Growing Decorative Plants in the Greenhouse

There are a great many decorative plants that can be grown under glass, but the gardener who has only one greenhouse should choose plants that thrive in similar conditions.

A recommended average temperature is a steady 55° F. (13° C.) in the daytime and 45° F. (7° C.) at night.


Plants that have large broad leaves and are quick growing often require water every day, while plants that grow slowly or have thick leathery leaves may not need watering more than once a week. Plants that are growing fast and are healthy need more water than sickly plants, or those that have been cut back or are starting to flower. A plant growing in a peaty compost requires less water than one in a sandy compost. Less water is needed in winter than in summer.

The following are some of the flowers that are successfully grown under glass.


Tuberous-rooted begonias are generally more popular than the fibrous-rooted varieties, for they produce large single or double flowers in various shades of red, orange, yellow, pink and white. Fibrous-rooted begonias produce larger plants, but the individual flowers are much smaller. Many fibrous-rooted species have attractive ornamental foliage.


These plants will flower in summer and autumn. The greenhouse should be shaded from direct sunlight and have a temperature of 65° F. (18° C.) during the growing season and 45° F. (7° C.) in the winter.

In March, plant the tubers in boxes in damp peat or leaf mould so that they are only half buried. When they are rooted, and have produced shoots 1/2 in. long, pot them into 6-in. pots in a compost of 3 parts fibrous loam, l part leaf mould and 1 part well-decayed manure. Water sparingly at first, but freely once the plants are growing strongly. After flowering, reduce watering gradually until the tops have dried off. Then turn the pots on their sides, so that the tubers dry out during the winter.

Recommended varieties are:

Victor Boret, orange.

Princess Victoria Louise, pale pink.

Evelyn Tavenat, salmon-pink.


These types of begonia flower in autumn and early spring. They are usually propagated by leaf cuttings taken in spring or summer, or by shoot cuttings taken in February or March.

Shade the greenhouse from the sun, and maintain a temperature of about 60° F. (16° C.) in spring and summer and 50° F. (10° C.) in autumn and winter.

Keep the plants moist in the early stages and syringe them daily. Water sparingly in the autumn, and when flowering is over, reduce watering still further. Keep the plants fairly dry until March, when they may be repotted into 6-in. pots.

Recommended are:

Begonia fuchsioides, 3-ft., scarlet flowers.

B. Gloire de Lorraine, 2-ft., light pink flowers.

B. imperialis, a short, creeping plant, with velvety, bright green leaves, white flowers.

B. rex, 4-ft., silver and purple foliage, pale pink flowers.


Plants with fairly large leaves and large heads of daisy-like flowers in white, pink, red, mauve or blue, which bloom from December to May.

Sow the seed any time between April and July in John Innes seed compost at a temperature of 65° F. (18° C). When the seedlings appear, pot them off into 3-in. pots and later into 6-in. pots, using John Innes potting compost No. 2 or Eclipse No-Soil compost.

Place the pots in a cold frame from July until early October, when they should be moved to the staging of the greenhouse.

Shade them from strong sunlight, and maintain a temperature of 55° F. (13° C). Feed the plants twice a week from September onward with diluted Liquinure. Always keep the soil in the pots moist, but do not over-water.


Recommended large-flowered varieties are:

Brilliant Ruby

Pink Pearl

Royal Blue

Recommended small-flowered varieties are:

King, rosy-carmine

Sky Blue

White Star


A perennial that produces flowers of white or various shades of pink, cerise, crimson or salmon-scarlet during the winter. The foliage is often marbled.

Sow seeds ¼ in. deep in John Innes seed compost any time between August and November, or between January and March, at a temperature of 55° F. (13° C). When the seedlings are about I in. high, pot them into 3-in. pots, containing John Innes potting compost No. l or Eclipse No-Soil compost, to continue growing at a temperature of 50° F. (10° C.) on the greenhouse staging. During the summer the pots may be placed outside in a cold frame, shaded from direct sunlight. Move them back to the greenhouse and a temperature of 50° F. (10° C.) at the end of September.

When in flower, feed cyclamen with diluted Liquinure once a week. After the flowers die, keep the corms almost dry from May to July, and repot them in August, leaving the tips just above the surface of the soil.

Syringe every few days until new-growth appears, and then water daily until the plants cease to flower.


Ericas, or heaths, are small shrubby plants bearing white, pink or mauve flowers from late November to August according to species.

The most commonly grown is Erica hyamelis from South Africa, which produces white flowers flushed with rose-pink from November to February. This erica is a lime-hater and should be given a peaty-sandy compost and watered with soft water. Maintain a temperature of 45 to 55° F. (7 to 13° C).


Plants with tuberous roots and huge, bell-shaped flowers of pink, crimson, purple, lilac or white, which bloom in the autumn.

Sow seeds in John Innes seed compost in March, and when the seedlings are 1 in. high, pot them into 3-in. pots, using John Innes potting compost No. 1. The pots should have good drainage, and should stand in a shady part of the greenhouse as near as possible to the glass. The temperature from January to October should be 65° F. (18° C), and from October to January 50° F. (10° C). Feed once a week with diluted Liquinure as soon as the buds appear, and cease feeding when flowering is over.

If gloxinias are raised from tubers, pot these up singly into 3-in. pots any time between the middle of January and the end of March. Do not completely bury the tubers, and press the soil fairly firm. When the tubers are growing well, pot them up into 6-in. pots, using John Innes potting compost No. 2. Give only a little water in the early stages of growth, but when the leaves are larger and the plants are growing vigorously, water more freely. When flowering is over, reduce watering until the leaves die off, and then keep the tubers dry until the following spring.


Zonal and ivy-leaved pelargoniums are known as geraniums; both these and a third type, show, grow well in pots. The leaves are green or variegated, and the flowers grow on firm stems.


These flower in spring and early summer. Stand pots near the glass of the house, in a temperature of 45° F. (7° C.) from September to March, and 50° F. (10° C.) from March until the end of May. After flowering, place the pots outside in the sun until the end of September.

Take cuttings of firm ripe shoots 3 in. long in July or August and root them in a mixture of sand and peat in a cold frame. When the cuttings have rooted, pot them into 3-in. pots in John Innes potting compost No. l and after a month pinch back about 1 in. of the growing point of each plant to encourage busy growth. Pot up into 6-in. pots early in September, and repot old plants at the same time. Water freely from March until June and moderately at other times.

Recommended varieties are:

Chelsea Gem, pink flowers, silver leaves.

Happy Thought, crimson flowers, dark green leaves with gold butterfly markings.

H. Cox, rose flowers, pale gold leaves marked with purple, red or cream.

Hills of Snow, purple flowers, creamy leaves with white markings.


These flower at almost all seasons, but should be shaded from the sun when in full bloom. The winter-flowering types will thrive in a sunny cold frame from June to September, and when returned to the greenhouse will need a temperature of 50° F. (10° C.) until the following March. For summer-flowering plants, maintain a greenhouse temperature of 40° F. (4° C.) from August to March, and 55° F. (13° C.) from March till May.

Take cuttings of zonal pelargoniums in late summer. When these have rooted, pot them up into 3-in. pots, and later into 6-in. pots. Feed with Liquinure twice a week when the plants are well established. At the end of the season prune back the old plants quite severely.

Recommended varieties are:

Barbara Hope, carmine.

Caledonia, purple,

Drummer Boy, vermilion.

Hope, turkey-red.

Mrs. S. J. Ward, rose.

Prince of Wales, Tyrian purple.

Willingdon Gem, mandarin-red with a white eye.


These flower in the summer and are propagated by cuttings taken in August or September. When the cuttings have rooted, put them into 3-in. pots, using John Innes potting compost No. 1. Cut back the plants in February or March and repot them when necessary into 6-in. pots. When the plants are well established in 6-in. pots, feed twice a week with diluted Liquinure. Water freely during the summer but moderately at other times.

The temperature of the greenhouse should be 50° F. (10° C.) from March to September, and -10° F. (4° C.) from September to March.

Ivy-leaved pelargoniums look well in hanging baskets or urns, or trained up trellises, and they also make a good cover for banks or high walls. They are not completely hardy, however, and should be moved back to the greenhouse in late September.

Recommended varieties are:

Galilee, double pink.

La France, imperial purple.

Lilac Gem, pale mauve.

Millfield Gem, a hybrid, rose-blotched and feathered with rosy-red.

Neon, vivid cerise.

The Duchess, white and Tyrian purple.


Many kinds of primula can be grown successfully in a greenhouse, and most of them flower in the winter and spring.

Sow the seed in March or April in John Innes seed compost, and when the seedlings are l in. high, pot them up into 3-in. pots, using John Innes potting compost No. 1. Always pot primulas firmly and a little more deeply than other plants. Roots often form from the base of the lower leaves, helping to give extra support to the plants, which otherwise tend to be top-heavy.

Primulas may be brought into flower in their 3-in. pots, or they may be potted up into 6-in. pots. Keep the pots in a shady corner of the greenhouse at a temperature of 50° F. (10° C.) during the growing season, and 55° F. (13° C.) during the flowering season. Give plenty of ventilation.

Feed the plants once a week when the compost is full of roots, but stop feeding when the flowers start to open. Keep the compost just moist; never over-water, or the leaves will turn yellow.

Some hairy-leaved primulas, particularly Primula obconica, may cause eczema or primula rash to break out on the hands and forearms, and those who are allergic to these plants are advised to wear gloves when handling them.

Recommended are:

Primula obconica, large flowers in shades of pink and mauve in winter.

P. malacoides, the fairy primrose, bears dainty flowers of lilac, pink, rose or white, in tiers round fairly tall stems. May be brought into bloom at almost any time by sowing the seeds at different times.

16. February 2012 by Dave Pinkney
Categories: Featured Articles, Garden Management, Gardening Calendar | Tags: , , , | Comments Off on Growing Decorative Plants in the Greenhouse


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