If you plan to devote your entire greenhouse to camellias, consider having no benches. Most greenhouse camellias are of average size, and though they grow slowly eventually they attain a height impractical for benches. In a narrow greenhouse, you might find it more practical to place a bench on one side and none on the other. In this arrangement, plants will not all be at one height, but low on one side of the house and high on the other, making it easier to move through the center of the greenhouse. As I do not specialize exclusively in camellias, I removed a 5-foot section of bench on one side and placed my five potted camellias on the ground, keeping the rest of the house benched for my orchids. Camellias require very little care, and even when not in flower the glossy dark green foliage of this evergreen shrub is pleasing.
Camellias are said to prefer a temperature of 42 to 45 F, but I have had unbelievable results with mine grown at 52 F night temperature. A soil mix of two parts garden soil, one part peatmoss, and one part sand is recommended. Camellias like soil on the acid side, and good drainage is necessary. They like plenty of water; I soak mine thoroughly every other day all year round, and mist the foliage every other day in cool weather, every day during summer, until flower buds begin to swell. Then I spray a fine water mist into the air above the shrubs rather than directly onto the foliage.
Applications of iron chelate and a complete fertilizer such as Ra-Pid-Cro or fish oil emulsion (my favorite) alternated monthly during active growth are beneficial in conditioning the shrub to bloom prolifically. Iron chelate corrects iron deficiency in soil. It can be used as a foliage spray (1 level teaspoon per gallon of water), or applied to the soil according to size of shrub: 1 teaspoon for plants up to 2 feet, 2 teaspoons for plants 2 to 3 feet tall, and 1 tablespoon per plant for larger woody shrubs. Dissolve the iron chelate granules in a convenient volume of water and apply to the soil; or mix with a small amount of soil or sand sprinkled on top of soil and watered in thoroughly.
When growth activity increases in spring immediately after flowering ends, maintain humidity of at least 50 per cent. Misting the foliage, as mentioned previously, helps to raise the humidity, as does wetting down the walk and surrounding area.
Camellias require light shading. My roller-type shades are kept halfway down the roof in winter, midway between eave and ground in summer. In addition, vinyl plastic shading covers the gable glass in the south end of the greenhouse where my camellias grow. Camellias like a free circulation of air. They may be summered in the garden in semi-shade, as under a tree or in a lath-house. If your greenhouse is climate controlled like mine, they may be kept under glass all year.
To restrain the size of the shrub, prune slightly in spring just after flowering. If you prefer fewer but larger flowers, remove all but the main bud from the cluster at the end of each stem when buds are still small (about the size of a pea). However, if cultural directions are followed carefully, you will probably not have to disbud to get good-sized blooms, and your shrubs will be a riot of flowers and color if all buds are allowed to mature.
Plants purchased from a camellia specialist will probably be growing in large metal containers, and it will be unnecessary to shift them for several years. Mine are still in the containers they came in, and I haven't even added new topsoil; the blossoms this fifth year were so prolific you could hardly see the leaves. When repotting is necessary, take care of this task in spring right after flowering ceases and before new growth starts. Small plants will probably require repotting each year. Larger plants can be given an annual top dressing of fresh soil for several years before shifting into larger containers.
Camellias are reproduced by seed, cuttings, layering, or grafting. It takes from four to seven years to produce flowering plants from seed, but if you would like to try, sow seeds K-inch deep in a mix of one part garden soil and one part peatmoss, with a little sand added for good drainage. Transplant to small pots when 6 inches tall. Cuttings are taken in fall from fresh growth, each at least 3 inches long. Place in sand in a propagating case with bottom heat of about 70 F; in two to three months cuttings will be rooted, ready to pot in 2 1/2-inch pots. Shift to larger pots as necessary.
Camellias may be susceptible to scale, aphids, mealy bugs, and red-spider infestations, but as they are grown so cool and moist, little trouble will be encountered if good air circulation is maintained. Flower buds may drop if humidity is too low, if temperature fluctuates markedly, or if soil is allowed to dry out at any time.
You will do well to purchase mature plants from a local garden center or camellia specialist. Choose varieties with different flowering dates so you will have camellia flowers for six months of the year. The selection is wide: pink, red, white with red markings, rosy-pink; single, double, semi-double, and peony-type blossoms. Mine are all in clear pink shades: 'Flirtation' has 3 1/2-inch single blossoms, 'Brigadoon' has 4 1/2-inch crisp, firm, double flowers.