Propagating Clematis from cuttings
Propagating some clematis from cuttings is easy, but others can be very difficult. First, the easy ones, which comprise most of the true species like Clematis montana, C. viticella and C. tangutica. The best way is to take semi-ripe shoots around late July or the beginning of August.
Take sections of shoot, about 6-8in long, from the central part of the stem to form the cuttings. Where you trim the sections doesn’t matter much. It was traditionally said that nodal cuttings should be used, but this is now known to be unnecessary. A nodal cutting is one trimmed so that the ‘node’ – the small swelling on the stem from which the leaves arise – is about half an inch above the base of the cutting. In order to form roots, certain hormones must be present inside the shoot, and although most plants have the highest concentration of these hormones at the node, it has been discovered that some types of clematis actually have the highest concentration between the nodes. Hence it makes sense to try inter-nodal cuttings, too – those cut at the mid-point between two pairs of leaves.
The answer is to try both sorts of cuttings, and see which works best for each of the varieties you grow. Dip the base of the cutting into hormone rooting powder and insert about an inch of it into a pot or tray containing a well-moistened mixture of 1 part by volume of peat and 2 parts of sharp sand or perlite.
Cover the pot with a plastic bag or rigid propagator lid and place it in a fairly warm place out of direct sunlight.
The cuttings should root in six to eight weeks, when they may be potted on into a potting compost in a 3in pot. After one year, pot them on into a Sin pot to give a strong plant ready for planting out in the following season.
The most difficult of the common garden varieties to root are the large-flowered hybrid forms such as ‘Nelly Moser’. Clematis nurseries raise plants under glass to produce soft shoots that are more likely to root than the tough, woody ones that outdoor plants tend to form. This is not practical in a garden where a gardener usually wants to take a few cuttings from an existing, established plant. The best chance of success with these more tricky varieties will come from taking the cuttings in the second half of June and ensuring that they are taken from no more than 9-12in back from the shoot tip. where the tissues are likely to be less woody. Alternatively, propagate the varieties by serpentine layering in July-August.
Propagating clematis by seed
Collect the seed heads in the autumn and sow the seeds immediately into trays of a soil-based seed compost. Place them in a cool spot in the garden, out of direct sunlight, and forget about them until the spring.
Once the seeds have been subjected to the rigours of frost and snow during the winter, bring the trays into the warmth of the greenhouse and keep them under close observation, for germination can occur at any time thereafter.
When the seedlings emerge, prick them on into 3in pots. Thereafter, treat them in the same way as cuttings