Unknown Type of Clematis Pruning

(Question)

My daughter moved into a house last fall with a huge clematis on the southwest wall of the garage. There were no signs of bloom. We didn’t prune it as we didn’t know the type. This year it did not bloom either although there was tons of foliage on it. The soil is mainly clay. Picture attached. When should we prune it? Thanks.

 

(Answer)

Thank you for contacting the Toronto Master Gardeners concerning your clematis.

Clematis can be a confusing group of plants to prune, since they are not all pruned the same way. Clematis fall into three different categories, based on bloom time. They bloom on either last season’s growth or on new growth. Unfortunately, you will need to determine which variety of clematis you have growing by your garage before going ahead and pruning.

As a result, the first thing we need to do is address the problem of why your clematis is not blooming. The most common cause of this problem is unsuitable growing conditions, there are three possibilities:

Fertilizer – Improper fertilization is one possibility for a non-blooming clematis. Usually, the problem isn’t lack of fertilizer, but too much. Is your clematis near a heavily fertilized lawn? If this is the case your clematis is receiving too much nitrogen which may produce lush foliage.  As a general rule, clematis benefits from a handful of 5-10-10 fertilizer in the spring, along with a layer of compost. Apply a water-soluble fertilizer once or twice during spring and summer.

Age – Would you happen to know the age of the clematis?  Clematis can take a year or two to produce blooms and may take a bit longer to come to maturity.

Light – Clematis prefer full sunlight on their stems and leaves and cool and moist but not wet roots. To provide ample sunlight, plant the vine where it will get at least six hours of daylight.

It is always a good idea to amend your soil each year with organic material: a layer of compost will continue to enrich and improve the soil throughout the year.

Once you have determined bloom time, the following information from one of our earlier posts describes the proper way to prune your clematis:

1) Early flowering clematis

Early flowering clematis typically bloom in April and May, from buds produced during the last growing season. Prune these plants immediately after blooming, but no later than the end of July in order to give the plant enough time to produce new buds for next year. Start by removing shoots that have bloomed. If necessary remove dead or damaged stems. If growth is congested then cut out older stems to the base and thin the rest. Avoid cutting far into the main woody trunks. Cutting off too much may affect next years flowering. This group includes C. alpina, C. macropetala, C. armandii, C. montana, and C. chrysocoma.

2) Large-flowered/mid-season clematis

Large flowered hybrids like ‘Nelly Moser,’ ‘Miss Bateman,’ Lasurstern,’ and ‘Duchess of Edinburgh’ bloom in mid-June on stems from the previous season and often will bloom again in late summer on new growth, though these blooms tend to be smaller. Remove dead or weak stems in late winter or early spring, leaving the best of last year’s buds. Once they finish blooming, deadhead all bloom stems or cut the plant back to 12-18” to force new growth for a second round of flowers.

3) Late flowering clematis

This group’s flowers are produced on the current season’s growth and are the easiest to prune. Some types begin blooming as early as June and continue into the fall. This group contains the greatest number of clematis. In late winter or early spring, cut the plant back to 24-36” since no old wood needs to be maintained. Varieties like C. ‘Jackmanii’, C. viticella, C. flammula, ‘Royal Velours,’ and ‘Duchess of Albany’ fall into this category.