Polytunnel vs Greenhouse

[DJmrcmb]

I'm looking into providing a new polytunnel at our gardening project.

At the moment we grow veg on a plot of land nearby, but that’s not a problem. We also grow veg in two rows frames on our main site and this is what I’m looking to change. This has been going on for a number of years and thought it would be more practical to replace them with a polytunnel or a greenhouse.

The idea being so we could grow things all year round. Now, I'm no expert at this kind of work so I'm look for advice.

The site is not based on open soil but a hard surface. So, is it possible to have a raised poly? i.e. a polytunnel sitting above raised beds/frames Or would a greenhouse be a more practical solution?

Would either of these solutions allow for temperature and/or light control?

Any advice on this would be gratefully appreciated

[Allan]

I can think of only these points.
A polytunnel could get a bit colder than a greenhouse as the infra red will go through polythene but not glass. Greenhouses cost a lot more than polytunnels.
It is difficult to fit vents in a polytunnel other than a vented skirt or something at the ends.
Either will need anchoring,weights are usually inadequate.

[richard p]

a polly tunnel frame can be bolted down to a hard standing, then add a wooden base rail to fix the poly to. if the wooden base is made a foot or so high vents could be incorporated all round easily.

[Geoff]

I think it depends on area you want to cover and your budget. I had a patch I was considering covering that was about 16'x22' and couldn't decide what to do. In the end I decided it was a bit small for a tunnel and I didn't fancy the hassle of cover changing. I bought the cheapest 16'x20' greenhouse I could find. It is an Elite. I bought it with 3 louvres and 4 roof autovents in standard hoticultural glass (only use this if it will be safe). I found the best quote I could on the Internet then asked Broadoak on Torrisholme Road if they wanted to beat it and they did. I have lost some glass but it has performed well.
Unless somebody tells you otherwise I think tunnels on hard standing could be tricky - maybe an intermediate design like Keder or the up market Northern Polytunnels design would work.

[DJmrcmb]

We do have a poly at the moment, which just sits on the tarmac, but it's more for the plants after they've left the greenhouse and maybe a small amount of veg in tubs.

Just suppose we went for a greenhouse, though a poly isn't ruled out. How high off the ground would you take it. I mean with a brick base. The frames we have are only about a foot from the ground, the soil level possibly slightly less. Would a bit more height be any better?

And another query. This greenhouse would be quite long. Would it be best to partition it to allow for so you could dig out or clean one end while the other is still growing? So there'd always be food growing throughout the year?

[Vegman]

may I offer my five penny worth re polys v greenhouses.

I used to grow commercially in polytunnels 6m wide by 20m lg and can say that they are fine for plants that only require frost protection or say for veg like Dwarf Beans, lettuce etc to raise the soil temp a bit to immitate spring. Anything that needs heat tends to be a bit high on the energy costs. A poly without side vent curtains depending on its length can suffer from 'dead spots' or stagnant air. They do need a door at each end for a thro draft no mater how short. In summer they also may need the side plastic raising to cool it down. Warm air rises and collects in the top zone. The thro draft is required to replace with cooler air from the base.

Greenhouses are easier to insulate, have roof and side vents but are expensive. I guess you need to ask what do the plants need. Our greenhouses grew the bedding and protected the baskets while the polys held the Herbaceous and veg plugs. plus the larger specimen plants in summer when the greenhouse can be too hot.

Polys will shade themselves after a while as the plastic becomes milky. Greenhouses can be shaded fairly easily with white fleece or insulated with bubblewrap. either way I think generally people do not pay enough attention to cleaning the greenhouse. Ive mentioned this in past threads and posts but without good light in the winter and good hygiene inside it wont matter what you grow in. We tried all sorts of fancy brushes etc that connect to hosepipes but generally the job was lousy to do and you got wet with trying to launch the detergent onto the high walls and roof.. The best thing we found which caravaers use is called a supepray hose end spray. looks like a miraclegrow plant feeder but can use with anything dilutable. we used jeyes for the inside and detergent for outside. Its about the only thing that can get detergent onto the top of apolytunnel to clean it without damaging the plastic. You need to get rid of that grey green mould that tends to build up on the surface which reduces the light. A good blast all round the inside with Jeyes fluid took care of the hygeine.

One comment I could make about hopw high the brick walls should be under a greenhouse. if you grow of waste high staging then no piont having glass down to the floor. if you have soil beds in the base then the bricks should be as high as the bed. If you build a brick base for a standard greenhouse. make it a least three courses high and incorporate a few ventilation bricks with slid covers. Much cheaper than glass wall vents and they are at ground level so the input of air is cooler and will push the warm air out the rooof windows in summer.

[DJmrcmb]

Ok, good information so far

Now, Artificial light. I've no idea how to go about this. Would this enable you to grow things, you'd normally grow in lighter conditions, during the darker times of the year?

And how would you install such a thing? Would it depend on what you were growing?

Would you perhaps need to section certain types of plants off that needed different growing conditions?