Tip of the month: May
Tools for the job
Clematis are favourite climbers, and we can’t get enough of them - but in small gardens you can soon run out of space. Luckily the plant breeders are onto the problem; they’ve come up with some stunning, but relatively compact, varieties in the 6-10ft (1.8-3m) size range, which are brilliant for growing in tubs.
The best time to plant is right now, at the start of the growing season. Choose a large tub that’ll withstand a long series of winters outdoors without breaking up; a wooden half-barrel or good quality terracotta or ceramic container is ideal. It needs to be big; at least 15 – 18 inches wide and a foot deep. Make sure it has several large drainage holes in the base. Stand it in position, since it will be very heavy by the time it’s filled with compost, and raise it up on a few bricks or strong ‘pot feet’ so that surplus water can drain away easily. Cover the drainage holes with a few handfuls of gravel or bits of broken clay pot, then half fill with John Innes No.3 potting compost. (As a worthwhile optional extra, mix some moisture-retaining gel crystals with water till they reach a wallpaper paste-like consistency and add those to the compost, plus some slow-release feed granules)
Next choose your clematis. Look for a compact variety with large, showy flowers produced over a long season. Some of the very best of the latest modern kinds include ‘Crystal Fountain’ (purple with a centre filled with long, shaggy, lilac stamens) and ‘Josephine’ (stunning rosette-shaped flowers in two shades of pink), but two old classics, ‘Florida Plena’ (double greeny-white rosettes) and ‘Florida Sieboldii’ (single white with shaggy purple centres) are also great for this job.
Lift your clematis carefully out of its pot and sit it down deep in the centre of the container, then fill it almost to the rim with more compost. (It’s always good practise to plant a clematis a few inches deeper than it was growing in its original pot, as an insurance against wilt or other problems killing off delicate stems). Water well, then provide something for the stems to climb up. If your tub is up against a wall then a piece of trellis does the job nicely; for a free-standing pot, stand a decorative obelisk or rustic twiggy wigwam in the tub itself. Untie the clematis plant from its cane, untangle the stems and spread them out, then tie them back up to the supports so they cover a wide area right from the base. Once the plant starts into growth, new shoots will ‘cling on’ by themselves using their twining leaf stalks, so from then on no further tying-in should be needed.
Water well, and spread a layer of large, smooth pebbles over the surface of the compost. This has dual benefits. It helps shade the compost from direct sun, which keeps the roots cool and shady, and it helps slow down water loss – in fact, dew often condenses on pebbles on summer nights and runs down into the compost, which is also a help in a dry summer.
Being hard-working plants, clematis need regular watering and an occasional dose of liquid feed to keep them flowering flat-out all season, and in tubs they can’t afford to run out of steam so all the extra TLC helps. Because they’re worth it.