Propagating clematis is always difficult for the amateur. Nurserymen find it easy as their cuttings are taken from young plants which are only one year old. This young thin wood is ideal for striking. Internodal cuttings are used - that is, those without a node or heel at the bottom of the cutting. These soon produce roots in the ideal set-up of the nursery. The amateur, however, has only the cutting wood from established outside plants, which is much thicker than the one-year-old cuttings that nurserymen have, and internodal cuttings cannot be used. So one has to make sure there is a node at the bottom of the cutting as well as one at the top. These take much longer to strike so one must have patience. To proceed, one needs a sharp knife or a razor blade, rooting hormone powder, a pot, preferably a clay pot, a clear plastic bag or sheet, a watering can, a dibber, and a small bowl of water. The best compost to fill the pot with is a mixture of vermiculite or perlite, or both, some sharp sand and some peat. Mix this thoroughly, watering it to make it moist. Put about 1 in (2.5 cm) of Levington compost or peat at the bottom of the pot, into which the roots can descend and feed the cuttings. Fill up the pot with the moist compost, firm it down and you are ready to insert the cuttings. The best time of the year to take cuttings is in the early summer. Cut a stem from the plant you are hoping to strike and, with your knife, cut off the tip of the shoot, which will be too soft to strike, down to where it is firm and semi-hard. At the bottom of the stem the shoot will be too hard and is usually brown in color. This should also be trimmed off, leaving the centre portion which may produce three or four cuttings according to the length of the stem. With your knife or razor blade cut close above the first node and underneath the node below, making a cutting of 1-2 in (2.5-5 cm) long. Cut off the bottom pair of leaves close to the stem and one leaf at the top, leaving one leaf to keep the cutting going until it is rooted. If the leaf is too big it can be cut in half. Dip the bottom inch (2.5 cm) of the cutting into the water and then into the rooting powder, shaking off any excess powder. Insert the dibber at the side of the compost and put the cutting in this hole with the leaf pointing inwards, making sure that the bottom node of the cutting rests on the bottom of the hole. Get the cutting as low as possible, but not so low that the bottom node is in the peat. Then, with the dibber, firm the cutting in the compost. Continue round the pot with as many cuttings as can be fitted in, but not so that they are overcrowded. Water the cuttings in thoroughly with a fungicide, leave them to drain and dry and then slip the polythene bag over them, tucking it in below the pot. If you have a soil warming bench in the greenhouse, this is a great help and will encourage rooting. If not, stand the pots in a warm but shady spot in the house. Remove the polythene bag after two weeks, turn it inside out, take off any diseased leaves and spray with a fungicide. Leave until they have dried. Cover the pot again, first making sure that the compost is moist, if not give it a watering, but the polythene bag should keep the compost moist for some time. Remove the polythene bag every two weeks and, after a month or so, test to see if the cuttings have rooted by gently tugging a cutting. If it stays firm then roots have been formed and you can leave the polythene bag off for longer periods until, after a few days, you can take it off altogether. Keep the cuttings moist by spraying them every day if it is hot and sunny; in dull weather this will not be necessary. Once the cuttings are weaned off, which will be in about two or three weeks, they can be potted into small pots in some good compost. Keep them close for the first few days in a frame, or cover them with polythene, spraying them occasionally to keep the leaves turgid. Give them some air for an hour or two each day until they look fit enough for you to leave off the covers. This all depends on the time of year. In the autumn the cuttings could be potted on into large pots, keeping them in a greenhouse or some shelter for the winter, and planting them out in the spring. If it is late in the summer when they are potted into the small pots, then it is best to leave them as they are until the spring, keeping them in a frame. They are perfectly hardy and will stand several degrees of frost, but if you are worried about them, simply cover them up with peat for the winter, potting them up into larger pots in the spring and keeping them in a cool greenhouse or shelter for a few weeks before planting them out into the garden.
The early-flowering species such as C. alpina, C. macropetala and C. montana will produce ripened seeds by midsummer, while the midsummer- and autumn-flowering clematis will have ripened seed by mid-autumn. Some may need help to dry off, especially the autumn-flowering species. lf the autumn is damp, rainy or cold, cut off a length of stem of about 60 cm (2 ft) once the seeds have become large and swollen. This can then be hung upside down in a dry room or a boiler room where the atmosphere is always dry but not too hot, otherwise the seeds will become dried out. When the seed is left on the plant to dry off and ripen, care must be taken that it is not dispersed by the wind. Those fluffy seed tails are so designed that once they are ripened and the wind blows, they will take flight. For this reason it is always advisable to place a muslin bag over the seeds before they are completely ripe. Once the seeds have ripened, they may be detached from the old flower stalks (pedicels). They break away in the hand easily. The seed should then be detached from the seed tail which again should break away easily in the fingers, though some may need a sharp pair of scissors or small secateurs. Take care not to damage the seeds in the process. Sow the seed in large or small pots or seed trays, depending upon the amount. The container should have good drainage and crocks, small stones or pea-gravel should be placed in the bottom to assist with the drainage. Then fill the container with a good seed compost to within 2.5 cm (1 in) of the rim and firm it gently, first with your fingers and then with a piece of wood or the base of a small flower pot to flatten it. Water the compost and allow it to dry off before sowing the seeds. Place the seeds evenly on the compost surface -do not sow them too densely as some species will germinate like mustard and cress and then become difficult to prick out. Cover the seeds with a thin layer of finely sieved compost so that they are only just covered and water them lightly. The seeds of most clematis will take some time to germinate. Some species, for example C. campaniflora, may produce a few seeds that will germinate the first spring after planting but the main batch may take a further year. Consequently, the decision as to where the seed container should be placed is an important one as otherwise it may have to be moved many times before germination occurs. It must not be a place where it will dry out quickly, so a cool site under a bench in a glasshouse or perhaps in a cold frame would be ideal. The most important aspect is that it should be placed in an area where it can be protected against mice, as they adore clematis seeds and will destroy the whole lot if not prevented. The old method of placing large sheets of glass over the seed container not only keeps mice at bay but also helps to warm up the soil, assisting with germination. Cover the glass with brown paper or newspaper to protect the seeds from being overheated by the sun. The seed container must be inspected on a regular basis to check the moisture level. Do not let the seeds become dried out. As the seedlings germinate and mature, the seed container can be watered with a light liquid feed to help the seedlings become established more easily. When the seedlings have produced two to three pairs of properly formed leaves they may be pricked out into a 7.5 cm (3 in) pot. Handle the seedlings by the leaf with thumb and finger and avoid touching the stem as this may become bruised and damaged, leading to damping off after pricking out. If only a few seeds have germinated and you decide to prick out the most advanced seedlings, use a dibber to ease the root system out of the seed container, tugging the leaves of the seedling very gently with the thumb and finger. Take care -these seedlings are delicate. The compost used for pricking out the seedlings can be either loam-based or peat-based. If the weather conditions are hot, the pricked-out seedlings must be shaded from the sun until they become established and have started to put on new root growth. As new top growth appears, it is advisable to pinch out the growing tips at about 10 cm (4 in) to encourage the plant to become more bushy. Tie the new growth to a split cane about 45 cm (18 in) tall. When the young clematis plant has become well rooted inside the base of the pot, it can be potted up into another pot of about 23 cm (9 in) in diameter. Once the plant has reestablished itself and grown away it can be planted out in the garden -or allowed to flower first to see if it has sufficient merits to be grown as a garden plant. Although the small- and large-flowered cultivars will not come true from seed, this can of course be used to advantage. If you are looking to produce new cultivars from seed, follow exactly the same procedure as for the species. However, more patience is needed as most of the small and large clematis cultivars take 9-12 months or perhaps even longer to germinate. Obviously, it is advisable to flower the plants to see what merit they have before going to the hard work of preparing a planting site and planting them out.
It is generally only the herbaceous clematis such as C. recta and C. integrifolia that are propagated by division. It is easy to remove their top growth and then lift them from the garden as with any other perennial plant. The method is as follows. The root and crown of the plant can be dug up with the use of a garden spade. Dig a circle around the plant of a diameter of about 45-60 cm (18-24 in) for large established plants and to at least a spade depth. By sliding the spade underneath the plant's root system you will be able to remove the root and crown from the ground. Then, with the use of two garden forks -or hand forks if the root ball is small-divide the root up by placing the forks back-to-back into the centre of the root crown and splitting it. It may be necessary to use a sharp knife to cut through the top of the root crown before the roots can finally be split apart. Division should be carried out from mid-autumn to early spring during mild weather. The autumn is preferable so that the new plant can become established before late spring. Some of the climbing forms of clematis, both species and small- and large-flowered cultivars, can be split by division but the success rate is not high. It would be impossible with the fibrous-rooted species such as C. alpina, C. montana and C. tibetana as their roots would just fall away and the original plant would be destroyed.
It is quite easy to develop new clematis cultivars just by collecting the seeds of the cultivars, sowing them, and waiting to see what comes up. With an intentional breeding programme using the small- or large-flowered cultivars, the end result is almost the same -the cultivars that we grow today are so inbred that the result of any cross is a bit of a guessing game as to the flower color. However, it is possible to predict in more detail the habit of a plant. If the parents are of the same habit, for example if two C. viticella small-flowered cultivars are crossed together, it can be expected that a new C. viticella cultivar will be produced (though this is not inevitable, as a throwback may result). Likewise, if two early large-flowered types are crossed together, the likelihood of the same type of habit being produced would be very high. The same applies when C. alpina and C. montana are crossed with cultivars from within their own group or type. Species of some countries, particularly New Zealand, are very compatible and produce interspecies hybrids in the wild. However, if two species are not compatible (because their chromosome numbers are different) then the likelihood of the pollination being successful is very slim indeed. Added to this, a breeding programme is obviously limited by the flowering period of the clematis. Therefore, to plan a careful breeding programme, you need to study what crosses should be attempted -but first you need to have a clear objective as to what sort of clematis you are aiming to produce. For your early attempts it is best to start with crosses where a good result can be reliably anticipated; if C. alpina types, C. macropetala types, C. montana types or early large-flowered types are used and crosses are attempted within these groups, seed should be produced. After some success with these groups of clematis, you can embark upon more interesting crosses.
The best and easiest method of all for increasing clematis is by layering. There is no need for greenhouses, bottom heat, stocks or special soil. All one needs is a well-developed plant with several stems that can be lowered down to the ground and layered at the point of impact with the soil. This can either be done by layering them directly into the soil, adding a little sharp sand to encourage rooting, or by sinking pots, into the ground and layering directly into the pots so that when they are lifted, in a year or eighteen months' time, the roots are not disturbed. Late summer is the best time for layering as the wood has ripened by then. Sink as many pots filled with good soil as there are vines to layer, bend each vine down to the soil, making sure that, when bending, too much strain is not put on the vine, which may snap. At the point in the stem where it touches the soil in the pot, make a lengthwise cut along the bark and dust this with a hormone powder to encourage rooting. A twist can be made instead of a cut, making sure you break the bark only and not the vine. Prepare some pieces of stout wire, bent double to form a hairpin, and peg down the vine in the pot. When this is done, cover the pot with soil and place a stone on top to keep the layer from springing up. The plant must be kept well watered and the pots of soil must not be allowed to dry out. Apart from that, leave the plant alone for a year or eighteen months. At the end of this long period of time, try tugging the end of the vine which was left sticking up out of the soil, and if it stays firm the layer is successful. Sever the vine on the plant side of the pot, and lift the pot from the soil.
'Nibbling' is different from root division. In nibbling the parent plant remains in the ground. Careful observation often reveals, especially in established plants, that the spread of the plant is so wide that it should be possible to nibble at it and take a piece away. You may even see an offshoot close to an established plant. Sometimes an established plant is so broad, it is possible to nibble away at two or three corners of it. The golden rule of nibbling is that one must never risk damaging the parent plant. The roots of clematis go very deep. Therefore a sharp spade must be placed between the parent plant and the portion to be nibbled, and the spade driven deep into the ground separating the roots of the nibbled portion from that of the main plant. The spade is then withdrawn and driven in again at three places to complete a square around the portion to be nibbled. By pushing the spade in on the side which is most convenient, the nibbled part is then taken out of the ground. The nibbled portion, if large enough, can be grown in a prepared hole as usual, while a small portion can be potted into a large pot and then 'grown on' for another year.
Grafting is a commercial method now used less and less by nurserymen. Before the Second World War most nurseries employed the grafting method to propagate, but since it has been discovered that clematis will grow equally well from cuttings, grafting has fallen out of favor and most nurseries now rely on internodal cuttings to produce their plants. The one advantage of grafting is that a plant grafted in the spring will be a saleable plant in the summer and will flower well the first year. The opponents of grafting have always suggested that this method encourages clematis wilt, but this is nonsense. They say that the grafted plant is not on its own roots, to the great detriment of the clematis, but again this is not true because a clematis is not grafted permanently on to its stock. The stock is simply used as a nurse stock to get the scion over its first six months, after which it will develop its own roots. By the time the clematis is planted in the autumn the scion will have taken over and the root stock will be discarded and will die away during the winter; provided, of course, that when potting on the young grafted plants from small pots into large ones, the union is potted well below the level of the soil in the pot. Before beginning, some thin pieces of raffia are soaked in water to make them soft and pliable. The young growth of the named variety is prepared by cutting it into sections, one pair of leaves to each section, which will provide two scions each. The top growth of the stock is removed and a suitable straight part of the root is selected for grafting. A clean straight cut, about 1 in (2.5 cm) long, is made along the side of the top part of this root, just paring off the bark. The section of the hybrid is then prepared by cutting straight down between the pair of buds, leaving the leaves on, and thus giving two scions. The cut is then tapered off to fit the cut on to the stock; a simple way of grafting known as whip grafting. Carefully fit the scion to the stock, making sure that the bark fits on both sides, for it is here that the union takes place. Hold the stock and scion together and bind them firmly but gently with the raffia, taking a turn or two above the bud and then tying round and round until you reach the base of the cut where you finish off with a half hitch. Trim off any part of the stem and scion sticking up above the binding and your graft is complete and ready for potting into a 2 1/2-in (6 cm) pot. Place the pots in a shaded propagating frame with bottom heat and keep them close for three or four weeks in a temperature of about 65�F (18�C), looking at them occasionally to see if they need watering, or to make sure that the leaf is not damping off. After three weeks look at the bud at the bottom of the leaf stalk, which should by now be swelling. When it is 1/2 in (1.25 cm) high, it is time to take the pots out of their close quarters and to a more airy bench in the greenhouse. Keep them shaded when the sun is shining as the spring sun can get very strong through glass and will soon shrivel up the tender little shoots. When they are 3 or 4 in (7.5-10 cm) high they should be given little sticks to support them and pinch out the growing tip, to encourage them to break into two shoots. Clematis are very hardy plants and do not like too much heat, so, as soon as possible, put them into a cooler house and ventilate well on hot days. They are now ready for their final potting into 5-in (12.5 cm) pots. There is little else to do, except to stake each plant with a bamboo cane, see that it is kept well watered and fed at the proper time, and tie the plant to its stake as it grows. By midsummer it will be at the top of the cane and in bud, and you can either keep it in the greenhouse, or plant it outside in its permanent position. If you are not ready for this yet, the clematis can be plunged in the ground outside in its pot; that means digging a hole or trench covering the pot completely, which will keep it moist for the summer, and then planting it out in the autumn.