Water is foundational to the growth and success of any and all plants. While it may seem either obvious or difficult to understand how much water to provide to plants, here are a few concepts and a list of best practices that can help you understand how to water your garden effectively.
Factors that Influence How Much to Water
Proper watering isn’t a one-size-fits-all approach—ideally each plant should be considered as a unique individual in order to provide the right amount of water. By thoughtfully pairing plants in the landscape that have similar water needs you can reduce the amount of work that goes into watering. There are several things to consider when watering your garden, including:
- Type of plant: Large-leaved plants tend to require more water, with drought-tolerant plants requiring the least amount of water.
- Exposure (sun, shade, wind, etc.): Sunny, windy locations will cause plants to dry out faster than plants in protected and shady spots.
- Growing conditions (in-ground vs. container): Generally, plants in the ground will need less frequent watering than the same plant in a pot.
- Soil type or planting media: Quick-draining soils and planting media will need to be watered more frequently as they hold less water than clay soils or those with a lot of organic matter.
- How long it has been planted: New plantings will need to be checked for water and watered more frequently than established, mature plants.
- Weather and season: Cooler, wetter days mean that nature can do some of the leg work for you, but you’ll need to water more in the heat and Summer.
Watering Application Methods
Depending on the size of your landscape and water needs, you have a variety of irrigation and watering tools and methods available. Although any of the below options will help you water your garden effectively, you’ll likely find a favorite!
- In-ground irrigation sprinklers: A blanket, automated approach to water where spray heads are set up in different zones to provide irrigation to the landscape. Even these automated systems should be tuned by an irrigation technician for maximum effectiveness.
- Drip irrigation: Surface or sub-surface hoses provide water to individual plants. Emitters can be used to adjust the rate and volume of water provided to each plant.
- Soaker hoses: Connected to a hose bib, these hoses slowly seep water, are limited to 100 feet or less, and are best used on level ground around vegetables or in landscape beds.
- Manual hose-bib sprinklers: Connected to the end of a hose, these sprays can be adjusted and manually moved around the lawn or landscape.
- Hand watering: Hand watering is the most responsive and engaged way to water because it is operated by a person in real time! Use a hose-end sprayer to adjust the flow, angle, reach, and intensity of water rather than an open hose.
A Guide to Watering Your Whole Landscape
Without rain, all landscape plants still benefit from a thorough watering periodically.
- Trees: Water established trees once a month during the growth period and during hot, dry weather. Focus watering efforts on the soil around the dripline of the tree, because this is where the most active roots are located.
- Shrubs: Water shrubs every 3-4 weeks—water should penetrate entire root zone (within the first 2 feet for most). Fall and winter blooming shrubs (especially Camellias and Rhododendrons) should be given supplemental water from July until rains begin since they are producing flower buds at this time of year.
- Lawns: Frequent, shallow watering is best to establish from seed or sod. Once rooted, lawns can be watered at the rate of 1-2 inches per week, split in half and applied 2 times week. Lawns may be watered every other day in extreme heat.
- Perennials & Roses: Perennial garden watering depends on the types of plants and other growing conditions. Generally, perennials always need more water when young and during growth and bloom times.
- Annual Bedding Plants: Keep annual plants moist by watering every other day or daily. Soil should never be soggy, and not dried out to wilting point.
- Annual Vegetables: Vegetables require different watering depending on crop and growing conditions, so pay attention to the soil moisture by testing it with your finger before watering. Typically, only container gardens and raised beds should be watered daily unless temperatures are extreme.
- Container Plantings, Raised Beds & Hanging Baskets: Water once or more per day during hot or windy weather. Hanging baskets can be taken down to sit on the ground or even sat in a shallow saucer of water to conserve moisture and reduce evaporation during extreme heat events if you plan to be gone for a day or two.
Remember—Container plantings will need to be regularly watered for the duration of their lives (even during winter if the area does not receive regular rainfall).
Concerned your plants may be stressed from lack of water? Follow our Guide to Heat & Drought Stress for tips about what to do during extreme heat or long periods without rain!
How to Establish Strong Plants through Watering
How to water your plants depends not only on the plant, but on the stage of maturity and how long it has been in the landscape. What it means and how to water your garden effectively changes depending on the age of your plants!
Set Up for Success: Watering When Planting
- Dig a hole in the ground twice as wide as the plant root ball, but no deeper and fill the hole with water to ensure proper drainage and pre-moisten the planting area.
- Pre-soak dry or root-bound plants in water, root stimulator, or compost tea; loosen up compacted roots.
- Amend native soil with 25-50% compost to increase water-holding capacity.
- Plant at proper level in the soil and water the plant again after covering roots with soil.
- Apply 1-3 inches of mulch to cover the root zone and prevent water from evaporating.
Pay Attention: Providing Water to New Plants
Deep watering is slow application of water to wet the root zone and surrounding area for 30-60 minutes. Deep watering is accomplished by hand watering at a very low flow rate, or with focused use of soaker hoses or drip irrigation.
Watering in-ground plantings: Newly planted trees and shrubs should be watered deeply every 2-3 days for the first week or two, then gradually tapered off to every 3-4 days, 4-5 days, etc. until you are able to provide deep watering weekly without the plant showing signs of stress. Newly planted perennials can benefit from deep watering for shorter durations and might need more frequent watering.
Watering container plantings: Container plantings often need more frequent watering when newly planted, but do not need to receive as much water as in-ground plantings since their roots do not extend far into the surrounding soil yet. When more established, the same plant will have roots throughout the container to better utilize moisture near the bottom of the pot, so they should be watered more thoroughly (until water comes out drainage holes) and more frequently than in-ground plantings.
Watering frequency may need to increase if temperatures rise above 85 degrees and/or if it is very windy.
Keep It Going: Establishment Watering of Perennials, Trees & Shrubs
Watering new plantings to establish healthy roots usually requires about 2-3 years before plants can be considered “established.” Even if your plant is technically drought tolerant, it will only be so once the plant is established.
Drip irrigation can provide deep watering, but most irrigation sprays only wet a shallow layer of soil and are not enough for establishing new plants, so hand-watering with the goal of deep watering in warm weather is necessary.
To determine if your irrigation system is effective:
- Dig down after watering to see how deep the moisture has penetrated to determine ideal duration of watering time.
- Test sprinkler coverage/volume by distributing shallow, open containers (tuna cans) around the lawn before running sprinklers, then measuring amount of water in the cans after a set amount of time. The average lawn requires 1-2 inches of water per week to stay green and healthy.
Year 1 (Infancy): Depending on the time of year of planting, begin watering regularly once it is no longer raining or anytime during periods of dry weather. Often, a light shower does not wet the soil deep enough to be considered hydrating to plant roots. Begin watering frequency at every 2 or 3 days for one to two weeks, then extend the break another day for another week or two until you are watering deeply once per week. Continue watering weekly until rainfall is reliable and significant.
Year 2 (Adolescence): Again, begin regular watering once dry weather has arrived and water deeply once each week, gradually skipping more days in between to get to watering about every 10 days or so.
Year 3 (College Years): A three-year-old plant should be fairly established, but will benefit from occasional deep watering every 2-3 weeks during hot, dry seasons—typically July to early September in the Portland area.