Poly tunnels

When we were offered the site there was an old frame of a poly tunnel in the field which we brought into use in the autumn of the first year. Since then we have been given two more tunnels which we have made into poly tunnels as well as the one shown below which was in rather poor condition and so we have replaced the netting and continue to use it as a growing cage. This blog describes how we have been developing and using our polytunnels.

An old frame which we were given in summer 2010 and now use as a fruit cage

Renovating the first poly tunnel

In winter months temperatures can go quite low, so the doors are always shut, with a little air filtration allowed in vents in the top of the doors. In Poly tunnel 1 we have the system which takes the warmer air from the daily solar gain, down below ground level into a covered pit of 300 water bottles which in turn warms them. Then the warmer air derived from the water bottles percolates out of the exit pipe during the night. The whole system is powered by a solar panel, battery and small fan. In the summer, we open the doors and put in the grilles to keep the wildlife out and allow the air to circulate. A Poly tunnel team was set up late in 2011 to manage the three tunnels.

Sue and Steve set up the solar gain box with 300 1pint milk bottles containing water

Warm air is extracted by a fan driven by a 12 v battery powered by a solar panel and pushed down into the solar gain box below ground level.

Currently we have three poly tunnels measuring 10m x 3.4 m, giving a total surface area of 103 sq m. In them the winter crops of Amsterdam forcing carrots, Mizuma, Mispoona, rocket, winter salad, over winter Chard are grown. It is possible to grow other crops, but not in sufficient quantities to satisfy the demand of the farm.

Good quality benching is very useful

Sue and Steve setting up the poly tunnel

Many crops are started off in our polytunnels

In the spring the main crops grown in the tunnels are tomatoes, sweet peppers, cucumbers and chillies. Crops are sown from January onwards. Sweet peppers need a very long growing season, so these are started off at home in the hot box (large propagator) by the team leader. Cucumbers are also started off with a bit of bottom heat at home, to ensure an early crop.

In the late winter and early spring one of the tunnels is available for the teams so start off their crops. Many Renovation seeds are sown here including onions, leeks, squashes and courgettes then transplant into individual pots, then harden off outside under sheets of glass before being planted into the plots.

Good husbandry is practiced and so few diseases develop in the poly tunnels. Some blight has occurred in tomatoes mainly as a result of blight on the potatoes being brought in. Now we are growing mainly blight resistant potatoes, but people who have been working on potatoes are discouraged from entering poly tunnels when the atmosphere is warm and damp. A little grey mould has been found on Cucumbers. With blight on tomatoes we have tried using Bicarbonate of soda, and eco washing liquid and olive oil in a spray, with good success on small outbreaks, but have resorted to Bordeaux Mixture in serious outbreaks, with great success.

The team uses good quality potting compost, some of which they make themselves in pots and trays. They try to apply “no dig” policy and at the start of each season when they cover the beds with manure and home grown compost. Sometimes a top dressing of chicken pellets is applied and in the case of the tomatoes, they apply tomato feed.

The team find that they can bring crops forward by at least two months using the polytunnel. Clearly the environmental conditions have to be right outside for leaders to consider planting out into plots or beds, but the fact that we can grow on plant materials earlier means that we can extend some crop seasons by as much as two months.

Thousands of seedlings start life here

Cucumbers growing in a polytunnel

At the moment the leader considers that the major obstacle to further continued development is a lack of power. We are currently using solar power to drive the pump to supply the water in the tunnels, but more could be done with more power. The polytunnel leader has considered hydroponics, but thinks that we do not have a suitable water supply for this. Currently our water supply is mainly from a pond which is shared with a model boat club who have added dyes in an attempt to suppress plant growth in the pond. The polytunnel team leader considers hygiene in the water supply is important and feels that there could be issues with our current supply of pond water. There could be a case for extracting water from the nearby River Itchen, storing it in IBCs, adding selected nutrients and letting it run slowly into the beds in the polytunnel.

Having more space, more poly tunnels and more people in the team would give the polytunnel team more crops, and a better facility for raising seedlings for external plots. We perhaps could experiment with other crops, including small melons, indoor grapes and strawberries. We would need two or three poly tunnels dedicated to strawberries in order to comply with our principle of supplying enough for 100 stakeholders. Growing in poly tunnels, by lengthening the season is very successful and productive and it is certainly an area where more thought and development is needed.