The types of plants that can be left in an unheated sunroom in U.S. Department of Agriculture plant hardiness zone 7 can vary greatly depending on a number of factors, including the type of sunroom, exposure to sunlight and the microclimate. At night in the winter, an unheated sunroom may be only a few degrees above the outdoor temperature, making it unsuitable for tender plants. For best growth, plants in a sunroom should receive at least eight hours of light daily.
If you’re unsure of whether any true tropical would survive a stint in your unheated sunroom, experiment with tough succulents. Many stonecrops (Sedum spp.) are hardy, evergreen and grow well in containers, like the eye-catching chartreuse "Angelina" stonecrop (Sedum rupestre "Angelina"), which has soft, bristly limbs. Hens and chicks (Sempervivum tectorum) also work well as container plants and are unfailingly cute. Each grows in U.S. Department of Agriculture 3 through 11.
Though many perennials withdraw their energy into their roots in the winter and forsake above-ground foliage, some keep their cloaks even in the cold of winter. Some, like Lenten rose (Helleborus spp.) work well as container plants, and their broad, leathery and fanlike leaves can bring a tropical feel to an otherwise plain space space. They are super-early bloomers, flowering from February through May. Many grow in USDA zones 3 through 9. Low-growing wild Asian and European gingers (Asarum spp.) feature dark green, heart-shaped leaves that can be speckled or streaked with silver, and grow in USDA zones 4 through 8; both Lenten roses and wild gingers can grow in lower light. Some types of garden spurge, such as the dark-leaved "Black Bird" spurge (Euphorbia "Black Bird") or "Mrs. Robb’s Bonnet" (Euphorbia amygdaloides var. robbiae), grow well as container plants and have unusual foliage and flowers. Both grow in USDA zones 6 through 9.
Some of the most essential herbs for cooking will continue to grow even in a cold sunroom. Some cultivars of woody herbs like rosemary (Rosemarinus officinalis) are hardy and evergreen in USDA zones 5 through 9. Oregano (Oreganum vulgare), mint (Mentha spp.) and chives (Allium schoenoprasum) all grow in USDA zones 3 through 9 and work well as container plants in a sunroom.
For cold-weather sunroom growing, some traditional annual spring and fall vegetables can continue to grow indoors in cool weather, provided their containers are large enough and have drainage holes. Root crops like carrots (Daucus carota var. sativus), beets (Beta vulgaris subsp. vulgaris) and radishes (Raphanus sativus) all like cold weather, but carrots in particular will need a wide, deep pot for best growth. Virtually any type of lettuce (Lactuca sativa) will do well in a pot, as they are shallow-rooted and only need protection from frost to continue to grow. Larger leafy greens also work well, such as kale (Brassica oleracea var. acephala) and Swiss chard (Beta vulgaris subsp. cicla).