Are you planning to lift your dahlias this winter, or take a chance and leave them in the ground? Tamsin Westhorpe helps you to make the right decision
THANKFULLY, we have all come to our senses and dahlias are firmly back in fashion. Why would a plant that produces a rainbow of colours from summer to autumn ever be out of favour?
What puts many gardeners off these incredible plants is the thought of having to lift and store them over winter. If you aren’t a risk-taker, then lifting them is probably wise. Your decision should also be based on your soil type. If you live in the South of England and have a well-drained soil, then leaving them in the garden is fairly low risk.
If, like me, you have a heavy clay or a waterlogged soil, you should consider storing them under cover.
How to lift your tubers
Dahlias shouldn’t be lifted until the foliage has been blackened by the frost. Once Jack Frost has hit, cut off the old flower stems to leave about 2in (5cm) of stem at the base. Before lifting, make sure you have a system for labelling your tubers – otherwise, you won’t know what to put where when it comes to replanting them.
Use a garden fork rather than a spade. Carefully lift the tubers and then remove any excess soil, but don’t be tempted to wash off the soil. At this point, you’d be wise to cut out any rotting tubers.
The next step is to dry the tubers – miss this step and your tubers are likely to rot. If you have only a few dahlias, make a wooden frame (like a large picture frame), cover it with chicken wire and nail the wire in place. Sit the frame over the top of an old wheelbarrow, place the tubers upside down onto the wire, and wheel the barrow into the sunshine or sunny porch or anywhere that’s dry.
The reason for placing the tubers upside down to dry is to allow any water to drain out of the hollow stems. The barrow makes it easy to move your dahlias into a sunny spot or bring them in before rainfall. This frame can also be used in the summer to dry your onions on the barrow, as it allows air to circulate and speeds up the drying process.
Where to overwinter
I am lucky enough to have a cellar that remains at a constant 6°C, so the dry tubers are placed here in old shallow apple crates. The roots are covered with dry compost (I use the old compost from my summer bedding containers), making sure that the crowns are left exposed.
I then forget about them until the spring, when they are either potted up and put in the greenhouse to get going early or planted out into the garden in May after the last frost.
If you don’t have a cellar, then choose a dark, frost-free, dry place and make sure it’s free of rodents. Your garden shed might be dark but not necessarily frost-free, so on cold nights cover the dahlias with newspaper for an extra layer of protection.
Leaving them outside
If you grow your dahlias in a cutting garden in a row or block, and the soil is well drained, it’s easy to cover them with a mulch instead of lifting them. You’ll need to add a mulch of at least 21⁄4in (6cm) deep. In the past I have used Strulch (8 strulch.co.uk), which is a mulch made of chopped straw. When you have the odd dahlia in a mixed flower bed, it’s not so easy to mulch them.
Don’t make the mistake of cutting your dahlias back once the flowers have faded and then leaving the mulching until later, as you’ll forget where they are. I always pop a short cane behind each plant to mark the spot.
One thing is for sure – whatever you decide to do, dahlias are worth that little bit of extra effort.
Dig up dahlia tubers for storing over winter once the foliage has been blackened by frost