Storage through winter

Dahlia tubers want cool, dry, dark and frost-free conditions. A garage, unheated spare room, cellar or frost-free shed all work. The target temperature is 4–10°C. Below 4°C and tubers freeze; above 10°C and they start sprouting prematurely. Humidity is the enemy. Damp air encourages mould, shrivelling paradoxically comes from damp storage where tubers try to grow and exhaust themselves.

Pack tubers loosely in shallow wooden or plastic crates lined with newspaper. Do not pile them deep. You want to inspect them monthly without excavating. Some gardeners pack tubers in dry sand, vermiculite or wood shavings. This works but is not essential. What matters is air circulation and the ability to check each tuber quickly. If you pack in medium, make sure it is bone dry.

Check your tubers every three to four weeks. Look for shrivelling, mould or premature sprouting. Shrivelled tubers can sometimes be saved by misting lightly with water and improving humidity slightly. Mouldy tubers should be discarded. Tubers that sprout in January can be potted up and grown on under lights, though they will be leggy. By late March you can move them to a cool greenhouse to harden off. In late April or early May, when soil temperatures hit 12°C and the risk of frost has passed, plant them back out. Each tuber you saved in autumn becomes a summer's worth of cut flowers.