Dahlias are the best value of all the summer bulbs. They flower from July till the frosts of autumn and their flowers can be single or double in a wide range of colours. You can also get small dahlias, ideal for patio pots or tall kinds for large borders and cutting.
You can grow the small kinds and those with single flowers from seed but most are grown from tubers. These are available now and sold in packs with colourful photos that show the flowers. But they don’t show the height of the plants so check the height of the mature plants on the back of the pack.
Packs may contain one or more tubers and each one will produce at least one plant. The simplest way to treat the tubers is to plant them straight in the garden or in a patio pot. Unfortunately dahlias are killed by frost. If the shoots are frosted or if the tubers are frozen they will be killed. It is for this reason that dahlias are usually dug up in autumn and kept frost-free in winter.
If you leave the tubers in the ground, they may survive till the next year, if the tubers are not frosted in winter. The other problem is that shoots may start to grow early in spring and get frosted if there are late spring frosts.
When you buy your tubers you can plant them in the garden or in patio pots, where they are to flower. But because of the danger of frost it is best not to plant them outside till late March. Keep the packs somewhere cool and dry until then and then plant them so the tops of the tubers are about 8cm (3in) below the soil surface so the shoots don’t emerge until at least a month later and then, if they do get frosted, the tops of the tubers themselves will not be frosted.
It is far better to start the tubers into growth, on the windowsill or in a greenhouse first, in pots to get them started, and then plant them out, in May, already growing.
Pot the tubers into the smallest pot they will fit into. The tubers do not need to be buried and the shoots will grow from the base of the old stem. If there are broken tubers you should trim these off. Shoots will not grow from the tubers themselves – these are purely food reserves.
Water the tubers sparingly at first and keep them in good light so the shoots are sturdy. Remember that you can’t plant these out until May, when there will be no more spring frosts so there is plenty of time!
When the shoots are about 8cm (3in) high, you can take cuttings. These have to be removed with a sliver of the tuber at the base and if you are not confident it is probably best not to bother.
But you can cheat and get more than one plant from each tuber a simpler way. Carefully take the tuber out of the pot and use a sharp knife or secateurs to cut the tuber into pieces so each has a piece of tuber, which will have fresh, white roots by now, and at least one shoot. You should be able to divide each tuber into two or three pieces. Then pot these individually and grow them on. You now have at least twice as many plants!
There is no disadvantage to this because if the tubers are allowed to grow as a cluster of shoots these often get too crowded – having plats with just one or two shoots results in better plants in summer.
But you should nip the shoots back and once they have two or three pairs of leaves you should pinch out the tips. It will delay flowering slightly but you will get more flowers.
You can then plant out in May. Dahlias like rich soil, and lots of sun and moisture. And they like lots of feeding in summer. If they are in pots you should give a liquid fertiliser every week. In the border they need a general feed at planting time and then every six weeks or two months to keep them growing and blooming.
Dahlias have so many good qualities we should all grow them! There are dahlias for every taste but the single-flowered kinds are deservedly enjoying a big boost right now. Their simple flowers look good in a mixed border and they are perfect for attracting insects to the garden. Bees, hoverflies and butterflies love their bright flowers from July to October.
