Topic: overwintering dahlias

[viv]

I have some dahlias in pots which I grew from seed this year.  They have done really well and I want to keep them overwinter.  I know I bring them in after the first frost and cut them down but can I leave them in the pots or do I need to lift them, trim them and dry them as seems to be suggested wherever I look?  Obviously it is not normal to grow them in pots!!

[Hugh_Jones]

You would be better to take them out of the pots, trim them to remove any dead or shrivelled material and long trailing roots. Make sure that the tubers are dry and dust them with flowers of sulphur (or a proprietory brand of fungicide if you prefer, and store them in a box of peat in a cool but frost proof place.  It is advisable to inspect then from time to time.

[Kerry]

hi,
going to play devil's advocate again...!
first year i grew dahlias i carefully dug them up for fear of losing them to frost. last year i bought some half price from willko's and thought i'd experiment with leaving them in the ground.
all bar one have come up this year and are very strong looking and floriferous, i'll be leaving them again this year. i'll confess i did think i'd lost them in spring but they surprised me by shooting up.
guess it depends where you garden and on your weather conditions. i'm in leicestershire, the garden is enclosed (walls) but we do get hard frosts. :)

[Mrs Ava]

Our older lottie chaps all grown stunning dahlias, and I asked them about digging them up, and they don't, they just cover them with a thick layer of compost, and forget about them.  Not quite so easy to keep the cosy if they are in pots though.

[Peter H]

Wonder if that would work up here in Durham as the frosts usually crack the pavement  :-\  might try it with half of them and take the others inside.

Peter

[Hugh_Jones]

Kerry, there`s all the difference under the sun between leaving dahlias in the ground when they`re there already, and leaving them in a pot for the tubers to freeze.  Had they been in the open ground already I would have suggested as an alternative simply covering them with a good layer of protective material - bracken, straw, compost or whatever.

However, some protection is usually necessary - we can`t always be sure of a mild winter like the last one. It`s not just the simple frosts that matter, but the depth to which the soil freezes during a long cold spell.

[Kerry]

Hi Hugh,
sorry, was not meaning to suggest Viv left her pots outside unprotected, having re-read my post this was not clear.
Having read your other posts you obviously have bags of know-how, so I'm interested in why you would take the tubers out of the pots even if they were kept in a frost free place? also, would you do the same with chocolate cosmos? I have one of these which is in a pot and I just bring it in the greenhouse over winter. Sorry-not meaning to hi-jack Viv's thread!

[Hugh_Jones]

There are several reason why I suggest removing the dahlia tubers from the pot over winter.  

1. I don`t regard a pot full of soil in which the plants have been growing for some time as a safe place for dormant tubers during the winter - especially in a greenhouse.  I`ve lost more tubers, corms and bulbs to vine weevil through leaving them still potted up than I care to tell.  A growing plant will let you know when vine weevil are present, but a dormant tuber can`t. If you remove the plant from the pot and wash the tubers any infestation can easily be dealt with.

2. Indoor conditions are artificial, and outdoor problems are magnified indoors, fungi spread more effectively and one rotting tuber on a potted dahlia can easily spread to all the other tubers on the plant.  If the plant is removed from the pot all the tubers can be inspected periodically, any rotten or withered ones removed, and the remainder protected with fungicide

3. Dahlia tubers can easily dry out and wither (and become useless) if the pot dries out completely. Stored in peat they can be regularly inspected and (as with chitting potatoes) any which are starting to wrinkle can be plumped up again with a fine mist spraying.  At the same time any tubers showing any signs of decay can be removed from the bunch.

I have never grown Cosmos Atrosanguineus, but as it is a half hardy tuber, I would expect the same considerations would apply.

[viv]

Thanks all - I have some chocolate cosmos as well so will treat them all the same, take them out of the post and store them after the first frost.

[Kerry]

thanks for the information Hugh, I may well decide to extend the experiment now! Thought chocolate cosmos might be comparable to dahlia tubers.
Best regards.

[teresa]

before you dig your dahlia's up lable them what type and colour they are makes thing easier next year when you plant them out.
If your dead heading now save the heads and dry them out makes seeds to sow next year you will get the same type but different colours.
Also when you dig them up stand them in a frost free place cool to dry out before cutting back the sap will swell the tubers for next year I cut back to 6 inches attach lable and leave on their sides for a week to let moisture escape from the stems then box up in peat.
Nice thing about them they get bigger and better each year and you can divide them I love them.

[Garden Manager]

Is it worth planting out pot grown tubers to overwinter them in the ground? I live in a mild area and whilst I have never tried leaving them in the ground with a mulch bfore i am sure theyd be fine. Point is I grow all my dahlias in pots, so usualy overwinter them in the 'traditional' way as bare tubers indoors. This however I have always considered a bit of a 'faf' to do (and takes up valuable space when i have it to spare in the veg plot in winter).

Any thoughts on this (Hugh?)

[Hugh_Jones]

It depends entirely on how you intend to grow them next year.  Seems a bit pointless to plant them in the ground now just to dig them up again and pot them next spring.  Personally, I always started off my dahlias in heat in the greenhouse in January to get an early start and plenty of cuttings, and you can`t do that if they`re sitting outside in frozen soil.

[Garden Manager]

Ok Perhaps not then. Best stick to the old tried and tested method.

Would be interesting to see how they overwinter outdoors in my garden though.

[teresa]

I seem to remember years ago people use to dig trenches under hedges and put dailias and fushias to bed and cover up with soil then leaves, bracken even spent peat.
Friend of ours dug a trench between her greenhouse and fence put fushias in covered over with soil and then an old duvet. Worked for her we tend to think that its either in the greenhouse or shed and forget the garden can come in handy.
If like Hugh you take cuttings thats another story but just to keep them going over winter perhaps look back to old ways?

[Hugh_Jones]

teresa, that`s the way I`ve overwintered my standard fuchsias for years - bury them in November and dig them up in February - far safer than an unheated greenhouse, and far cheaper than  heating one.

[Andy H]

I asked a man at allotment yesterday and he doesn`t lift them just puts about 6-8" layer of mulch over them, exactly as EJ said earlier.

[viv]

The pots are in the greenhouse - do I still need to lift them? (trying to save work here :D)

[teresa]

Viv if you have treated against vineweevil you will be ok to leave them in pots good idea is to leave the pots on their sides this helps them dry out.

[viv]

Ok that's great, thanks.  Is there an organic treat ment for vine weevil (don't use chemicals)