If Your Clematis Suddenly Collapses in Midsummer, It Could Be Clematis Wilt – Here's How to Save It
Discover expert advice to treat clematis wilt
Clematis wilt is a devastating fungal disease that strikes plants in summer. It primarily targets large-flowered clematis and blocks the movement of water, causing stems to blacken and die within 48 hours.
When you grow clematis, you need to know the signs of clematis wilt. The disease can be confused for other issues, but when clematis wilt is present, you want to cut back infected stems quickly to stop it spreading. The good news is that a healthy clematis can recover and send up new shoots.
The best way to avoid clematis wilt is to keep plants healthy or plant wilt-resistant varieties like Clematis montana (you can get a live Clematis montana Rubens plant at Donahues Clematis). Here, two clematis experts reveal the signs of clematis wilt you need to know, along with their tips for preventing and treating wilt.
What Causes Clematis Wilt
Clematis wilt is a condition caused predominantly by a fungus known as Calophoma clematidina. However, other factors can cause healthy clematis to wilt over the season.
Starting with the fungal clematis wilt. This is a dramatic disease that causes otherwise healthy-looking clematis to collapse quickly. It can be individual shoots, sections of shoots, or the entire plant that wilts.
The fungus gets into the plant through a cut, abrasion, or insect bite. It blocks the uptake of water and nutrients, causing the affected stems to collapse. It can strike plants in the ground or clematis growing in pots.
Certain types of clematis are more susceptible to the disease. Linda Beutler, Curator at the Rogerson Clematis Garden, explains how genetics impact which plants are susceptible to clematis wilt.
‘Clematis patens, a large-flowered species from China and naturalized in Japan, is the weak link,’ she claims. ‘This means that hybrids from it (often called early-flowering large-flowered hybrids) are susceptible to wilt.’
However, not all large-flowering varieties are vulnerable, as it depends which plants they have been bred with.
‘Other clematis species used in hybridization, such as Clematis lanuginosa and viticella (which were combined to create Clematis ‘Jackmanii’), are highly wilt-resistant,’ adds Linda. ‘If they collapse, the reason is usually a traumatic injury.’
You can get a Jackmanii Clematis at Burpee for large purple flowers
Small-flowering varieties are less at risk of clematis wilt, while non-climbing clematis will not get the wilt disease. On top of type influencing risk, so does environment. The fungus that causes clematis wilt prefers humid climates, and otherwise susceptible clematis can be unaffected in low-humidity areas.
‘If a clematis develops wilt, it is usually the environment that was the cause,’ claims Kathy Donahue Nass from Donahue's Greenhouse, a specialist clematis nursery. ‘This can be a time of wet, cloudy weather, and the plant would have to have a crack in a stem where the fungus can enter.’
As mentioned earlier, a clematis can wilt in summer without the fungus being culpable. ‘In addition to airborne fungal diseases, clematis may collapse from irregular watering, slug and snail damage to stems, horizontal stems breaking when trained upright, and stress from being heavily fertilized when they are about to flower,’ says Linda.
Linda Beutler is the Curator at the Rogerson Clematis Garden, which houses the most comprehensive collection of clematis within a public garden in North America. She is also the author of Gardening With Clematis: Design & Cultivation, available at Amazon. She has a small garden around her house, Tanglevine Cottage, in the Sellwood neighborhood of Portland, Oregon, with a lot of clematis in it.
Kathy Donahue Nass is one of six siblings who own and operate Donahues Greenhouses Inc. It is one of the largest clematis growers in the US and has been running for over 50 years. Kathy has been working in the family business full-time since 1987. She loves to garden and share her knowledge of plants with people.
The Signs of Clematis Wilt
To treat or prevent clematis wilt, it pays first to know the right symptoms to look out for. It allows you to recognize when you are dealing with clematis wilt, or when your plant is suffering from another issue.
The symptoms appear when the plant is vigorously growing. Kathy Donahue Nass claims it often starts when the plant is in full bloom. ‘You will notice a stem turning black at the bottom of the plant and then quickly moving up that stem, turning the whole stem black,’ she adds.
The stem dies and wilts because the fungus is obstructing the vascular system. It can take only 24 to 48 hours for a vine to go from looking healthy to drying out and wilting.
‘The clematis may look like it needs water. It does! But the fungal disease is blocking water movement,’ adds Linda Beutler. ‘Within days the whole plant will be limp from top to bottom, with the foliage going gray before drying up.’
Other symptoms commonly seen in clematis are often mistaken for wilt. For example. drought stress can cause wilt, but the plants will also have sunburned patches and crispy brown clematis leaves, rather than black stems.
How to Treat Clematis Wilt
The safest approach to suspected clematis wilt is to cut back all affected stems. It is important to clean up the debris, bag it, and destroy it, and to wipe down your pruning tools with bleach or alcohol wipes (get alcohol wipes at Walmart) to destroy any fungal spores on them.
‘Give the cut-back plant some organic rose and flower food and water it in,’ recommends Linda. ‘Because true clematis wilt disease fungus is airborne, removing affected top growth, fertilizing, and keeping the plant sufficiently watered should have you seeing fresh new growth in 30-45 days on average.’
You can get an all-in-one rose and flower care feed at Amazon to use for fertilizing clematis.
If your clematis has succumbed to wilt in previous years, Kathy Donahue Nass recommends using a fungicide in the spring as a preventative measure.
‘Some good choices are Daconil (get Daconil fungicide on Amazon), Ortho All Purpose Fungicide or Neem Oil. Any fungicide that is recommended for roses can be used on clematis,’ she says.
‘Apply on the foliage and drench the roots. Do the same application 6-7 weeks later. If the plant still turns black and dies back, chances are you won’t be able to salvage the plant.’
If your clematis regularly gets hit by wilt, consider discarding it and trying an alternative shrub or a more resistant cultivar.
Some of the best clematis for glorious blooms without the fear of wilt include Clematis montana (get a live ‘Moongate Mocha’ Clematis montana at Amazon), Clematis macropetala, or Clematis viticella.
How to Prevent Clematis Wilt
The best way to prevent clematis wilt is to keep your plants healthy and stress-free. This includes keeping them well-watered to avoid drought stress, protecting them from wind, tying them in well to prevent damage that creates entry points for the fungus, and planting susceptible varieties deeply.
‘Generally, all large-flowered hybrids should be buried three or so inches deeper than they were in the pot you bought it in,’ advises Linda Beutler.
‘Burying the lowest nodes is like insurance that healthy growth points are dormant below the soil to produce new crowns and vines should anything traumatic happen to the above-ground growth, be it a collapse due to wilt disease or a spouse with an over-active string-trimmer.’
Mulching clematis plants also helps keep the soil moist and cool during the summer. Baking roots dry out quickly, and pests are more attracted to stressed-out clematis. Consider putting a 2-3 inch layer of pine bark mulch like this at Lowe’s around the plant.
Avoid drought stress as this meter tells you quickly and easily when your plants need watering.
A pair of sharp pruning shears is a must for pruning clematis. This tool is made from strong Japanese-grade, high-carbon steel.
Clematis growing in pots benefit from a fortnightly feed with a liquid bloom booster fertilizer during summer for the best displays.
When you have a clematis that you adore, you can easily get more for free by taking cuttings. You can take softwood cuttings in summer or hardwood cuttings in the fall to propagate clematis plants. Perfect if you want new plants or to gift a clematis to a friend, family, or neighbor.
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