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I would like to make a basic cold frame but haven't been able to find a suitable bit of glass/old window for the top. I did find a bit of perspex that a neighbour was throwing out, but my dad says you can't use perspex as it doesn't behave in the same way as glass. Anyone know if this is the case, please?
Thanks.

I don't see why it should be a problem, I use a mixture of ex secondry double glazing glass and twin wall plastic from a friends damaged green house. They seem to work fine
I suppose in technical terms perspex might not be as efficent as glass in letting light through, but I have'nt found that the plants noticed

i would have thought that if it lets the light in like glass it would work, after all i use milk and pop bottles as mini cloches!

i did do a search and some one has used perspex before

http://www.gardenersown.co.uk/Garden/Ga ... jects2.htm

it seems like it can do the job ok!

Thanks so much pelmetman and crowsashes - looks like my dad may (for once) be wrong. Never thought about doing a search for other's experiences - many thanks for the link.
I will try it and let you know what happens!

I think I have perspex on mine (must check with hubby!), but it's definitely not glass as I consider that too dangerous, and it isn't polycarbonate as that's way too expensive. So it is something like perspex and has been going strong (home made by hubby) for years and years.

the Norfolk greenhouse company make all theirs out of perspex,

Yup just checked and mine is perspex, nothing like on that link, it's just single layer normal perspex and has overwintered plenty of things that would have died had they not been in it!

crowsashes wrote:i would have thought that if it lets the light in like glass it would work

Not necessarily. Letting light in is only half the story. Keeping infra-red from getting out is the other half. (That's where the greenhouse effect gets its name.). That said, I think perspex and other clear plastics are sufficiently similar to glass that it doesn't make a whole lot of difference.

If anyone's kids want a cool science fail project, they could try measuring the differences in performance between glass and perspex to see just how much of a difference it makes.

In the short term there is no reason not to use Perspex and it has the advantage, as others have suggested, that it doesn't break so easily. Older perspex will discolour in time and it will scratch, reducing the passage of daylight, but if your bit looks ok it will be good for a few years yet.

I have a cold frame with perspex and it has worked fine for the last 4 summers

Thank you so much for sharing all your experiences - my dad is a great gardener, but looks like in this case he may have got it wrong! Don't think I want to be the one to tell him, though!
I will go ahead and try the perspex - at least it will keep it out of landfill for a bit, even if it does discolour after a while.
Cheers everyone - very grateful.

Mines made out of polycarb left over from roofing our old winepress. Its the most expensive coldframe ive ever had!! Works an absolute treat too.

Very grateful for all the tips and info - just a quick bit of feedback, tomatoes growing very happily in coldframe with perspex. Even dads don't get it right all the time!

Question, please!

I have an enormous photo frame that I got given, honestly it must be A1 size if not a bit bigger. The 'glass' is plastic - could I use that as the 'roof' to a cold-frame, do you think? I too thought that things 'had' to be glass - somewhere in my brain went thoughts of light refraction and all kinds of clever things I actually know nothing about, but I haven't tried it because I thought plastic wouldn't work........

I can only say that I imagine so, if plants will grow under perspex or polycarbonate. But I am not a scientific person and didn't even know there was a glass vs. perspex debate in existance (before I found this thread)!