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Irrigating Vegetable Plants
This section discusses the timing and amount of water to apply to vegetable plants in a home vegetable garden, whether planted into soil or in containers:
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- When vegetable plants need to be watered.
- How much water to apply at each watering, and how much in total per week.
- Methods of irrigation and water application for vegetable plants.
- Common watering problems in vegetables.
- Overwatering.
- Soils that drain too quickly or absorb too little water and have runoff.
Watering Amounts and Timing
Vegetable plants need regular and repeated cycles of sufficient watering from rains or irrigation.
Keeping track of the amount of rain water that nature supplies will help you know when to irrigate your garden. Most vegetables need the equivalent total of 1–2 in. (25–50 mm) of water applied per week.
Always apply water at a rate that allows it to be absorbed, and wait to apply more whenever puddling or runoff occurs. A good goal is to fully saturate the top 4–6 in. (10–15 cm) of soil with water at each watering.
For most garden soils, this means applying the equivalent of about 1 in. (25 mm) of water across the soil surface, and watering every 3–4 days.
Allow time between each application for the soil to absorb the water and for the plants to use it before applying water again. Either too much or insufficient water can cause vegetables to fail.
Water applied too quickly will saturate the soil and cause either puddles or fast runoff, eroding the soil and exposing plant roots.
Watering too frequently or too lightly causes plants to become shallow-rooted and subject to drought. When a plant’s root zone is dry, it grows hair roots near the surface to gather moisture.
It’s easy to check for insufficient or “shallow” watering. If you find that the soil remains dry 3–4 in. (10–15 cm) beneath the surface after watering, you should slow the rate of application and lengthen the time of irrigation until all of the soil is saturated.
Over- And Underwatering
Avoid overhead watering that splashes soil onto the plant or wets its foliage. Apply sufficient water slowly and allow it to penetrate deeply.
Whether you grow your plants in the garden or in containers it’s always best to apply water at least 5 in. (10 cm) away from each plant’s main stem. An imaginary circle—called the “drip line”— around each plant, about the diameter of the outer edge of its foliage is the area of the soil where fine roots take up the soil.
Apply water slowly to the drip line area at the rate it is absorbed. This encourages strong root growth. Always avoid runoff or erosion when watering.
The best times to water are in morning after the sun has warmed the soil so that any water splashed on vegetable plant foliage dries completely before evening.
Watering at these times helps prevent fungal infection of plants by soil-borne spores splashing onto their leaves when you irrigate.
Always allow the soil surface to dry completely between waterings. The soil at the root zone, a depth of 8–16 in. (20–40 cm), should be evenly moist yet should maintain good texture and hold sufficient air. Drying usually takes 2–4 days, though soil may dry more slowly if it rains.
Soils that are loose and sandy drain too quickly. You should balance this tendency by watering more frequently and amending your soil with compost before you plant [see Amending Soil].
Because vegetable plants need air as well as water around their roots, plants left too long in saturated soil are subject to suffocation, root damage, and fungal infection.
Many failing plants that appear to be wilting result from overwatering plants rooted in dense, clayey soils.
Use one of the watering methods demonstrated to ensure your plants will receive adequate and regular moisture during the growing season [see Watering Techniques].