Because I finished construction in the early autumn I put in just a few plants that would get going before the winter. I used this book as a guide: How To Grow Food In Your Polytunnel. I grew some salad - lettuce, rocket and mizuna; onions and spring onions; cabbage, kohlrabi and peas. I also had some herbs that I brought in from the garden in containers - parsley, mint, chives and thyme. I also grew some coriander from seed. I also tried growing some potatoes in bags for harvest in December.
The salads have been fantastic. Once established they provided plenty of leaves right through the coldest months. I draped fleece over them when there was frequent frost and that seemed to be enough protection to stop all but a few frost-burnt tips. The onions, cabbage and kohlrabi are growing nicely. The peas have done well, but I have tried growing them up string and think they would have done better up solid sticks. The potatoes weren't a success. I think I left them a bit late to put in and by the time I harvested them at Christmas there were hardly any tubers. On the whole I was very happy with the outcome.
Now that the days are getting longer and temperatures rising I've been getting the tunnel ready for the spring and summer. I've been improving the soil in the rest of the tunnel that I haven't planted so far. I've been using compost from our local tip. It's only £1 for a 40 L tub if you fill it yourself and is very rich. I'm planning on growing tomatoes, chilli peppers, cucumbers and courgettes amongst other things so I've been adding compost to the thin chalky soil. Now that I've mixed it in and watered it I'm planning to leave it alone until the seedlings are ready to go in. The tomato and chilli seeds are planted out in modules now and the others will follow soon. I'm also sowing more salads to replace the overwintering ones.
To make a little more use of the space I've put in a couple of lengths of square section guttering on the south side of the tunnel above the benches where I raise the seeds. I've filled them with soil and have put in some strawberry plants. The higher temperatures higher in the tunnel should bring them on more quickly. They will need care to make sure they don't dry out though.
I've been measuring the temperature in the polytunnel and seeing how it compares to that outside. I had also read about how a water butt in the polytunnel can help moderate the temperature, especially overnight, so I put another temperature sensor in the water. The image below shows how the temperatures have changed over the last few months. Date is left to right and hour is top to bottom.
The air temperature in the polytunnel (the middle plot) is much warmer in the middle of the day when the sun is shining. The warmer hours clearly get longer over this period and the temperatures rise. However, for the rest of the day the temperatures are similar to the outdoor ones. Having said that, I think the plants benefit from being protected from the wind during those cold hours and the added benefit of fleece for some of them. The warmer temperatures in the middle of the day are definitely warm enough to allow plants to grow.
The water butt temperature in the lower plot is interesting. It shows some of the variation in temperature that the outdoors sees but it is generally warmer. The temperature rises after midday and I believe this is due to the sun shining on the surface of the water butt. The temperature remains high through to the early morning. The water temperature seems to correlate with the high midday air temperatures in the polytunnel caused by the sun. I'm not sure how much the water butt helps the air temperatures in the polytunnel as whole. The air temperature sensor is on the other side of the tunnel about 1 m off the ground. However, I suspect is will help the plants close to it. Also, the paving path along the centre is also probably acting to absorb the heat and release it more slowly, helping out the plants close to the ground.
At the moment I don't have a temperature sensor in the soil. I'm thinking it might be a good idea to help time planting things out.