When gardeners overwinter their plants, they are providing special care for tender plants that would otherwise not be able to withstand the cold season.
For a helpful guide, get the Fall Gardening Checklist here.
What is Overwintering?
Some garden plants survive winter conditions fine on their own while others need help with ‘overwintering’.
When we overwinter a plant, we provide conditions such as insulation or shelter that enable it to survive the colder months.
Perennial trees, shrubs, flowers, and vines suited to our climate overwinter naturally. It’s the long-living tender plants that benefit from our help.
Know Your Hardiness Zone
Do you know your plant hardiness zone?
This is a measure of the average low temperatures for your area. Garden plants and seeds are sold with tags indicating what zones they are suited for.
Anything long-living plant not suited to your winters could be a candidate for overwintering.
Long-living Annuals and Tender Perennials
A popular example of a plant we overwinter is geraniums (Pelargoniums). These are long-living plants sold as annuals because, without protection from freezing temperatures, they cannot survive.
To overwinter geraniums, we can move them indoors to grow as houseplants or provide cool storage where they go dormant (rest) until spring.
Trees growing in containers may also need extra help to get through the winter. Tropical trees must come indoors to warm and humid conditions while semi-hardy and hardy trees do best with dormant overwintering in cool storage.
While the same hardy tree might survive the winter when planted in the ground, a container does not have the same insulation soil and mulch provide and the root ball may freeze. If the water within the plant cells freezes, it’s game over.
To overwinter a potted tree suited a zone warmer than our own, we can either insulate the container in place or move the tree to a sheltered location like an insulated shed or garage and bundle it up so temperatures remain above freezing.
Related: Gardener’s Dictionary for Beginners
Cool-tolerant vegetables like kale, broccoli, spinach, carrots, and leaf lettuces can also be overwintered. These guys can survive whatever winter has to offer when tucked in with frost cloths, polytunnels, covered raised beds (“cold frames”), or greenhouses, also known as ‘season extenders‘.
Again, it’s all about preventing the water within their tissues from freezing. Growth is stalled when temperatures and light levels dip, but the plants will resume growth when warmth and light return.
Bulbs & Tubers
Flowering bulbs like tulips and daffodils are hardy and can stay in the ground throughout the winter months.
Tuberous roots like dahlias are not that hardy and need extra protection to survive the cold.
The most common method of overwintering dahlias is to dig them up and keep them dormant in cold storage for the winter.
- When we overwinter we take action to protect plants in the winter that would not otherwise survive.
- Candidates include long-living annuals, semi-hardy plants, potted trees, cold-tolerant vegetables, and tender perennial bulbs and tuberous roots.
- Options depend on the type of plant and include providing shelter, covers, or insulation with deep mulch or other materials to keep temperatures above zero and prevent plant tissues from freezing.
~Melissa the Empress of Dirt ♛