Dahlias: One for the Pot
Susan Rowe

Enthusiastic gardeners like their borders to look good throughout the year and even hardy planters turn to half-hardy plants from time to time to fill gaps and ensure continuity of display.

A few years ago dahlias were deeply out of fashion, but since they were re-popularised by Christopher Lloyd, who used them to great effect in his exotic garden at Dixter, more of us have been willing to give them a try.

They have a lot going for them. They come in a wide range of colours and flower forms, and bloom reliably from mid-July until they are cut down by the first frosts. They are planted out in late May/early June – just at the time the spent foliage from the daffodils is cleared away, so they are obvious candidates to fill those spaces. Some of them even have attractive dark foliage too.

So far, so good, but their problem is that they are not reliably hardy. Some have come unscathed through the mild winters that we had until recently, but the last two severely cold spells have seen them off.

Standard advice is to lift the tubers in late autumn, dry them off and store them in a frost-free place during the winter. This is easier said than done.

Problem number one is that when lifting the plants some seem to have made no tuber at all, whilst others have developed massive great things – like dinner plates with tentacles. These huge tubers pose a problem in finding space to dry them off and then store them. They don’t fit into pots and boxes. Problem two is that during the winter some tubers will insist on rotting off despite all the TLC you have given them. Problem three is that when the time comes to start them into growth in early spring they take up a lot of bench space in the greenhouse just at a time when you need it most for other things.

There is, however, a trick to overcome these problems and I wish I had discovered it sooner. The answer is to grow ‘one for the pot’.

Have you ever wondered why the dahlia tubers in packets that are sold in the garden centres in spring are small, shrivelled things that bear only a passing resemblance to the tubers you have dug up? This is because nurserymen have manipulated the growing conditions to make the plants produce small tubers – and we can do the same.

In spring dahlia tubers begin to send up new shoots. These can be taken as basal cuttings and they root quickly and easily. In fact, dahlia exhibitors will tell you that the best plants come from cuttings. When the cuttings are rooted and potted on, one is set aside as a stock plant. This is potted into a 10cm (4”) plastic pot in gritty compost without additional fertiliser. At planting out time this pot is sunk up to the rim in a spare piece of land – in my case, on the vegetable plot. The plant may need watering until growth shows that it has put roots out through the drainage holes in the pot into the soil. When the flowers open, check that the label is correct, and then cut the plant down to about 30cm (12”). This encourages it to develop lots of future growing points on the crown of the developing tuber. During the growing season the plant will remain small and a bit stunted. In autumn the plant is cut down in the normal way and the pot is lifted and cleaned off. The tuber will have developed in the pot and be contained within it. These stock plants in their pots can then be stacked on their sides in a dry frost-free place and take up very little room. The tubers have not been disturbed and so they should be untroubled by rots. The chances of getting tubers through the winter are enormously increased if they are grown and stored in this way.

When spring comes the tubers are given water, light and warmth and will produce the shoots you need for your next lot of cuttings. Some people re-pot the tubers into better compost before starting them into growth though this is not absolutely necessary. If you take the cuttings carefully without damaging the crown of the tuber, it will respond by producing a second lot of shoots. Then, after a week or two, you can harvest another crop of cuttings.

No method of overwintering dahlias is fool-proof, but growing ‘one for the pot’ has worked for me. I have managed to hang on to my favourite varieties and grow enough to fill those late summer gaps.

Finally, a word on dahlia flower size: if you are buying new plants for the garden stick to those that describe themselves as ‘small’ or ‘miniature’. Flowers on these plants are between 52mm and 152mm (2” to 6”) – anything bigger is susceptible to weather damage, particularly from the wind. These glorious but seriously large flowers are best left to the dedicated exhibitor who will give them the protection and cosseting that they need.

First published in the East Yorkshire Group Newsletter November 2012
and subsequently in Cornucopia Issue 34.
© Copyright for this article: Susan Rowe

This article was taken from a copy of Cornucopia that was published in 2014. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.