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Written by davethetreecenters • October 10 Growing Clematis – large-flowered hybrids

Few sights are as glorious as a well-grown clematis in full bloom. It’s a delight in any garden. Although there are around 300 wild species, and the range grown in gardens has expanded a great deal in recent years, the ones that turn the heads of ordinary gardeners are almost always the large-flowered hybrids, so in this post we’ll stick with them. Since the needs of these plants differ, knowing what you are growing is as important as knowing how to grow it. If you inherit a plant when moving house, we’ll give you some tips on figuring out the what part.

Where to Grow Your Clematis

With some exceptions, the ideal place for a clematis is in the sun, all day in cooler zones, and all morning in hotter ones. There is an old rule of thumb that says, “Head in the sun, feet in the shade”, because clematis enjoy having cool roots. Probably the most important exception to this is the Nelly Moser Clematis, and all the varieties with striped petals. These very popular varieties are notorious for fading in the sun to an unsightly beige, so they should be grown in light shade, perhaps on an east-facing wall, or where they get scattered shade from trees overhead.

The easiest way to give that shade is to plant it behind a smallish shrub, perhaps an evergreen, to create a cooler pocket. Almost as good is to simply lay a large flat rock over the root area, and a thick layer of mulch will have much the same effect. The goal is simply to stop the sun shining directly on the soil, raising its temperature.

All the large-flowered clematis are climbing plants, so support is needed. This can be just about anything reasonably strong, depending on your garden. A trellis panel attached to a wall is popular, and so are free-standing trellis and tripods standing in beds. In fact, a great way to grow clematis, if you don’t have a pergola or lots of wall space, is to stand tripods in your flower or shrub beds. You can buy metal ones, or make your own from some poles and string. This is a great way to raise the height of a bed, without waiting years for shrubs to grow, and a column of flowers beats a column of green every time. Another great idea is to copy nature and let your plant grow up into an old shrub or even a small tree. As a vigorous clematis has a lot of leaves, don’t choose a shrub you really value, as it will be weakened a bit. A super-great idea is to use the support of a climbing rose. It doesn’t matter if the clematis flowers with it, or later – the effect of great and you get a fabulous two-for with garden space as well.

What is the Best Soil?

You can grow a large-flowered clematis just fine in any well-drained soil, but it will definitely do best in soil that is moist, rich and alkaline. Smart gardeners on acidic or neutral soils add a handful of garden lime when preparing the planting soil – it really makes a difference. Enrich the soil with plenty of garden compost or similar, and use a couple of inches as mulch each spring, over all the root zone, but not touching the stems at all. If your soil isn’t great, start off with a tough and reliable variety like the Jackmanii Clematis, and see how it does. If it’s happy, branch out into others.

Planting a Large-flowered Clematis

Often the plant you buy will be small – that’s just how they are sold, and doesn’t mean there is anything wrong with the plant. So sometimes it is best to give your new plant a year in a pot to grow before transplanting it into your garden – this is especially a good idea if your soil isn’t great. Chose a pot size that adds about 3 inches of soil around the pot it came in. Use regular potting soil – not ones for azaleas or other acid-loving plants – and plant the same way we are about to describe, but in the pot. Water and fertilize regularly through the season, and transplant in fall to the final spot.

Either way, when you plant, there are two important secret you should know. Normally when planting it is emphasized to plant at the same depth as the plant is in the pot. With large-flowered clematis only, don’t do that. These plants are grafted, and it is best if the stem of the actual plant is able to grow its own roots over time. To allow that, place the pot a full 2 inches deeper in the hole, and cover that area, and the stem, with your soil.

The second secret can be hard to do, but here it is. Once you have planted and watered your plant in, cut it back so that only the buds of stems at the lowest point are left – yep, that’s right. I know that if you have buds or flowers on the plant when you get it that is going to be hard. So you can wait until they are over, and THEN cut back hard. This step is important in building the strength of your plant – you will be amazed, so do it, really.

Caring for Your Large Flowered Clematis

Keep a new plant moist, but wait until you see new growth before starting to feed. Fertilizers for roses are best for clematis, or a special clematis food, and for new plants liquid types work well. Older plants can he fed with a granular fertilizer in spring and again in mid-summer, but if you use a rich mulch that will probably be all that is needed. Older plants can be left a little drier, but regular watering will make a big difference during dry weather – such beauty deserves a little attention.

Pruning Large Flowered Clematis

This is the trickiest part for many gardeners, but it isn’t so hard once you understand. First, ignore all what follows while your plants are young. In their second spring, all types should be pruned back in spring to 12 inches tall. In the third spring, prune back to 18 inches, always cutting just above a pair of healthy buds. It is worth sacrificing some flowering in these formative years to develop a strong, well-branched plant for a long future full of flowers. It can be hard to tell which parts of your plant are alive, especially in cold zones where some winter-dieback is a fact of life. Best to wait until you see the buds swelling or sprouting an inch, because that makes it very easy. The first step should always be removing whatever is dead.

Start pruning properly the following year, and the first step is to determine what pruning group your plant is in – there are three such groups. If you know the variety it’s easy to find out. If not, try the following:

Ask yourself, does your plant bloom before July? If ‘yes’, then it’s either group 1 or group 2. If ‘no’, then it’s group 3. Here are the groups for pruning:

Group 1: I only mention this group for completeness, because the only clematis in this group are species or varieties of species.

Group 2: These are some of the best hybrids, all plants that bloom in spring, and then (usually) in late summer. The popular varieties with striped flowers, of which ‘Nelly Moser’ is the most famous and popular, belong here. Prune in spring, once you see growth, by simply removing all dead stems. You can leave everything else, although most gardeners like to shorten the living stems back to between 3 and 5 feet long, for neatness and to keep plants more compact. You decide what is best for your situation, but remember that once a plants becomes very large and overgrown it can be harder to prune without losing a year’s bloom. So light pruning each year is usually best. Removing spent flowers with a trim as soon as the petals have dropped will encourage that second blooming.

Group 3: These are the summer flowering hybrids, and the best-known is ‘Jackmanii’, one of the first hybrids created, and still the most popular of them all. In warmer zones (but never in cold ones) you can tidy these plants in fall to prevent breakage in storms by pruning back to 3 or 4 feet tall. Then – or otherwise – prune in late winter or early spring, as soon as you see the buds swelling. Cut each healthy back to 12 inches tall. Fast-growers, they will reach full height each year. If you leave them unpruned they develop long, unsightly bare stems and don’t flower so well.

So To Work. . .

That’s it, no you know everything you need to have the best clematis of all, and get lots of applause from family, neighbors and friends.