As the nights draw in and temperatures start to fall, it’s time to start thinking about protecting your plants from the British winter. A polycarbonate greenhouse is an excellent place to shelter tender plants, overwinter pots and keep some of your garden plants going until spring.
With a little preparation, your greenhouse can provide a safe, sheltered environment throughout the colder months.
Which Plants Should You Bring Into the Greenhouse?
You don't necessarily need to bring everything indoors. Focus on plants that are particularly vulnerable to frost, cold winds and prolonged wet weather.
Good candidates include:
- Geraniums and pelargoniums
- Fuchsias
- Begonias
- Tender herbs
- Citrus trees
- Young plants and cuttings
- Some vegetables and salad crops
- Tender perennials
- Plants grown in containers
Before moving anything into the greenhouse, check plants carefully for pests, disease and dead leaves. You don't want to introduce unwanted visitors that can spread to your other plants.
Give the Greenhouse a Good Clean
Autumn is a good time to give your greenhouse a thorough clean before filling it with plants for winter.
Remove old leaves, weeds and dead plant material from the floor and staging. Clean the polycarbonate panels where possible to allow as much winter daylight in as possible.
Pay particular attention to corners and underneath pots, as these can harbour slugs, snails and pests.
It's also worth checking the greenhouse for damaged panels, gaps or loose fittings before the weather gets worse.
Don't Pack Plants Too Closely Together
It can be tempting to squeeze every plant into the greenhouse, but good airflow is particularly important during winter.
Leave some space between pots so air can circulate. This helps reduce condensation and the risk of fungal problems.
Try to keep plants slightly raised from the cold greenhouse floor where practical, particularly more vulnerable plants.
Protect Against Frost
Polycarbonate provides better insulation than single-glazed glass, but it doesn't make a greenhouse frost-proof.
During particularly cold weather, temperatures inside can still fall below freezing.
If you have valuable or tender plants, consider using greenhouse fleece or horticultural fleece to provide an additional layer of protection.
Bubble wrap can also be used around the inside of the greenhouse, particularly in colder areas, although avoid blocking too much valuable winter light.
For very tender plants, a greenhouse heater with a frost-protection thermostat can provide additional peace of mind.
Be Careful With Watering
One of the biggest mistakes people make during winter is overwatering.
Plants generally grow much more slowly during the colder months and therefore need less water. Waterlogged compost combined with low temperatures can quickly lead to root problems.
Check the compost before watering rather than sticking to a regular schedule.
Water earlier in the day when possible so that excess moisture has time to evaporate before temperatures drop overnight.
Keep an Eye on Ventilation
It might seem strange to open a greenhouse in winter, but ventilation is still important.
On sunny days, temperatures inside a polycarbonate greenhouse can rise surprisingly quickly, even when it's cold outside.
Open vents or doors slightly when conditions allow, particularly on mild, sunny days. This helps reduce condensation and keeps the air moving.
Close everything again before temperatures fall in the evening.
Protect Plants From Pests
Pests don't disappear just because winter has arrived.
Check the underside of leaves and around the stems regularly for aphids, whitefly, spider mites and other pests.
Slugs and snails can also find their way into greenhouses looking for somewhere warm and sheltered.
Removing dead leaves and keeping the greenhouse clean will make it easier to spot problems before they get out of hand.
What About Plants That Go Dormant?
Some plants don't need much attention at all during winter.
Many dormant plants can be kept in a cool, frost-free greenhouse with very little watering. The aim isn't necessarily to encourage growth — it's simply to keep the plant alive until spring.
Don't worry if some plants lose their leaves or appear to stop growing. This can be completely normal during their winter rest.
Check Your Greenhouse After Stormy Weather
British winter weather can be unpredictable, so make a habit of checking your greenhouse after strong winds and storms.
Look for:
- Loose or damaged polycarbonate panels
- Cracked panels
- Loose clips or glazing bars
- Damaged vents
- Water leaks
- Gaps around doors and panels
- Signs of movement in the frame
Sorting out small problems early can prevent a much bigger repair later.
Get Your Plants Ready for Spring
As the days begin to lengthen towards the end of winter, gradually increase watering and start checking plants for signs of new growth.
Avoid moving tender plants outside too early. A late frost can undo months of careful preparation.
Once the risk of frost has passed, plants can gradually be acclimatised to outdoor conditions before being moved permanently back into the garden.
A Little Preparation Goes a Long Way
A polycarbonate greenhouse can be a fantastic winter shelter for your plants, but it still needs a little preparation before the cold weather arrives.
Clean it, check it for damage, protect vulnerable plants from frost, avoid overwatering and keep an eye on ventilation and pests.
Do that, and your greenhouse should give your plants a much better chance of coming through the winter ready for another season of growth.
