How to Grow and Care for Clematis
Athough Clematis are generally easy and rewarding plants to grow, they are not immune to problems. Among them, Clematis Wilt, and, worse, sudden death.
To avoid that, I have found the following guidelines helpful.
Too Much Sun
Clematis grow wild in temperate climates around the world. Garden Clematis thrive in moist, well-drained fertile soils. While a few require full sun, the blooms of others, such as Clematis 'Nelly Moser', will be bleached by it. Red and purple Clematis are the most susceptible, so try to plant them in the shade if they can tolerate it.
Too Little Moisture
Lack of moisture will probably do Clematis most harm. Don’t let the roots dry out. Shading them from the sun with a covering of broken crockery or low-growing plants are popular ways of achieving this. Watering regularly is another.
How to Plant Clematis
Never plant Clematis that has already dried out. Immerse the plant in a bucket of water first. Then, dig a hole about two inches (5cm) deeper than the root ball. If necessary, throw in some grit to help drainage. Mix the soil from the whole with manure, compost or other organic matter. Put the Clematis in the hole, making sure the crown is at least two inches (5cm) below the soil surface. Fill in with the soil and organic matter. Water well.
After planting, to encourage new growth, you can cut stems back to above a healthy pair of leaf buds between seven and 12 inches (30cm) above the ground, although you may not want to do this straightaway if the plant is flowering. If you want the Clematis to climb, make sure you give it something to climb up, or it will just sprawl unattractively. Lean the plant and the stake that it came with towards a wall, trellis or fence and off it will go. Keep it moist, well mulched, and, while it’s growing, well fed.
When to Prune Clematis?
As a general rule, if it flowers before the longest day; it flowers on last year’s growth; or it’s a Group 1 Clematis, prune it lightly straight after it flowers or not at all. Remove only dead and untidy stems to just above a live leaf bud.
Group 2 and Group 3 Clematis usually flower later, after midsummer. They do so on new growth, so they must be pruned in February to allow it to regrow before the flowering season. Prune Group 2 Clematis lightly and Group 3 hard. Cut back all stems to around 12 inches (30cm) above the ground, cutting just above a leaf joint. The reason? Group 3 Clematis will quickly become leggy, flowering high up, if they’re not cut back. An alternative is to turn the long stems back down towards the ground.
Large-flowered varieties have been bred from wild Clematis native to Japan and China, and although their big blooms make them popular garden plants, they can be vulnerable to Clematis wilt, which turns the leaves black.
Cutting the infected plant down to ground level, burning the cuttings and hoping for the best is about all you can do unless you want to spray with a fungicide. Wilt strikes stressed plants more often than healthy ones, so don't plant a wilt-prone variety in heavy clay soil or starve it of moisture or food. In fact, what appears to be Clematis Wilt may actually be caused by thirst, starvation or soggy roots.