How to grow clematis and the best varieties

You can grow clematis in the ground or in containers, and by planting varieties from the diverse groups that flower at different times of the year, you could be enjoying the delights of clematis for many months. 

Which? Gardening magazine grew a range of popular varieties to see which would give us the best display throughout the year.

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Key facts

PLANT TYPE Hardy climber 

POSITION Sun or partial shade with shaded roots

SOIL Well-drained and fertile

How to grow clematis: month by month

Best clematis varieties

Which? members can log in now to see the full results and which are our Best Buy varieties. If you're not a member, join Which? to get instant access.

Full testing results for clematis

Spring-flowering clematis

USING THE TABLE OVERALL RATING Ignores price and is based on flower coverage 30% , flower impact 30%, flower duration 20%, seedhead attractiveness 15%, pest and disease resistance 5%.

Early to mid-summer flowering clematis

USING THE TABLE Overall rating ignores price and is based on: flower duration 20%, flower impact 20%, flower coverage 20%, plant shape 20%, pest and disease resistance 20%, using ratings from the third year of the trial. Plant shape ratings are based on the vigour of the plants and how well they covered their support.

Mid- to late-summer flowering clematis

USING THE TABLE OVERALL RATING Ignores price and is based on: flower duration 25%;flower impact 20%; flower coverage 20%; vigour 20%; pest and disease resistance 15%, using ratings from the second year of the trial. Vigour ratings are based on the vigour of the plants and how well they covered their support. Height and spread given for the second year of growth

Patio clematis for growing in a pot

USING THE TABLE OVERALL RATING Ignores price and is based on: Flowering duration in the North 25%, Flowering duration in the South 25%, Flower impact 20%, Flower coverage 15%, Foliage 5%, Suitability for pots 5%, Pests & diseases resistance 5%

Caring for your plants

How to plant clematis

Preferably buy plants in 2-3L pots and plant at any time of year when the ground is workable, although the dry summer months aren’t ideal. Provide shade for the roots so they stay cool. Plant them so the rootball is 5-7.5cm under the soil so that buds underground can regrow if the top growth gets damaged or diseased and has to be cut back. Water regularly for several months after planting until they’re well established.

Help your plants with a recommended soil improver

Feeding and watering

In fertile soil they may not need feeding. In poor soil use a general fertiliser, such as Growmore, in spring. Mulch annually with 5-7.5cm of well-rotted compost. Established clematis shouldn’t need watering unless the soil is very dry.

Discover our Best Buy garden hoses

When to prune clematis

Group one Trim back after flowering and tie in stems as needed. Cut back by around half to renovate if needed.

Group two Dead or weak stems can be removed or shortened before flowering in February or March. After flowering, some stems can be cut back by half to side-shoots or strong buds to encourage new growth and a second flush.

Group three In February or March, cut all stems to a pair of healthy buds around 20-30cm from the ground.

Try our Best Buy secateurs

Can you grow clematis in a pot?

Yes, you can. See our Best Buy patio clematis varieties above.

• Use a large pot to give roots room to grow; roughly 45cm in diameter and depth.
• Use a Best Buy compost for containers and mix in a Best Buy controlled-release feed.
• Avoid clematis wilt by planting deeply so the top of the roots are below soil level.
• Buy a good-quality obelisk that will support your plant for a number of years; we found that cheap wicker obelisks soon broke. Ensure the diameter will fit your pot.
• Topdress with fresh compost and controlled-release feed annually.
• Water regularly; daily during hot weather. 
• Most varieties will grow better if you site them away from potential cold winds. Strong sun can fade flower colours. Move the pot so the plant gets some midday shade if necessary.

Make life easier with a Best Buy garden irrigation system

How to take a clematis cutting

These can be done several ways using both softwood and semi-ripe material (ie getting firm at the base in late summer) ;they all root easily. Taking internodal cuttings of the current-season growth will give you good results. 

1. Pick out healthy growth and look for strong buds between the leaf and the stem, weaker buds may not root as well. 

2. Trim the stem to about 5-7cm from below the point the leaf joins the stem.

3. Shorten the top to just above where the leaf joins the stem, just leaving a single growing point with a pair of leaves either side of that point.

4. Trim the leaves by half to reduce water loss.

5. Insert the cuttings into a Best Buy compost for raising young plants right up to where the leaf joins the stem. Leave lots of space between the cuttings as clematis tend to rot off if they touch. Label, water and put in a coldframe, greenhouse, or propagator. Clematis root better in humid conditions, so if you’re using a windowsill, cover your pot with a clear plastic bag.

6. Pot on individually once rooted.

Are clematis poisonous to dogs and cats?

Clematis aren't generally considered poisonous to dogs, although according to The Dogs Trust, C. armandii can potentially cause dermatitis, gastro-intestinal  and nervous-system problems so you may wish to avoid it. In cats, clematis can cause skin irritation so discourage your cats from rubbing on them.

Common growing problems

Clematis wilt

This is a fungal disease that causes the whole plant to wilt. Planting deeply will mean that you can cut back the whole plant and it should regrow from the base. Sometimes the cause isn't clematis wilt but actually physical damage such as slugs nibbling the stems at the base.

Greenfly

Greenfly can quickly build up and cause poor growth by sucking the plant’s sap. Treat by squishing any colonies by hand.

Read more about greenfly.

Green petal

Green petal occurs if there is a late cold snap in the spring, while the buds of the plants are forming. It causes some of the petals to become bright green and distorted. Though it might be unsightly, there are no detrimental effects to the plant.

Slime flux

This is a bacterial problem that can cause the plant to collapse and horrible ooze to come out of the base. Cut back the whole plant and it should resprout from the base.

How we test clematis

We grow different varieties alongside each other so we can compare them as they grow. We assess the weekly through the growing season so we can see how they perform. We grow them for two years to see how well they do through winter as well as summer.