For productive, healthy vegetable gardens, irrigation is typically needed during the growing season. A lack of rainfall and irrigation leads to a deficit of soil moisture. This reduces yields and produce quality more than any other aspect of vegetable gardening. When rain doesn't provide adequate soil moisture in the vegetable garden, it must be done through supplemental irrigation.
Conserving Soil Moisture | How Much Water to Apply | How to Apply Water | When to Apply Water | Effects of Drought | More Information
Conserving Soil Moisture with Mulch
The first step in providing adequate water is conserving the water in the garden soil.
Water can be lost from the plant (through a process called transpiration) and from the soil (through evaporation). The weather influences both transpiration and evaporation, with greater water loss on hot, windy, low-humidity days.
Covering the soil surface with mulch provides a barrier to reduce the rate of evaporation. It has the added benefit of reducing weed growth.
Effective mulch options for vegetable gardens include grass clippings, shredded leaves, coco hulls, and weed-free straw.
Apply several inches of mulch in early June after the soil has warmed; applying it too early can slow plant growth. These materials decompose quickly and can be tilled into the soil in fall or spring.
Biodegradable materials like newspaper, cardboard, and planter paper can also be used. Learn more in this article: Using Mulch in the Garden.
Other factors can influence soil moisture available to vegetable plants. Good weed control is necessary so the weeds don't rob the vegetable plants of any available soil moisture. Utilizing windbreaks also reduces transpiration and evaporation from the soil surface.
How Much Water to Apply
In most cases, a vegetable garden requires a moisture supply equivalent to one inch of rain per week to maintain vegetative growth and good production. This water can be supplied by both Mother Nature and the gardener. Install a rain gauge near your garden to know how much water is provided by rain. When rain provides at least one inch of water over a week, supplemental irrigation is not necessary.
Water slowly and deeply. Avoid a quick splash that can promote shallow rooting, leading to poor drought tolerance. Water in the morning or early afternoon allows wet foliage to dry quickly in the morning sun. Morning watering also ensures the plant is fully hydrated as it goes into the hottest part of the day.
How much water to apply at any one time depends on how porous the soil is and how much water it will hold. A fine textured soil, such as a silt loam, will hold more water than a course, sandy soil. Watering should wet the soil to a depth of 6 to 12 inches where most roots are.
When using sprinklers, it is a good practice to measure the amount of water applied by placing straight-sided containers, such as tin cans, in the wetting pattern. When one inch is accumulated in the can, you can assume you put approximately one inch of water on the garden area covered by the sprinkler. A good watering once a week is recommended when utilizing a sprinkler.
When using soaker hoses or drip/trickle irrigation methods, turn the water on and check regularly to see how deep the soil is wet. The first watering using this system should thoroughly soak the garden to a depth of 10 to 12 inches. After the initial soaking, you only need to replace the water lost to evaporation or transpiration. Typically, this means running the system every one to two days for a few hours. To check the wetting depth, simply dig a hole. Once you know the time it takes to wet the soil to 12 inches, you know how long to run these systems for future waterings.
After watering, don't cultivate or walk on the wet soil. The soil is dry enough to walk on when the foot does not sink down into the soil.
How to Apply the Water
Hand Watering
Hand watering with a hose is probably the most inefficient way to water a vegetable garden. The water flow is faster than the infiltration rate of most soils, leading to runoff and washing soil away, exposing roots to drying temperatures. Most people do not water long enough to wet the soil deeply, leaving the surface wet but the root zone dry.
Sprinklers
Sprinklers can be an alternative to hand watering. It is easier to apply an adequate amount of water to wet the entire root zone down to the appropriate depth with a sprinkler. They deliver water at a rate that can more easily infiltrate the soil, leading to less runoff, but the amount of water they supply can vary greatly depending on the sprinkler type and your water pressure. Most sprinklers will distribute about 3 gallons per minute at a pressure of 25 to 35 pounds per square inch (psi), which is common for household faucets.
While better than hand watering, sprinklers still have some drawbacks. Depending on the size of your garden and the type of sprinkler, they may need to be moved around to cover the entire garden area. Sprinklers wet the foliage, which can promote more disease issues. They also water the plant's root zone and all the spaces in between, such as the middle of the row. This provides weeds with enough moisture to compete with the vegetables.
Learn more about using sprinklers in this article: Using Sprinklers in the Landscape and Garden.
Drip and Trickle Irrigation
Drip irrigation offers several advantages over traditional watering methods like hand-watering and sprinklers. It conserves water by delivering it directly to plant roots, using 30-50% less water overall, and keeping surrounding areas dry. This method provides slow, even water distribution, minimizing runoff and evaporation.
Drip systems save time by allowing for automated operation, freeing gardeners from the need to stand with a hose. They can also be used for fertilizer application.
Additionally, drip irrigation aids in disease management by keeping plant foliage dry, reducing the risk of diseases.
However, potential drawbacks include emitter clogging without proper maintenance and higher installation costs, which may deter some home gardeners.
Learn more about setting up and operating drip and trickle irrigation systems in this article: Using Drip Irrigation in the Garden.
When to Apply Water
Plants perform best when never under water stress. Despite this, there are critical periods of growth where adequate soil moisture is important. These include seed germination, flowering and fruit set, fruit or head enlargement, and rooting. Younger plants have fewer and more shallow roots than older ones and need more frequent watering. Some common water stress periods for commonly grown vegetables are included in the table below.
| Crop | Most Critical Water Need Period |
|---|---|
| Tomato, Eggplant, Pepper | Flowering, Fruit set and development |
| Broccoli, Cabbage, Cauliflower | Head development |
| Potato | Tuber enlargement |
| Sweet Corn | Tasseling and ear development |
| Cucumbers, Melons, Squash | Flowering, Fruit set and development |
| Bean, Pea | Flowering, Fruit set and development |
| Carrot, Radish, Beet, Turnip | Root enlargement |
| Onion | bulb development |
Effect of Drought on Vegetables
When adequate moisture is not provided, plants experience drought conditions. Typical symptoms of vegetable plants under stress are wilting of soft stems and leaves, curling and rolling of leaves, and scorching of leaf edges.
Water-stressed plants are more susceptible to diseases and fruit quality is reduced and more likely to have certain defects. Tomatoes, peppers, and squash develop blossom-end rot. Leafy greens are less crisp. Lettuce and celery become fibrous and bitter. Strawberries are small and seedy. Many fruit-type vegetables (any vegetable that develops from a flower, such as green beans and tomatoes) blooms and small developing fruit are aborted.
More Information
- Watering Tips for the Garden, Lawn, and Landscape
- Using Drip Irrigation in the Garden
- Using Sprinklers in the Landscape and Garden
- Watering Home Lawns
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