Greenhouse Flowers and Crops: All Year Round

Some planning and organization is essential if you are to maximize the potential of your greenhouse. As already mentioned, the limitations or advantages of die site regarding light, shade and warmth, must be taken into account when you choose what to grow.

Once you have chosen the varieties, their positioning in the greenhouse is the next consideration. Those needing shade can be put under staging or under shrubby plants or climbers, or a part of die greenhouse can be deliberately shaded for them. Plants needing good light must be sited along the south side, where the greenhouse is not overshadowed and, if low growing, put on raised shelves. Those sensitive to chill must be set well away from doors or draughts. Conversely, those needing airy conditions can be placed near ventilators.

During summer, many plants like moderate humidity. To satisfy this need without raising humidity excessively in the whole greenhouse, group plants with similar requirements. You could stand those needing more humidity together on a surface of moist peat, shingle or on capillary matting, and use polythene sheeting screens to localize the higher atmospheric humidity. If you want to accommodate a wide range of plant types, partitions or screens can be used to divide off larger sections of the greenhouse so that several areas with different conditions and temperatures can be obtained.

Don’t forget that you can use the greenhouse roof to support a variety of climbers. You should, however, avoid perennial types that need permanent positions as these make cleaning and sterilizing difficult if not impossible. Annuals, such as ipomoea, thunbergia and cobaea, are no problem, and can be cleared out at die end of the year. You can also use hanging-baskets or plastic pots with holes drilled in the rims and fitted with wires to display many lovely plants. These are indispensable items for the conservatory and give the greenhouse a professional touch.

Also, with careful planning it is surprising how wide a selection of plants can be grown. Flowering pot plants, cut flowers and vegetables can be fitted in, and even specialist subjects like orchids and chrysanthemums.

A greenhouse year, for example, can run as follows: In winter, if the greenhouse is kept frost free, winter salads, such as lettuce, and herbs, such as parsley and mint, can be grown most of the time. Using a frame with a soil warming cable for gentle forcing, beetroot, carrot, radish, salad onion and turnip can be added. (Being small, these also make useful ‘catch crops’ to fit along-side larger plants like tomatoes and sweet pepper, so utilizing space to the full.) In a warmed section under the staging, vegetables such as chicory, rhubarb and seakale can be forced and blanched. Potatoes can also be forced for Christmas if seed potatoes are sprouted and potted up in autumn. Climbing French beans can be started early in the year and grown on where the tomatoes will follow. Along a south side is best. The bean crop has to be gathered over a very short period, and there should be plenty of time to set out the tomatoes. The tomatoes should continue to give fruit from about June to almost winter if the late weather is favourable. From late winter to spring, bedding plants can be raised together with many plants for later display in the greenhouse, conservatory or home. This is also the time to start cucumbers, melons, sweet peppers and aubergines, all of which can be grown in the same greenhouse if carefully positioned and trained.

Most of the greenhouse ornamentals can be placed on or below staging, opposite the tomatoes and vegetables during summer. The tomatoes can be followed by chrysanthemums grown on outdoors during summer and moved inside in autumn. Cymbidium orchids can also be moved in and will give a wonderful show from late winter to spring. Pot plants, such as cineraria and calceolaria, sown in late summer should provide a dazzling show from Christmas onwards (some varieties make fine gifts), and hardy spring-flowering bulbs, potted in autumn, give added colour and interest.

There follows a detailed, month-by-month planner to help you organize your greenhouse year. Indoor cultivation has the obvious advantage over outdoor gardening that plans and routines are not interrupted by unfavourable weather.



Sow lettuce and other salad vegetables. Begin sowings in the propagator of summer-autumn flowering pot plants and plants requiring long growing period, such as F1hybrid geraniums. Some bulbs already in the plunge may be ready to bring in. Propagate chrysanthemums and carnations from cuttings. Sow freesias, seven seeds to each 130mm (5in) pot. Rhubarb can be brought in for forcing under the staging. Pot-on actively growing pot plants such as primulas, calceolarias and cinerarias. Be cautious with watering and ventilate freely if there is a mild spell. Keep the greenhouse glass clean.


Sow antirrhinums and fibrous-rooted begonias, if not done in January, and also more pot plants: thunbergia, schizanthus, salpiglossis, exacum, torenia and heliotrope, for example. Sow lilies, and pot-up scales which you have carefully detached from saved bulbs for propagation. Sow sweet peas and border plants, such as delphiniums, for later transfer to the garden. Sow Christmas cherry (solanum). Make more vegetable sowings including radish, peas and beetroot. Start dahlia tubers into growth. Sow vegetables for later transference to the outdoor plot. Late in the month, sow tomatoes for early crops. Prune vines, cutting back lateral growth to two eyes.


The majority of bedding plants can now be sown. The sowings of some seed should be staggered over two-week intervals until end of April. Sow greenhouse plants which are extra-sensitive to cold such as Cape primroses, tuberous begonias, ipomoeas, gloxinias (F1 seed) and African violets (F1seed). Sow cucumbers, sweet peppers, melons, aubergines, and cape gooseberries, and also tomatoes if not done in February. Sow plants for sub-tropical bedding, such as ricinus and ornamental maize. Many bulbs, corms, and tubers can be started into growth, for example, achimenes, smithiantha, gloxinia, gloriosa, caladium (for foliage), hippeastrum, polianthes (tube-rose) and sprekelia. Some early sown tomatoes may be ready for permanent planting. Start fuchsias, geraniums and other pelargoniums, and any other perennial pot plants into growth that have been dormant over winter.


Sow quick-maturing and warmth-loving bedding plants such as African and French marigolds and zinnias. Nemesia is also best sown now without artificial heat to get short sturdy plants. Be prompt with the pricking out now required, and water-in the seedlings with Cheshunt compound to avert damping-off. There should now be masses of flowers and colour from spring flowering pot plants and bulbs. Be careful not to let temperatures rise too high now that the sun is more powerful. Some shading may be essential to maintain cool conditions and prevent plants from wilting or fading quickly. Use Coolglass shading which can be wiped off later if necessary. Sow epiphyllums and other cacti and succulents. Take cuttings of stephanotis.


Sow cinerarias, calceolarias, and all pot plant primulas – if sown now some quick-flowering varieties may be ready for Christmas. All vegetable plants should now be in their final positions, and the canes or strings to train them set up. New plants brought in earlier as rooted cuttings, such as chrysanthemums, carnations and pelargoniums, should be potted on. Many plants saved from the last year will have made sufficient growth for cuttings to be taken. By about the middle of the month, bedding plants and others to go out later, should have the hardening-off treatment started. Keep a constant watch for pests.


Over the next three months the sun’s power can cause greenhouse temperatures to shoot up to a dangerous level for all plants. Most structures will need almost permanent shading. Damping down and watering must on no account be neglected. (Automatic systems for these can be set up.) Ventilation is also important, but don’t let the wind rush through the greenhouse as this can cause serious damage. Early sown tomatoes should be cropping, and so should the all-female cucumber varieties, which are very prolific. Sow sub-tropicals such as the Abyssinian banana (Musa ensete), the bird-of-paradise flower (Strelitzia reginae) and palms. These need plenty of warmth in the early stages for germination and quick growth, but can be acclimatized to quite cool conditions later. Hardened-off bedding plants should now have been taken out of frames and replaced by greenhouse pot plants being grown on or rested, as long as they are not tall growing. This can save much space at a time when it’s in great demand.


Keep an eye on tomatoes to see that all is well with flowering, pollination and fruiting. Spray the flowers with a mist of water and/or shake the plants to distribute pollen. Water evenly and regularly so that the compost is always moist. Avoid temperatures over 27 C (80 degrees F) whilst tomatoes are ripening. Keep cucumbers and melons properly trained and also moist, never wet. Many ornamentals require supports and/or training. Perpetual flowering carnations may need disbudding and also calyx menders if splitting is a problem. Large-flowered begonias should have the female buds (with winged seed capsule) removed at an early stage. Keep a special watch for red spider mite, especially if the weather is hot and dry. Many plants potted earlier may now have exhausted their potting compost and need feeding. Cyclamen corms can be started, convex side down, in 130mm (5in) pots, with their tops just above the compost. Place in shaded frames. Cuttings from many ornamentals can be taken, including pelargoniums.


Continue to take cuttings when they become available. Melons in the ripening stage should be watered more sparingly but not allowed to dry out. Pot up nerine greenhouse hybrids, but not the garden forms, one to a 130mm (5in) pot. Pot arums and also lachenalias, which may flower around Christmas time; keep them cool. Chrysanthemums standing outdoors should be protected from possible wind damage and checked for pests and diseases, especially leafminer. Feeding, generally, must be continued and be punctilious with the dead-heading of flowers as they fade, to prolong blooming. Hardy annuals can be sown now for overwintering in the greenhouse and early colour in spring.


This is usually the time to clean and tidy up. Any plants past their best, looking sickly or scruffy, should be critically assessed and discarded if necessary. The house should be cleared of fallen leaves, flowers, plant debris and any weeds that have managed to get in during the summer. Plants that have been grown-on in frames can be brought in. Decoratives, such as nerium and callistemons, that have been standing outside for summer must also be put under cover, depending on weather conditions but before the first frosts. Check all pots are clean and free from soil pests, and all plants for health. Begin potting hardy bulbs and put them in the plunge. Leave tulips for next month. Sow salpiglossis for flowering next spring, also butterfly flower (Schizanthus) of which the large-flowered varieties are best for sowing now. Tomatoes that have ceased useful production can be cleared to make way for chrysanthemums. Ornamentals, such as calceolaria and cineraria, may need potting-on. Sow suitable lettuce varieties for winter-spring cropping, such as ‘Dandie’, ‘Kloek’, ‘Kwiek’, ‘May Queen’ and ‘Sea Queen’.


Reduce watering of all bulbs and corm ornamentals that have finished flowering, such as gloxinias, begonias, achimenes and gloriosas. Let the pots go dry and store the bulbs and corms in clean dry sand or turn the pots on their sides. By now the tomatoes should have been entirely cleared and replaced by chrysanthemums. Stools (roots) of outdoor chrysanthemums should be boxed up in potting compost after freeing them from soil, to provide cuttings later. Heating equipment and the operation of thermostats should be checked. Put up insulation and check for draughts generally. Shut down automatic watering and keep conditions dryer.


Moulds and mildews can be troublesome from now on. Always ventilate freely if the winter weather permits. Routine fumigation with TCNB is wise, especially where there are chrysanthemums, pelargoniums or lettuce. Pot plants, such as cineraria and calceolaria, should be treated with a systemic fungicide to prevent leaf mildews. Sow cyclamen in a warm propagator, spacing out the seed well. Just cover with a thin layer of fine peat. Germination is erratic, so prick out each seedling as it emerges. Grow on at a temperature of not less than 10 C (50 degrees F). Sow more lettuce. In plastic or plastic-lined greenhouses, knock condensation off the plastic as often as necessary to get maximum light entry.


If planning has been successful there should be plenty of Christmas colour. Some plants, such as the dwarf strains of calceolaria and cineraria should be ready as gift plants, also various primulas and spring bulbs. Tidy them, carefully removing any tatty foliage and, if they are to be transported as gifts, give them a neat support if necessary. Cyclamen sown 14 months ago should be giving a fine show and make delightful gift plants. If you keep them, try to maintain a steady temperature of not less than 10 C. More winter salad crops can be sown, especially with the help of a soil warming cable. There may be lots of empty pots, seed trays and other equipment at this time. Clean them all thoroughly and disinfect if necessary before storing them in a clean place. Now is also a time for further planning by reference to the seed catalogues. Orders are best placed early because popular varieties tend to sell out. The worst of the winter weather usually begins about now. Have a paraffin heater at hand in case of severe cold spells, fuel shortages, or breakdowns. If conditions are severely cold, keep all plants on the dry side and cover them with several sheets of newspaper or bubble plastic. Clear snow off the roof, to admit maximum light.

25. April 2013 by admin
Categories: Featured, Greenhouse Gardening | Tags: , , , | Comments Off on Greenhouse Flowers and Crops: All Year Round


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