If you are new to Clematis go straight to the section called ‘Avoidance Techniques!’
What is Wilt?
Clematis wilt is a condition that seems to affect the large flowered, spring blooming clematis more than other varieties. It is characterized by a complete collapse of either the entire plant, just one of the shoots, or just part of a shoot. Wilt will also occur with very small infants soon after they are placed in their permanent spot in the garden.
It will hit a healthy looking plant overnight and will look as though the plant was being starved for water. With clematis wilt, however, the plant has plenty of water and is loaded with flower buds that are about to open. What a disappointment! One must not confuse the dying off of lower leaves in the heat of the summer with wilt. The growing tip will become very limp with the wilt.
What is the Cause?
The cause of clematis wilt is really unknown but the most common theory is that it is caused by a fungus. Presumably this is a very selective fungus that can attack only one shoot, leaving the rest of the plant healthy including the root system. This is something I have never observed in other plants.
Another theory is that snails or slugs attack the stem of the plant causing a portion of the plant to be cut off from its water. Other possible causes are genetic weakness due to hybridization or damage caused burrowing animals such as moles, chipmunks, or voles(mice) that disturb or feed on the root system causing the plant to prune itself accordingly. It is curious, though, that wilt most often hits the plant at the most critical pre-blooming stage.
Others have observed that clematis, even large flowered hybrids, that are planted in a spot where there is a subsoil water source such a spring, a stream or at a river bank, wilt is almost non-existent. The wilt is truly a mystery. University studies, supported by the British Clematis Society and others, into the exact cause(s) of clematis wilt are presently under way in England.
Will my Clematis Recover?
The good news is that wilt is rarely fatal to the plant. It might take up to a year, but the plant will usually sprout a vigorous shoot from under the ground to live another day. This is why it is important to place the transplant deeply, at least two to four inches deeper than the level in the starter pot. One wants to bury some latent buds so that the plant has a bud to sprout from if it is hit by the wilt or chewed off to the ground by one of natures many four legged animals. Also make sure that the plant is well marked so you know that the new shoot that emerges next spring is not a weed.
Chemical Prevention
Until the real cause of clematis wilt is known, most growers use a systemic fungicide called Benomyl (Benlate) (see Editors note below) both as a prophylactic and as a cure for the problem. Most mix up a solution from the powder and soak the roots with a generous watering. This can be done at the time of planting, every spring, and right after the wilt occurs. The wilted portion of the plant should be pruned away and thrown in the trash or burned.
Practical Experience
I have tried doing all and none of the above and the plant seems to do just as well (or poorly). I have also used Benomyl (just in case) but its use does not insure wilt prevention for me. The wilted section will begin to really look bad if left on the vine and it should be removed for cosmetic reasons. Benomyl has been linked with some nasty human physical problems and there has been some talk about its use being outlawed in the U.S. in the future. As the label states, USE CAUTION WHEN USING BENOMYL.
Avoidance Techniques!
[Editor’s note: The Society would like to suggest that, if you are new to growing clematis, you choose one of the clematis on our Recommended Clematis. These clematis have been recommended by our Members as being good, reliable plants, easy to grow and resistant to the more common pests and diseases. – Ken Woolfenden, Webperson]
Many first time clematis growers get discouraged by wilt damaged vines and then just give up on the plant. It takes about three years and lots of fertilizer and water for a vine to develop a root system that will produce a robust and productive vine.
Once you have a well established wilt resistant vine that is covered with blooms every year you will want more. Clematis wilt is a fact of life for clematis enthusiasts, but as annoying as it is, the reward of many beautiful blooms that comes with patience is worth it! Want to beat “the wilt”? Plant lots of clematis – “the wilt” will not get all of them!.
Bill Bird, New York, USA.
Editors note 1:- Benomyl is banned in UK and USA and probably many other countries. An alternative to Benlate has been suggested as Topsin from Ciba-Geigy.
Editors note 2:- The 1998 Journal contains an update on the Recent Advances in Clematis Wilt Research by Pieter van de Graaf from the University of Derby in Great Britain. Join our Society now to get your copy. Details of how to join are available on the Web page How to Join.