When to plant Dahlias in the UK

Sit the tubers in trays of moist compost, eye-side up, and cover lightly. Keep them at 15–20 °C in a bright spot from late March to early April. Water sparingly until shoots appear.

• Only moisten the compost if it feels dust-dry. Overwatering at this stage quickly causes tuber rot. If the tuber arrived soft, dry it for a day before potting.

When shoots are 5–10 cm tall, pot each tuber on from mid-April to early May. Grow them on in a bright, frost-free place.

• Support the tuber from underneath when potting on, not by the shoot. The shoots snap if you use them as a handle.

Harden off from early May to mid-May over 10–14 days. Put them out on mild days, bring them in at night, and keep them off frost.

Plant out from mid-May to late May after frost, in well-drained fertile soil in full sun. Space plants 60 cm apart and water in. Use fleece if a cold night is coming.

• Set the potted-on tuber so its top sits at soil level. Do not bury the neck; that is for dry tubers planted straight out, not plants started indoors.

Stake at planting. From mid-May to late June, pinch the growing tip when plants reach 30–40 cm so they bush out.

• Tie main stems to the stake every 30 cm with soft garden twine in a figure-of-eight. That stops them rubbing and snapping in the wind.

Keep the soil moist from late May, especially in dry spells. Feed every 14 days with a high-potash fertiliser. Stop by early October.

• Once the soil is warm, apply about 5 cm of leaf mould or compost, leaving a gap around the stems so they don't rot at the collar.

Take spent flowers back to a leaf joint from mid-July. That keeps new buds coming.

• Spent dahlia flowers have a pointed, cone-shaped seed head. New buds are round and firm. Don't pinch the wrong ones.

After frost blackens the foliage, cut the stems back and lift the tubers from late October to early November. Dry, label, and store them frost-free in dry compost or sand.

• Lift with a garden fork, not a spade, so you don't spear the tubers. Dry them upside down for a few days so moisture drains from the hollow stems.