Horticulture Magazine

How To Overwinter Dahlias So They Grow Back Each Year

dahlia tubers in compost

Dahlias are beautiful flowers that many love to have in their gardens, but how can you overwinter them successfully?

It is all well and good being able to grow dahlias successfully in your garden. But it is important to know what to do with your dahlias over winter to make sure that you can keep hold of them. Overwinter them successfully and they will grow back each year. Read on for instructions to do so successfully, no matter where in the UK you live.

In warmer and more southerly parts of the UK, Dahlias tubers can frequently be overwintered successfully in your garden. This strategy may even work further north if you have a relatively free-draining soil and conditions do not become too waterlogged in winter. With additional protection over the winter months, you might not need to dig up your dahlia tubers for storage.

In cooler and wetter parts of the UK, however, dahlia tubers must usually be lifted, cleaned, dried and stored over winter before being planted back out in the garden.

Read on for more detailed information about how to overwinter dahlias successfully in the garden, or by lifting and storing them over the winter months:

Overwintering Dahlias in the Garden

pink dahlias blooming in a garden
Pink dahlias

First of all, let’s take a look at how you might be able to overwinter dahlias in your garden successfully without having to lift them out of the ground. This is a lower-maintenance option but can yield varied results. Whether or not dahlias will overwinter successfully outdoors will very much depend on the specific details of the area where you live, and even the characteristics of the particular planting spot in your garden. Bear in mind that even if you have successfully overwintered dahlias in your garden in a previous year – you could experience losses, or even lose the lot during a particularly cold winter.

Mulching Dahlia Tubers

Mulching dahlia tubers can certainly work in the south, and has even been known to work as far north as Scotland’s central belt in a mild year. A thick organic mulch can help protect the tuber from freezing as long as the temperatures do not get excessively low.

You can use a range of organic materials to mulch dahlia tubers. The most common options are dry mulches of autumn leaves, wood chip or bark. Straw, or dried bracken are other options to consider.

The mulch should be laid thickly – around 5cm thick or more. And it should entirely cover the area around the tuber waiting below the ground. This should be laid in place before hard frosts threaten, and then removed before growth commences in the spring.

Additional Protection for Overwintering Dahlias

Where mulch is not enough to protect dahlia tubers from cold winter temperatures, additional winter protection will be required. Cloches or other protective covers could potentially be used both to shield dahlia tubers from winter cold and from excessive wet.

Another thing to consider is that materials with high thermal mass (such as rocks or containers full of water, for example) can be placed around dahlias to catch and store the sun’s energy during the day and release it slowly at night when temperatures fall. In essence, what this does is create a warmer microclimate around the area where the tubers are buried in the soil.

If you would like to overwinter dahlia tubers in the garden, then choosing the right site in the first place is key. Make sure you choose a location with relatively free-draining soil, in a sheltered position which does not become a frost pocket in winter.

Lifting and Storing Dahlia Tubers Indoors

It will not be easy to overwinter dahlia tubers outdoors in all gardens. And so for more reliable results, it can often be the best policy to lift the tubers. Here are some tips to help you make sure that your dahlia tubers make it through unscathed to spring.

Lifting Dahlia Tubers

dahlia tubers that have been freshly lifted
Dahlia tubers

First of all, using a garden fork, carefully pry up the dahlia tubers from below the ground before the first hard frost. Take care not to damage the tubers as you do so. Any damaged tubers should be discarded as these are more likely to succumb to rot in storage over the winter months. It is also usually a good idea to discard the ‘mother’ tuber (the oldest, original tuber) as this is also more likely to rot than newer parts of the plant.

Cleaning and Prepping Dahlia Tubers for Overwintering

Once you have lifted the tubers, knock off any large clumps of soil, and wash the dahlia tubers to get rid of pests, soil and debris. Cut off any remaining above ground growth to a short length above each tuber.

Drying Dahlia Tubers

Next, you need to spread out the tubers on a rack, some newspaper, or another absorbent surface to dry out and ‘cure’. They should be out of direct sunlight, in a well-ventilated location. This should take around 2-3 weeks.

Storing Dahlia Tubers

dahlia tubers in a wooden crate
Overwintering dahlia tubers

Once the tubers are dry, you should prepare a box for their storage. This can be a cardboard box, or another breathable container. This container should be filled with a just-moist medium. A peat-free compost, damp sand, or damp wood shavings can all work for this purpose. Place a thin layer of this material in the base of the box, then place in the tubers carefully before covering them over with another layer of the damp medium. Store this box in a cool, dark place that remains frost-free over the winter months. A root cellar, basement or unheated garage can be a good spot.

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