What to Grow in Autumn in the Greenhouse

A greenhouse is more than a building for growing tomatoes in summer.  Once you invest in a greenhouse you will see the way in which it can extend your growing seasons.  When the weather is hard to battle against, like the recent wet conditions we have been experiencing, you can retreat into the secluded sanctuary of your greenhouse dry and warm and continue to enjoy your garden.

The following are a few ideas of plants and crops to grow in the greenhouse as we slip into the autumn and winter period.  We hope these ideas inspire you to get the most from your glasshouse.

Hot or Cold Greenhouse

Most new greenhouse gardeners get a little confused by what they can grow in a greenhouse over winter and whether they need to add a heat source to keep crops alive.  The following is a summary of the four main greenhouse types with pros and cons.

Cold Greenhouse - Unheated except by the sun

Pro’s - Plants are protected from the elements; growth is approximately 3-4 weeks ahead of outdoor plants.

Con’s - No growth in the depths of winter; unsuitable for overwintering frost sensitive plants

Cool Greenhouse - Heater required during cooler months

Pro’s - Plants are protected from the elements; growth is approximately 3-4 weeks ahead of outdoor plants; minimum temperature is just high enough to support plant growth; frost tender plants can be overwintered

Con’s - Some form of heating is required between autumn and spring

Warm Greenhouse - Heater required during most months

Pro’s - A wide range of plants can be grown during the winter months; exotic fruits and flowers can be planted

Con’s - Fuel costs* are about three times higher than a cool greenhouse equivalent.

Hot or Stove House - Heater required all year round

Pro’s - Tropical plants can be grown; a real statement building

Con’s - This can be too warm for many plants to be happy; fuel costs* are prohibitively large.

For this blog we are looking at crops for a Cold or Cool greenhouse only. If you are looking to invest in a greenhouse heater for your greenhouse we have a range available to suit most greenhouse shapes and sizes.

Making Space

If you have had a full and productive greenhouse throughout the summer months with crops of tomatoes, cucumbers, chillies, etc.  the first issue you will need to address is making some space for your winter crops and cuttings.  Keep harvesting crops while they are still productive but remove any plants that have gone over to free up space.

With tomatoes you can pick all the ripe tomatoes and use them up in a range of delicious recipes including tomato soup.  If the weather is still warm and sunny in early autumn some of the green tomatoes might still ripen.  If you need the space however, then you can either pick all the green tomatoes and place them in a warm spot to ripen.  Alternatively you can pull up the plant shake off all of the compost and hang it somewhere warm upside down.  You can do similar with chilli plants to help speed up the ripening of unripe fruits.

Herbs for Cooking

Chives, coriander, mint and parsley  can all be grown in a greenhouse over the autumn and winter period.  They need a cool but frost free place to grow so you may need to add a little heat on the coldest of nights in winter.  We recommend a few 30cm (12in) pots and a soil based compost.  Herbs need well-drained compost so mix the compost with a few hand-fulls of fine horticultural grit.

Chives can be dug up from the garden in a small clump and pot them into the above mixture trimming any dead leaves.  Mint can also be kept in the greenhouse, cut a few pieces of root with shoots and plant them in another pot.  Thinly sow coriander and parsley in separate pots and cover the seeds with vermiculite or horticultural grit.  If you have pots of these herbs already growing outside simply lift them and bring them into the greenhouse to ensure an extended crop of culinary herbs through autumn and into winter.

In addition to herbs you might still have time to sow a few winter lettuce and rocket seeds to keep you with a fresh supply of salad crops.

Take Cuttings

The cold greenhouse is an ideal spot to keep cuttings from established plants to ensure a continuation of plants from your garden.  In some harsh or very wet winters certain plants might struggle to survive.  By taking cuttings now you will ensure you can continue to enjoy your favourite plants again next summer.

Good plants for taking cuttings for the beginner are verbena bonariensis, lavender and rosemary.  To do this choose a non-flowering shoot that is about 5 to 10cm long.  Cut the bottom of the stem just below a set of leaves or leaf nodes with some sharp scissors, a knife or secateurs.  Remove the lower leaves.  It is advisable to try to half in size the rest of the foliage to not put too much stress on the new plant.  Then simply push them into a gritty compost around the edge of a 7cm (3in) pot.  Label the pot and keep the compost moist.  On rosemary and lavender remove the bottom two-thirds of leaves and follow the above process.

Over Wintering plants

Summer bedding plants such as fuchsias, pelargoniums and marguerites can be brought inside to see them through the winter months.  Do not overwater them, you just need to avoid the compost from completely dying out during this dormant period.

Citrus Plants

Citrus plants including lemons, limes and kumquats are one of the joys of owning a greenhouse.  These can be grown in pots to sit outside all summer then bring inside during the winter months.  Be mindful not to overwater Citrus plants through the winter period they are best treated like house plants.  Let the compost dry before watering and its is best to keep a watering can of rainwater inside the greenhouse for this task so it is at a tepid temperature.

Whatever you choose to grow or protect in your greenhouse we hope that you maximise the use of it to enjoy your garden through the long autumn/winter months.  Even if that is just a space to place a comfy seat to escape the elements and enjoy a cup of tea.

*Fuel Costs - It is hard to calculate exactly the cost of fuel because there are so many factors influencing this.  Size of greenhouse, quality of insulation, external temperatures, quality of heater.