Water is essential for plant growth but too much can be just as detrimental to plant health as too little. Even if overwatering doesn't damage your plants, it’s a waste of a precious resource that can be avoided.
Watering efficiently to meet your garden's needs can be tricky, because how often and how much to water depends on a whole range of factors. Here are a few key considerations.
- The water needs of the species (low, medium, or high)
- The age of the plant (young or mature)
- The soil type and drainage capacity (loamy, sandy, clay, or silt)
- The weather (amount of precipitation, sun or overcast skies, temperature)
- The microclimate (topography, sun and wind exposure)
This article walks you through the watering needs of different plant types and explains why some plants need more frequent watering than others.
When and How to Water Your Plants
If a plant looks like it’s under drought stress, do not delay watering. Otherwise, watering in the early morning hours is ideal. In the late afternoon or early evening is second best.
If you have kept a consistent watering routine and a plant looks wilted, the problem may not be due to underwatering. Wilting can also be a sign of overwatering. Checking the soil moisture is the best way to decide whether you should water.
How you water your plants is just as important as watering often enough. Water needs to reach the roots, so it is crucial to water deeply. Target the base of the plant and apply water slowly. When you water the soil surface too fast, a lot will be lost to evaporation and run-off, especially when the soil is dry.
You want to avoid wet leaves for most outdoor plants since this can lead to fungal problems. If it is necessary to use an overhead system, watering in the morning gives leaves a chance to dry before nighttime temperatures drop.
The rule of thumb for watering a vegetable garden is one or two inches per week Include rainfall amounts and reduce the water you need to provide accordingly. In the spring and fall, one to two inches can serve as a baseline but it is not enough during summer when many vegetables are flowering and fruiting. Watering more often supports the nutrient uptake needed to produce a healthy harvest. Checking soil moisture is a much more reliable indicator than going only by the one inch rule. Insert your index finger about an inch deep into the soil. If it's dry, water until it feels moist.
During a heat wave, a vegetable garden might require daily watering. Waiting until crops look wilted can lead to drought stress which, in turn, can lead to pests and diseases. Also, if crops don’t get enough water during key times of their development, such as fruit set, it will affect the quality of the crop.
Another exception to the one inch rule is moisture needed for vegetable seeds. Depending on soil type and weather conditions, they may need to be watered lightly but daily to keep them from drying out during germination. Even seeds that need light to germinate will not produce a plant if they are allowed to dry out.
Young seedlings also require more frequent watering than established plants. Insufficient water leads to stunted growth and poor crops, as well as higher susceptibility to pests and diseases. It is not possible to put a number on how many times per week vegetable seedlings need watering—let the soil moisture be your guide.
Water requirements for herbs depend on the type of herb. Most herbs are fairly drought tolerant and require infrequent to no watering but there are exceptions. Herbs with thin, delicate leaves such as parsley, cilantro, dill, and basil need watering during dry spells, about one inch per week, or enough to soak the soil around the base of the plant. Mediterranean herbs with woody or fibrous stems and thick leaves or needles such as rosemary, sage, and thyme can make it through an entire summer with very little applied water, unless there is an extended drought.
Plants in pots, whether moved outdoors only during summer, or in containers that remain on your patio year-round, have the highest watering needs of all outdoor plants. Several factors cause container plants to dry out much faster than those grown in the ground: full sun exposure, hot weather, small container size, container material that heats up, such as black plastic, and surfaces that radiate heat such as stone or asphalt.
To determine if a potted plant needs water, insert your index finger into the soil up to the second knuckle. If the soil feels dry, it's time to water. In the spring and fall and in cooler climates, it might be sufficient to water container plants every two to three days. In the summer and in warm climates, container plants usually require daily watering, unless they are succulents or other drought-tolerant xeriscape plants. Water deeply and slowly until water runs out of the drainage holes.
Plants in hanging baskets are another step up in terms of watering needs. Exposed to sun and wind with virtually no root protection, they dry out even faster, especially those with coir liners. Count on having to water them at least daily and even twice a day in hot weather.
What applies to container plants also applies to raised beds—they need more frequent watering than in-ground vegetable gardens because the soil heats up and dries out faster. The frequency of watering depends on the size of the raised bed. The smaller the raised bed, the more frequently water is needed. A small, raised bed in hot summer weather might need daily watering, where a large, raised bed may only need to be watered twice a week.
You might also find that soil towards the outside of a large, raised bed dries out faster than in the center, which is better insulated from heat. You need to adjust your watering schedule accordingly.
Trees and Shrubs
Whether ornamental trees and shrubs need watering and how often depends very much on your plant choices. If your plants are a good fit for local growing conditions, you shouldn’t have to water mature plants at all unless they are newly planted or when there’s a drought. Native plants are superior in this respect because they are the best outfitted for the precipitation levels in your climate. Non-native tree and shrub species, that require more water than average precipitation in your area, are likely to need watering during the growing season—about once in week in the absence of rain, until the soil is saturated within the dripline of the tree.
Fruit trees and fruit-bearing shrubs have different watering needs than landscape trees. They need water during the six week period before, during, and after bloom, and in the weeks before harvest. If there is a dry spell or a drought during those times, water them deeply until the soil is saturated and repeat as needed, depending on how fast the soil dries out.
Water needs for flower beds also depend largely on whether you choose species and varieties that are suitable for your climate and soil type. For example, if you plant a cardinal flower, which requires wet soil, in consistently dry soil, you will have to water it regularly.
Annuals, especially those purchased as flats, tend to need more frequent watering because their entire growth happens in only one short season. In the absence of rain, or in hot weather, they may need watering two to three times a week. Perennials, grow slower and should only need watering once a week.
New Plants and Transplants
New plants and transplants need watering right after planting and for an extended period of time until they become established.
Water herbaceous perennials at least twice a week in the absence of rain. Once you see new growth, you can switch to a weekly watering schedule for the rest of the growing season.
Trees and shrubs need longer to get established and require additional watering during this time to make up for any lack of regular precipitation. A new tree or shrub should be watered daily for the first two weeks after planting, then twice to three times per week during the first three months, and weekly after that for the remainder of the first growing season. In the second growing season, water it at least once every two weeks in the absence of rain.
Winter and Dormancy Watering
When plants enter dormancy, their roots are still very much alive, and need water to survive. Usually, fall, winter, and spring are the seasons with increased precipitation but there are winter droughts during which watering might be required. Desiccating winter winds can dry out the soil even more, especially if there is no snow cover. This can lead to root damage and plant death.
Trees and shrubs with shallow root systems such as dogwoods require supplemental watering during extended dry fall and winter periods. All newly planted trees are also susceptible to winter drought injury.
If there is a three week stretch without precipitation, water trees with about ten gallons of water for each inch of trunk diameter. A three foot shrub needs about five gallons and large shrub of six feet or more needs about 18 gallons. Apply the water at the dripline and repeat monthly if drought persists.
If you have planted perennials late in the fall and they did not fully establish before dormancy, water them once a month during winter droughts.
Make sure to water only when air and soil temperatures are above 40 degrees Fahrenheit and there is no snow cover. Do not water when the soil is frozen, as it won’t absorb water. The warmest mid-day hours are the best time to water so the water has time to soak in before nighttime freezing temperatures.
Winter Watering for Trees, Shrubs. Denver Water.
Fall and Winter Watering. Colorado State University Extension.