Named after Dr Anders Dahl.
There is a Tree Dahlia that flowers at Christmas.
Dahlia Imperialis grows up to 18ft high.
Open centred Dahlias are better for wild life.
Propagation.
Dahlias can be grown from own saved seed, but they don’t come true to type.
Cuttings can be taken in the spring when growth starts. You need to cut a small amount of tuber with each shoot, apply rooting hormone, pot up and keep in a propagator or put poly bag over pot. You may need to spray mist in the first few days. When there are signs of growth, pot on to individual pots when needed. Remove central stem from cuttings to produce more stems. If you have a big tuber you can divide it. Wait until you can see new growth and then cut into sections with at least one shoot. Dress any cuts with yellow sulphur dust and then pot up.
Lifting and storing Dahlias.
Lift after frost has blackened tops, cut off tops, shake most of the soil off and place in frost free environment upside down to dry. Dust tubers with yellow sulphur powder, especially on any damaged tubers, before putting in boxes of compost right way up with the stems just showing.
I store in boxes lined with newspaper in a mix of cheap compost and vermiculite (approx 10:1). A cheap form of insulation is polystyrene tiles placed under and around the boxes. In very cold weather you can also throw over horticultural fleece but don’t use bubble wrap over the top, as this does not allow any air into the box and the tubers could rot. Bubble wrap is ideal for lining greenhouses to provide extra insulation in winter. Check during the winter and if the compost becomes too dry, give a light watering on a frost free day. Also remove the fleece to allow fresh air to circulate or mould can develop.
Around mid March start to apply some water to encourage growth.
In April I put the tubers into big pots with good compost to give them a good start before moving them outside on sunny days to harden off before planting out in late May – June. If you have free draining soil and wish to leave in the ground cut back after the first frost and provide an insulating mulch of compost or bark. You will need to apply slug protection early in the spring.
Pest and Diseases
Virus - yellowing of the plant. (Destroy plant don’t compost.)
Powdery Mildew – spray.
Earwigs – only a problem if growing for show. My Grandfather use to put inverted flower pots stuffed with folded newspaper on canes by each Dahlia he would then shake the earwigs out into a bucket and feed to the chickens! If you want to use as cut flowers, cut the Dahlia flower, hold upside down and shake vigorously to dislodge insects before taking inside the house.
Slugs - use any method that you find works. I use organic slug pellets and nematodes in the garden.
Dahlias are heavy feeders; good garden compost can be incorporated into the planting hole along with a high potash fertilizer, Vitax Q4, a Rose fertilizer or for organic gardeners Blood, Fish and Bone. A second application will be needed later in the growing season to keep them flowering. If grown in pots use a slow release fertilizer and some water retaining gel.
Except for dwarf varieties, Dahlias will need staking, a good method is to tie a piece of string to a stake and then loop the string around each of the main stems and tie back to the stake.
Dead head during the flowering period and you will have a good display all summer.