A clematis in full bloom can take your breath away. Who hasn’t erected a trellis with the dream of seeing it covered with vibrant red or purple flowers in late spring? But how do you get your clematis to grow as lush and beautiful as you see in magazines or in your neighbor’s garden?
First, you need to know your vine so you can understand the proper pruning that it needs. Your clematis will survive, and even bloom, with no pruning. But with the right pruning, it’ll grow and bloom more vigorously.
Before that, though, let’s understand how to plant for success.
- Start with the soil. It is true that clematis prefer slightly alkaline soil. If a soil test* tells you that yours is on the acid side, your vines will benefit from some agricultural lime. But if it’s already alkaline, don’t add lime — you can overdo it. A pH of 7 to 7.5 is just right. Dig the hole 18 in. deep and wide, and work in lots of moisture-holding compost. Set young plants deeply so the first two sets of leaf nodes will be underground. This encourages plants to send up more stems so you’ll have a thicker plant.
- Mulching matters! “Head in the sun, feet in the shade” is old clematis advice. However, a 4-in. layer of mulch keeps the roots cool and moist just as well as shade does. To prevent stem rot, keep the mulch about 8 in. from the stems.
- The best place to prune a stem is just above two strong buds — where two leaves were growing the previous year. These buds will quickly develop into new vines. Don’t worry about making angled cuts — it’s not necessary.
- Recognize disease quickly! Clematis wilt is easy to spot: a portion of your vine wilts quickly, often just as the plant starts to bloom. Wilt is caused by a fungus that enters the stem, usually just above the soil line. There is no cure other than to cut the entire stem to the ground and dispose of it in the trash. Do this as soon as you notice the wilt. That’ll prevent spores from moving to other stems. Systemic fungicides can help prevent wilt from spreading to healthy stems and the rest of the plant will usually survive, providing there are enough other healthy stems. That’s another reason to plant clematis deeply: if a stem becomes infected and has to be removed, more will come from the base to replace it. Cultivars that have proven resistant to wilt include ‘The President’, ‘Ville de Lyon’, Nelly Moser’, ‘Betty Corning’, and ‘Jackmanii’.
- Clematis like to be well fed but not overfed. Feed them once a year right after pruning with an all-purpose, granulated fertilizer, such as a 10-10-10.
- Choose the right trellis. Clematis climb by twisting petioles, or leaf stems. The vine itself does not twine. So, if your structure is too large, the leaf can’t wrap around it. Anything over 3/4 in. in diameter is too large for a leaf to grasp. Nylon fishing line is a great way to get a clematis to climb a light pole or arbor post. Put a knot every foot or so to keep the vine from sliding.
So, how do you prune a clematis? Timing is important: don’t prune in the fall. It will encourage the plant to emerge from dormancy at the first hint of a warm day — which could be in January and your plant will die. No matter where you live, let your clematis stay dormant until spring.
Before you start cutting, you’ll need to know which pruning group your clematis is in: A, B, or C. If you don’t know, just watch it for a year. First pay attention to when it blooms. Second, notice whether it blooms on woody stems that grew last year and then survived the winter (old wood) or green, flexible stems that came from a main stem this year (new wood). Once you know this, you can usually put your clematis into group A, B, or C.
The University of Maryland Extension has created a wonderful little brochure that explains exactly how to prune each of the categories of clematis to ensure the best results.
Now that you know these secrets, you no longer have to wonder how to get those spectacular flowers you see in photos — you’ll be enjoying your own!
*Not currently testing your soil before planting? Shame on you! To ensure the best success for your gardens, it’s important to know if your soil is helping or hindering your efforts. Read our earlier blog post on doing soil testing here.