by Charlotte Glen, agricultural agent, N.C. Cooperative Extension
RALEIGH — Correct watering can make the difference between a bumper crop and complete failure.
As we experienced earlier this summer, and again this past week, too much water can result in fruits and herbs having less flavor, increased disease problems and plants drowning.
On the other hand, if there is too little water, seedlings fail to come up, yields are reduced and plants can die.
Correct watering relies on many factors, including weather conditions, soil type, and what you are growing. As a result, how much and when to water is not a simple formula.
Understanding water needs key
Fruits and vegetables are composed of up to 90 percent water that is absorbed from the soil by plant roots.
If adequate water is not available from the soil while fruits and vegetables are growing, plants will be stunted and may drop flowers or fruits, reducing yields.
When rainfall does not provide adequate water for developing crops, gardeners have to supplement with irrigation to protect yields and quality.
The most critical time to water vegetables, herbs and fruits is the first few weeks after planting or seeding.
August is the time to sow seeds of many fall vegetables in the garden, including carrots, turnips, beets, spinach, lettuce, cabbage, collards, broccoli and kale, as well as cool season herbs such as parsley, cilantro and dill.
Once seeds are sown, it is critical to keep the top 3 to 4 inches of soil moist until seedlings reach 4 to 5 inches in height. This may require daily watering on hot, sunny days.
For fruits and summer vegetables, it is also critical to water from the time plants bloom until harvest is complete.
Water shortages during this time will reduce yields and cause fruits to be smaller than normal.
Because they grow in the cooler times of the year, cool season crops usually do not require additional water unless we have unusually dry weather. This is most likely to happen in fall.
Perennial herbs such as oregano, thyme and rosemary need less water than vegetables and fruits.
Once established, these plants often thrive with no additional watering, even in sandy soils. Overwatering these herbs reduces their flavor intensity and can kill plants.
If you garden in clay or heavy soils, or your garden is in a low lying area, too much water can be a serious threat to plant health.
Plant roots need air as well as water to survive. When soils become waterlogged, all the air space in the soil fills with water. As a result, roots drown, usually causing the whole plant to die.
This can be a problem even in soils with good drainage during extended periods of wet weather like we have experienced this summer. Gardening in raised beds that are at least 6 to 8 inches above soil grade will help avoid issues with waterlogged soils.
Choose best watering systems
The best way to water vegetables, herbs and fruits is by applying water to the soil using soaker hoses or a drip irrigation system.
If you have a small garden, or garden in containers, you can water plants with a watering can or watering wand attached to a hose.
When watering by hand, avoid wetting plant leaves. Keeping leaves dry helps reduce foliage disease problems such as leaf spot and downy mildew.
Soaker hoses provide an inexpensive way to water your garden but they clog easily and usually last only a few seasons.
Kits to install more durable drip irrigation systems are available from many garden centers and hardware stores.
While more expensive initially, these systems are more reliable and cost effective over the long run. Another option for slow watering is to drill several holes in the bottom of a 2-liter bottle.
Bury the bottom third of the bottle in the soil beside each plant or in each container. Fill the bottle to water crops.
This methods works best for large plants such as tomatoes, peppers, or broccoli rather than plants that are spaced closely together, such as beans or carrots.
It’s all about location and timing
When watering edible crops, your goal is to avoid water stress by keeping the top 6 to 8 inches of the soil moist.
For most vegetable and fruit crops, this requires at least 1 inch of water per week from rainfall or irrigation during the growing season, April-October.
When gardening in deep sandy soils or during a heat wave, up to 2 inches of water per week may be needed. If rainfall does not do the job for you, you will need to water.
Water applications should be split, to apply .5 inch of water, twice a week. In very sandy soils where water drains quickly, three applications per week are often needed.
Plants grown in containers will likely need to be watered every day during summer, but only once or twice a week during winter and spring.
Check soil moisture levels 30 minutes to an hour after watering by digging a hole 6 to 8 inches deep.
If the soil at the bottom of the hole is dry you should water some more. If the soil is soaking wet, you have watered too much. Allow the soil to dry before watering again.
Reduce your garden’s water needs and improve plant growth by adding compost to the soil each year. Mixing compost into the soil helps soil hold water and nutrients.
This is particularly important in sandy soils.
In addition, mulching with leaves, straw, or bark mulch also reduces water needs, adds organic to the soil, and helps control weeds.
Learn more about vegetables and herbs you can plant now for a fall garden by visiting the fall vegetable gardening guide at pender.ces.ncsu.edu/2012/08/fight-rising-food-costs-plant-a-fall-garden.