You can find countless articles praising the benefits of mulch and I totally agree that it is a fabulous entity to introduce to your garden. However, I think it can’t be stressed enough that you should never place mulch too closely to any soft stemmed plant(s) (i.e. clematis, roses or other prized plants) because it may cause them to rot. And, may and I go out on a limb here and add woody plants to the equation? The reason being is that one of the attributes we love most about mulch is its ability to retain water. Nevertheless, we do not want to retain excess water directly around the crown of our plants since this can suffocate them (i.e. deny them oxygen) and/or may lead to disease problems (such as root rot). So, too much mulch can be an unhealthy thing if you’ve incorrectly placed it around the plant.
I was recently asked the question “if the mulch up against the stem will cause rot, why won't that happen when you burying the stem a full 3 inches?” I was happy to see the person asking me this had taken to heart my recommendation to bury your clematis deep when planting them and her inquiry lead me to writing this article. So, here is my answer: When you plant clematis deeply you should be incorporating only some organic compost along with native soil which allows the clematis roots to breathe. This is opposed to planting the roots, deeply or not, directly into straight mulch because it could easily waterlog them and eventually cause rot. So, do it right and they will be alright.
The bottom line is please, mulch your clematis but give them some breathing room, i.e. a “no-mulch zone” of about four inches around the base of each plant. I know they would thank you if they could!