Planning the Greenhouse Year
With careful planning and good hygiene, flowering pot plants and many food crops can fill the greenhouse the year round.
The greenhouse adds an extra dimension to gardening, enabling tender plants to be grown which would not survive in the garden, and providing an all-weather retreat for the dedicated gardener. The greenhouse is also invaluable for raising bedding annuals and propagating plants.
It is important to plan how you propose to use the greenhouse. A year-round growing programme is possible provided suitable plants and crops are chosen and a meticulous care routine is followed. For obvious reasons, avoid plants with widely differing needs although it is easy to lodge shade and sun lovers within the same greenhouse and to create an micro-climate on capillary matting for plants requiring moist growing conditions.
Stocking a greenhouse with crops and ornamental plants is easier if a plan is made every year. With few other tasks in the garden, mid winter is a good time to do this.
During mid winter, regularly examine plants that are in flower — such as primulas and cyclamen —removing any faded flowers or discoloured leaves.
Take care when watering not to splash the flowers or to leave water lodging in the crowns of the plants, as this may lead to rotting. Avoid over-watering tender or young plants, or the fine roots may be damaged.
Examine cuttings of zonal pelargoniums inserted in autumn Remove any leaves showing signs of mildew and discard cuttings which have diseased stems. Water these plants only when the soil in the pots shows signs of drying out.
If you have a propagating case and can maintain a temperature of 16-18°C (61-64°F) during, sow florist’s carnations, wax begonias, gloxinias and streptocarpus towards the end of mid winter. Otherwise delay sowing for another month. Sow sweet peas in slight heat — about 4°C (39°F).
Move dormant fuchsias, heliotropes and hydrangeas on to the greenhouse staging, if possible in a warm spot where a temperature of 10°C (50°F) can be maintained. Spray the plants with water on sunny days, and give them increasing amounts of water as growth becomes active.
Sow seeds of coleus, tuberous and fibrous begonias, celosias and streptocarpus. Place the seed boxes in a propagating frame heated to 16-18°C (61-64°F). When the seedlings are large enough to handle, prick them out and grow them on at normal greenhouse temperatures.
Stop florist’s carnations when they have made nine or ten pairs of fully developed leaves.
If you want to plant tomatoes in a cool greenhouse during mid spring, sow the seeds in late winter at 16°C (61°F).
Prune greenhouse climbers, such as plumbago and passion flowers, by cutting back the growths made last summer to within one or two buds of their point of origin. Keep watering to a minimum and ventilate freely on mild days.
Increase your stock of ferns by dividing old plants. Use the vigorous pieces from the outsides of the old plants and discard the old wooden centre. Pot on any other pot-bound ferns.
Tomato plants grown from a late winter sowing now need extra space to encourage sturdy growth. If you aim to plant tomatoes in late spring, sow the seeds now in a heated propagating frame.
In a cool greenhouse, prepare the bed for planting tomatoes in mid spring. Dig in plenty of well-rotted manure or compost and apply a dressing of tomato base fertilizer at 100g (4oz) per sq m/yd.
Sow seeds of many half-hardy annuals in trays of seedling compost at temperatures of 10-18°C (50-64°F). Sow seeds of Campanula isophylla at a temperature of 13°C (55°F) or take cuttings from overwintered plants. Sow seeds of primulas in trays on the staging at normal greenhouse temperatures.
Take cuttings of fuchsias and coleus, rooting them in compost at a temperature of 10-16°C (50- 61°F). Take cuttings of chrysanthemums, and also of zonal pelargoniums to produce plants for flowering next winter.
Plant hippeastrum bulbs in 15cm (6in) pots. Provide a temperature of 10-13°C (50-55°F) and water sparingly until buds appear.
Apply liquid fertilizer every ten days to pelargoniums, heliotropes, fuchsias and overwintered annuals.
Prick out carnation seedlings and pot on and stop florist’s carnations. Disbud flower stems.
Complete the greenhouse sowings of half-hardy annuals. During sunny weather, shade the seedlings and newly potted plants —the changeable weather often experienced at this time of year can cause violent fluctuations in temperatures. Keep the greenhouse well ventilated. Move established half-hardy annuals into a cold frame for hardening off.
Give increasing amounts of water to plants repotted in early spring. Continue to liquid feed established plants, such as pelargoniums Hydrangeas in pots are now in active growth and need a temperature of 10°C (50°F) and generous watering.
In a cool greenhouse, plant tomatoes in the bed prepared last month and provide suitable supports. Sow seeds of winter cherry (Solanum) and outdoor tomatoes at a temperature of 16°C (61°F).
Sow melons and cucumbers at 16-18°C (61-64°F), setting them individually, about 2.5cm (lin) deep in 7.5cm (3in) pots.
Move boxes of annuals sown in mid spring to a cold frame for hardening off. Apply a liquid fertilizer to boxed plants if the leaves show signs of yellowing.
Sow cineraria seeds at a temperature of 10-13°C (50-55°F) to produce plants that will flower in early winter. Sow cucumbers and melons if not done already.
On warm days, provide shade for plants now in flower, such as calceolarias, pelargoniums, cinerarias, primulas and hydrangeas. Increase the humidity by damping down the staging and floor. Provide adequate ventilation. Give plenty of water and a weekly liquid feed to vigorous plants.
When fuchsias are 10-13cm (4-5in) tall, pinch out the growing point of each plant to encourage bushy growth. Later, pinch out the side shoots as necessary.
Pot carnations on to 15cm (6in) pots. Stop side-shoots when they are about 15cm (6in) long; stopping until the middle of early summer results in autumn flowers, from early to late mid summer produces winter blooms and stopping up to the end of late summer gives early spring flowers.
Stop laterals growing from the main stems of cucumbers at two leaves beyond the first or second developing fruit. Pinch out subsequent sub-laterals as soon as they have made two leaves beyond their first fruit. Remove tendrils and all male flowers — those without an embryo fruit behind them on old varieties; modern varieties are all-female plants.
Twist the stems of tomato plants round the support strings, or tie them to the canes, and remove side-shoots regularly. Feed the plants every week or ten days from the time the fruits on the first trusses begin to swell. In an unheated greenhouse, plant tomatoes in the border.
Plant out into cold frames melons which have been raised from a mid spring sowing, one plant to each light.
Plants which have finished flowering — such as azaleas — can be put into the open garden for the rest of the summer to make more room in the greenhouse. Young cyclamen, seedling cinerarias, calceolarias, primulas and solanums can also be moved to a cold frame.
Pay particular attention to watering — plants in earthenware pots may need two or more applications daily during hot weather. Maintain a humid atmosphere by frequently damping down the staging and floor.
Sow cineraria seeds if this was not done in late spring, and also sow Primula malacoides.
Pot on streptocarpus plants, raised from a winter sowing, to 1315cm (5-6in) pots. Make a further sowing at 16°-18°C (61-64°F) to provide flowering plants next year.
Plants such as pelargoniums and fuchsias which are now flowering must be dead-headed regularly and given liquid fertilizer every ten days.
When young polyanthus primroses for growing outdoors are being set out in nursery rows, pot a few strong specimens in to 7.5cm (3in) pots to provide greenhouse flowers next winter.
Propagate African violets (Saintpaulia) and Begonia rex from leaf cuttings, rooting them in a propagating frame at a temperature of 16-18°C (61-64°F).
Continue to pot on young carnations into 15cm (6in) pots and move year-old plants into 20cm (8in) pots. Continue stopping side-shoots.
Examine the stems of tomato plants. If they are becoming thin, change to a liquid fertilizer containing extra nitrogen. Harvest the first cucumbers when they are about 30cm (lft) long.
Towards the end of early summer artificial heat can be dispensed with and more ventilation given in a cool greenhouse. If the weather becomes very warm, leave the top ventilators on the sheltered side of the greenhouse open a little way at night.
Damp down the borders, path and staging at least once a day during warm weather, but do not spray overhead, as the water droplets may mark the flowers. Unless the plants are standing on self-watering capillary matting, most require watering daily and possibly two to three times a day during hot spells.
Tomato plants should be in full cropping, with a few fruits requiring picking almost every day. Continue to feed and twist the stems round the supporting strings, or tie them to canes, and remove side-shoots regularly.
Continue picking cucumber fruits and removing any male flowers as soon as they show. If white roots appear on the surface of the bed, apply a 5cm (2in) deep dressing of well-rotted manure or leaf-mould.
To encourage prolonged blooming of pot plants now in full flower, shade the plants during sunny weather and give ample ventilation, especially in the early morning. Except during unusually cold or windy weather, leave the roof ventilators on the sheltered side of the greenhouse open a little way all night.
Take 10cm (4in) cuttings from non-flowering shoots of regal pelargoniums — the best material will come from stock plants which were cut down by about half in early summer and are now producing lots of fresh growth. Root them in a propagating frame.
Renew shading if necessary and damp down during hot weather. Continue to feed plants and watch out for pests and diseases.
This is a good time to repair and paint the greenhouse in readiness for the winter. Wooden greenhouses must be painted before heavy autumn dews soak into the timber. Mastic tapes are ideal for sticking over glazing bars to cure stubborn leaks. Also check over the heating system if you have one before you need to turn it on.
Hippeastrums should have died down by now and can be stored just as they are in their pots under the greenhouse staging, until required again in early spring.
Continue to take cuttings of regal pelargoniums. Zonal pelargoniums should also be propagated by cuttings at this time — choose firm, medium-sized, non-flowering growths, with 7.5cm (3in) of stem, from healthy plants.
Take 7.5cm (3in) cuttings of Campanula isophylla, setting three or four to a 5cm (2in) pot. As soon as rooted, pot on the whole clump to the next pot size.
During the second half of late summer take 7.5cm (3in) fuchsia cuttings from sturdy young growths if young plants are required for growing on as standards next summer Sow cyclamen seeds at a temperature of 16°C (61°F) for flowering the winter after next.
Annuals such as clarkias, cornflowers, nemesias, schizanthus, godetias, antirrhinums and pot marigolds, sown in early autumn and grown in pots in a cool greenhouse, make a colourful display during spring and early summer. Sow the seeds in trays of seedling compost at a temperature of 13-16°C (55-61°F).
Continue to take cuttings of regal and zonal pelargoniums, and also fuchsias. Other greenhouse plants to propagate from cuttings in early autumn include coleus, busy Lizzies, heliotropes, shrubby calceolarias and Plumbago capensis. They will root in pots standing on the staging, but speedier and more certain results can be obtained by using a propagator.
Disbud florist’s carnations as they become ready; remove all buds except the top or crown bud.
Towards the end of early autumn remove any permanent shading from the glass. In sunny weather provide local shading for seedlings and cuttings. Before the nights turn cold, bring into the greenhouse cinerarias, primulas, cyclamen, solanums, regal pelargoniums and begonias which have been standing out in frames.
Bring into the greenhouse without delay any tender plants still standing outdoors in cold frames.
In the greenhouse, reduce syringing, damping down and watering as the days get shorter and the nights colder. Where possible, carry out any watering and damping down before midday.
Thin out the shoots of climbing ornamentals, such as plumbago, passion flower and Tibouchina semidecandra, to admit more light and air during the coming winter.
Maintain a temperature of 7°C (45°F) for carnations and continue disbudding and cutting stems. Water and feed sparingly.
Clean the glass inside and out, then line the greenhouse with clear polythene sheeting, to within 30cm (1ft) of the ridge, to conserve heat during the winter. Cover the ventilators separately so that they can still be opened.
Check heating systems during the evening to make sure that they are working properly and that the thermostats are operating at the required temperature.
Ventilate the greenhouse freely on all sunny days, but avoid coldand close the ventilators fairly early in the afternoon to trap some of the daytime warmth. Keep the greenhouse closed during damp, foggy weather.
Complete any outstanding potting as early as possible. Annuals raised from seeds sown in early autumn will now be ready for moving to 7.5cm (3in) pots.
Cuttings of pelargoniums, fuchsias, heliotropes and campanulas will now be rooted and also ready for potting up into 7.5cm (3in) pots of a proprietary compost.
Dry off fuchsias, begonias, heliotropes and hydrangeas which have flowered during the summer and early autumn. Store the pots under the staging in a cool greenhouse or in a frost-free shed, but do not allow the compost to become dust dry at any time.
Pinch back new growths on solanums, which may otherwise hide the berries. When the earliest cinerarias begin developing their flower heads, give the plants extra space to allow them to grow freely and ensure that they get as much light as possible.
Plants grow very slowly or remain dormant in early winter due to the brief hours of daylight. Don’t try to make them grow more rapidly by raising the temperature — you will just encourage soft, weak and straggly growth.
At the beginning of early winter give extra attention to plants that you hope to have in flower in the next few weeks. Select the warmest spot for any cinerarias, cyclamen or primulas which are a little backward. Move to a cooler spot any plants that are too forward.
Propagate carnations from cuttings of side-shoots with four or five pairs of leaves. Ideally, root them in a mist propagator.
Open ventilators a little on sunny days but close them again quite early in the afternoon. Most plants — except those actually in flower — must be kept fairly dry. But do not allow them to dry out so much that the soil begins to shrink from the sides of the pot.
If the floors and paths need damping down to increase humidity, do this during the early part of the day. Discontinue overhead spraying of the plants.