How to Windproof Your Greenhouse

If, like me, you garden in a very windy location, you’ll know what havoc it can wreak. Twice I’ve had panes of glass blown out of my greenhouse. Both times I was fortunate enough to spot the problem quickly and temporarily patched the gap with a sheet of plastic-covered cardboard, preventing further problems. I was lucky – while buying replacement glass I got talking to a lady who had lost almost every pane out of her large greenhouse, and not for the first time!

On both occasions the glass blew out on the leeward side, which should have been relatively sheltered. That seemed odd, so during the next storm I decided to go out and observe what was going on. Imagine my surprise as, fighting to stay upright against the wind, I witnessed two panes, one above the other, billowing outwards from within, barely held in place by the S-clips that joined them!

Keeping Wind Out of Your Greenhouse

Once wind gets inside a greenhouse it will do its best to force its way back out again. It rarely leaves the same way it came in. As more air is channelled in the pressure builds up until, inevitably, something has to give. Glazing clips pop off, and panes are blown outwards.

The most obvious way for wind to gain entry is via a missing pane of glass, so replace any that have already been blown out as soon as you can. Most good glazing companies keep standard sizes of horticultural glass in stock, but if you have unusual sizes or need toughened glass or polycarbonate then you may have to order it. Cracked glazing can be temporarily fixed with glazing repair tape but, again, it’s best to replace it as soon as possible as the repair could fail during further high winds or under snow.

When I installed my new glass panes I doubled up on W-clips (the ones that hold the glass into the frame) all round; the number of clips that originally came with the greenhouse was nowhere near enough! Silicone sealant can be used to secure the glazing clips in place for additional strength.

Some greenhouses can be fitted with bar caps to hold the panes in. These seem to be the most secure option, so it’s worth checking if they’re available for your model. Unfortunately they’re not made for my greenhouse, so instead I taped each pair of overlapping panes together with glazing repair tape, inside and out, as this seemed to be the weak point.

Wind can creep in through the tiniest of gaps in a frame, so it’s important to block them up. If you look carefully you may find that the frame doesn’t meet perfectly at the corners or at either end of the ridge. I used tape inside and out to cover the holes because that’s what I had handy, but silicone sealant would be a more permanent solution.

If your greenhouse door has a lock or catch, make sure it holds the door very securely shut. Otherwise, a heavy brick wedged against it should stop it from blowing open.

Make sure any rubber glazing strips and seals around the door, windows and other vents are in good condition, and replace if necessary. Windows and vents must close snugly. I have found that sticking a strip of foam anti-hotspot tape (intended for polytunnel use) around the frame of my greenhouse’s roof window vent gives it a much better seal and stops it rattling in the wind.

In some cases a whole greenhouse can become airborne, especially lighter ones with polycarbonate glazing. Avoid this by making sure that it’s well anchored down. Mine is bolted to a metal base, which sits on soil but is deeply concreted in at each corner. It has never moved.

Greenhouse Protection from Wind-borne Missiles

So that’s how to keep the wind out – but what about flying objects? The most obvious thing is to tidy up your garden before a storm. Put away or tie down garden furniture, plant pots, children’s toys and gardening tools. The ease with which wind can hurl heavy objects about is astounding, but even quite light wind-borne objects have the potential to smash glass.

That doesn’t stop things blowing in from elsewhere however, so in some cases you may need to physically shield your greenhouse. In areas where winds are really ferocious, some gardeners surround their greenhouses with slatted wooden fences, wind netting, or hedging to filter the wind and deflect wind-borne objects. There is a downside to this as it can also reduce the amount of light reaching plants inside, but if your greenhouse is in a serious wind tunnel or on a very exposed hillside, a wind barrier may prove essential.

Once the strong winds have died down, take some time to check over your greenhouse. Occasionally glazing clips can jiggle loose and end up behind the glass, so make sure they’re all still in their correct position, securely holding down the glazing. Cover up any gaps left by broken or missing panes until you can buy replacements. Sheets of plastic, tarpaulin, or even an old blanket is better than nothing as a temporary wind-blocking measure.

What other methods do you use to protect your greenhouse from wind? Drop us a comment below and share your tips with us.