Starting off dahlias

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Dahlias are stars in the summer and autumn border and the smaller varieties do well in pots, too. Although you can plant the tubers straight into your border, I prefer to start mine off in pots for planting out after last frosts.

This has a few advantages: first of all an earlier start means earlier flowers. By starting off tubers now, I often have flowers by June and with a little care they keep flowering until October or even November. Secondly, slugs love to nibble the first shoots. By starting dahlias off in pots I can control their environment much better and since good sized specimens will be planted, they are less susceptible to slug and snail attack. Last but not least, dahlias are half hardy and will be spoilt by an early frost. Starting them off in the shelter of a greenhouse (or even indoors) means a reduction in risk to frost damage.

Armed with my stored tubers, plastic pots of varying sizes, cardboard, compost, plant labels and marker pen, the fun can commence.

In previous years I used to start off dahlias at the end of February or early March at the latest. I gave up most of the space in my study for them. As I look after so many gardens now (and most of them have dahlias), this solution no longer works for me, so this year the potted up tubers will go in a growhouse.

My stored tubers: most tubers have now shrivelled up and the stems have dried out altogether. I check each plant for soft/rotten tubers which should be removed before planting. Luckily this does not happen often as I let my tubers dry out slowly before I store them for winter.

Some tubers are starting to sprout "eyes". These will become long green shoots once exposed to sufficient light.

Choose a pot just big enough to hold the tubers. They can be shallow pots, too as you don't need to plant them deep at all. In fact a bit of tuber showing is no problem. In addition, I am lining my pots with thick cardboard. As dahlias don't need much water in the early stages, the drainage holes in the pots are not needed. If you start off your dahlias indoors, the cardboard inserts (cutting up my storage cardboard boxes) will prevent compost falling through the bottom and making a mess of your floor.

Last but not least check that the label is attached to the old stem. Once sturdy new stems have formed, I move the label onto the new stem. The old stem often falls away during the season. The spindly bits of dried root on the tubers can be cut away if you like your pots tidy...

They need very little water until proper shoots have formed and will be alright as long as the compost is not drying out altogether. No feeding is required as the tubers are the plants natural food storage and most compost commercially available will have nutrients added. Within 6 - 8 weeks the tubers will be ready to be planted into their final position, either in the border or in a decorative planter. 

You can multiply your dahlias by taking cuttings, I will come back to that in good time....