Wilt not water

I know I've read, somewhere, that if plants are wilting, get watered and perk up, but then immediately are wilted again, it is likely not a matter of their needing water. Unfortunately I cannot remember either what the real problem is or what the right solution is. Can someone help me out here?

Here is one answer:
Several summer vegetables, especially with large leaves (many squash & pumpkins for example) cannot pick up enough water in hot weather. So the leaves wilt in the heat of the afternoon.
When it gets cooler, the leaves will perk up, as long as there is a reasonable amount of water in the soil. Watering while the leaves are wilted may or may not perk them up right away. It will help with the recovery if the soil it dry.
They could very well wilt again the next time the weather is hot.
This does not seem to hurt the plant or production.

Another reason plants wilt:
Roots need oxygen as well as water. If the soil stays too wet this excludes air, and the roots suffer. The growing tips may die, and this is the part that picks up the water.
Roots with problems like this cannot pick up enough water to replace what is evaporating out of the leaves, so the leaves wilt.
Soil borne diseases can invade these compromised tissues, too. Ultimately these diseases get into the plant's circulation and kill it.
If you suspect this is going on you could water with some hydrogen peroxide in the water (1 tablespoon per gallon), or repot into good soil with better drainage. If the soil is OK, but the container has no drainage, then addressing this issue may be all the plant needs to recover. If it has gone on too long, then the fungal or other diseases have probably killed the plant.

It depends on the plant. Plants engage in transpiration which is like sweating. Some plants, like squash, are also capable of guttatation, which entails sapping.

Willting in heat allows for plants to reduce the surface area of their leaves. In addition, the release of fluid helps cool the leaf. A similar example outside the garden is in the greenouse. I grow orchids. There are thick leaved and grassy leaved types. When greenhouse temperatures go into the hundreds, thick leaved plants will burn (literally cook in their water) because they are designed to hold on to moisture and do not transpire well. Thin leaved orchids are fine.

It's probably not a problem in your zone but if wilting is seasonally prolonged I would guess that it weakens the plant and decreases productivity since it is a coping mechanism.

Thank you both.

If plants are wilting when the soil goes dry, you're obviously under-watering.

If plants are wilting when the soil is moist, they have compromised root function or they cannot take enough water to keep up with transpiration. High root temps are a possibility, but often, the remedy is LESS water in the soil, not more. As alluded to in a previous post, water uptake is an energy-driven process, and the plant must burn carbohydrates in the presence of oxygen to produce the energy that drives the process. Lack of O2 = impaired root function. Plants don't wilt to reduce leaf surface, they wilt because they cannot take up enough water to maintain internal water pressure (turgidity).

If you have a houseplant that wilts during the day, but perks up again at onset of the dark cycle (w/o you having watered it), you can be >95% sure you're over-watering.

Al