Greenhouses and Cold Frames Autumn Tips

Greenhouses and cold frames are essential aids for many gardeners. And it’s important to keep your greenhouse clean and tidy to prevent pests and diseases spreading rapidly in the humid and sometimes heated conditions of soil and plants.

We are none of us perfect. However, setting yourself the task of cleaning the interior and exterior of your greenhouse just twice a year should be achievable.

That regular clean will help maintain the structure of your greenhouse as well as care for the plants growing inside.

Personally, I find that mid-autumn and mid-spring are the best times for me and the plants I keep in there. The days are warm enough for cuttings, seeds and tender perennials such as citrus trees to be happy outside whilst I get on with the cleaning.

Now, rather than having convoluted sentences, I’ve mainly referred to greenhouses when giving help. But there are sections on cold frames, polytunnels and plastic greenhouses where you’ll find relevant tips.

All these structures need regular maintenance too in order to perform to their best for you and your plants. And for most home and allotment gardeners it makes sense to do both greenhouse and cold frame at the same time.

Greenhouses

Check door hinges, handles, auto open vents are all still good. You wouldn’t want vents stuck in the open position when its frosty! With sliding doors, clear out the runners and ensure they close fully.

Frames will be wood or aluminium. Both types can develop moss and mould along the frame, so remove this before cleaning the frame. Check for general stability – ie does the greenhouse move when you push 😉

Cold Frames

You may have one or more of these instead of a greenhouse or as well as. They may be permanent structures built with brick or concrete walls, or perhaps physically attached to your wooden greenhouse. But cold frames can also be found as independent structures, often quite solid. And then there are lightweight ones which can be easily moved around to suit your needs.

Depending on the materials used to build yours, follow the relevant tips for cleaning and maintenance. With the additional advice that lightweight cold frames benefit from being secured to the soil or ground to prevent them from blowing around in winter storms. Or place them in a more sheltered spot – which will help protect your plants in there too!

wooden greenhouse, raised beds Photo by Anna Guerrero from Pexels;

Cleaning your Greenhouse

If you can, clean on a moderately windy day and have windows and doors open. That way, the breeze will help to dry out the greenhouse as it’s washed.

Firstly, check the panels for any broken or cracked glass. These panes should be replaced. If you are planning on doing the job yourself, then you should wear proper gloves and goggles.

If you have an electricity supply to the interior of the greenhouse, ensure that the electricity is turned off before you start cleaning. Yes this sounds like stating the obvious, but you’d be surprised how many people forget to turn off the electricity!

Before you clean inside, do the obvious of removing all the containers, pots, shelving and staging that can be removed. Throw out old, used grow bags (store these elsewhere, they have uses still!)

Remember to brush down and scrub any brick walls and hard paths you have inside the greenhouse.

Use a suitable proprietary disinfectant, or make your own recipe using a dilution of white vinegar 1:8 plus 1 tbsp bicarbonate of soda per litre of water.

polycarbonate greenhouse, raised beds, original photo by elisabeth coelfren

Glass and polycarbonate greenhouses and cold frames

Dirty windows affect sunlight levels and over winter there’s less daylight generally. This is especially relevant when you have polycarbonate, as it lets less light through than glass. Cold frames may have solid walls and only a clear lid. Others have a clear top and sides.

So to maximise the light your over-wintering seedlings, tender and young plants are getting, wash the panes of glass with warm water. Add a dilution of white vinegar 1:8 for extra cleaning power.

The higher parts of the greenhouse roof can be reached by attaching a sponge to the end of a bamboo cane or using a floor mop. Remember to wash both the inside and the outside of the panes.

Garden Teacher Tips

If you can’t stand the smell of vinegar, then add a few drops of citrus essential oil to the solution, or swop out the vinegar for lemon juice. The citrus essential oil does seem to help both with the cleaning and with any pest and disease removal.
Lastly, sweep the floor to remove any dirt, spilled soil, leaves that have fallen from the plants and the mess you’ve created by cleaning higher up!

Does the structure need more than a clean?

Wooden frames of greenhouses and cold frames can be protected using a wood preservative. This is particularly so when you have a softwood greenhouse or have used a colour and want to maintain it.

Because of drying times, applying preservative to the whole structure is a task I prefer to carry out in the spring as the wood needs to be dry not damp when preservative or paint is applied. But touching up a few areas that obviously need it is fine in the autumn.

It’s much easier to do this before you put the plants back in. But if you need to do it when they’re in, be sure that none of the preservative touches the plants.

Polytunnels

As well as the cleaning tips above, you will also need to check that –

the different elements of the frame are attached securely to each other (you don’t’ want them coming apart in winter storms if you can avoid it!)
where possible, also check for any splits in the metal rods and repair or replace
the polytunnel is still securely fixed to the ground. You may have used the trench method or base rail method, so check and amend / repair accordingly.
the door and frame and any openings, vents, etc are most likely made of wood rather than metal. Check these over for repairs. And then replace screws, oil hinges and add preservative as required.

Polytunnels can have fleece added inside for overwintering insulation. Horticultural fleece is definitely better than a fully plastic material which would increase humidity levels.

small plastic patio greenhouse, grow your own, small gardens

Temporary Plastic Greenhouses

These can be really useful for that extra protected space that you need at certain times of the year.

Perhaps you washed yours before tidying it away as it wasn’t needed during summer? (eat a chocolate biscuit as a treat for being organised😉) If not, then you can give it a clean when you put it up.

Either way, it’s a good idea to put it up now and check for splits in the plastic before the need for it is great. Generally, lining the inside with fleece will negate small drafts from the split. Packing tape will help keep the edges together on longer splits. And if the cover is beyond repair, you have two or more options.

For example, if the frame is still okay –

Easy option – you should be able to purchase a new cover for it.
DIY option – the plastic that came wrapped around your new wardrobe and you shoved in the garage? Hopefully there’ll be enough of it to make a cover to fit. Or drape & tie it on. Remember to allow for a door flap.

But when the frame has had it, you could –

buy a new one
create your own, using outdoor shelves as the structure. This has the advantage of then turning into an open plant display over the warmer months.

Padme, Border Collie Puppy exploring greenhouse, basket

What other autumn maintenance do we need for our greenhouses and cold frames?

Pick the items that are relevant for your polytunnels, greenhouses and cold frames out of the following to check that –

lighting works (it’s got to that time of year!) this may be mains / solar / battery operated but its still worth checking before you need to use it
heating – be these electric heaters, oil stoves or something else, check theyre fully functional. Yes, even if you did that in the spring, give them a quick once over, because you don’t want to discover next month that they’re not working…
watering / irrigation systems are working – these may well not be needed overwinter, so if they’re not fixed, you could take them away to overhaul.
Heating mats, propagators (electric or otherwise), etc – if you’re not going to be using them until spring, store them elsewhere. Having first checked that they’ll be usable in the early spring, of course.

Preparing for Winter’s Cold

Insulating greenhouses and cold frames can help you over winter plants that might not otherwise survive. You could do this before replacing plants or leave it a couple of weeks. The decision may depend on where in the country you live.

Once the panes of glass are dry, insulate the greenhouse with horticultural fleece, hessian, bubblewrap, cardboard or bought in greenhouse insulation.

See blog below for lots of getting your greenhouse ready for winter tips.

wooden greenhouse, sliding door, staging

There’s more??

Nah. Cleaning out of plant pots can be left until winter. After all, you’ve got plenty of other tasks to be doing in the autumn garden!

And finally

Whatever you do, enjoy your garden and if Plews can help you with your greenhouse gardening, please do get in touch. Whether you need our Garden Consultancy & Advice Visits, a planting rethink or a birthday present. Plews bespoke Gardening Lessons, where your classroom is actually your own garden make a wonderful and practical gift.

For further gardening advice and inspiration, check out Plews Potting Shed blogs, including the selection below.

And you could come and find us on Instagram Pinterest Facebook YouTube

Feeling nosey? You can have a peek at the progress of my garden renovation, Spitfires and Slow Worms, on Instagram and Facebook Find & follow to discover when the garden open day is.

You’ll also get to see it in person if you come to the Plews Gardening Workshops

And why not get your local garden club, allotment, WI, U3A or other group to ask me along to give a talk?