Diamantina Clematis

(Question)

Help!!, My 3 year old dementia is loaded with beautiful flowers in a pot on our south w facing terrace. It overwinter well and is blooming well, but suddenly some of the leaves are turning brown black and you the young buds are drooping and dying.
How do I prevent the whole plant from dying or not having its 2nd bloom?
Hope you have an answer.
Thank you so much

(Answer)

Thank-you for contacting Toronto Master Gardeners with your question. It is so worrying when a plant that has been thriving suddenly shows signs of distress! You must be concerned about your poor clematis!

Your description fits the symptoms of clematis wilt. This is a common disease of clematis, especially the large-flowered varieties such as your ‘Diamantina’. Clematis wilt is caused by the fungus Ascochyta clematidina.¬†Typically, the disease starts out with reddening stems, but very soon withering of stems and buds, and blackening of leaves occurs. Your experience with a seemingly robust plant, blooming well, suddenly exhibiting these symptoms is very common. The good news is that the disease affects only the top growth, not the roots. This means that your plant can probably be saved. The bad news is that all stems with any sign of disease must be cut back right to the ground so you may lose most, if not all, of your top growth. The plant will begin to sprout and grow again from the base but you are unlikely to see any blooms on the new growth this season. When you cut the stems back, be sure to put them in the garbage, not the compost. The fungus lives and overwinters in leaf debris, so removing all diseased material is essential to reducing the chance of an infestation later this year or next year. Like many fungi, A. clematidina thrives in a humid environment and on damp foliage. Ensuring good air circulation is key to inhibiting fungal growth.

These articles from The Spruce and Missouri Botanical Garden  provide useful general information on clematis wilt.

Good luck rescuing your clematis!