Dahlia tubers can be planted outside when the risk of frost has disappeared. Normally mid-to-late May for most of the country or early June in the north and Scotland.
If you wish to get them going earlier, then you can grow them undercover in a greenhouse, cold frame or even a porch from late March.
7 Types of Dahlias
Dark Leaf Dahlia
Dinner Plate Dahlia
Powder Puff Dahlia
Where To Plant Dahlias
Dahlias are a native to Mexico, so they like full sun with plenty of space between their neighbours.
They prefer light free-draining soil, where they are more likely to survive the winter.
Dahlias will grow on heavier soil, but you will more than likely have to lift the tubers in the autumn, so they don’t rot over the winter.
Planting Dahlias Early
In late March bed the tubers into a tray of damp compost to encourage shoots to grow before you pot them on.
Leave the tubers in the tray for the whole of April, and pot them up individually in May. Once you have potted them up, continue to grow undercover until they are ready to be planted out in the garden around June time.
How To Plant Dahlias
Dahlias are very greedy plants, so before planting improve the soil where you plan for them to live by adding well-rotted manure or fish, blood and bone.
If you want to plant your tubers straight into the ground, then they need to be planted 4 inches (10cm) deep in the soil.
If planting a dahlia that you have raised yourself or purchased, then plant so the soil level of the pot is at the same level as the soil level in the ground.
If your dahlia is already in flower when planting it is worth cutting these flowers off to conserve the plant’s energy, and you’ll be rewarded with many more flowers throughout the summer.
Dahlias should never be short of water as they are very fleshy and succulent and are mainly made up of water.
Liquid feed every couple of weeks after planting until early September.
Deadhead once flowers are spent, cutting back the stem to a leaf joint.
If you are growing a taller variety of dahlia, then you will need to stake your plant with a bamboo cane or dahlia stake.
End of Season Care
As temperatures drop so will flower productivity, and when we are hit by a frost in autumn, your dahlia’s foliage will be killed off.
It is then time to cut back your dahlia, and either leave the tubers in the ground and mulch them, if you have free-draining soil. Or lift and store the tubers if planted in heavier soil.
Storing Dahlia Tubers
When digging up your tubers, cut the stems back to 2 inches (5cm), then lift and shake off as much soil as possible. Trim off any damaged tubers too.
Allow the tubers to dry for a few days where they are free from frost and direct sunlight.
Place your tubers in a shallow crate or polystyrene fish box. Surround them with a dry potting mix.
Check on them occasionally too if they have signs of rot and discard any unhealthy tubers.
Pests to watch out for on your dahlias include aphids, caterpillars and of course slugs.
If the flowering performance is poor, check your dahlia is getting enough sunlight and is not overcrowded by other plants, and check that your plant isn’t dry at the roots.
Poor flowering and lots of foliage can also be due to being overfed with a high-nitrogen feed.