Dahlias are easy to grow, they come in a profusion of shapes, sizes and colours, flower from summer until late autumn and you can both propagate new dahlias from existing stock and grow them from seed. However, they have two big enemies which can render growing them challenging - frost - they are tender and frost will kill young dahlias if you plant them out too early - and slugs and snails.
I have a tremendous battle each year to help my dahlias survive the spring onslaught of mean little molluscs which munch their way through the fresh young leaves. I have tried everything - chemical warfare, copper rings and tape, jam jars full of beer and night time patrols to pick off the little blighters before they do too much damage (and then what do you do with them once you have collected a bucketful?).
Ever the optimist - I am about to start my annual dahlia challenge yet again.
This week I sowed some dahlia seeds in a heated propagator - I like a selection called Bishops' Children which are easy to raise and which flower in their first year. (I got mine from Promesse de Fleures - www.promessedefleures.com) The flowers are a mixture of rich oranges, yellows and reds and they have have the characteristic dark foliage of the taller Bishop series of dahlias (Bishop of Llandaff being the first and, in my view, best of the lot). At the end of year one you can lift the tubers and store them for the following year, when they will be bigger and better. Once the seeds have propagated I will transplant them into small pots and keep them in a frost free environment until the end of April/early May when I will plant them in the garden.
Bishops' Children are also single flowered dahlias (see picture above) which means they are most attractive to pollinators. The more pom-pom like or petal filled flowers are much less attractive to them.
Although beautiful to look at, these dahlias on the left, with tight heads of petals, are not as attractive to pollenating insects.
This year I have also bought two new varieties of dahlia as dry tubers. They are available in all garden shops at the moment as now is the time to start them into activity for the coming summer and autumn. To add to these I also have some tubers which I have overwintered from last year. One variety - Art Nouveau - I dug up, allowed to dry completely and then stored packed in bamboo chaff in a frost free environment. The others, Bishop of Llandaff, I left in the ground (in a very sheltered spot) with a heap of bamboo chaff over the top of them. We have had some heavy frosts, so I am curious to know if they have survived.
Dahlia tubers look particularly unpromising when you buy them or unearth them from their winter storage - a little bit like some over-dry and dusty saucisson held together at the top with a bit of old sausage meat casing (this is the old stem).
On the left is one of last year's Art Nouveau tubers which is now ready to plant for the coming summer.
Have faith - plant your tubers (any time from now onwards) in a pot. If you plan to leave the dahlias in the pot for the entire season, then choose a pot which is at least 30cm x 30cm for each tuber and invest in the best quality compost you can, as dahlias can be very vigourous. If the pot is temporary then it can be smaller and the compost more basic. Half fill the pot to comfortably accommodate your tubers with the potting compost and stand the little bunch of them on the compost with the stem uppermost. Cover them completely with more compost. Water once, label them and then keep them in a frost free place in a shed or greenhouse until they start to show green growth above the soil. Once you see this initial growth you can move them into the light (but keep them frost free), start to water them as necessary and commence your preferred means of anti slug protection. Aim to keep the growing dahlias nice and bushy - pinch out the centre of the growing stems to encourage side shoots and don't allow more than half a dozen stems to develop. Once you are happy that there will be no more frost either transplant them from the pot into the ground or move the pots outside for the summer.
If you are happy to take the risk of a late frost, or you accept that the first flowers will be later in the summer, then you can skip the planting in a pot stage and plant the tubers directly into the ground in the place in which they will ultimately grow and flower. However, wait until April before you plant the tubers directly into the ground and then follow the same principles as you would for planting in a pot.
Dahlias need to be in a sunny but sheltered spot. The soil should be nutritious and well drained - so add organic matter/compost and, if the soil is heavy, then mix in a little grit to open it up.
You can also propagate more dahlias from last year's tubers and so increase your stock. When the tubers begin to sprout, use a clean, sharp knife to slice off a section of the tuber which has sprouted one or more healthy shoots (these should be established shoots - so about 10cm long). Pinch out the central growing tip to help the plant develop side shoots and also remove all of the remaining leaves except the top pair (this is to minimise water loss due to transpiration while the roots have a chance to develop). These are called basal cuttings. Partially fill 1 litre plant pots (i.e.13cm in diameter) with a grit and compost mixture and put a couple of basal cuttings in each one - position them at the edge of the pots and make sure they do not touch one another. Then top up the compost/grit mix so that the leaves are just above the level of the compost and water well to bed everything down. Label each pot. Put them in a bright, warm spot (but not in direct sunlight which will cause them to transpire to strongly) - you can use a heated mat if you have one. Once the roots have formed (in about a month's time) transfer to individual pots - and label them individually. Plant out after the risk of frost has passed. They will flower later than an uncut tuber, but they will still flower this year and at the end of the season each will have developed tubers which can be stored for the following year.
During the growing season do not allow your dahlias to dry out and, if they are in pots, feed regularly. Depending on the variety they can grow to over a metre high and so are hungry, thirsty plants. To keep them flowering deadhead regularly - which could mean every day at the height of the season. They will flower until the foliage is blackened by the first frosts - at which point you need to dig them up, remove the dead foliage, dry them off and then tuck up in a frost free place for the winter.
Here is a photo of mine - this weekend I will take them out of their winter storage and pot them up for summer 2022.
They also make marvellous cut flowers and the petals are edible (as are the tubers, so I am told).The petals taste of carrots/apples and make a colourful addition to salads.