I have mentioned having bubble wrap in mine in Belgium. You can add extra insulation by making a fleece tent over more susceptible plants but both of these reduce light levels, no matter how clean the glass, bubble wrap and fleece so are devices for keeping plants alive rather than actively growing.
To grow plants actively in a greenhouse thru winter you'll need insulation, special daylight effect lighting and heat. Cheaper to buy your veg at the shops.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
@pansyface Yes, Benson is often reported as one of the coldest places in England, but it tends to be localised cold, and the rest of us are usually several degrees warmer :-)
I used to work in Redhill, Surrey, read it was officially the coldest place in England, got frosts there earlier, and later in the year, than where we are now.
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To grow plants actively in a greenhouse thru winter you'll need insulation, special daylight effect lighting and heat. Cheaper to buy your veg at the shops.