Tuesday, 14 September 2010

Mini greenhouses

I don't have a proper (glass) greenhouse in my garden. In fact I don't think there is a good place to put one. Instead, I have a couple of what I call "mini greenhouses".

The two mini-greenhouses

They are made of PVC stetched over metal frames. I have had them for several years and they have turned out to be really useful. You can buy them for about £15 in any good garden centre at the "right" time of year, meaning the times when most gardeners are thinking about acquiring some crop-protection - generally early Spring and late Summer - but they are seldom available in high Summer.

In the Spring I use them for "hardening off" young plants, giving them a bit of shelter from cold winds and heavy rain whilst allowing them to benefit from as much natural light as possible. Tiny seedlings often go stretched and "leggy" if you keep them indoors on a windowsill, because however assiduous you are with moving them around to follow the daylight they never get enough of it. You really need to get them outside. The mini greenhouses are ideal for this since you can move them around the garden if you haven't got a place that gets the light for most of the day. When I am at home I often shift mine in the middle of the day to ensure that the plants get both morning and afternoon light. A point to note though: although the plastic covering will stop any frost settling on the plants underneath it, the temperature inside the mini greenhouses won't be much different to the outside temperature -- just a degree or two at most -- so you still need to think carefully about what can survive and what can't.

The mini greenhouses come in a variety of different sizes. The ones I have are two-tier ones, but you can get three- and four-tier ones too. I think the taller ones might be a bit unstable, though they do come with anchor points on the back so that you can strap them to a wall. I sometimes have to weight-down even my two-tier ones with a few bricks to stop them being toppled over by the wind.

2-tier variant

The various components are easily assembled and disassembled, so several different configurations are possible, and if space is scarce you can always pack them away when you're not using them. Wire mesh shelves are provided, along with rods to support them. When I am using the greenhouses to hold seed trays, which are quite shallow, I use both shelves, as shown in this next photo, but when I'm using bigger pots or containers I often omit the lower one and just place them on the ground rather than on the shelf. (Point to note: the supporting rods cannot be fitted or removed without first removing the cover.)

Two shelves fitted, one with supporting rod, one without

Later on, when some of the plants get quite tall, I remove both shelves and the supporting rods, to make a single taller unobstructed space, which is good for things like young tomato and chilli plants.

A tall unobstructed space

One unfortunate aspect of the design is that no matter what you do the top of the construction is bound to sag a bit, and does tend to collect rainwater. It ought to have a third hoop in the middle. Still, thinking positively, I see the extra weight the rainwater contributes as being just another aid to stability!

The roof tends to sag

Replacement plastic covers are available separately, though I don't think you can buy the metal frames separately. I am on my second set of replacement covers now (Each one has lasted 2 or 3 years). After a couple of years the PVC goes cloudy and brittle (and my first ones were savaged by cats wanting a bit of shelter and trying to get inside!). They cost about £5 each for the two-tier version, and are readily available on the internet. I got my most recent ones from a place called Garden Centre Online A point to note here is that it pays to shop around -- exactly the same product is often available from several suppliers at completely different prices, and NB: delivery charges vary enormously.

The PVC cover is attached to the frame with some fabric ties. The cover has a zipped front that can be rolled up and secured out of the way with another fabric tie.

Zipped cover rolled up and secured

I think these products are a very worthwhile investment, and I have used mine extensively.

Now that Autumn is coming on, I'm thinking about putting a few things under cover, and my "Son-of-Wilma" tomato plant will be one of these. I do hope it can produce some ripe fruits before the cold weather gets it.


  1. You're right, the plastic top does give way. I've scrubbed the top of mine several times, but it's getting to the end of its life.

  2. Mark, I have 7 of these in different sizes but never use them outside. I use them for places to hold my seedling in the summer and early spring. I do however have 3 small portable greenhouses that I move into in April until time to plant. One is 7'X7', one 6'X8' and one 6'X6'. They are wonderful. I then move the mini greenhouses without the cover into the portables for the shelving. It works great.

  3. Just stumbled across your blog looking for something to expand my growing space for starting seedlings - these look great! Just wondering, how many seed trays can you fit per level?

    1. Hi Tamsin; I usually fit three standard-sized seed trays on each level. Two would give plenty of airspace around them, but I like to squeeze the maximum benefit out of my kit!

    2. Thanks Mark, I've picked up two - just need some weather suitable to build them in now!

  4. Hi Mark, I have the same mini greenhouse as your pic shows. I'm wondering about the open bottom as my cover is about an inch off the floor. I have baseboard heat so the humidity tends to get very low. I'd like to keep my greenhouse close to the window (where the baseboard heater is - only window available) and think the dry air will be a bit much as it would go right through the bottom of the greenhouse. Would it be ok to close off the bottom with attaching a sheet of plastic underneath? Any ideas?

  5. Sounds as if your plan would be OK, but if you are worried by dry air, why not put a bowl of water in the greenhouse to assist with humidity?

    1. Thank you for responding. I had plants set on stones with water in containers but my croton - Bush on Fire - was still dropping leaves unless it was covered with its own plastic as well. The leaves weren't even changing color, they would just wilt and flop, starting with the smallest plant, then the next size all in the same pot - still have the largest but under plastic which is kind of sad because its a beautiful plant and hard to view this way. My snake plant and dieffenbachia are doing great without covering and are outside of the GH. I'm pretty new at this and really hate it when plants die on me. lol

      Also have twin orange trees (started from same seed) in the GH also under extra plastic. The one has done really well and is about 2 inches, has 6 leaves while the other is staying at about 3/4 inch but has grown 3 leaves. Maybe its a runt?

      So I've now covered the bottom shelf in plastic to block some of the dry air from the heater as its at the same level as the open bottom of the GH. Can you give me an idea of what the humidity should be inside a GH for houseplants? I'd like to be able to take plastics off the plants to be able to enjoy them at some point.

      Thanks again, I appreciate the response.


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