In the wild, clematis seed themselves in cracks between rocks, in open ground or wherever the seeds are blown by the wind. However, it would appear that the most successful are those which find themselves a spot where there is some shade from direct sun or where there is sufficient moisture to survive. From observations in large-scale clematis production, we know that if the soil temperatures reach above 27�C (80�F) the roots stop developing and therefore top growth becomes very woody and rather stunted, with short internodes.
Clematis do not seem to require high light levels to grow, and in the garden they will tolerate semi-shade as they do in the wild. However, they do need long days to grow well. As days shorten in mid-autumn, clematis start to go into dormancy in central Europe. This happens earlier further north and, naturally, later further south in the northern hemisphere. In a Mediterranean climate clematis will start into growth much earlier as a result of warmer temperatures and higher light levels and some of the species from such a climate will go into a summer dormancy, reserving their energy until the autumn rains come when they grow again. Some even flower during the late autumn or early winter, for example C. cirrhosa 'Freckles'.
The ideal garden location is in a deep loam or prepared site where the clematis root system can grow in some moisture with shade to its root system, allowing its top growth to enjoy the sunlight. However, with careful cultivation, extra watering and feeding, clematis can be grown in more difficult locations and certain species and cultivars may be grown very successfully in containers for the patio or a small terraced garden. If the entire range of plants currently available is taken into account, you can plant clematis so as to have one in flower from late autumn (as with C. cirrhosa 'Freckles'), right through the winter (in mild locations) into spring, summer and mid-autumn.
Most clematis are bought today as container-grown plants, so with some extra care and extra watering the season for planting can be all year round. The natural and most logical planting time is during the period from late summer (unless the weather is still hot) right through until late autumn or the early winter. The ideal moment is while the soil is still warm from the summer sunshine, before it becomes too damp and wet. Planting at this time of the year allows the clematis the chance to establish some new roots before the onset of winter. During mid-autumn, clematis can produce a considerable amount of new roots, thus giving the plant a chance to establish well in the new site before the following spring and summer. This planting period will also save you from doing a good deal of watering while it is establishes.
Today however, many people are fine-weather gardeners and planting is mainly carried out in the spring or very early summer when gardening is much more pleasant than during a rainy autumn day. Even if soil conditions are favorable it is not advisable to plant in the depths of winter, but depending on weather and soil conditions planting can resume once that season is over, early to mid-spring being ideal. Planting until early summer is also possible, but the later you plant the more watering will be required to help the plant become established.
The preparation of the planting site is most important. Clematis will be expected to adorn their host or support for many years and you should regard the time spent in preparing the planting site as an important investment that will truly be rewarded in the future. Dig a hole of 45 x 45 cm (18 x 18 in) and discard the soil unless it is a good loam. Break up the base and sides of the hole with a garden fork, especially on clay or compacted soil, as otherwise the hole will become like a large clay pot where the clematis root system may not penetrate. Add well-rotted farmyard manure or garden compost to the base of the hole to a depth of 7-10 cm (3-4 in) and fork it well in. It is important that this is kept well away from the new clematis root system. Back fill the hole with good loam or old potting compost mixed with two or more bucketfuls of peat or peat substitute, which should have two handfuls of bone meal or the appropriate amount of general fertilizer added. Tread the soil down so that shrinkage will be at a minimum.
Before planting, it is important to 'condition' the clematis plant. Submerge it in its container in a bucket of water for at least 20 minutes so that the compost is thoroughly wetted and the roots have had time to take up water. This is necessary because, once planted, the roots will take time to re-establish and be able to take up moisture. After the plant has taken up water, remove it carefully from its container. The roots at the very bottom can be gently loosened to help them re-establish, but the main root ball must be left intact.
A garden trowel can then be used to remove enough soil from the prepared site to accommodate the clematis root ball. Plant the root ball at an extra depth of 6 cm (2 1/2 in) below the soil level in its container to help the clematis establish a basal root crown of buds below soil level. Once the basal buds become established most will lie dormant, waiting there just in case of need. They will be forced into growth if the top growth becomes damaged in cultivation or, in the case of a large-flowered cultivar, the plant succumbs to clematis wilt. If the disease does strike, the plant has a much better chance of survival and regrowth if it has been planted at this depth.
After planting, carefully firm in the root ball with your open hands and fists. The clematis stems will need a firm support to the host plant or structure; the existing cane can be removed gently from the clematis stems or another cane can be used. The cane should be pushed into the ground outside the clematis stems at an angle sloping towards the host. This will also give protection from damage to the clematis root crown and basal stems during cultivation. At the time of planting or a little later, a low-growing plant or shrub should be planted near to the clematis root ball to give added shade to the root system. Stone slabs can also be used to give coolness and shade, but plant material looks much more natural. However, the shade plant should be shallow rooting so that it does not take too much moisture away from the clematis plant's root system. The clematis root systems found their way from the border to grow underneath a wide concrete pathway, and once they reached the moisture and coolness of the rubble there they romped away. Such cool conditions for the root systems of clematis are ideal.
After planting, the most important job is to water the clematis. They will require constant attention in this respect after planting. Immediately the clematis has been planted, it should receive at least 4.5 liters (1 gallon) of clear water. This should be repeated within two days if the weather conditions are hot and dry. If you have planted the clematis in early summer almost daily watering will be required until the clematis has established a new root system that has started to take up moisture. This will be signified by substantial new growth. If clematis are planted to grow up into large trees or shrubs or at the base of a dry sunny wall, daily watering will be needed to help them establish.
If a clematis is to be replanted from an existing site, the late winter before bud break is the time to do this. However, it is only the large-flowered cultivars or the C. viticella cultivars that generally can be replanted from an open ground position due to their large fleshy roots. The clematis species and their cultivated forms have a very fibrous root system that usually breaks up when it is being dug up. The montana types and the Meclatis Section are also extremely difficult to replant once they have been established for more than two or three years. If a clematis is to be relocated, it is advisable to prune down the top growth to a pair of strong leaf axil buds on each stem to within 60 cm (2 ft) of the soil level. Place a strong bamboo cane or stick firmly into the soil near the base of the stems (not too close or you will cause damage to the base of the main roots) and tie all remaining stems carefully to the support provided. It may be tempting to leave longer stems, but remember that a very large percentage of the plant's root system will be destroyed and the remainder will be unable to provide enough moisture to support the top growth if a large amount is left on the plant.
The digging up of the clematis is also an operation that requires care. First dig a circle around the root ball as deeply as possible (at least a spade depth), leaving a root ball with a diameter of approximately 45 cm (18 in). It may be necessary to go around the root ball several times to ensure that all the roots have been cleanly cut. Then get the spade well under the root ball to at least a spade depth from all angles to ensure that all the roots are cut. Enlist the help of another person if possible, so that two spades can be used to remove the clematis root ball from its site. Place the clematis root onto a large piece of strong polythene or sacking and keep it moist until it can be replanted -ideally, the new planting site will be prepared and ready. It is important that the clematis root ball be planted an extra 5-8 cm (2-3 1/4 in) deeper than the previous soil level. The remaining stems should be carefully tied and trained to the new support or host plant. It is essential for the replanted clematis to be watered during the coming spring and summer, together with the following spring and summer if the season is at all hot and dry.
As new growth appears during the spring, it should be tied and trained to its support. If the growth is at all weak and spindly, it is advisable to pinch out the soft tip growth to help the plant develop a good bushy stem structure. If the clematis belongs to the early large flowered group, do not expect large flowers during the first or maybe even the second season after replanting. This is because these clematis flower from the previous season's ripened stems and with the hard pruning that took place before removing it from its previous site nearly all the flowering stems will have been removed.
Whichever group the clematis belongs to, all top growth should be cut back to just above the base of the previous season's stems during the second spring after replanting. This will encourage the plant to become bushy and well furnished towards its base.
Growing conditions for climbers of all types are rather more exacting than for most other groups of garden plant, because the soil close to their support is likely to be impoverished in some way. If they are planted against a wall or fence, the soil will be dry as it is sheltered to a considerable degree from rain. And if the support is provided by a hedge or a tree, the situation will be compounded by a shortage of nutrients. Once the climber is established, regular feeding and watering will help maintain it in a healthy state, but initial preparation before planting is vitally important if your plant really is to produce of its best.
It's worth looking at the way in which different soils vary to see how far they fall short of the ideal for clematis; and how they can be improved. All soils contain greater or lesser amounts of sand, silt, clay and humus and the relative proportions of these components give each soil type its characteristic features. A soil with a high clay content is slow to warm up in spring but it then retains warmth well; it's also likely to be generously supplied with nutrients. In dry conditions, however, such as those in which clematis tend to grow, it can be hard and impenetrable whereas in wet winter weather, it may become waterlogged. By contrast, a light sandy soil will warm up quickly, cool down quickly and, being free draining, lose both water and nutrients rapidly. Humus (part-decomposed organic matter) will improve both types of soil, for it contains natural glues that bind together soil particles to form crumbs, and it also helps with the retention of moisture because of its sponge-like properties. Always dig in plenty of compost or other organic matter before planting.
But there's another aspect of soils that is especially important with all types of clematis: their relative acidity or alkalinity. This is usually expressed as the pH, measured on a scale from 0 to 14. Soils with a pH above 7 are alkaline, those with a pH below 7, acid. Most soils are naturally somewhere between about pH 6 and pH 7.5 (more or less neutral) and most plants will thrive in these conditions. But there are exceptions.
Clematis are among the most important garden plants that tolerate more alkaline conditions and, although soils around neutral will be perfectly adequate, any soil with a pH below about 6 will be too acid and should be altered by adding garden lime before planting. The amount of lime to add depends, not only on the initial pH, but also on the texture and structure of the soil. This information should be given on the bag. Garden lime or ground limestone (finely ground calcium carbonate) is the most convenient form of lime to use and is best applied in the autumn. A few years after application, the acidity may rise again, largely as a result of the use of acidic fertilizer. It's worth checking the soil close to the plant from time to time, therefore, with a pH testing kit; especially if the overall performance of the plant begins to decline in a garden known to be naturally acidic.
Aspect is important for growing clematis but only in so far as you must choose the most appropriate type for each situation. One of the great virtues of clematis is their diversity and the fact that, soil and other conditions being appropriate, there is a variety for almost every garden position.
Along with their varying tolerance of different aspects, there are varying degrees of shade tolerance but two general points are worth making here. All clematis will grow better if the lower part of the stem and the roots are relatively cool. Even those growing in full sun will benefit from the provision of some shade over the soil; often this can be achieved simply by placing old tiles and a thick layer of mulch over the soil surface. And some of the large-flowered varieties, in particular, will produce better and more intense flower color if the upper part of the plant is in very lightly dappled shade rather than the full glare of the sun. Remember that, many are derived from plants that naturally grow in woodland.