Friday, June 24, 2011

Dig In- Tips from Nettie at Uncanoonuc

Early Blue Clematis

Clematis ( klem’-a-tis ) is  an enormous, diverse  and often glorious group of plants. They are classified as either large-flowered hybrids or species. There are shrubby and herbaceous clematis, but most are woody vines.  Species clematis tend to have smaller flowers of various shapes, some with handsome foliage, others with decorative seedheads. The large-flowered hybrid clematis are the most familiar, prized for their stunning floral displays. Most clematis prefer a sunny exposure.  Plant in an area that receives at least four to six hours of direct sun a day. Some varieties have pastel colored blossoms that tend to bleach. Filtered light during the hottest part of the day would be appropriate for them. Clematis prefer a rich, moist, well-drained soil. Dig a hole at least  18” deep and 18” wide. Enriching your soil with a generous  amount of organic matter such as compost, well-rotted manure or peatmoss is highly recommended. Add lime if your soil is acidic. Plan to fertilize every spring with a balanced granular fertilizer such as 5-10-5.  Deep planting is important. Set the top of the rootball 2-3” lower than it was growing in the pot. Clematis prefer their roots cool. A mulch or under planting of a shallow-rooted plant will accomplish this.  Some gardeners position their clematis in such a way that the roots are shaded by a nearby shrub or rock.

Clematis are twining vines climbing by wrapping their leaf petioles (stems)
around nearby supports. They cannot climb by themselves and must be provided with something suitable to cling to. A trellis or arbor with narrow crosspieces, sturdy netting or chicken wire on a post, fence, or a rock works well. Clematis can be trained to ramble through other plants using them for support. Climbing and shrub roses, shrubs and trees have all been used this way. Consider bloom time, flower and foliage color, vigor and pruning needs of both the host plant and the clematis when arranging such pairings.

Clematis wilt is the most common disease of the large-flowered hybrids. It is a nasty but rarely fatal fungus. Young plants with lush, early season growth are particularly susceptible. Leaves and stems droop and then quickly turn black. Cut back all the infected stems even if it means pruning out all top growth.
Dispose of the infected plant parts. Do not compost them. Often the plant will sprout from dormant buds below the soil - sometimes not until well into the following year. Be patient . To quote the late Henry Mitchell from his highly recommended book The Essential Earthman - “Now there is the matter of Clematis wilt. This is a disease that can carry off a clematis plant in the matter of a few days and is, needless to say, the strongest argument against divine providence that I can think of. Some put their faith in benomyl sprays and drenches. But it would be sheer perversity to worry so much about wilt (from which the clematis often recovers if you do absolutely  nothing) as to forgo the pleasure of growing these happy vines.”  The UNH Cooperative Extension agrees. Sanitation and selecting resistant types (the species clematis are reported to be resistant) are recommended; spraying is not.


Annual pruning results in a thrifty plant that will remain the desired size and flower heavily. Pruning  clematis becomes a much less daunting task once the reasoning for different approaches is understood. Because clematis bloom at different times of year, some on old (last year’s) wood, some on new (this year’s) wood - and some on both - their pruning requirements differ. Clematis are divided into three basic pruning groups. A brief description, explanation and some examples follow. Pruning cuts should be made straight across the stem just above a strong pair of buds. Waiting until the buds begin to swell can simplify this decision. If you’re unsure about the liveliness of a stem remember that if it’s brown all the way across the cut stem - it’s dead. If there’s green  (the cambial layer) underneath the bark -  it’s alive. 

GROUP 1: Includes spring blooming species and their cultivars that flower on last year’s wood. This group is pruned very lightly (either in very early spring or right after flowering), thinning dense growth and cutting back weak or damaged stems. This invigorates the plant and where necessary keeps it in bounds. Clematis alpina, C. macropetala, C. montana are examples. Note: These species and their cultivars are often listed as hardy to Zone 6. All the varieties we offer have been rated hardy to Zone 5. Planting them in a sheltered spot (not in a frost pocket or out on an exposed hillside) can’t hurt.

GROUP 2: Includes all the large-flowered hybrids that flower in early summer on old  wood and again in early fall on new wood. Prune in very early spring to thin the plant to a framework of one and two year old stems. Cut away any weak, twiggy or damaged growth.  ‘Henryi’, ‘Nellie  Moser’, ‘Niobe’ and  ‘General Sikorsky’ are examples.  Plants in this group often develop “bad knees” or bare stems at the base of the plant as they mature. Neighboring plants can be used  as screen - the situation literally disappears.

GROUP 3: Includes the species and large-flowered hybrids that bloom mid to late summer on current season’s growth. Every year, in very early spring, cut them back to within 12 -18“ of the ground. ‘Jackman’, ‘Comtesse de Bouchard’, ‘Ernest Markham’, Sweet Autumn Clematis, Clematis viticella and its cultivars are examples.

Recommended reading:
Clematis. By Charles Chesshire. DK Publishing, Inc., New York, NY, 1999.

This well-made little book is one of the American Horticultural Society and Royal Horticultural Society Practical Guide series. It is jam- packed with information and lovely photographs. Most valuable of all might be the section devoted to pruning. The straight-forward text and the excellent drawings demonstrating the techniques used on the three different pruning groups are as clear cut and helpful as it gets.

For more gardening tips from Nettie at Uncanoonuc, click here.

To learn more about Uncanoonuc Mt. Perennials, visit their website at


  1. Wow...this post is a fantastic resource Joe. I am now wishing I had planted Clematis this year. You will have to let me know if you ever create a post on growing tomatoes....we are in a bit of a muddle on that one these days.

    Many thanks for this very informative post!


  2. Thank you, Jeanne! I'll pass your comment on to Nettie. Nursery shoppers in our area are so lucky to have Uncanoonuc as a resource because with every single plant you buy, you also get one of Nettie's famous info sheets that tells you just about everything you need to know about how to care for the item you just purchased. --Joe


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