June 2009 — 'Ask the Expert' Print

Q.  When should Clematis be pruned?

A.  This is a question that puzzles many people. Clematis have developed a sort of mystique that intimidates even experienced gardeners.  Clematis are placed into groups depending upon their habits, flower type and flowering times and each group is pruned in a different manner.  Knowing the ‘group’ of your plant should tell you when to prune it.  But wait... it is simpler than that.  All you really need to know is when it flowers.

Clematis that flower before the middle of June (approximately) are blooming on ‘old wood’, that is, they formed their flower buds during the previous season.  An early pruning would remove these buds and thus the current year’s flowers. (Similar to spring blooming shrubs such as Forsythia and Lilac).  Therefore it is best to prune them AFTER they flower — except to remove any dead or damaged canes.  

However if the Clematis first blooms after about mid-June, it is doing so on ‘new wood’ or current season’s growth and therefore a heavy pruning in very early spring is recommended.  

Clematis that are completely herbaceous and die to the ground each autumn, simply need their dead growth removed to tidy them up in the spring.  So... if you know the name of your Clematis you could look up its pruning group and/or flowering time.  But if you don’t know its name, or perhaps you have just purchased a house with existing landscaping, do nothing until it flowers and then proceed with a light pruning as appropriate. Waiting until you get to ‘know’ your plants is always advisable.

Q.  More and more frequently plants have the letters PPAF or PP#### after their name.  What does this mean?

A.  PPAF means “Plant Patent Applied For” whereas PP#### indicates that a Plant Patent has been granted and the numbers are the actual patent number.  The ability of plant breeders to protect their investment by controlling the propagation of their plants and obtaining a royalty from those that do propagate and sell their plants is an integral part of the modern system of plant breeding and marketing.  It takes a lot of money to develop new and interesting plant selections and if breeders can recoup that cost, a few pennies at a time, when nurseries grow and sell their plants then it is possible for that breeders to continue their work and bring more new cultivars to the market.  Simply, the right to propagate a patented plant is controlled by the patent holder.  Generally words to the effect of “unauthorized propagation is prohibited” will also be on the label.  Does this mean that a patented plant is ‘better’ than one that is not?  Not necessarily. But the process of patenting is not inexpensive and breeders do not generally invest the money unless they believe that their plant is an improvement over what is available in the current marketplace.

Q.  What ground covers are good for shady areas?

A.  This is one of the most commonly asked questions and the answer depends upon several factors, the most important probably being — what is making it shady?  If it is a large tree, or a hedge then the soil is also likely to be quite dry, as the larger plants will be taking most of the available moisture.  If it is sheltered under the eaves of a building so that it receives no natural rainfall, the problem is more difficult unless one is prepared to irrigate.  Several low growing plants will actually do quite well in this most difficult of garden conditions — dry shade, but most will take longer to establish and require more upfront care for a couple of seasons until they can be left to cope on their own.  

Suggest the following to your customers:
  • Galium odoratum (Sweet Woodruff): bright green foliage borne in whorls around the stems.  Small white flowers in early spring. Once established can spread quite rapidly.  Height: 3” to 4” (8cm to 10 cm)
  • Epimedium spp. (Bishops hat, Fairy wings, Barrenwort etc.):  Slow to establish and slow to spread but a reliable performer in difficult conditions.  Light airy foliage and lovely flowers in early spring. Height: 8” to 24” (20cm to 60 cm) depending upon species and cultivar.
  • Asarum canadense (Wild Ginger, Canadian Ginger): Large kidney shaped leaves with a matt appearance. Great for naturalizing.
  • Ferns generally prefer a more moist and shady location but those in the genus Dryopteris (Male ferns) are more tolerant of dryer sites.
  • Many early spring flowering bulbs (Crocus, Scilla, Galanthus) can be planted among the above-mentioned ground covers if the shade is produced by deciduous trees.  As the underground bulbs are replenished for next year’s blooms through the process of photosynthesis, the foliage of bulb flowers must be exposed to light and then left to wither and die naturally — no tying, bunching or braiding of leaves!!  In many cases the bulbs will have flowered and their leaves withered before the trees become fully foliated.