Coming in from the cold: overwintering tender bulbous plants

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4 October 2024

On 4 October 2024

Coming in from the cold: overwintering tender bulbous plants

Many bulbous plants are hardy but some of our garden favourites are too tender to survive the frost. Dramatic dahlias, exotic-looking cannas, showy gladioli, elegant eucomis and flamboyant tender begonias all require a bit of extra care and protection over winter. They need to be carefully stored until they can be planted out again in May.

Plants like these with underground, fleshy parts are often referred to as bulbs, although some are actually corms or tubers, which are different to true bulbs. What they all have in common though is the ability to store nutrients for the plant (like a sort of plant larder) and to survive in a dormant state when lifted and stored in the right environment.

In milder areas you could simply cut your plants back, leaving the bulbs in the ground over winter and covering them with a thick mulch (20-25cm) of bark chippings, compost or even straw. However, given increasingly unpredictable weather patterns, this is risky; it’s entirely possible that there’ll be a sudden, deep freeze even in mild, sheltered areas.

Another way to manage this hazard is to grow smaller plants in pots and move them indoors to a cool place. But large pots or containers are needed to display dahlias and eucomis at their best, or for bigger plants such as cannas, so moving them can be something of an undertaking.

This means that lifting and storing may be the best option, particularly if you garden on heavy soil which can become waterlogged in winter. Most bulbous plants can’t tolerate overly wet conditions – they have a tendency to rot.

You’ll need:

Clean, sharp secateurs

A border or digging fork, hand fork or trowel

Plant labels and a pencil (so that you can reuse the labels)

Pots, trays or nets (depending on what plants you’re storing)

Compost, sand or coir

A cool, dry/well-ventilated, frost-free storage area – for example a shed, garage or unheated greenhouse

Cannas, dahlias and tender begonias are all lifted after the foliage has been blackened by the first frost.

Cannas

Cut back the stems to about 5-10cm from the base and carefully dig the plants up.
Take off any remaining loose soil by hand.
Replant, with the crown of the plant just showing, in pots of spent compost or leaf mould. You could also use coir or sand or a mixture of the two.
Water lightly.
Keep them slightly moist while in store.

Dahlias and tender begonias are also lifted once the foliage has been blackened by the first frost but need to be kept dry.

Gently unearth the plants and cut off the old flowering stems to about 5cm from the base of the plant.
Trim away any tiny, spindly roots.
Remove soil by hand and place the tubers upside down indoors in a cool, well-ventilated place for a few weeks. This allows them to dry off.
Bury the tubers in trays of dry sand, soil or compost leaving just the old flower stalks exposed.

Gladioli

Lift before the first frosts, usually around six weeks after flowering.
Cut the foliage back to about 4 or 5cm above the corms.
Spread them out and dry in trays on newspaper for a few weeks, making sure they sit separately from one another.
You’ll see that there are old, shrivelled corms at the base of each plump new one. Once the corms have dried off, twist off and discard the old one.
You may also see a few tiny, juvenile cormlets. Remove these and store them separately if you want to save them. They can be potted up and used once they’re bigger to replace old plants.
Gently rub away any dirt and dead skin and store the corms in trays or hang them up in nets. They don’t need sand or compost.

Eucomis

Opinion differs as to the best way to overwinter pineapple lilies, but whichever method you choose they should survive as long as they remain dry.

When flowering is over, cut off the flower spikes but leave the leaves.
Place them in trays and allow to dry off for a week or so.
Replant them into very free-draining, dry compost in pots (you could use a mix of 50:50 horticultural grit and multipurpose compost). Alternatively, you could leave them where they are in their drying trays.

Keep your plants in a cool, dry, frost-free place such as a shed, garage or unheated greenhouse. Some gardeners recommend a dark place over somewhere with light but it isn’t essential so just use whatever you have.

Tips:

Be gentle with your plants when you uproot them. Damage such as cuts or bruises, even minor ones, can trigger rot while they’re being stored.

During the preparation process check for any bulbs that look rotten, diseased or damaged and discard them.

Labelling the pots or trays will help you to remember what’s what! Especially if you have a number of different cultivars.

Check them regularly over winter to make sure they aren’t rotting (or drying out in the case of cannas). If you do find a rotting bulb, throw it out. It won’t grow again and the rot may spread to its companions in store if you leave it in place.

Monty Don demonstrates how to store cannas, eucomis and galtonia here:

https://www.bbc.co.uk/programmes/p00l9hjv

And Alan Titchmarsh shows you how to store dahlias here:

https://www.gardenersworld.com/how-to/grow-plants/how-to-lift-and-store-dahlias2/

https://www.rhs.org.uk/prevention-protection/overwintering-tender-plants-lifting-or-mulching

The thought of digging plants up and putting them to bed for the winter may at first seem like a terrible palaver. But embrace the idea and you’ll find that pottering around, fussing over plants and making sure they have all they need becomes a soothing autumn ritual, and one you may even begin to look forward to.