New Gardener Series: Keeping a Greenhouse

You may have got to the point in your gardening and are thinking that you need some undercover space. There may have been a few years of you using those pop up plastic cover greenhouses, the ones that are referred to as mini-greenhouses in garden centres and have four shelves which tend to collapse under the weight of seed trays. The kind of greenhouse that is easy to build, gives you a real sense of achievement and then kicks you in the crotch when the first puff of wind knocks it over and you realise you should have weighed it down. We have seen many a gardener give up at this point and go back to the front room to ignore their plot for another season their seedling smeared against the plastic cover of the mini-greenhouse. However, a permanent greenhouse is a completely different beast and you may want to consider building one.

How to maintain a greenhouse


We have had our greenhouse now for four years and it has gone from a brand new spanking looking thing to being bashed by gales. Now, we have broken one of the most important rules about building a greenhouse. Most garden journals recommend that you position a greenhouse nearer the home for easy access, our greenhouse is halfway up our garden and worse still, on a slope. The problem is that most of our garden is on a slope, what can you do? We could have terraced but the earthworks would have been costly and in the end we plumped for positioning it on the flattest part of the garden we had where an old shed was and where our first 20x15 gardening plot sprung up.

Where to position a greenhouse

We come to orientation - no, this doesn't mean get a map and a compass, though the compass will come in very handy - you need to make sure for year round growing that the ridge runs from west to east (1), and the whole structure faces south. Now, in small gardens that can't always happen and you can run the ridge north to south (2), with the long sides on west-east orientation. There is a difference if you choose to do either one, with (1) you can grow crops pretty much all year round if you supply some heat, and insulation (you can see in the photo below that we opt for fleece but you can use bubble wrap as an additional layer in the greenhouse), but; (2) means you can only grow in summer as you won't get enough light in autumn/winter. Sometimes we gardeners have to work with what we have.

How to keep a greenhouse clean

It's important to keep your greenhouse clean, this stop the build up of bugs and viruses that could kill your seedlings. You can clean the inside of greenhouse over autumn, after you have cleared summer crops and before planting any late crops for harvesting over winter. You can clean with any garden glasshouse cleaner, we don't want to name any because the choice should be your's as there are organic ones and sprays that would kill a moose in Canada as you spray in Croyden. We clean the external glass too as it does maximise light at this time of year. Clean glass helps to heat up the greenhouse on sunny days (just because it's cold and sunny doesn't mean it is under glass and some of the most pleasant cold sunny winter days can be spent in warmth in a greenhouse). We will also clean the external glass again in spring. You can also get sulphur bombs for greenhouses too, they're not as readily available anymore because some dumb fools thought they could light them and stay in the greenhouse, cue ambulance and some deaths. A sulphur bomb kills bugs and mites that will attack your crops and if you do use them, do so in an empty greenhouse (no crops), light them, walk away, close the greenhouse door and don't come back until the instructions tell you to do so. If in doubt, read the instructions! It is advised not to position your greenhouse by trees or anything that can shade it with it's canopy (tree) or falling leaves (tree, hedge, confused Icarus). We broke this rule too. We are on an exposed site and that means we have opted for hornbeam hedges,  now in their fourth year and around six feet high. This has actually helped our greenhouse, along with bar capping (you can see the white plastic strips that hold in our glass in the photos) which makes the structure more rigid, this stops (in theory) the greenhouse from being blown away. There have been hair raising moments with winds in our garden and the last three gales, Abigail, Kate and Barney, have made us wonder whether the greenhouse would still be there in the morning. Which brings us to a couple of final points, get yourself some bricks or stone, use it on windy days to hold the door from moving (basically our stone is put in position from autumn and we don't move it until spring - except when we want to get into the greenhouse). A common mistake many new owners of greenhouses make is they do not secure the door in windy weather and doors are often the weakest point on greenhouses. By simply placing some bricks or stone at the bottom and on either side of the sliding door you won't see your door sail off in the first wind and your greenhouse lift up in the air like a hot air balloon. Finally, after any bad weather, check your greenhouse, check the clips (you can see our's in the first photo) and the glass to see if it has shifted (you can buy your greenhouse with horticultural glass or toughened glass, we advise the latter, it can be more expensive but it is worth the money). Tease the glass back into place and bend back the clips. A greenhouse takes maintenance and care but it does pay dividends, our 12 x 8 greenhouse is the powerhouse of our garden and frankly we'd love a second one, and we bet you will too.

Ventilate your greenhouse, it is not a hot house

In the photo above you can see our greenhouse before we bar capped it, no white strips, but you can also see two windows - also known as lights or vents - you can choose with greenhouses to have automatic openers which respond to heat inside the greenhouse or manual (you do it yourself). We don't use automatic vent openers because we are on an exposed and sometimes very windy site. You will also notice that our vents are on the north side of the greenhouse away from prevailing winds, which for us tend to come from the west and south - when they come from the north we know we are in trouble, the last one shifted a huge shed we'd just finished building. Good ventilation is important in summer, remember that this is a greenhouse not a hot house, so your greenhouse door should be open during the daytime during summer months and at least one vent should be open too to circulate air or else you will cook your plants. Don't forget good staging too, you can see more about how we built our's for £2.78 here.

New Gardener Series

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