I live in the middle of the South Island of New Zealand. Similar climate to the UK. I have wondered about growing some things under cover in winter before. The closest I have come up until now is using a proper second-hand cold frame. Once that fell apart, I used the panes of glass to cover early seedlings in punnets within polystyrene open-topped boxes which I got for free, placed in the sunniest spot. That was a really great way to get seeds off to an early start as early as the beginning of August here (equivalent to the beginning of February in the UK).
This year I finally decided I could make good use of a small glasshouse. For the first time, I managed to successfully grow over summer a good number of tomatoes in containers and I know these plants can be kept going if I can keep them under cover. I also have some citrus bushes in pots, and some feijoas in containers which actually have fruit on them, which will only survive to ripen if kept under cover.
I have grown some (still tiny) seedlings from tamarillos and they will need protection if they are to survive the winter.
So there was nothing for it really. This year is the year, this winter is the winter, for me to launch into using an actual glasshouse.
I have had various thoughts of how to build my own. The final result has been to use the frame from an old gazebo which previously gave me many years of protection for my stall at markets, but has suffered from metal fatigue so can no longer serve that purpose. However, with a few modifications, basically reducing the size down from 2.4m x 2.4m x 2m high. I needed to reduce the size really because the frame is not over-strong and we do get strong winds where I live and I don't have a very big area which is protected from winds from all directions, plus the smaller it is, the less I have to spend on plastic sheeting to cover it.
The aluminium poles were each made up of several pieces, so I just left out sections when I made up the frame. I used short lengths of hose duct taped to the inside of the tubes to fill in gaps in the frame where needed. I have ended up with a frame approx. 2m x 2m (wider at the bottom than at the top) and 1.5m high at the corners but peaking higher in the centre.
The frame has been up for a few weeks so I can check that it's in the best spot with regard to sun and protection from wind. I braced the bottom of each pole by duct taping it to heavy pots containing plants inside the structure. Because it's so small, I have had fun shifting plants in and out, deciding what needs to stay and what can be left out over winter. I do have to be able to get in with buckets of water to water the plants, so I did have to leave a few small gaps between plants! There won't be a door, just a gap in the plastic at one corner which I will squeeze through with buckets (I am a small person - it helps ).
I have placed the frame up against the sunniest wall of my metal-clad cottage and I will decide as the weather gets colder whether to leave the back wall without any plastic at all - that gap will be the only ventilation for the glasshouse - or whether to put black polythene up as the back wall of the glasshouse to radiate more sun/heat into it.
I have bought the clear plastic sheeting now. Total cost NZ$24 = total cost of glasshouse! We are having a very hot March. Hopefully April will be cool enough for me to finally attach the clear plastic sheeting with, of course, duct tape.
Happy gardening!
From Judith in New Zealand