How I’m Overwintering Dahlias This Year

Written by Hannah Miller. Checked by Daniel Woodley. Published to Blog on the 3rd November 2023.

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For the last 5 years, we’ve been growing dahlias in our garden and as the winters are so unpredictable here, we’ve taken a cautious approach to overwintering the tubers. So far it’s worked really well and our stock of dahlias has grown considerably.

For those of you new to gardening; dahlias grow from tubers that look like long potatoes and are very sensitive to frosts and cold weather.

In cold climates, they should be lifted from the soil and stored over winter.

The climate where I live is mild but unpredictable so each year I’ve lifted and stored half of the dahlias and the remainder, I’ve left in the ground.

So far, so good and I’ll be doing the same again this year.

Anyway, here’s how I go about lifting and storing them:

A bunch of dahlias lifted from our garden

A bunch of dahlia tubers lifted from our garden

Step 1: Timing

To ensure the dahlias are strong enough to survive the winter, timing is crucial.

I’ll wait until the first frost has blackened the foliage of the dahlias, and then I’ll wait about a week as the tubers will start to harden up if they are left a little longer in the ground.

Then I’ll lift them, one by one:

Step 2: Use a Fork, Not a Shovel

First, I’ll cut the stem about 12 inches from the ground – this gives me something to hold onto.

I’ll use a garden fork and not a shovel to pull them out of the ground, as I want to reduce the risk of slicing the tubers.

I usually work around the edge of the dahlia in a clockwise direction, gently lifting the bunch an inch at a time.

If the ground is hard, I’ll soak it with water the night before to loosen it up.

Step 3: Preparing the Tubers

Once I’ve lifted the tubers, I’ll give them a gentle shake to loosen off any excess soil and will then go over them with soft brush.

Next, I’ll store them upside down on cardboard on the garage floor for a few days, up to a week.

This gives them time to dry out – I don’t want to put wet dahlia tubers into storage as this will increase the risk of rot or fungal infection.

After they’ve dried, I’ll then give them a final brush-over to loosen off any remaining dirt.

Dahlia tubers in my hand

Me preparing the tubers for overwintering

Step 4: Preparing The Boxes

Next, I’ll cut the stems to about an inch or so above the tuber bunch.

Then I’ll wrap them in loose newspaper as this will insulate them and place them into cardboard boxes (one dahlia tuber bunch per box, making sure they don’t touch other tubers) with a hole cut into each side for ventilation.

In the past, I’ve used sawdust, vermiculite, peat moss and even clean airy compost.

As long as the insulating material is clean and well-ventilated, I’ve found that it will be fine.

Step 5: Storing The Boxes

We have an attached garage with one wall up against the side of the house and this will be the warmest part of the garage, so I’ll stack the boxes here, ensuring there’s adequate ventilation on each side of the box.

The ideal temperature for overwintering dahlias is between 40-50°F (4-10°C) so the garage is the best place within my property.

Too cold and the tubers may die, too warm and they may start sprouting early.

Other good places to store them are:

  • Basement.
  • Unheated indoor porch.
  • Unheated utility room

Step 6: Monthly Check

I’ve never had any major problems with rot or fungal infections but I check the tubers every month during the winter and remove any that have gone squishy or look obviously ill.

That’s it. That’s how I lift and store my dahlias over the winter.

As I stated in the introduction to this page, I only lift half of my dahlia tubers and leave the others in the ground as I live in a borderline area – it’s not always cold enough to damage the tubers but sometimes we get a few days of very cold weather.

I guess you could say I’m hedging my bets but so far, all my dahlias have survived, including the ones I left in the ground.

If You Want to Leave the Dahlias in the Ground: Do This

Whether you can leave your dahlia tubers in the ground over winter or not will depend on how cold and frosty the winters are in your area.

If you do leave them in the ground, I suggest laying about 6 inches of mulch over the soil to give them some added protection from the cold.

I have done this for the last 5 years and it’s done its job.

What I Won’t Be Doing This Year

I won’t be doing this at all this winter:

Washing The Tubers: This can help to remove soil and pathogens and some reputable organisations recommend it, but also soaks them which means it will take longer to dry them out and increases the risk of them rotting in storage. There are pros and cons to washing dahlia tubers but I won’t be washing them this year. I’ve done a few experiments (washing some and not others) and so far, I see no benefit to washing them as I’ve never had issues with fungal infections.

Wash or Dust With Fungicide: This is entirely optional and probably only worth the effort if you’ve previously had problems with fungal infractions killing them off in the winter. I’ve found that if stored correctly in a dark, well-vented box at the right temperature, fungal infections do not develop.

Separating The Tubers: I will put the entire tuber bunch into the box as I’ve found it very hard to find the eye on the tuber when they are fleshy. It’s much easier in the spring when they have shrivelled (for beginners: Dahlias only grow from tubers with an “eye” and this can be hard to locate in the autumn).

That’s it – Thanks for reading!

Meet The Author: Hannah Miller

Hannah is a former NHS administrator, mother of two and keen gardener with a horticulture qualification who loves growing new plants and experimenting in the garden.

She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.

This year is all about pollinators, and Hannah has set herself the goal of only buying new plants that attract pollinators; she aims to make the garden as bee and butterfly friendly as possible.

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Hannah Miller wrote this guide to lap vents. Hannah has a horticulture qualification and has been growing dahlias for 5 years. The photos of the tubers were taken in her garden within the last few years.

As accuracy is important, we asked Daniel Woodley to review and fact-check and review any claims made in this guide.

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