Mulching dahlias

Listening to GQT this afternoon there was strong advocacy for mulching dahlias and overwintering them in situ rather than digging them up and faffing.

Cover with 3-4” of mulch was the advice. My questions: how wide an orbit should the mulch be spread? A dinner plate? A tray? A patio table? Second, is 6+” better than 3-4”? Third, should the mulch cover the crown of the plant or is a ring doughnut arrangement better? Fourth, I have plenty of wood chip, compost and leaf mould but would Strulch, with its mollusc repelling properties, be better for when leaves emerge in the spring?

Thanks for any wisdom.

 

As I have mentioned before in another thread we haven't dug up our dahlias for about 5 years now. We haven't mulched them either. Each year the plants produce more foliage and even more flowers. We also (and don't ask me why) don't have slug/snail problems with the emerging or mature foliage or flowers.

 

I'll add, that I am an absolute garden novice, who two years ago had no idea you were supposed to mulch them (or dig them out). They come back bigger and better each time. I'm on well well drained soil in NW England..

 

As long as the ground doesn't freeze the tubers will be unaffected, I still think rot and underground slugs are the main reason for tubers not growing the following years.

I can remember many years ago nearly breaking a garden fork trying to get parsnips out the ground, its never been that hard recently.

I can guess that the new shoots in spring will be "hardened" already so less likely to slug damage above ground in spring.

So I believe it depends on your location a soil type, drainage, they usually reappear around here each year even without a mulch.

 

Well it must be me then. I have lost Dahlias, both by leaving them in and digging them up, but I have also kept them by both methods too.
I garden on London clay so maybe that's the reason. Last winter was so wet they simply rotted in the ground. A few years back I thought they had rotted but when I dug them up it was obvious that as the new shoots had emerged the slugs had eaten them all. One year having dug them up and put them in an insulated shed in spent compost, but they just dried up. There is a GC near us that keeps it's stock plants in the ground all the time but after last winter I noted several gaps in the field so they lost some too. I noticed on GW that Monty used newspaper to wrap his so perhaps I should try that.

 

That's why you can't leave them in the ground here - far too wet and cold.
The slugs would be a massive problem even if they did manage to survive and grow.
Covering them would just exacerbate it IMO. The rain would simply get through any mulch, and sit there. Even a solid cover - ie a glass/plastic cloche wouldn't work as the tubers would absorb the moisture from the ground nearby.
I use wood shavings around mine @Allotment Boy . Newspaper stays too damp for me, which then transfers back to the tubers, but it's another case of experimenting with them to see what works. My shed wasn't dry enough for storing them in there, but hopefully this year it'll be fine as I've rebuilt it. I've got a few in a plastic container and so far, they're ok. It's getting them dry enough for storage that's the hard part for me.

You'd need to have a site that was reliably dry/well drained and frost free, long term, to leave them in the ground and mulch etc. 'Long term' is the most important part of that sentence.

 

I've used a bark mulch of about two inches thick in the past over the entire border and they have reliably returned each year, until I decided to replant the border! The winters are comparatively mild here and I have free draining, sandy soil. With too much wet, and not necessarily cold wet, tubers planted in pots indoors in spring can rot easily.

 

I sometimes pile up some fallen leaves around mine, but that's as far as it goes. I think covering them with anything that tends to hold moisture would do more harm than good, particularly if it's not pulled back before the new shoots start to appear.

 

I have some that I overwinter in the cold greenhouse, but have had D imperialis outside in the ground since 2018, it grows much better in the ground than in a large pot. It came through last years wet autumnand winter with out a problem, but didn't come into growth until June due to the cold spring. This year I've planted out D excelsa and that will also stay in the ground. I also intend to leave D merckii planted in the ground next year. If I remember I do put a mulch of either garden compost or leaf mould around the remains of the stems as next years buds come from the bottom of the previous years stems. I also have a reserve plant of each of these in the greenhouse.

 

I grow mine in (large) pots due to slug ravaging. In the past I've dug them up, wrapped them in newspaper and kept them in cardboard boxes in the shed Generally they were fine but I did lose some.
Now I just cut them back and move the pots into a cold frame. I don't dig them up. The soil dries out slowly but I don't water them and they never get to the point of actually drying up, and the soil seems to insulate them a bit. In spring I take them out and check for damage / rotting (very little, if any) and repot. This has worked for several years.
My uncle has a front border full. When a frost has blackened them, he cuts them back and covers the lot with old, weighed down compost bags. I would have thought that would be a nightmare for slugs and/or rotting, but they're fabulous every year!
A near neighbour of his, who seems to grow 'show' type Dahlias in his front garden (in rows, enormous blooms) puts a big pile of straw over the crowns - about 4-6". I've no idea if the ones I see each summer are the same ones, but they look like it.
So there's lots of ways to do it.
We're all in SE London.

 

I remove the bark once the shoots start to appear and place a collar around them made from a plastic pot with the bottom removed to keep slugs and snails at bay. The bark supposedly provides protection from frost damage and seems to work.

 

I think it depends on the weather we have during the winter … I’ve done both methods. When I left them in the ground I didn’t lose any in the first year but lost 50% in the second year which was very wet and cold.

Since then I’ve dug them up and stored them in my garage, I roughly clear the old soil off, leave them to dry out and then wrap them in newspaper and store in cardboard boxes. I’ve not lost any whilst using this method.

 

It's the wet cold, epsecially long term, that's the problem @CatDouch . Same with so many plants.
I had to laugh when I watched G's World the other day, and Monty was prepping his. He hosed the soil off then talked about storing with newspaper. No mention of how he dried them off before storing. That's the bit of info that matters most! It's fine if the weather's suitable and you can keep them outside to dry off, or have a convenient building/gr'house to put them in, but not so easy if you don't have either of those and have to faff around with them for a good while. That's what always annoys about a lot of advice that's given - it's really important for novice [and more experienced] gardeners to understand the whole process.
The one good thing this autumn here is that's it's been very dry. Even so, I've had to be careful with the ones I've lifted so far, because it just stays damp for very long periods ,so I need to check them every day before putting them away permanently.
Mine are all potted, as it's absolutely no use leaving them in the ground here. Some of the more vigorous, tougher ones can cope better left in pots and covered etc, but even so, it's a risk. I got one through the winter by lying it on it's side in the growhouse, up off the ground. Terracotta pot which helps a bit. I might do the same with it this year. The remaining two are completely frosted after yesterday, so I'll need to see to them today.

And then there's those slugs....

 

First frost -2 last night so the dahlias have been hit. I leave them and gradually the stalks dry out and the birds perch on them. Come the spring they are cut back ready for the new growth.

 

It all depends on your soil and where you live. I leave my dahlias in the ground at OH's cottage in Norfolk. The soil is sandy and Norfolk is a dry county. There are hedgehogs and blackbirds and not many slugs. I mulch with about 2 inches of bought compost.

I also have dahlias in my garden at my house in SW France. Not many slugs there either, the summers are hot and often dry. The winters can be cold. The soil is clay but I've dug in a lot of compost. I mulch them too. Usually they are OK but this year the spring was very wet and the dahlias were munched but when the hot weather came the slugs disappeared and the dahlias grew, bushier and shorter than usual.

I have found that some dahlias are hardier than others. Park Princess and Arabian Nights are hardy, Bishop of Landaff isn't.