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| the garden on 29 December 2017 ... |
The mercury hasn't dropped below -6 C, i.e. only our typical winter low, but I think it's the sheer number of very cold frosts we've had, many of them on consecutive nights.
Usually, we'd get around a dozen or so sharp frosts all winter, but this time around it seems as if there's been a dozen every month for three months (not that we've been at home for most of the winter, but we kept an eye on the house and weather via our webcams and also talked to friends on Skype).
Having only recently returned to Blighty and surveyed the destruction of the plants, I immediately started thinking about heating a small area of the greenhouse during future winters. We also brought back more seeds of sub-tropical plants from our travels, which should do well enough outdoors in our summers but won't tolerate even a sniff of a frost and will need protection throughout the winters.
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| killed off by the cold ... |
Heating the whole greenhouse space is a non-starter economically, because it's 14 cubic metres in volume and isn't very well sealed, which is not usually a problem in the summer months when maximum ventilation is the order of the day.
One option would have been to heat our smaller aluminium greenhouse, but even this is 5 cubic metres or so, and it's also of low height and quite awkward to move around in there. Unlike the larger greenhouse, it's just not a place to potter about or enjoy a contemplative cigar amongst the flora, although it is very useful for growing peppers and aubergines in the summer.
Anyway, I looked around on eBay for suitable used materials available for collection locally. I considered one of those mini-plastic greenhouses with a clear flexible polythene cover, which was the cheapest option though not very durable, and also looked at old windows and large all-glass display cabinets.
However, a 1,200 x 800 x 1,850 mm quadrant shower enclosure caught my eye, and I snapped it up for thirty quid. It was brand new and boxed but the owner had never got around to fitting it.
Installing this cubicle in the front corner of the greenhouse furthest from the door would create a walk-in section of around 1.6 cubic metres in volume, much more manageable to heat. I already have a couple of 60W electric tubular heaters which we used in the garage of our previous house, to reduce the condensation when I had my machine tools in there.
On the basis that a typical older house needs around 1 kW of heating power for each 14 cubic metres or so, 120W would be enough for the cubicle volume if it was totally enclosed and insulated. However, the shower panels and the existing greenhouse windows are only single glazed, and anyway I'm not looking to make a hermetically-sealed capsule in which to maintain sub-tropical temperatures, rather just to always keep the space at well above freezing.
Initially I'll try only one 60W heater on a thermal switch that kicks in when the temperature drops to say +6 degrees C. Again, I already have a couple of these thermal mains switches.
I first had to buy a few new lengths of timber, and made a pair of uprights and a baseframe to which to fit the enclosure. I painted the back faces of the uprights before I fitted them to the greenhouse structure, because they're inaccessible when installed. The uprights have a thinner timber edging piece attached which extends out to touch the greenhouse glass.
I measured up and cut the baseframe sections in a series of six mitred lengths to accommodate the curvature of the cubical doors, and glued and screwed them together after I'd first trial-fitted the loose pieces. The assembled baseframe was screwed down onto the floor slabs.
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| trial fit of the baseframe segments ... |
The pre-works completed, I then assembled and installed the shower cubicle. This was easy enough, everything went together as it should.
Inside the cubicle, I made up some strips of thin wood to mount horizontally to the greenhouse framework at the same height as the top rail of the shower enclosure, to create a continuous landing frame on which to sit the roof section. Similar to the vertical uprights, these strips were profiled around the greenhouse mullions so they contacted the greenhouse glass, to make it easier to seal.
I had intended to make the roof from a single piece of rigid multi-wall plastic, typically used as roofing for carports and cheap conservatories. However, these panels are very pricey to buy new from the DIY chains, so I'll keep an eye out through the year for any secondhand pieces coming up for sale locally.
In the meantime, I've made up a simple framework from wooden slats and covered it with a large piece of bubblewrap. The bubblewrap actually came from the shower enclosure packaging, where it was used to protect the glass panels.
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| making the framework for the bubblewrap roof ... |
I used stainless steel staples to fix the stretched bubblewrap to the edges of the frame.
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| trial fit of the bubblewrap roof .... |
I then ran a power cable from the greenhouse mains supply and fitted an outlet socket inside the cubicle, for the heater.
I'd ordered 20 m of self-adhesive neoprene rubber strip to seal all the gaps around the existing greenhouse glass panels. They've arrived, but it's too cold and damp for the adhesive to stick properly, so I'll wait for a few warmer days before I clean the glass and surrounding framework with meths and stick the rubber into the corners to cover the gaps.
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| just about finished - testing the new electrical socket with the tubular heater ... |
As an afterthought, I had an offcut of artificial grass in the shed and I fitted that so it covers the lower vents and any gaps between the greenhouse base and the ground, and also between the frame and glass at the bottom edge.
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| astroturf in there ... |
In addition to the £30 I paid for the enclosure, there was around £15 in timber, £13 for the sealing strips, a tenner for the power cable and outlet socket, and so the total cost was a few days' work plus £70.
So we've now a place to shelter the tender plants during the winter and also to start off seedlings etc in the early spring before the warmer weather arrives, which will be its first use during the next couple of months. The roof will then be stored in the shed over the summer. With the cubicle doors left open, the enclosure area just becomes part of the greenhouse again - there's no reduction in total growing space for the tomatoes and cucumbers etc.
Next winter we'll perhaps hang bubblewrap insulation on the inside of the glass panes, to improve the insulation and help save on the heating costs.
But we certainly haven't seen the last of the frosts yet, so I'll post an update on the cubicle max-min temperatures after a sub-zero night or two with the heater on.
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