Cultivation of Clematis
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.
Planting out the clematis
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
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.