When to plant Dahlias in Cardiff

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 11th March - 25th March. 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 8th April - 15th April. 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 22nd April - 6th May over 10–14 days. Put them out on mild days, bring them in at night, and keep them off frost.

Plant out from 6th May - 20th 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 13th May - 10th 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 27th May, especially in dry spells. Feed every 14 days with a high-potash fertiliser. Stop by 14th 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 8th 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 28th October - 11th 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.