Plant Dahlia imperialis outside after frost, or start off in pots under glass in late winter to early spring. Plant tubers horizontally approximately 12cm (5in) deep, making sure the growing points (‘eyes’) are uppermost. Allow plenty of room between each tuber so the plants can grow and spread to their full size without being overcrowded. While in growth, provide a high-nitrogen liquid feed each week in June, then a high-potash fertiliser each week from July to September.

Stake with a cane as it becomes necessary (it may be worth installing a sturdy stake when planting to avoid root disturbance). In mild areas, leave tubers in situ over winter, but protect the crown with a generous layer of dry mulch. In colder areas, carefully lift and clean the tubers once the first frosts have blackened the foliage and allow them to dry naturally indoors. Then place the dry tubers in a shallow tray, just covered with slightly moist potting compost, sand or vermiculite and store in a frost-free place until planting out again.