canopia.com - Palram Canopia (polycarbonate greenhouse kits)
exaco.com - Exaco (European greenhouse kits)
gothicarchgreenhouses.com - Gothic Arch Greenhouses (Mobile, AL)
littlegreenhouse.com - ACF Greenhouses (hobby greenhouse kits)
solexx.com - Solexx greenhouses (made in the USA; greenhousecatalog.com now goes to maker Adapt8)
sturdibuilt.com - Sturdi-Built (redwood greenhouses)
ceresgs.com - Ceres Greenhouse Solutions (energy-efficient year-round greenhouses)
growingspaces.com - Growing Spaces (geodesic greenhouse domes)
pacificdomes.com - Pacific Domes (geodesic dome greenhouses)
arcadiaglasshouse.com - Arcadia GlassHouse (custom glass greenhouses)
hartley-botanic.com - Hartley Botanic (English glasshouses)
bootstrapfarmer.com - Bootstrap Farmer (greenhouses and growing supplies)
farmtek.com - FarmTek (greenhouses, high tunnels, hydroponics)
greenhousemegastore.com - Greenhouse Megastore
extension.org - Extension Foundation (find your local Cooperative Extension)
extension.psu.edu - Penn State Extension
extension.umn.edu - University of Minnesota Extension (cold-climate growing)
greenhousegarden.com - Greenhouse Gardener's Companion (Shane Smith)
hobbygreenhouse.org - Hobby Greenhouse Association
ncat.org/attra - ATTRA (NCAT sustainable agriculture, season extension)
nrcs.usda.gov/high-tunnel - USDA NRCS High Tunnel Initiative (cost-share for hoop houses)
umass.edu/greenhouse-floriculture - UMass Extension greenhouse crops