Generally speaking, if you keep your tomatoes happy, the rest of the vegetables will receive enough water. Obviously, irrigating a garden containing many kinds of vegetables is not simple. Early in the season when plants are young and have small root systems, they remove water from the soil near the center of the row. As the plants grow larger, roots penetrate into more soil volume and withdraw greater quantities of water faster. In sandy loam soils, broccoli, cabbage, celery, sweet corn, lettuce, potatoes and radishes have most of their roots in the top 6 to 12 inches of soil (even though some roots go down 2 feet) and require frequent irrigation of about 3/4 to 1 inch of water. Vegetables which have most of their root systems in the top 18 inches of soil including beans, beets, carrots, cucumbers, muskmelons, peppers and summer squash. These vegetables withdraw water from the top foot of soil as they approach maturity and can profit from 1 to 2 inches of water per irrigation.
A few vegetables, including the tomato, cantaloupe, watermelon and okra, root deeper. As these plants grow they profit from irrigations of up to 2 inches of water. For fruiting crops, the most critical growth stage regarding water deficit is at flowering and fruit set. Moisture shortage at this stage may cause abscission of flowers or young fruits, resulting in insufficient fruit for maximum yield. The longer the flowering period, the less sensitive a species is to moisture deficits. For example, the relative drought resistance of beans during flowering and early pod formation is the result of the lengthy flowering period — 30 to 35 days with most varieties. Slight deficits during part of this period can be partially compensated for by subsequent fruit set when the water supply is adequate. More determinate crops such as corn or processing tomatoes are highly sensitive to drought during the flowering period.
In terms of food production, the period of yield formation or enlargement of the edible product (fruit, head, root, tuber, etc.) is critical for all vegetables and is the most critical for non-fruiting crops. Moisture deficits at the enlargement stage normally result in a smaller edible portion because nutrient uptake and photosynthesis are impaired. Irrigation, especially over irrigation during the ripening period may reduce fruit quality. Ample water during fruit ripening reduces the sugar content and adversely affects the flavor of such crops as tomatoes, sweet corn and melons. Moisture deficits at ripening do not significantly reduce yield of most fruit crops, irrigate at this time with extreme caution.
