Blooming Times - Chill Factor

Blooming Times – Chill Factor

by Flo Whitaker

Got plants to overwinter but no greenhouse to put them in? With a little thought and care, many plants can survive in the great outdoors.

When it comes to overwintering patio plants, you’ll often hear the phrase, “place them in a frost-free greenhouse” casually chucked about. That’s all very well, but what if you don’t have a greenhouse? Fear not, many plants are far tougher than we give them credit for.

Extreme weather will see off the strongest specimens but most plants are killed by us; we overwater and we overfeed. When a plant is in a dormant state, it only requires a little moisture at its roots – and it certainly doesn’t need any food. If you feed now and the weather turns mild, the plant will be encouraged into re-growth. New shoots are tender and unable to withstand frost, so when the temperature finally plunges, the new growth dies. This gives the plant an enormous shock, which can prove fatal.

A cold frame is a fantastically useful bit of gardening kit. If you don’t have one, a polite letter to Father Christmas might do the trick? As the name suggests, a cold frame is a glazed, unheated structure with opening lid panels for ventilation on warmer days. They vary in design and size but can usually accommodate plants up to about 50 cms high.

Place larger plants in a bright and sheltered part of the garden. The base of a wall is a good place. Walls create ‘rain shadows’, which gives some protection, even from the most torrential rain. Positioning several plants together creates a micro-climate where the temperature will be slightly warmer than in an open space. It may not seem like much but a couple of degrees can make all the difference. It’s tempting to cut back old stems, but leave them on as they will help insulate the plant. Only remove material that is decayed and likely to spread mould spores. Cover the compost surface with a thin layer of horticultural grit – this assists drainage and protects compost and plant roots from becoming waterlogged.

Lightweight horticultural fleece is cheap and reusable. Drape it over plants when extreme weather is forecast, or use it to wrap around the outside of favourite pots to prevent them cracking. Old net curtains work well too – although you might get a few odd looks from your neighbours!

Many plants can be overwintered in this way.

Bedding geraniums need a cosy windowsill to survive, but pots of herbaceous geraniums, along with lavenders, hardy fuchsias and salvias, hebes, shrubby herbs and ornamental grasses are usually tough enough to cope outdoors. Potted primulas and border auriculas are practically indestructible, even in the harshest winters. Agapanthus has huge, fleshy roots that quickly rot when waterlogged.

Keep them snug and dry-ish and they will repay you next summer with their astonishing, mesmerising blooms.