Overwintering Dahlia Tubers in Frost Prone Areas

Dahlias are one of the most popular and versatile of ornamental flowering plants. They have a long history as garden plants; today there are over 50,000 different dahlia varieties in cultivation and they come in a huge range of shapes sizes and colours. They are generally easy to grow, but only half hardy and some gardeners are deterred from growing dahlias by the need to protect them through the winter. However, overwintering dahlia tubers is quite straightforward, and in many parts of Britain no special treatment may be needed.

Growing Dahlias in Their First Season

Dahlias will grow in almost any situation, and dahlia cultivation is quite easy. However, they give the best result in full sun and a good loam soil enriched with plenty of organic matter.

Dahlia seeds are available in a limited range of varieties. However, since dahlias don’t breed true from seed, most varieties are normally sold as tubers (some people know them as dahlia bulbs) or pot grown cuttings.

Treat them as half hardy bedding plants in their first year, starting the tubers into growth under glass, and not planting out seedlings, rooted cuttings or sprouting tubers until after the last frost.

When the first autumn frosts return, further action may be needed to protect your dahlias through the winter. There are two possible solutions.

The Traditional Method of Overwintering Dahlia Tubers

The traditional solution is to lift and store dahlia tubers as follows:

• After the first frost has blackened the top growth, dig the tubers up carefully, trying not to damage them with the spade or fork.
• Brush, or if necessary wash off any caked soil – but leave them for a few days to dry off thoroughly before storing if you wash them.
• To increase your stock, divide clumps with a sharp knife, leaving a section of the old stem with each tuber.
• Dust lightly with sulphur powder to protect them against rot and mildew, and cover them with dry sand, soil compost or sawdust.
• Put them in a cool dark place, as described under cultivation, and check them every couple of weeks, throwing out any showing signs of rot.

The Easy Option

If this all seems a bit too much like hard work and your soil is well drained and not too heavy, simply cut down the top growth after the first frost and leave the dahlia tubers in the ground through the winter. In colder areas, cover the ground with straw or black plastic sheeting for extra frost protection.

Many gardeners now grow dahlias successfully like this except in very cold areas of Britain. However, it’s still wise to lift and over-winter a few tubers of rare or highly prized varieties as a precaution.