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Deep and infrequent — carrots, beets, potatoes, other root vegetables. These roots are strong enough to chase the water down. A quick splash on top just trains them to stay shallow, lazy and hairy! Who wants a hairy carrot!! Make them work for it! Water until it puddles slightly on the surface, then fully soaks in — then do that once more. Two soak-and-absorb cycles gets water past the surface roots and down to where the deep roots actually are. One splash just wets the top and evaporates by noon.
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Frequent and shallow — lettuce, spinach, most leafy greens. Shallow means water enough to wet the top 2 inches. The roots of leafy greens live close to the surface and that's where you want the water to be. Frequency means every 1–2 days in warm weather; daily if it's hot and windy, less if it's cool and cloudy. The mistake people make here is treating shallow like it means "less water overall." It doesn't. It means smaller bites, more frequently. Think, feeding a baby.
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Deep and frequent — tomatoes, peppers, squash. Think about how watery the fruit is. Think about how big the fruit is. Think WATERMELON! Two full soak-and-absorb cycles, often. Are the leaves curled? They are trying to prevent evaporation by curling up. Are the leaves wilted? Their water reserves have been depleted. Be certain not to water shallow and often for these plants. The surface looks fine, but the deep roots and fruit are running short. This shows up as blossom end rot on tomatoes or split fruit on squash.
Timing
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Water in the morning if you can. It sets the plants up for the heat of the day and for photosynthetic processes
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Evening watering leaves things damp overnight and allows the soil to stay damp. Plant take up much less water during the night. Also, wet vegetation is basically a welcome mat for fungus bacteria and slugs.
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Never EVER water during the midday sun. EVER. They don't make sunscreen for plants. They will burn.
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Watering in the heat will encourage the soil to form a hardpan (think crusty pizza) and water will run off instead of infiltrating.
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Acceptable is midday when it is cloudy. Although UV does get through it isn't enough to burn the plants.
Water
Here's the Cheat Sheet: