When the leaves of a plant wilt it is a sign that the plant needs water, and therefore it is a good time to water–right? Maybe. The plant might need to be watered, but it is also possible that water will harm the plant.
Why do Leaves Wilt?
When we get thirsty, our bodies are letting us know that we need more water. It is a feeling we have. Other people looking at us can’t really tell we need more water. Part of the reason for this is that we have a skeleton structure that keeps us standing straight. Green leafy plants don’t have a similar structure; they use water pressure to keep them standing upright.
You can think of the plant leaf as being similar to a garden hose. With the water turned off, the hose is limp–its wilted. When we turn the water on, the water pressure inside the hose increases and the hose becomes stiff. The stiff hose no longer looks wilted. Plants work exactly the same way. In order for a plant to maintain its normal shape it needs a certain amount of water pressure inside the leaves.
Water pressure is maintained in the leaves by the roots which are absorbing water from the soil and pumping it up into the leaves. Leaves naturally loose water, especially during photosynthesis. Water is constantly flowing from the roots to the leaves.
If roots can’t get enough water, they can’t maintain the correct water pressure in the plant and the leaves droop or wilt.
Why Can’t Roots get Enough Water?
When the soil gets dry, the roots will be unable to get enough water. If this is the problem, watering the soil will certainly help and wilted plants will regain their turgor (ie stiffness).
There is another possible reason why plants can’t get enough water. The roots may be damaged. If the normal root size is reduced substantially, you have a situation where there are not enough roots to get enough water for the whole plant. In this case the soil might be quite wet but the plant will still wilt. Adding more water will not help.
Roots might be damaged during transplanting or they might have rotted.
Damaged Roots During Transplanting
When you move a plant, especially a larger established plant, you will damage a lot of roots. It is quite normal for such a plant to show wilting right after being moved.
It is quite common for people to water far too much after transplanting in order to try and fix the problem. Too much water does not help the problem. One solution is to move plants in spring and fall when the temperatures are lower and plants are not growing at full tilt. At these times of the year water evaporation from leaves is less and you get less wilting.
If you do move a plant in summer, it will wilt much less if it is covered for a week or two so that it receives less sun light.
Over-watering a plant can cause the roots to rot. Some diseases can also cause roots to rot. With less roots, the plant wilts. Some people will then water the plant even more, causing even more root rot.
Wilted plants should only be watered if the soil is dry. If the soil is not dry, it is not a water problem and watering can only make things worse.
Does Wilting Hurt a Plant?
The short answer is YES. Occasional short term wilting will not do too much harm, but it is still not good for the plant.
Some people think that wilting is a natural phenomena in plants and it shows that they are conserving water. That is simply not true. When plants do not have enough water they go into crisis mode. They stop growing, they close stomata to conserve water and they shut down other vital processes. Wilting is a sign that the plant is in crisis mode. If this is due to a lack of water, the plant should be watered right away to reduce long term damage to the plant.
Some plants, like ligularia, which have very large thin leaves, wilt more easily than most plants. By mid-day my ligularia are all wilting even when grown in shade and in wet soil. By 6:00 pm they are back to normal, showing fully stretched out leaves. Is this the best situation for these plants? NO. But some plants are better able to survive the crisis than others and a few hours of wilting does not seem to cause permanent damage to ligularia.
The best time to water is the day before the plant wilts. Wilting is never good for a plant.
1) Photo Source: Mountain Empire Community College