A greenhouse with good light and sufficient warmth to prevent the temperature ever falling below 7°C (45°F) can be a flowery place throughout the year but many home gardeners may prefer to use it for crops such as tomatoes, cucumbers and aubergines in the summer and concentrate more on flowers from about October, when chrysanthemums begin to require protection, until the spring, when it may be required mainly for raising seedlings before it would be safe to do so outdoors. Among the best plants for this purpose are various kinds of winter-flowering Primulas, Cinerarias, Cyclamen, greenhouse azaleas and early bulbs, particularly hyacinths, daffodils and specially prepared hippeastrums. There are also winter-flowering begonias and poinsettias as well as various winter-flowering heathers (ericas) but these are not generally as easy to manage.
Browallia speciosa Browallia speciosa is another attractive annual which will make a good pot plant for winter flowering. An early sowing in March in a temperature of 15°C (60°F) will give plants to flower from July to October, a second, made in May or June, will provide a succession until December. Treatment is exactly as for exacum and 10cm (4in) pots are suitable for the fully grown plants. Bushiness will be improved if the tips of shoots are pinched out occasionally during the summer. Plants are about 30cm (12in) high and have bright blue flowers.
These are the gayest of the spring-flowering greenhouse biennials, at their peak in May but continuing into June to link up with the summer flowers. There are a number of different species,
Many perennial and even sub-shrubby, but the popular greenhouse varieties are all biennials sown one year to flower the next. They are bushy, rather leafy plants with big clusters of distinctively pouched flowers, yellow, orange, red and crimson often with one colour splashed or spotted on another so that the display is very striking. There are several types including Large Flowered and Multiflora Nana, the latter rather shorter, 20cm (8in) instead of 30-40cm (12-16in), compact and with smaller flowers.
Seed should be sown in May or June as described for primulas and pricking out and first potting are also the same. These are also plants that like cool conditions in summer and so are easier to manage in a frame, which can be left wide open when the weather is warm, than in a greenhouse, which can become uncomfortably hot. Even in winter there is no need for much artificial heat provided the temperature never drops below 7°C (45°F) but plants do want all the light possible and careful watering, with the leafy crowns of the plants kept as dry as possible. Big plants will need to be potted on into 15cm (6in) pots in September or October and will need some staking in spring because of the weight of the flowers they will carry.
Exacum affine Exacum affine is an easily grown annual which deserves to be better known. It makes a neat bushy plant about 30cm (12in) high with lilac-blue sweetly scented flowers. If seed is sown in a cool greenhouse in March plants will flower from August to about October. A second sowing in June will give a succession of flowers from about October until Christmas or later. Seed germinates readily in a temperature of 15°C (60°F), seedlings thrive in a peat or soil-based potting compost, will need no artificial heat in summer, should have normal watering and will reach full size in 10cm (4in) pots.
Kalanchoe blossfeldiana is a small, bushy succulent cultivated for its abundant sprays of small scarlet or yellow flowers in winter. It is an easy plant to grow, readily raised from seed sown in March or April in a temperature of around 18°C (65°F) or from cuttings rooted in sand and peat any time in summer. It will grow in a mixture of equal parts soil, peat and coarse grit or sand with just a peppering of fertilizer such as John Inns base or En Mag. Watering is normal and artificial heat is unnecessary in summer and is only necessary at other times to maintain a temperature between 7 and 13°C (45-55°F). Plants require all the light possible. Good flowering plants can be produced in 8-10cm (3 to 4in) pots.