Lifting and storing dahlias for winter

Lifting and Storing Dahlias for Winter

We learnt earlier about how to protect plants left in the ground over winter. Now we'll look at another option - to lift and store plants indoors, using dahlias as a common example.

The traditional way to overwinter dahlias, which are from Mexico and Central America, is to lift them.

• With winters being a bit milder, it's becoming possible to leave them in the ground in mild areas, with some protection. We will still lift them from the cutting garden.

The Right Time to Lift

Wait for the stems and leaves to be 'blackened' by frost. It's the tubers we want to protect.

• If you don't have frost first, the tuber still feels like it should be growing.
• Waiting as long as possible before lifting allows the tuber to keep on gathering strength to get it through the winter.
• The frost then stops the growth of the tuber (without killing it).

Now, in late November, we've had a couple of frosts and the stems and leaves have gone brown, so it's an ideal time to lift.

Growing Dahlias for Cutting

We try to use mainly cultivars from Vita's time, i.e. before 1962. Some of the dahlias we grow for cutting include:

• Dahlia 'Cafe au Lait', the queen of dahlias (bred in 1968)
• Dahlia 'Pontiac' (1958)
• Dahlia 'Requiem' (1952)

For the cutting garden we plant three tubers of each variety in a triangle, with the trios all forming a long row.

We have a row of stakes on either side of the row of dahlias, and then we put a string round all the stakes to hold the dahlias in place.

• We use chestnut stakes - a fantastic wood that we use a lot of for staking where the stakes need to be here longer than just a season.
• Hazel lasts one year, chestnut will last at least two or three years as it's naturally oily.

Lifting the Dahlias

It might seem scary, but lifting dahlias is a simple process.

1. Cut off the top growth down to a few inches. This stops us losing track of where the plants are and also provides handles to hold while dealing with the plant.

1. Use a fork to lever up the tubers, but put it in some way away from the stems to avoid spearing the tubers. You might need to lever the clump upwards from a few directions.

1. Once the clump feels loose, use the stems to pull up the whole plant and knock off the excess soil.

• One tuber planted at the start of the season has become a whole clump of tubers. You can either clean off and divide the clump now to make many more plants, or store it over winter and divide it in spring.

1. Use a tray or barrow (I line mine with a hessian sheet) to take these for dividing and boxing up for winter, being careful to keep different varieties separate and/or labelled on the way.

Storing the Dahlias

You can't store dahlia tubers straight away after lifting - they have to be dried first.

1. Bring the clumps of tubers into the greenhouse and lay them down on their side so that any moisture drains away out the top of the old stems.

1. You don't want them to dry out completely and start to lose turgidity or shrivel, so keep an eye on them - it should take around a week.

1. Then, it's time to store them. You'll need a box or crate and a material to surround them - we use bark. Put an inch in the bottom of the crate.

• The ideal material is something that doesn't make the tubers moist again, but also doesn't make them dry out further.
• As well as bark, other examples include newspaper, sawdust or vermiculite - anything that keeps them stable.

1. Cut off the stem stubs, which are no longer needed. Arrange the clumps of tubers in the crate without them touching.

• I use stackable crates, so I make sure the tubers are below the level that the bottom of the next crate will sit at to avoid squashing.

1. Cover the tubers with bark. They don't have to all be covered - they're still being protected and being kept not too wet, not too dry.

1. Make sure to put a label in the crate.

1. Keep them in a garage, in the greenhouse under the bench, in a garden shed that isn't too cold, or somewhere else with a temperature of around 4-10 degrees.

• Anything colder could potentially damage the tubers, and warmer temperatures would start them into growth.

1. Leave them until February, and then take them out of the bark, divide them and pot them up in the greenhouse.

We always divide in spring, but you can also divide in autumn.

1. Wash the soil off the tubers when you lift them so you can see what you're doing.
2. Dry the clump as above
3. Divide the clump into separate tubers and store the individual tubers as above.

Further Resources

RHS dahlia growing guide: how to plant, propagate, overwinter and care for dahlias