I found this thread very interesting. Please folks don't convict and sentence me. We have a good mix of gardeners here fro various parts of the world. So IMO does growing zones come ito it but also costing, what individuals can afford etc.
So a friend might say to me. Mike, I want to buy a greenhouse. Great says I. have you any idea just what you expect to grow in it.. Friends, this has actually happened. Well, I'd like to grow lots of exoctic plants.. Me thinks, but matey, you don't know one plant from another. So First hurdle. You want a greenhouse. OK what do you want to grow? you can hear the cogs working. No joke friends, this happens to all of us.
Thoughts of growing exotics. Take trip to your supermarket. Local produce compare to exotics. To grow and cultivate exoctics involve so much, tropical heating misting, dank lower conditions. What's your annual income? Forget it.
In simple terms. Wanting a greenhouse is good, but be sensible. A cold GH is one thing. Basically it amounts to a covered protected area for winter storage. Progessing on. So many gardeners have this mis-conception of early seed sowing and stronger better plants. Wrong! Scientifically and according to the common quote, Mother nature. Each tiny seed has an inbuilt program. You might be able to speed up germination but to continue to proved that extra ongoing heat, light , ventilation and watering plus feeding. Check this against your annual fuel bill.
Sad to say, many garden lovers are duped into believing a GH is the answer to all thing. Believe me. Wrong. OK get a greenhouse, don't wast time heat and money by sowing seeds that actually do best sown direct into the garden. Be sensible. Calculate your calender. Planting out time is when the true spring arrives, when frost are over for this year. Think. Plan. Research. Any fool can stand and drop coins down the drain.