A dedicated band of enthusiasts never lost the faith with dahlias but it is a sad fact that for too long dahlias fell from fashion. It is with great relief; actually more like joy, that dahlias are finally not only acceptable but actually embraced by gardeners.
Part of the reason for the revival in dahlias is the interest in single-flowered dahlias, often, for no obvious reasons, called ‘orchid-flowered’. I am sure that this was initiated by the popularity, several decades ago, of ‘Bishop of Llandaff’ a glorious plant with vivid red flowers and beetroot purple foliage. Many dark-leaved dahlias were then bred, leading to a whole range of ‘Bishops’ and then a range with the ‘Happy’ prefix. You can even buy seeds of ‘Bishop’s Children’ – the name of which seems wrong somehow! But they produce a range of plants in various colours and all are good.
Single dahlias are wonderful plants for pollinators and bees love them. No other plant, apart from buddleia, attracts so many butterflies.
Growing from seed
Dahlia fanciers will dispute whether growing from seed produces good dahlias and the problem is that they are unlikely to produce large, double flowers on tall plants – the kinds you see at flower shows. But they will produce perfectly acceptable garden plants with single flowers. Personally I would not bother with seeds of tall, double kinds no matter how good the photo looks. But it is a good way to grow the dwarf, double kinds and dahlias are easy to grow from seed. Because the seedlings grow so fast I would delay sowing till early April. The seeds are large and flat germinate fast. Avoid overwatering and grow them in good light. I sowed some tall, single seeds I had collected last year. I had forgotten I had them and did not sow them till June but the plants all flowered in September and flowered till the frost. I marked the best and have saved the tubers.
Growing from tubers
Tubers are the only way to grow the big, bold doubles. Unlike from seed, you can be sure of exactly what you will get. As mentioned above, all dahlias make tubers and even if you grow some from seed they will make tubers that you can keep and grow the next year.
There are two ways to treat tubers you buy. The simplest is to plant them in the border where they are to grow. Dahlias are not hardy so it is best to wait till April to plant so that shoots do not emerge till May. A tuber consists of a stem with fleshy tuberous roots below. These thick roots do not sprout – the shoots come from the base of the old stem so any tubers that get broken off will not grow – they are just to store food for the plant. (oddly, if you do plant the broken off tuberous roots they will make roots but will never produce shoots)
A better way to start dahlias is to put them into pots (photo above). Plant them so the top of the fleshy tubers is at compost level. Keep them warm and moist, in light, and you will soon see green or purple shoots. If several shoots appear you can cut the tuber in half, slicing vertically through the old stem. The two halves can then be repotted to grow on: two for one.
If you are very adventurous you can remove the shoots when they have grown a bit bigger and root them as cuttings, but let’s stick to basics.
By starting the dahlias early like this you can plant them out, in late May, and they will flower earlier than just planting the dry tuber. And, unlike gladioli and lilies which only produce one set of flowers, dahlias bloom on and on until the first frost of autumn, making them wonderful value.