As our summers get hotter and drier, landscape watering is increasingly important. Here are tips on watering your trees, shrubs and other plantings. Photo: Olek Poplavsy, Flickr.
Have you watered your plants yet? Now is a good time to make sure your landscape watering strategy is ready for the growing season.
Seattle had less an inch of rain in April (0.86 inches), far less than the average of 2.71 inches. The forecast for the next few days is for warm and dry. It may reach 80 degrees by this weekend.
Summers in Seattle have been drier and hotter over the past few years. This trend is likely to continue as the earth’s climate changes. We need to adapt to the new reality and make summer watering a new habit. You will need to water your entire landscape, including trees, shrubs and lawns, to keep it healthy and alive.
Landscape watering is important
Plants need water to survive and thrive. Plants use water for many important functions, from photosynthesis to plant growth. Water helps plants stay healthy, so they can better resist diseases and insects. A stressed plant is more susceptible to damage. A lawn that has been allowed to go dormant in summer will be more prone to weeds and moss when rains return in the fall.
Landscape watering is an investment. Watering your trees, shrubs and other plants in the dry months is an investment in the landscape. An attractive landscape is an asset. It is not only beautiful, making it appealing for relaxation and entertaining, but it can increase home value by tens of thousands of dollars.
Water is a necessary maintenance cost. Paying to water your landscape is like paying for maintenance for your car. Cars need tuneups, new tires, fuel, insurance and other regular maintenance. Water is a very inexpensive “maintenance” cost for your landscape. The cost of keeping plants alive and well is much less than the cost of replacing them.
Watering trees is cheaper than replacing them. In recent years we have been urging our clients to water not just annuals and perennials, but trees and shrubs. We have seen more and more drought stress in trees. If you do not water regularly, trees can die. Then you have the financial expense of tree removal and replacement. And you need to wait many years for the tree to grow into a mature plant with height and stature.
What to do now
Maintain your watering system
If you have not gotten your landscape watering system ready, don’t delay.
- If you have an automatic irrigation system, check to make sure it is working properly. Look at water pressure, check for broken sprinkler heads, look at head angles and more. Here is information on maintaining a sprinkler system.
- If you have a drip irrigation system, flush it and check for missing or clogged emitters. Here is information on maintaining a drip system.
- If you use sprinklers and hoses, are they in good shape?
Add a thick layer of mulch
A few inches of mulch in your planting beds is an effective way to reduce your plants’ water needs. Mulch insulates the soil and helps to keep it from drying out. With hotter and drier summer, mulch is increasingly important to help keep your plants and trees from getting drought stress. Mulch also limits weed growth and prevents erosion.
If you want to add mulch now, apply it after it has rained hard. Or water the soil deeply before you lay down the mulch. This will help to retain water in the soil. See our blog post from last spring about using mulch to reduce summer water needs.
Water new plantings
If you have newly planted trees, shrubs, grasses, lawns or perennials, make sure to water deeply and often. New plantings are especially vulnerable for the first two or three growing seasons, until their roots are established.
If you have new trees, you may want to buy water bags called Tree Gators. Here is a link to our short video about how to use a Tree Gator to water a new tree.
Choose plants that need less water
If you are investing in new plants for your landscape, choose plants that are less thirsty. There are many choices for attractive and versatile drought-tolerant plants. Many are Pacific Northwest natives.
Some of our favorite native plants for partly shady areas are evergreen huckleberry (Vaccinium ovatum), vine maple (Acer circinatum), low Oregon grape (Mahonia nervosa), and sword fern (Polystichum munitum). Native plants have the advantage of providing food and shelter for birds, wildlife and beneficial insects.
For sunny areas, herbs and ornamental grasses are a great choice. Rosemary and lavender add fragrance as well as color. For grasses, consider maiden grass (Miscanthus sinensis), pheasant tail grass (Stipa arundinacea), and Mexican feather grass (Stipa tenuissima).
Even drought-tolerant plants need water. Every plant and tree will need regular watering for the first two or three years until the roots are firmly established. And even drought-tolerant plants will need some supplemental water over the season.
Here are some resources.
- Great Plant Picks has a list of drought-tolerant plants for sun.
- The Oregonian/Oregon Live has a long plant list and tips on managing hot, dry weather in the garden.
- The Natural Yard Care Program has a list of drought-tolerant plants.
- Native plant nurseries will have many choices for drought-tolerant plants.
Landscape watering: how to water
The best practice is to water deeply and less often.
Shallow, frequent watering creates plants with shallow roots. Deeper watering creates plants with deeper roots. They will be healthier and will tolerate hot, dry conditions better.
You need to water your plants in such as way as to maximize the water penetration in the soil and minimize the amount of evaporation. If water cannot get into the soil, it is essentially wasted. If your soil is already dry, it may take a few waterings to “soften” up the top of the soil layer so water can penetrate.
Soil is like a sponge. If it is allowed to dry out completely, you cannot just pour water quickly onto the top of the sponge. It will run off and not penetrate the top at all. But if you slowly pour water on the sponge and allow it to soften up the surface, then it will begin to percolate through the rest of the sponge.
Check your soil. If it is dry, you will need to water slowly to get the top to soften. We highly recommend oscillating sprinklers as they allow the water to infiltrate slowly. The water will penetrate more deeply into the soil.
Swanson’s Nursery has a great article on best watering practices. And check out our video: Watering 101: Create Strong and Healthy Plants.
Water the entire root zone area, and then let it partially dry out.
Oregon State University Extension Service.
Where is the root zone? For most trees and other plants, the active root zone is at the outer tips of the leaves or even further out. The area under the outer edge of a tree is also known as the dripline. For many trees this can be a large area.
Most water is absorbed at the dripline and beyond. This is where tiny terminal rootlets take up water and nutrients from the soil for the tree. Trees should be watered here.
It will not do any good to water nearer the trunk of the tree. No root tips are there bringing in moisture for the plant. If a tree is watered by the base of the trunk, it may develop root rot.
Make sure you are watering the entire root zone area of the plant. Then wait until the upper few inches of soil are dry before watering again. This encourages deeper roots.
Know your plants and trees. Some have shallow roots near the surface. Others have deeper roots. They will need more water to soak down to their feeder roots.
No roots want to be waterlogged all the time, except for rice. Unless you are trying to grow rice, the roots need oxygen. Roots get air when the soil is allowed to dry out some between waterings.
The water needs of your plantings will vary. Drought-tolerant plantings that are well established will need less water. Trees may do well with a deep watering once a month.
Water your lawn one inch per week
Your lawn needs one inch of water each week to keep it growing and healthy. As discussed above, it is much better to water once or twice a week rather than daily. This will encourage the lawn to grow deeper roots, making it more resilient.
You may be able to reduce watering in areas of your lawn that don’t see much traffic. But you still need to water it occasionally to keep it alive. Your lawn will need an inch of water at least once a month to provide some resiliency for the plants.
In order to know if you are watering one inch, you need to measure the sprinkler’s output. Here is a short video on how to measure one inch of water.
Landscape watering resources
YouTube playlist
Our YouTube playlist on Watering Your Lawn and Garden has several videos on the basics of watering, watering systems, watering new plants and trees, and more.
- Watering 101: Create Strong and Healthy Plants
- A Good Start: How to Plant and Water a New Plant
- Tree Gators: How to Water a New Tree
- Water Timers: Make Your Watering Easier
- How Much Water? Rain Gauges, Sensors and Tuna Cans
- Watering Systems: Wands, Hoses and Sprinklers
- Choosing and Using Mulch
- Measuring One Inch of Water
- Natural Lawn Care: Smart Watering
Blog posts
Check out some of our blog posts for information about how and why to water.
- Smart watering: how much, when and how long to water
- Plants need water to survive and thrive
- Invest in watering for landscape dividends
- Summer lawn care: watering, mowing
- Watering will help manage insect problems
- Choose drought-tolerant plants and reduce time you spend watering
- Give your plant a good start: how to plant and water it
Other resources
- The Saving Water Partnership has loads of information on watering, including automatic systems, choosing and using drip irrigation and soaker hoses and more.
- Seattle Public Utilities has a guide on Smart Watering.
- HGTV has tips on Wise Watering.
- American Society of Landscape Architects has 7 Tips for Saving Water in Your Landscape.
- The Environmental Protection Agency has landscaping tips for a water-smart landscape.
