Sarah Raven's Kitchen and Garden

Planting dahlia tubers is easy and will give you flowers for months at a stretch.  This is my essential guide to planting dahlias.

Planting dahlia tubers

• Begin by planting dahlia tubers (or cuttings) in March or early April, in a generous pot. Plant the tuber stem end upwards, 2.5-5cm (1-2in) deep, in a light, frost-free place.
• Keep the compost moist.
• If you don't have a suitable place to grow the potted tubers, put the dahlia tubers straight into the ground when the frosts are nearly over and, if the foliage appears before the frosts end, mulch or protect them with a cloche.
• Planting dahlia tubers is best done in sunny situations where they will thrive, but they will do best in a fertile, moist soil with good drainage.
• Dig a hole, 30cm (1ft) wide and deep, for each one, spacing them 60-90cm (2-3ft) apart. The larger varieties need at least 90cm spacings, or they will crowd each other out.
• You will need a stout stake, not just a bamboo cane, to support each plant - knock this in first and then place the plant by its side. It needs to be about 30cm shorter than the expected height of the plant.
• Put the plant in the hole and backfill with soil mixed with lots of compost or well-rotted manure, then give it a good dousing with a full watering can.
• Whether you have raised your dahlias outside or under cover, it's good to remove all but five shoots sprouting from the tuber (stem thinning). If you want to build up your stock, these can be used for stem cuttings.
• Then pinch out the tips of the remaining main shoots between your thumb and forefinger (or with a knife, see pic left) as they grow. This encourages bushy plants with vigorous shoots that produce lots of flowers.
• After about a week in the ground, scatter fish blood and bone fertiliser around the clump at the manufacturer's recommended rate, and give them another good soaking. From midsummer onwards, try to feed them every week with a liquid fertiliser that is high in nitrogen and potash. If it's dry, water them at least once a week, with a flood, not a sprinkle.
• Having put the stake in place at planting, tie the shoots in every couple of weeks, as once they get going they grow very quickly.
• When deadheading, remove the whole flowering stem, back down to a fat, healthy bud.
• In recent years, our winters in the south of England have been so mild that dahlias left in the ground, mulched deeply to protect them from the frost, have survived, bulking up and flowering well before other plants grown on in pots. Even the wet autumns and winters haven't killed my plants left in the ground.