. By working together, we can help to protect our prized trees and manage Colorado’s drought conditions successfully.