Rooftop Deck Greenhouse


I have a deck garden on the 3rd floor of my home in Riverdale. I grow both flowers and vegetables. I’d like to be able to extend my growing season in both directions. I’m pondering eventually adding removable polycarbonate panels to my critter-protection-structure. In the meantime I’m wondering how much protection those “greenhouses” with just a plastic cover would provide to seedlings? I have fairly good wind protection and lots of sun (until the maples leaf out.)

  • I’m not sure what type of “critter-protection” structure you have on the deck. However, polycarbonate is likely a great choice for the panels, as it’s lighter than glass and does not break easily, and has good heat retention properties.   As well, polycarbonate tends to diffuse light that passes through it, so the light can reach areas that it would not if it were passing through glass.  Polycarbonate panels used for “greenhouses” should permit good light transmission while protecting plants from harmful UV rays.  Newer polycarbonates do not cloud or yellow, as did the old ones.  Greenhouse clear plastic film can also be used, but will likely need to be replaced each year; look for sheeting that has UV and thermal protection, as well as anti-condensation properties.

What you are proposing is similar to a cold frame, which is simply an unheated structure that uses energy from the sun and insulation in order to create a microclimate that prolongs the growing season (at both ends). See Toronto Master Gardeners Extending the season with cold frames: A Toronto Master Gardeners Guide.  Although we usually think of cold frames as being located on the ground, the principles – e.g., insulation, draftproofing, proper ventilation, watching for excessive temperatures to prevent plants from being fried – are the same for deck-top gardening.