Allotment // Overwintering Dahlias

One of the questions I’m asked the most at the moment is, “what should I do with my dahlias over the winter months”, aka To Dig Or Not To Dig. Everyone knows that you have to do something with them but which is best. Well, I don’t think there is necessarily a best way so I thought it might be helpful to list some of questions I asked myself before I decided which was better for my garden or allotment. Just so you know, I’m planning on digging mine up and once I’ve finished listing the questions I think it’ll be clear why!

1. What are my options?

Digging them up or mulching them over.

Digging them up, and safety storing them (another post on that to come later!), is the only way to completely guarantee them not getting ruined by a frost. I’ve never tried the mulching option so can’t give too much advice on that but you would have to mulch reasonably thickly as you want to eliminate the risk of frost penetrating the ground and getting to your tuber if you can.

There is a third option which I hadn’t heard of until earlier this week when we visited Anglesey Abbey. They had their dahlia plants in plastic pots which they had sunk into the ground in their borders and they stated on their leaflets that they would dig these up and store them in a frost free greenhouse over the winter, stacked on their sides. Sounds like a great idea but I imagine it would limit tuber growth and have some of the same cons as the mulching option (more below). But if you had literally hundreds of dahlias like they do at Anglesey Abbey then I imagine this is the least painful option! If only I had to worry about that!!

2. How likely are you to get frost?

Dahlia tubers are a bit like potatoes, imagine what would happen if you put a raw potato in the freezer – what would the potato be like after you defrosted it? It would certainly not be in the same state you left it it which is why it’s important that if you are likely to get frost in your part of the world, then you have to do something. If you’re in the UK like me, then you will inevitably have a frost, how bad depends on where exactly you are.

Where your dahlias are located can also affect the amount of frost you’ll get – is it sheltered or is it on an open allotment?

3. Can you be bothered?

How big is the area? If you have to mulch, you’ll have to think about what size of ground you have to cover first and how thickly you intend to mulch. Lots of people think mulching is the easy way out but if you have a large area to do, like an allotment, and want to cover it thickly, not only will this take a reasonable amount of effort and time but it could also be expensive if you don’t have any homemade mulch to start with. But if you just have to cover a border then it might be the way to go for you.

If you are thinking about digging, then consider how many dahlias do you have? If you’ve only got a few to dig up versus 50 that might also take a bit of time and effort as digging by its nature is going to require some effort!

If you grew them in pots, then mulching probably isn’t going to work as the frost can reach the tubers through the pot but you could try wrapping them in fleece and mulch the top, or you could move them into the shed.

4. How early do you want the dahlias to flower?

Dahlias won’t start growing until the temperature hits a consistent day and night temperature of 10C. This year that didn’t happen until the middle of May down here in Cambridgeshire. So if they’re in the ground, it will take a lot longer for them to germinate and could be further impacted by the location of the bed and how much sun it gets. If the tubers were dug up the previous year, you will have more control over the amount of warmth it gets.

The tubers don’t need light to get started so you could plant the tubers up and store them inside until they get going and then move them out later if you don’t have a heated greenhouse. I didn’t have a greenhouse last year and I kept mine in cold frames, making sure to open them during any particularly warm days so they didn’t get fried. There were a couple of colder nights though and all the pots came indoors into the kitchen overnight because I wasn’t taking any chances!!

I planted the pots up at the end of April, some more in May, and ended up getting my first flowers in the last couple of days of June. The ones that I planted at the end of May/start of June didn’t flower until late August and I still have one plant at the end of September that hasn’t yet flowered. With a heated greenhouse to get a head start, you might end up with flowers at the start of June, maybe even May if the weather is mild enough to plant them out. Even if you can’t plant them out they’ll be growing nicely in their pots, storing up lots of energy ready for when you do plant them.

5. Do you intend to use the bed for anything else?

If you don’t intend to use the beds for anything else then you might want to just leave them where they are.

If you want to get the most use out of your garden or allotment, or if you have limited spaces you might want to recycle your beds in between. Like I said above, the dahlias are not able to get planted out until the risk of frost is over so you can use your beds for other things like early flowering plants such anemones or ranunculus. They like the cooler weather and hate the warm so will be starting to fade by the time your dahlias are keen to go in the ground. You won’t be able to put tulip bulbs in though as your dahlias are still probably going strong in September which is when you would need to plant them – you can’t risk stabbing a tuber by digging holes for the bulbs.

6. Do you want to split any of your tubers?

Splitting tubers is a great way to get more plants, and free plants at that! I’ll definitely do a post when I do split my tubers to show you how but this is definitely a key factor in whether or not you dig them up because you obviously can’t do it if you leave them in the ground! Splitting tubers is reasonably easy with a bit of care and it’s the perfect way to beef up your dahlia display, especially if you have a flower that you particularly like and want more of them.

7. Do you have any precious varieties?

Ask yourself how heartbroken you would be if you lost any or all of your tubers if they got damaged by frost. This will probably be the most important question. Dahlia tubers are relatively inexpensive these days so you could easily replace things varieties like Cafe au Lait and Linda’s Baby (albeit at a cost) but the more precious ones like Caroline Wagemans are much harder to find so you might not get it again the following year. Can you live without her blooms?

As you can see it’s not as simple as saying “dig them up” or “just leave them in the ground” because there is lots to consider first so I hope that helps you decided what to do!

It’s nearly time to dig the up though, probably only a couple more weeks, so if you want more dahlia tips, I’ll be doing another post about digging them up when that day arrives!

If you’d like other dahlia related posts, please let me know in the comments below or by messaging me on Instagram.

Nicole x

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