Autumn Gardening | Lifting Perennial Tubers

Lifting perennial tubers in the Autumn is often seen as a complicated gardening task. But it isn’t really. Dahlias and Begonias often flower well into November, depending on when you first get a frost in the garden.

When those glorious orange begonias finish flowering, what do you do? If your dahlias are still flowering when we get a heavy frost that blackens their flowers and foliage do you just think “oh well, that’s it”? Or would you like to have the same display next year without having to buy the flowering plants again?

Dahlias, tuberous Begonias, Canna and Gladiolus are popular perennial plants. Unlike herbaceous perennials with a mat of fibrous roots, these plants have a thickened root or underground stem. This thick root is variously called a tuber or rhizome, depending on type. Its purpose is the same, to store food for the plant over winter and develop into a new plant next spring.

Do I have to lift my Tender Perennials and Tuberous Perennials in the Autumn?

And you’re maybe wondering what the difference is? Lets look at Dahlias as an example. They are often called tuberous perennials as the flower grows from a swollen root which is called a tuber. But they are also herbaceous perennials as the foliage dies back over winter. And they are tender perennials as the tubers do not often survive in the cold wet winter soils of Great Britain and the northern USA.

The easy maintenance answer which I often give to my time stressed clients when we’re discussing planting designs and their favourite flowers, is to treat them as annuals and do nothing. If they survive the winter and come up again next year then that’s a bonus.

Whether dahlias, chocolate cosmos, cannas and so on survive over winter in your garden soil depends on three main key points, How: –

wet the winter the winter is
free draining your soil is
prolonged a frost there is

Other tuberous perennials which are treated in a similar way to dahlias are Chocolate Cosmos, Begonias and Mirabilis jalapa (‘Pride of Peru’, ‘four o’clock plant’). Canna and Gladiolus are not tubers but a rhizomatous herbaceous perennial. They can be treated in the same way to ensure survival.

Lifting Perennial Tubers

If you have heavy clay soil which stays wet all winter, then the tubers will rot. The obvious solution is to improve all the soil in your flower borders, by adding plenty of coarse organic matter and possibly some grit. This will improve the drainage. For the meantime grow your dahlias and cannas in raised beds, which are easily filled with free draining fertile soil.

Or grow them in pots and containers, on the patio or in your borders to fill in empty area in the late summer flower border. These methods will enable you to leave the tubers in the soil over winter.

Of course, currently your dahlias may be flowering merrily in the garden and you know that you will have a heavy wet winter soil. Continue to enjoy their floral display until the frost blackens their foliage.

Remove all the foliage and flowers, taking any which are still passable into the house to enjoy as a cut flower
Cut the stems down to about 4” or 10 cm high
Then dig up the tubers, this is also known as ‘lifting the tubers’, and give them a wipe over to clean the soil off
Stand or hang the tubers stem down for a few days so they can dry out
Store them frost free in the dark until spring
A garage, shed or cellar is usually fine as the tubers may shrivel if they’re kept somewhere too warm (so don’t store them in the airing cupboard!)

Not Lifting Perennial Tubers

If you have a sandy soil there should be no problem, as this is a free draining soil. I have known Mirabilis jalapa survive for years left in a free draining soil. This tender perennial is nearly always treated as an annual but in a free draining flower border it is certainly happy, even on the west coast of Scotland.

Likewise, if you live in an area where the winters are cold but not particularly wet, the tubers should be fine. In this last scenario, it may be advisable to lay mulch over the tender plants such as chocolate cosmos for extra frost protection.

If you’d like to learn about lifting perennial tubers and other seasonal tasks in your garden, Plews offers 1-2-1 Gardening Lessons where your garden is the classroom. You may like to read about some of the things you could do in a garden lesson. Of course, having read all of this you may well decide that it’s too much effort. So you’ll just treat all of these tender perennials as annuals, or bedding plants. And you know what? That’s fine too.