Protecting Plants from Frost: A Winter Guide for Seaham Gardens
The RHS notes that the first warnings of frost usually come between September and November. Most hardy plants in a Seaham garden will cope without help, but tender plants, young plants and anything growing in a pot can suffer. A little preparation now saves a lot of disappointment in spring.
This guide covers when frost is likely, which plants need protection, simple ways to give it, and what to do if a plant has been caught by frost.
When is frost likely?
The Met Office separates two kinds of frost. An air frost is when the air itself falls to freezing point or below. A ground frost is ice forming on the ground, on objects or on plants, and it can happen even when the air stays just above freezing, because surfaces lose heat faster than the air.
The nights to watch are clear and still. With little or no cloud and light winds, frost can form overnight even if the air temperature only drops to between 0 °C and 4 °C. Cloud acts like a blanket and slows the loss of heat. So when the forecast shows a clear, calm night in the low single figures, it is worth getting the fleece out.
Which plants are most at risk?
According to the RHS, the plants and places most likely to suffer are:
- Tender plants, such as dahlias and cannas, whose leaves blacken and collapse after the first autumn frost.
- Young or newly planted shrubs, which are more easily damaged than established ones.
- Plants in containers, because their roots are not protected by the surrounding soil.
- Frost pockets – low ground, or spots where cold air collects against a fence, wall or hedge.
- Exposed, windy sites. Cold wind after a freeze makes damage worse and can brown the leaves of evergreens.
- Plants that catch early morning sun. A quick thaw can spoil flowers and new growth; camellia and magnolia flowers are particularly at risk.
Cover plants with fleece on frosty nights
Horticultural fleece is the simplest protection. The RHS suggests covering vulnerable plants overnight with a double layer of fleece, or an old sheet, when frost is forecast. Heavier grades of fleece give about 2 °C of protection. Weigh or tie the edges down so the wind cannot lift it.
During long mild spells, take covers off so the plants do not sweat and start to rot underneath, and put them back when the cold returns. If you already have fleece from last year, reuse it.
Mulch the roots
A layer of mulch over the root area helps protect evergreens, conifers and tender shrubs and perennials from cold. Organic matter such as garden compost, spread around the base of the plant, does the job. Dry straw or bracken packed around the crown of a tender plant gives extra insulation, but it must stay dry: the RHS warns that water trapped under wrappings can rot the crown.
On tender perennials such as penstemon, leave last season's growth in place over winter. It shelters the plant, and you can cut it back in spring.
Look after pots and containers
Pots are where frost does the most damage, because the roots have nothing around them for insulation. When frost is likely, move containers to a warm, sheltered spot. Wrap the pots in fleece or bubble wrap to protect the roots.
Stand containers on bricks or pot feet so the drainage holes stay clear and the compost does not become waterlogged. Truly tender plants are safest in a frost-free greenhouse, conservatory or enclosed porch over winter.
Avoid frost pockets and soft growth
If one corner of your garden always stays white long after the rest has thawed, cold air is probably collecting there. The RHS suggests improving cold air drainage by opening a small gap in a fence or hedge, or by removing some of the lower growth. When planting something new, choose a spot away from the frost pocket.
Avoid feeding with high-nitrogen fertiliser late in the season. It encourages soft new growth, and soft growth is easily damaged by frost.
If a plant has been caught by frost
Do not rush to cut it back. Damage on woody plants can take weeks or even months to show. The RHS advises waiting until no more frost is expected, then pruning damaged growth back to a healthy bud or sideshoot.
After a hard winter, check newly planted shrubs: frost can lift them, and the soil around them may need firming back down. And do not give up on a plant too soon. Many plants regrow from buds at or below soil level, sometimes not until early summer.
A note for coastal gardens
In Seaham, cold nights often come with wind off the sea. Because wind after a freeze makes frost damage worse, sheltered spots matter even more here. For more on keeping plants, pots and fences safe from winter gales, read our guide to making a coastal garden wind-proof for winter.
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