Success with Clematis

Clematis are a great-looking and deservedly popular climbing plant in any garden. There are clematis varieties for early, mid-summer and late-summer flowering and with varieties like Clematis ‘Freckles’ and Clematis armandii in particular, it’s possible to have flowering clematis for 11 months of the year. Clematis stems are hardy once established and can range in length from anything between 6ft to almost 40 ft. At Winsford Walled Gardens I grew over 120 clematis varieties to cover the walls and provide colour throughout the gardens.

Garden visitors greatly admired our displays and I was often asked how to grow clematis. The clematis vine is a hardy plant that will reward the gardener with magnificent blooms for years once established. And here I must emphasise the ‘once established’ bit. Because the trickiest part of growing clematis is getting your newly purchased plant through its first winter and most of THAT depends on WHERE you plant it, HOW you plant it and how you PREPARE your young plant for its first winter.

So let’s begin at the beginning of your own clematis experience. . .

Purchasing and hardening off

The best time to plant clematis is around Easter/mid-April whichever is the later. This gives them the maximum time to get established in their new location. Occasionally, you may obtain clematis late in the season at reduced rates, if this happens, do not be in a hurry to plant. Indeed, it will pay you to keep them under cover and maintain the pot compost just slightly moist through the winter until its planted out in mid-April when the ground is getting warmer once more.

Always try to avoid buying a clematis plant with no flower buds on. If your plant has no flower buds, it could be because the ‘runt’ of the collection and have no flowers ever. By purchasing a plant with flower buds at least you KNOW it can flower.

The Clematis vine arrives in especially tall, slim pots. First thing to check: Is the compost moist, not wet. If it isn’t choose another plant, if your chosen plant is the only one available, pop it out of its pot to check the roots are looking good. They should be yellow with healthy white growing tips. If those tips are not white discard – the roots are rotting.

When you purchase your new plant always ask your supplier if the plant has ‘hardened off’. ‘Hardening off’ is the process that gardeners use to acclimatize a plant which has previously been grown under cover and get it used to being outside.

You need to avoid buying a plant which has been grown in a greenhouse and imported from a warmer country and then you plant it straight out in your comparatively ‘cold’ garden before it has hardened off.  Normally, it  takes about two to three weeks of progressive treatment of putting the plant outdoors during the day and returning it under cover each evening. On particularly bitter days it is best to keep the plant under cover. The important thing during hardening off is to ensure plenty of fresh air around your plant(s).

Having got the right plant, already hardened off you can not just stick it anywhere in your garden any how.

How to Plant Clematis

Planting is key to successfully growing clematis. Let me say that again… Planting is key to successfully growing clematis.

Clematis grow best when their roots are located at least eighteen inches (45cms) away from their support – be it a wall, pergola or shrub.

In common with many climbers, clematis varieties prefer to have cool roots and warm, sunny foliage, so always locate your clematis roots on the cooler, shady side of any post or plant.

Clematis much prefer to grow in the company of other plants. It’s also better for your garden design if they do. Being a vine, clematis are much happier if they grow through another plant, and with careful planting, that other plant will provide the necessary shade and protection over the clematis root.

Notice I mentioned ‘shade and protection’, because  a clematis scrambling through another plant not only has cooler roots in summer, but those roots are better protected through the winter too.

I have heard it often said that a concrete paving slab over the roots does the trick. I disagree. The reason why is because a concrete slab will get as hot as the ground in summer and just as cold in winter! It also ‘blocks’ air and water to the roots directly below. Whereas a growing plant over the roots allows air and water to the clematis roots and provides much cooler shade in summer and greater protection from snow and frost in winter than any concrete slab may provide.

In Winsford’s example, we have seven clematis montana varieties which grow upwards of 30ft (10m) and these are all rooted up to 3ft (1m) away from the base of the south-facing north wall. A wall which can attain over 140F degrees in summer. Furthermore, and most importantly because the wall faces south, planting the clematis was postponed until sufficient shrubbery was established beneath the wall which could shade the clematis root system in summer and protect the young plants in winter. Click on image for enlarged photo.

Measure the pot height against your spade depth and dig accordingly. The excavated hole needs to be at least twice the width of the pot it came in and at least 1.5 times its depth. Time spent digging the larger hole will pay you dividends. Because by digging the bigger hole you are making it easier for those soft young roots to establish themselves in the loose soil you return back to the hole.

Sprinkle some bone meal at the bottom of the hole is always a good idea too. Then plant your new clematis with about 2-3 inches of soil on top of the original pot soil level. That’s right! You are burying your new plant… But this will help to encourage new additional shoots to emerge.

Grow more clematis stems!

Too many gardeners get too fixated upon achieving maximum foliage growth during that first summer. Even experienced gardeners do it with new plants. All in the belief that their plants will have a ‘flying start’ next year.

BIG MISTAKE! Gardeners who purchase new clematis in spring and then leave the stems on in autumn for the winter are almost certainly halving the chances of their plant surviving the winter months.

Why is that?

Consider this. Every new clematis will put on its minimum foliage growth at the expense of the all-important rootstock. And its not the top growth, but the root stock that will ensure your plant survives the winter. So you need to compel your young clematis to do the exact opposite, to build up its root stock at the expense of its foliage. Otherwise, all the top growth that remains on a young clematis vine is just more plant that can rot back in to the juvenile root stock and kill your new plant.

The best thing you can do for the newly planted clematis is to cut its stems down to about 18″ high (45cms) – FOR ITS FIRST TWO WINTERS in your garden. In this way, you compel the plant to rest, to save its resources in the root to give it a better chance of pulling through the winter.

By chopping the stems at the end of the first two winters you are also reducing the chances of the stems rotting back in to the roots. By chopping the stems back you are encouraging your clematis to do what all plants do in the same circumstance – grow more shoots! Do this for the first two winters and then in the third and successive autumns chop your clematis stems to one third their length to obtain vigorous growth and masses of blooms. This what I did with great success.

Clematis montana varieties appreciate a good ‘hack’ every five years.

Clematis montana varieties are best treated as all young clematis described above. However, growers of established montanas will no doubt have noticed that their plants run on a 5-year cycle. That is, clematis montana varieties do respond well to a hard prune every fifth year. They flower best in years 2 and 3, by year 4 flower abundance is starting to wain slightly, year 5 more so, and if not pruned harder than normal in year 5, the flowering in what otherwise would be year 6 their flowering is markedly reduced.

Having established your clematis root during its first two years in your garden, its then best to follow the established technique described below, for the third and successive years:

Clematis Groups and pruning
There are three distinctive clematis pruning groups.

Group One – Light Prune after flowering
Following the initial first year’s hard prune members of this group need only receive an annual trim and tidy-up after flowering. Group members include clematis amandii, C. alpina, C. macropetala and the large montanas.

Group Two – The larger flowered hybrids
Group members include the larger flowered hybrids which flower on the previous season’s growth and sometimes flower a second time in late summer on new growth. Pruning should be completed around February (late winter).

Group Three – Hard Pruned late flowering clematis.
This group flowers on the current season’s growth because of this, there is no need to retain the old stems. Around late February group members need their stems pruned back to about 2-3 feet. Never mind that you will undoubtedly remove some good stems and buds. Over time the stem will extend itself with maturity.

Examples of Clematis groups.

Group One	Group Two	Group Three
amandii	Alanah	aromatica
Broughton Star	Barbara Dibley	Barbara Harrington
Cartmanii Joe	Dawn	Earnest Markham
cirrhosa	Fireworks	Hagley Hybrid
Freckles	Lemon Chiffon	Hendersonii
Freda	Marie Baselot	Jackmanii
macropetala	Mrs Cholmondley	Perle d’Azur
Montanas	Wada’s Primrose	viticella