Watering
Newly planted clematis will need regular watering whilst they establish. All clematis will need watering during hot, dry periods. A thorough, deep soaking once a week is better than watering little and often.
Fertilising
Feed your clematis each year in late winter or early spring, but hold off fertilising while flowering as this can shorten the flowering period. Spread a slow-release, potassium-rich fertiliser around the base of the plant and apply a mulch of organic matter such leaf mould or compost.
Staking
Clematis are among the showiest of climbers and they need a support to scramble over, so consider where it will be positioned carefully. You can transform a pergola or wall, or be more adventurous and plant one through a tree.
Tie plants in strongly to the frame, as they will – at full tilt – carry a lot of weight.
The late-summer-flowering, viticella-type clematis (usually group 3) need training and guiding up and over shrubs and climbing roses to maximise their impact. Without this they tend to make a congested nest. Spread the stems out on their support or frame, tying them in with gentle flexi-tie or sweet pea twizzles as you go.
Deadheading
Whether you should deadhead your clematis or not will depend on the type of clematis you have. Deadheading some clematis will encourage further flowering, but some offer just a single-flush of flower. It is typically early summer-flowering Group 2 clematis that can flower again and will benefit from deadheading after flowering.
Propagating
Clematis can be propagated by cuttings, layering and seed sowing.
Overwintering
Most cosmos are annuals and will need to be resown from seed or planted as seedlings each year.
Cosmos atrosanguineus, or chocolate cosmos, is the exception – it is a tender perennial. It’s ideal for container gardens as the pots can be brought undercover over winter. Alternatively, you can protect the plant from the cold with horticultural fleece or straw.
How to prune
Clematis are divided into three groups or categories for pruning purposes: winter and spring-flowering, early-summer-flowering, and late-summer and autumn-flowering. A lot of people worry about pruning and if and when they should cut back their clematis plants, but it is very simple if you follow these guidelines.
How to prune Group 1 Clematis
(winter & spring-flowering clematis, e.g. Alpina, Montana, Armandii)
When to prune: tidy after flowering in June or July
The clematis in group 1 are mostly the early spring varieties that flower on the previous year's growth. Little or no pruning is needed, unless they have outgrown their allocated space, in which case they should be pruned immediately after flowering.
Every few years they may need a tidy when they finish flowering. Don't leave this too late or you'll lose next year's flowers – June/July is the perfect time. Trim back to a permanent framework of branches. Always hold your pruners vertically to avoid cutting into a central vine.
How to prune Group 2 Clematis
(early summer-flowering clematis, e.g. Nelly Moser)
When to prune: February
The clematis in group 2 produce their flowers in May and early June on stems grown the previous year. These need to be pruned lightly in February. To do this, follow your way down from the top of each stem until you reach a healthy bud and then cut on a slant just above it and remove old, dead stems above it. Do not prune too vigorously or you will lose the flowers. Prune again after flowering if required to tidy up the shape, if not, just deadhead the spent blooms and leave for a second flush of flowers.
How to prune Group 3 Clematis
(late summer-flowering clematis, e.g. Prince Charles, Madame Julia Correvon & Texensis)
When to prune: February
The clematis in group 3 produce their flowers on the new season’s growth in summer and autumn. These need hard pruning in February. Cut back all stems (just above a healthy new bud) to approximately 30cm (1ft) from the ground. Remove all dead growth above this. It sounds drastic, but they will grow and flower in one season.
If you are unsure or forget which group your clematis fall into, the simple way to remember is that if they flower before June, prune lightly as they will flower on the previous year's growth. If they flower from late June onwards, hard prune in February as they will flower on new season’s growth.
