Planting in containers

The best time to plant clematis in a container is in spring, a container will heat up quicker in spring and the optimal temperature at the roots will be achieved. Most clematis can be grown in containers, but the best varieties to grow are those with the longest flowering season and the shorter or dwarf forms.

The container should hold at least 20 litres of soil, but the bigger the better! The growing medium has to be of the highest quality. You can buy special garden soil from the garden shop or, of course, make your own compost and peat mixture, but whatever you use; there must be good drainage and suitable climbing facilities. You could plant up a large container (volume = 20-50 litres) with about 3- 5 plants, depending on which variety you want. Your container, pot, or whatever can remain outside or on the balcony from spring until autumn.

In the cold winter months it has to be placed in a frost free situation or, alternatively, with some additional frost protection and the plants should never be allowed to dry out completely. After about 2-3 years a complete change of soil is necessary, which should be carried out just as the clematis is starting into growth for group 3 clematis, but groups 1 and 2 should be re-potted after their initial flowering has completed. You can use the same container again; just simply remove the soil from the plant; shorten the roots and prune back the stems; put in new soil and replant the clematis.

If you have enough space, another method to over-winter the containers is to sink the whole pot in a hole in the garden – this method is known in the trade as “clamping”.     

General care

Normally, clematis does not require as much looking after as is generally thought. Basically, one should always water regularly during the half year of summer and, when watering, special attention should be paid to keep the lower leaves of the plant dry! Always feed with an application of well balanced general fertilizer, and begin, naturally, in April when growth starts. Every product is different, so always read what the dosage is; how long it is active and carefully follow the manufacturer’s instructions. Further applications of fertilizer could be needed during the summer.  For most of the large group of wild clematis species, lime is important but this is not the case for the hybrids sorts. If your garden soil is acid, give a dressing of lime once a year, if need be.

Always take care not to damage the stems, as many types of fungal infection can enter into wounds. Try and remove all spent flowers, dead or damaged stems as well as diseased leaves as often as possible. Any leaves which suddenly look abnormally different are more than likely to be infected by pests or a fungal disease. Inspect the underside of the leaves as pest attacks will often start here but a fungal disease, on the other hand, often starts on the upper side of the older leaves lower down the stem. When the lower leaves start to go yellow and eventually go brown, this could be caused by a lack of light or moisture – promptly take the appropriate corrective measures.

Clematis can grow quite quickly, up to 20 cm per day! It might be necessary, therefore, that you have to guide and tie the stems in the right position. Suitable ties are available at your local garden centre.

Clematis – the recommended pruning techniques

Pruning is one of the most important subjects in the cultivation of clematis! But there are, unfortunately, many different and contradictory theories on this subject. What is right and what is wrong?

Pruning for shape in the first year of planting

Quite apart from when you plant or when your clematis actually starts flowering, you should always radically prune all newly bought and planted clematis before it starts its first year of growth. This is to encourage a strong framework of stems lower down. You start by cutting back all stems to about 20-30 cm above the ground in November or December and, just once, you will have to be satisfied with just a few blossoms on the early flowering species but be happy to have a good framework of stems for later. The following year you can prune as normal.

Clematis specialists, professional or amateur gardeners and authors of books agree that all clematis should be pruned at one time or another and, therefore, belong to any one of the three different pruning groups. These are referred to as groups 1, 2 or 3 (or A, B or C). A precise time is only given to group 1 and it is debatable when exactly the other two groups are pruned. When ought clematis to be pruned?

Pruning in late autumn or spring? Influenced by climate change – yes or no?

The facts are: Year after year we are getting milder winters, so clematis start growing earlier. I have always maintained that pruning ought to be done in autumn rather than in early spring when the new shoots are already quite a few centimetres long. However, it is entirely up to you when you prune, but autumn pruning is definitely more advantageous!

Pruning group 1

Month: May-June

This rule applies to many of the wild clematis and to those sorts which need to be pruned back in late spring (only when absolutely necessary), directly after they have flowered. This includes all of the C. alpina and C.montana groups. Both these species start developing their flower buds in the previous summer and autumn in readiness for flowering the following spring. This is known as “flowering on last year’s wood” and examples of this in shrubs are the Forsythia and Rhododendron. If you do not know, and prune at the wrong time of year, you will only forfeit the flowers just for that year! Should, however, quite a radical cutting back be needed to renew an old clematis, wait until after it has flowered in April/May and then cut back in June. This will give the plant enough time to produce more shoots which flower the following year. An alternative approach is to cut back a few selected stems annually to partially prune the clematis.

Pruning group 2

Month: November/December (or June)

Reduce all stems by half, or about 1 metre above the ground in the case of older plants. This method is to be carried out on hybrids which flower twice a year. You will see these varieties in my catalogue with the flowering times given as, i.e. 5/6 & 8/9. Just the same as C. alpina and C. montana, these have short flowering stalks produced on wood made the previous year.

Depending on how many branched stems remain on the plant, the number of flower-bearing short stalks is increased. I would like to comment at this point that most of the double flowering hybrids only produce such flowers on short stalks in the spring.

After they have flowered in spring, all hybrids within this group will produce new long shoots on which a second flush of blooms appear in either summer or late summer.

A light pruning in June

You can improve the quantity of the second summer flowering by cutting off the seed heads together with the next underlying pair of leaves. Your clematis will happily send out new shoots and will abundantly flower again about 6 weeks later.

A radical cutting back of this group about every 4-5 years ensures a compact shape.  

Pruning group 3

Month: November/December (or late February)

Cut back radically, leaving only about 20 – 50 cm of stems above soil level. This applies to many hybrid varieties and wild species which only flower in the summer. All these varieties and species produce long shoots at the end of which are masses of flowers. Included in this group are all herbaceous clematis, C. viticella and, the well-known, C. Jackmanii hybrids.

Pruning group 2/3

Month: November/December

This is quite a special section which can either be pruned according to either group 2 or to 3. The reason for this odd placing can be traced back to a cross-breeding of two clematis groups.

Pruning to alter the flowering times

There is the possibility to either bring forward or to delay the actual flowering dates of the summer flowering clematis by 2-3 weeks. Even the position in the garden could delay flowering for up to 4 weeks quite naturally. Take two clematis plants of the same variety and put one in shade and the other in sun, and you will notice the difference. This could be taken a step further and what would normally be a 4 week flowering period could then be one of 6 weeks or longer. The way to do this is to use the method known as “pinching out”, which simply means to snip the tops off young shoots

To alter the flowering time of:- 

- Pruning group 3. Pinching out takes place in April/May, when the new shoots have reached about 20-30 cm in length. These young, very soft shoots are shortened by half and then, 2-3 weeks later, a great many more shoots appear which will bear flowers later. If you pinch out at a later date, the flowering period will, accordingly, be even later. You could even pinch out those already shortened shoots for a second time and delay the flower by a further 3 weeks!

A five year old established clematis could have one part pinched out, followed by another part a few weeks later and, finally the remaining part even later still. By forcing additional flowering intervals (stages), means that the clematis in question will bloom for a noticeably longer period. There are some clematis that belong to the pruning group 3 which start to flower in June (e.g. Hagley Hybrid or Rouge Cardinal), and these can be brought into flower for a second time. After the main flowering period is over, about the middle of July, reduce the plant right down to just 60 cm above the ground, and a second show of flowers will appear in September.

- Pruning group 2. It is possible to completely cut back to ground level, all members of this group and the result would be that the first main show of flowers do not appear in May but in June instead, thus avoiding a gap in the middle of the two flowering periods. Another advantage to this rather radical action is that the clematis plant itself is regularly renewed and its general vitality is greatly improved upon. The disadvantage, though, is that this clematis will only flower one time in the current year and the early double flowers of some varieties will be lost to single ones.

NOTE; to carry out the above procedure in England will result in group 2 clematis not producing flowers until August or September. Group 2 clematis can be cut down to ground level after their first flowering period (in June/July), which will generally allow them to flower again in August/September?

Bringing the flowering period forward can only be successful in a sheltered spot, such as a winter garden or amateur greenhouses.

Pruning group 1 can only be made to flower earlier as stated above. It is not possible at all to pinch out any of them successfully.