If you have newly transplanted weigela shrubs suffering from leaf-wilt, it is important to realize that there may be more than one cause. The first step to finding a solution is to determine which of these reasons applies to your wilting plant:
- Root damage due to transplant shock or other causes
- Improper watering
- Fungal infection
Plant roots draw water out of the ground and send it up through the above-ground parts of the plant. If the roots are damaged, the flow of water to the leaves is reduced, often resulting in wilting leaves.
Dealing With Transplant Shock
It is common when transplanting shrubs, including weigela shrubs, to cause transplant shock. The disturbed roots find it difficult to nourish the leaves with sufficient water in their damaged state, as the roots of a healthy, established shrub would. Conditions such as high winds simply exacerbate the problem: they have a drying effect that further robs the leaves of moisture. The result is leaf-wilt.
The best way to prevent or minimize leaf-wilt is to choose the right time to transplant. By avoiding transplanting at the hottest times of the year, you put less stress on the plants' root systems, thereby keeping them healthier. But if you've already planted your weigela, the good news is that your bushes are not dead: they just need time to recover.
Here is what not to do: fertilize. Fertilizing would foster extra leaf growth, which you do not want, since the weigela shrubs' disturbed roots are already struggling to support the current amount of foliage.
Physical Root Damage
Root damage can also be caused by digging too close to your plant while cultivating. For example, some gardeners will dig around a plant to remove weeds and accidentally sever roots in the process. You can largely avoid this problem by mulching. Others make the mistake of cutting into root systems when working compost or manure into the soil. In this case, the solution is to apply, instead, a compost tea or manure tea, which involves no digging. Once the damage has occurred, resist the temptation to combat the resulting leaf-wilt by overwatering (which will do no good).
Overwatering itself can damage plant roots. The roots essentially rot and lose their ability to take up water. Adding more water in such a case can be like adding fuel to a fire.
Watering Your Weigela
Do water your weigela shrubs when the soil is dry, but do not overwater. When a plant's roots have been damaged (from transplant shock or any other cause), they have to be given time to heal. Flooding a root system with water when that system is incapable of absorbing the water is, at best, useless and, at worst, counterproductive.
On the other side of the coin, leaf-wilt can be caused by a lack of water. Indeed, sometimes the reason is no more complicated than that the soil has dried out around your plant. If you do not see scorched leaf margins on your plant and have no reason to believe that root damage has occurred, you're lucky. Solving the problem is as easy as giving the plant a drink of water.
Fungus on Weigela Shrubs
Another possible cause of leaf-wilt on weigela is soil fungus. Weigela shrubs are, in fact, one of the plants susceptible to the fungus Verticillium wilt. According the University of Minnesota Extension (UVM), one way to identify this fungus is to look for "a scorched appearance" on leaf margins. To combat Verticillium wilt, UVM recommends selecting resistant plants and providing basic care (proper watering, fertilizing, etc.).