Vegetable crops need 1 inch of water each week–as a general rule of thumb; this is the equivalent of about ½ gallon of water or slightly more per square foot of garden. Some crops need more water, and some need less.
The best vegetable crop production comes from consistent watering. It is important to avoid having vegetable plants go dry-then wet-then dry; this will cause plants to grow in stops and starts. Uneven watering can lead to uneven production and often uneven appearance and size of vegetables. Vegetables that are under-watered and come to harvest with a low water water content can be bitter or tasteless.
The objective of watering vegetables is to replace the moisture lost from transpiration and soil moisture evaporation. The goal is for soil moisture to remain more or less constant–just moist, not wet or dry is optimal. Vegetables generally need the most water during mid- and late-summer and when the weather is particularly hot.
It is time to water your garden when a handful of soil squeezed into a clump falls apart when lightly touched.
One-inch of water each week is the average needed to keep the soil just moist. In arid or particularly hot regions, about 2 inches of water each week is required. The amount of water may vary from ½ inch per week early in the season to more than 1 inch later in the season.
Vegetables that receive too little water (or too much water) will stop growing. When a vegetable begins to wilt from lack of water, it has already stopped growing for a day or more. (Temporary wilting of fruiting crops such as squash and cucumbers on a hot summer afternoon is not necessarily a sign of inadequate watering–this can be a sign of normal photosynthesis at its water-demanding peak.)
As each crop grows toward harvest, it is important to keep the soil evenly moist and allow the crop to attain its optimal water content–this will make for the best form, color, and taste. Under watering can leave vegetables bitter; overwatering can leave vegetables tasteless.
Percentage water content of vegetables:
• 96 percent: cucumber, butterhead lettuce, crisphead lettuce, zucchini.
• 95 percent: celery, witloof chicory, romaine lettuce, radish.
• 94 percent: Chinese cabbage, collards, endive, looseleaf lettuce, rhubarb, scallop squash, summer squash, ripe tomato.
• 93 percent: green cabbage, sweet pepper, Swiss chard, green tomato, watermelon.
• 92 percent: asparagus, beet greens, red cabbage, cauliflower, eggplant, Casba melon, mushroom, bunching onion, pumpkin, spinach, strawberry, turnip root.
• 91 percent: broccoli, savoy cabbage, mustard greens, dry onion, turnip green.
• 90 percent: green beans, honeydew melon, netted melons, okra, rutabaga.
• 89 percent: edible-podded pea, winter squash.
• 88 percent: carrot, parsley, hot pepper, Hubbard squash.
• 87 percent: beet roots.
• 86 percent: Brussels sprouts, butternut squash.
• 85 percent: kale.
• 84 percent: artichoke.
• 83 percent: leek.
• 80 percent: parsnip.
• 79 percent: green pea, potato.
• 77 percent: salsify.
• 76 percent: sweet corn.
• 73 percent: sweet potato.
• 70 percent: lima bean.
• 67 percent: Southern pea.
• 59 percent: garlic.