How to overwinter plants so they survive the frosty season

‘Tis the season of wrapping up warm when leaving the house, defrosting cars before travelling and lighting fires to keep away the chill on long, winter nights. Although we take great pains to keep ourselves cosy over the colder months, often gardens are forgotten.

It’s important to protect plants as temperatures drop to help protect them and ensure they survive a colder snap. This process is called overwintering, but, what is overwintering, why is it so important and what’s the best way to do it? Rob Grayson, Head of Plant Distribution at leading plant experts, Hillier, explains and shares his top tips for caring for gardens over winter.

What is overwintering?

“Overwintering is all about giving plants extra protection from frosts and the cold, giving them the best chance of success to keep snug over frosty months and help them to thrive in the new year. This could mean protecting tender plants such as ferns or palms with horticultural fleece (available on a roll, or in different-sized “jackets”) in situ, or could mean bringing some of your plants into a greenhouse or conservatory. A cloche or coldframe can also be useful for tender plants in your borders.”

Catalogue and plan

“Each plant has its own degree of hardiness, or the extent it will tolerate cold weather. Extremely hardy plants will endure temperatures well before freezing, but more tender plants will need to be protected during periods of frost to avoid damage.

“A gardener’s first job then, should be to create their plan for the season – they should catalogue what plants they have and whether they will need more protection or not, come winter.”

Before the first frost

“Before the first sign of frost in the garden (which is often in late autumn), tender plants should either be cut back, lifted and stored indoors or left outside under a layer of mulch. Don’t wait until the first frost arrives to do this, as it will be too late by then! Tender herbaceous perennials like such as Dahlias and Cannas should be able to survive winter in a dormant state, if they are lifted and stored correctly, and then stored in boxes of peat-free compost in a garden shed. Don’t let them completely dry out, but keeping them too wet will lead to rot. A light water over the compost once a week should be plenty.”

Protect plants in pots

“Plants in pots are especially at risk from the cold, as the entire rootzone in the pot can freeze, especially in frost after a wet period. The soil temperature in borders remains higher and roots can grow deeper, giving more protection from the ground frost. Cold winds combined with frozen rootzones will cause foliage to go brown, crispy or even drop entirely. So long as the core of the plant remains protected, they should shoot back next spring.”

Keep greenhouses warm

“Some may think that simply moving tender plants into a greenhouse will protect them in the event of severe cold. Unfortunately, that’s not quite the case! By heating the greenhouse, plants can be kept in peak condition through the winter, but this can be a costly option. Another cost-effective form of greenhouse heating is specially designed-bubble insulation. Reduce the risk of frost damage to your plants while also cutting your greenhouse heating bill by clipping a layer to the inside of the greenhouse frame.

“That being said, it is also worth having a good heating system installed in your greenhouse. An electric heater will help move air around the greenhouse, avoiding the existence of cold spots which can be deadly to tender plants, as well as reducing the risk of disease.”

When to start

“To know when to start overwintering plants, keep an eye on the weather forecast. Once overnight temperatures drop below 10-12 degrees Celsius, tender plants will need some protection. Remember, bright sunny days often lead to cold nights without cloud cover, so be ready!”

For more information about Hillier visit www.hillier.co.uk

Ends

Editors notes

“To inspire the creation of green living spaces for now and the future”

Hillier is the most successful exhibitor in the history of the RHS Chelsea Flower Show, having been awarded 74 consecutive gold medals.

The company was founded in 1864 by Edwin Hillier and remains a family-run nursery with the fifth generation now actively involved in the family business as it continues to grow. The company employs over 750 staff across its nursery, amenity trees and 22 garden centre divisions, and grows over one million plants a year. It is the largest tree grower in the UK.

Over the years, Hillier has been responsible for numerous plant introductions, many of which have become essentials in British gardens and it continues with the tradition of innovation and the introduction of new garden plants in the present day.