The temperature you maintain in your greenhouse plays an important part in plant growth. Greenhouses are classified as cold houses (unheated), cool houses (55 to 60 degrees at night), or warm houses (60 to 70 degrees at night). Whenever night temperatures are cited you should figure on a daytime requirement about 10 degrees higher. Each of these three classes of greenhouses is suitable for growing certain kinds of saleable plants.

If you live where outdoor night temperatures never dip below 32 degrees, you can run a cold (unheated) greenhouse the year round. Otherwise, you might find it profitable to operate a cold greenhouse until late fall, close it down during the coldest winter months, then resume operations in early spring. In such a house, you can make money on annuals, spring-flowering bulbs, and bedding plants by forcing or starting them in late February or early March. The cold greenhouse is also an excellent place for growing lettuce.

In summer, use the unheated greenhouse for tomatoes, seedling perennials, or almost any plant that flowers in summer. In this type of greenhouse, winter-grown plants should be planted directly into the bench soil. Here they will withstand lower temperatures than if planted in pots. In the following lists are plants I have found profitable to grow under the various conditions specified

FLOWERING PLANTS FOR THE UNHEATED GREENHOUSE
(* Denotes plant usually grown from a bulb, corm, or tuber.)

Spring

Anemone*    Larkspur
Astilbe    Lily-of-the-Valley
Carnation    Narcissus*
Columbine    Pansies
Crocus*    Primrose
Cyclamen*    Saxifraga
Daffodil*    Scilla*
Forget-me-not    Sedum(Myosotis)    Tulip*
Fritillaria*    Viola
Hyacinth*    Violet
Iris*

Summer

Begonia (Tuberous and    Campanula
semperflorens)    Canna*
Browallia    Carnation
Calceolaria    Celosia
Chrysanthemum    Hibiscus
Crinum*    Lobelia
Delphinium    Oxalis *
Dutchman's Pipe    Petunia
(Aristolochia)    Sedum
Flowering Tobacco    Sweet Peas
(Nicotiana)    Tigr idia *
Geranium    Vallota*
(Pelargonium)    Watsonia *

Autumn

Carnation    Nerine*
Chrysanthemum    Sternbergia*
Gladiolus*    Sedum
Hosta*    Sempervivum
Kniphofia*    Zephryanthes
Lily*

Winter

Anemone*    Iris alata9
Crocus*    Jasmine
Cyclamen neapolitanum*    Saxifraga
Erica    Solanum
Fatsia    Viburnum
Freesia*    Violets

THE COOL GREENHOUSE

In the cool house the night temperature in winter should be about 55 to 60 degrees with the usual rise of 10 degrees during the day. In this temperature range, you can grow a variety of plants including all of those suggested for the unheated green house, as well as the plants in the following list, and your heating costs will be far less than those in a warm house of the same size.

FLOWERING PLANTS FOR THE COOL HOUSE
(Winter night temperature: 55-60 degrees.)

Spring
Aquilegia
(Columbine) Azalea Browallia

Camellia Carnation Cineraria Clematis

THE PRACTICAL GREENHOUSE FOR YOU

Clivia*    Lachenalia*
Convallaria    Lilium*
(Lily-of-the-V'alley) *    Nasturtium
Freesia a    (Tropaeolum)
Geranium    Rhododendron

(Pelargonium) Summer

Achimenes*    Clematis
Agapanthus*    Morning Glory
Asarina    (Convolvulus)
(Maurandia)    Cup-and-Saucer Vine
Begonia    (Cobea scandens)
(all types)    Crinum *
Bougainvillea    Datura
Cacti    Fuchsia
(Some varieties)    Habranthus0
Caladium*    Hoya
Calceolaria    Hydrangea
Campanula    Impatiens
Canna*    Lantana
Carnation

Autumn
Bignonia    Mignonette
Browallia    Nerine*
Chrysanthemum    Salvia
Fatsia    Streptocarpus
Flowering Maple    Vallota*
(Abutilon)

Winter
Begonia    Chrysanthemum
(Fibrous-rooted)    Cineraria
Bouvardia    Cyclamen*
Carnation    Stocks
Christmas Rose
(Helleborus Niger)

THE WARM HOUSE
The actual temperature range of a warm house is 60 to 70 degrees during winter nights. However, most of those who grow African violets, gloxinias, and so forth, as well as foliage plants of tropical origin and nature, find they get more rapid leaf growth and plant increase when the night temperature is 2 to 5 degrees higher than that range. The warm house is also used for growing many of the "stove" plants described in old garden encyclopedias and English gardening books.

(Winter night temperatures: 60-70 degrees.) Spring
Acacia    Bromeliads
Aeschynanthus    (various species)
(Trichosporum)    Calceolaria
Amaryllis*    Camellia
Arum*    Carnation
Azalea    Cineraria
Begonias    Epiphyllum
(Tuberous,*  semperflorens,     Episcia some rex)    Freesia*