Conservatory and greenhouse cultivation of houseplants

A beautiful feature may be arranged by grouping flowering and foliage plants so that they can be seen from inside the house, especially if they are illuminated at night.

The decision has to be made whether a glass structure built on to the house is to be used primarily for growing plants, or if it is essentially an extra living room in which some plants may be grown. Obviously if the latter is the case the choice of plants will be limited to those which in the main enjoy the same conditions of heat and humidity as human beings require. This would include the full range of plants that are normally recommended for growing in a normal living room, with the addition of some which require more light than they would normally receive in a living room.

greenhouse cultivation of houseplants

In practice it would be best to concentrate on the plants recommended for the cool greenhouse because the plants for a warm house would probably need more humidity than human beings would find comfortable.

One of the attractions of an extra room or sun lounge is that, provided it can be heated, you can sit and enjoy any sunshine that is going any day in the year. But this means that the heating apparatus is capable of keeping the temperature at around 21°C/70°F for British people, considerably more for most Americans, at least during the periods the sun room is being occupied.

Conservatory cultivation of houseplants

One could have a background heat of about 15°C/60°F with a supplementary heater capable of raising the temperature an extra 6LC/ 10°F quite quickly. Many plants, most of those indicated as suitable for a cool greenhouse will not object to fluctuations of temperature of this order provided the higher temperatures are not maintained for long periods – not more than several hours – and provided that the atmosphere is reasonably humid.

There are various humidifiers on the market – electrically operated types, trays of water to fit over radiators, and of course trays of metal or plastic which are filled with small washed gravel or pebbles and water. The plants are stood on these trays and enough moisture evaporates around them to create a microclimate that is acceptable to them.

Plants in a conservatory, as indeed in a living room, are usually happier when they are grown quite close together so that their foliage forms a canopy, as it were, over the bench or ground upon which they are growing. If the pots are packed around with peat kept always moist, or stood on a sand or gravel tray, which again is always moist, the ‘canopy’ of foliage tends to keep the moist air from rising too rapidly as it ;o would when plants are dotted about singly.

One very attractive feature of a conservatory could be a series of hanging baskets. There are many plants that really need to be viewed from below if their charm is to be fully appreciated. Among them are the pendulous varieties of begonia, the many brilliantly coloured forms of Christmas cactus – schlumbergera – and, of course, the pendulous types of fuchsia. Other popular plants for hanging baskets, of course, are trailing lobelia, tradescantia and zebrina, ivy leaved pelargoniums, and both the blue and white forms of Campanula isophylla.

Watering hanging baskets poses a minor problem, and it is probably best overcome by suspending them on a nylon cord over a small pulley so that they can be raised or lowered as required. Of course, it is not always possible to

fix a pulley in the roof of a conservatory or a home extension. But it is usually possible to fix brackets to the rear wall at several heights and suspend the baskets with a nylon cord over a pulley at the horizontal extremity of the bracket. Otherwise you have to stand on a pair of low steps to do the watering.

There are some very ingenious and inconspicuous pot holders available. They consist of a partial circle of green plastic-coated wire, with two hooks at the back. The partial circle can be bent open or closed to accommodate pots of various diameter. Square meshed panels of similar plastic wire are fixed 2.5em/lin or so away from the wall. The rings are then hooked on to the wire panel, and a delightful arrangement of pot plants can be made against the wall.

But if, as is most likely, it is to be a general purpose house intended for raising seedlings of all kinds in the spring, and for growing tomatoes and cucumbers in summer to be followed by chrysanthemums in the autumn, then it is best sited to run east-west with the door at the west end. Sited thus the house will gain the most benefit from the low-angled winter and spring sunlight.

When choosing the site for a greenhouse it is worthwhile spending a little time working out how the supplies of electricity, gas and water may be most easily taken to the house. As we shall see later, electricity is almost essential in a greenhouse if it can be installed reasonably cheaply – even if it is used only to provide lighting. But electricity can be a boon in a greenhouse even if you decide to heat the house by alternative means – by a paraffin or gas heater. It can provide soil warming in a border or on a bench, supplementary lighting for the plants, an extractor fan for ventilation, a heated propagating case, and mist propagation.

So try to site the greenhouse where an electric cable, a gas pipe and a water pipe may be easily taken to it in the same trench.

While you are thinking about the site for your greenhouse, keep in mind that you may almost certainly wish to extend it one day, or place another house alongside it. Also, you will need some frames to take care of the overflow of seedlings and cuttings produced in the greenhouse until they are ready to be planted out when danger of frost is past. Ideally the frames should be placed on the south-facing side of the greenhouse.


Now we must look at a very controversial matter – double-glazing. A firm once tried to sell a greenhouse with really complete double-glazing – both walls and roof. It was expensive. The double-glazing effected a saving in cost of heating the greenhouse of the order of about 30-40 per cent.

But plants are not happy in this fully double-glazed house. Even when fitted with an extractor fan for ventilation, the air changes around the plants are neither sufficient nor uniform enough. Hence we get more trouble with

moulds and other diseases. Also, extractor fans and other automatic ventilation systems are activated by some kind of thermostat or device that works by temperature. The thermostat is set to operate the fan when the temperature rises to, say, 10°C/50°F in summer, or 15.5°C/ 60°F in winter. Now on dull cloudy mornings the temperature in the house may take a long time, several hours, to warm up and start the ventilation. Added to the cool night hours this often gives disease spores time to germinate and enter the foliage while it is still slightly damp from moisture condensed from the air as it cooled during the night.

A traditional type of glass single-glazed house will ‘breathe’ naturally and, even without the fan or other ventilation working, may have half a dozen air changes an hour through air being drawn in between overlaps of the glass and other places.

If it is really felt essential to effect a cost saving by lining a house with plastic sheeting, it is best only to line it partially. Line say the north and east walls, or line the inside but leave, say, 60cm/2ft at the top unlined to allow moist air to rise to the ridge.

Propagation in the Greenhouse

One of the greatest uses of a greenhouse is for propagation, by seed or by cuttings. If soil warming is installed on a bench, or even in a border, a simple wooden frame may be placed on the bench and covered with a couple of large sheets of glass. Or, of course, a more elaborate propagating case with thermostat-controlled air and soil warming may be installed.

Mist propagation is the latest refinement, consisting of a soil warmed bench capable of being maintained at 21°C/70°F. Above this, nozzles are placed capable of delivering automatically a fine misty spray so that cuttings, or even seedlings, are always covered with a film of moisture. Thus, the cuttings never wilt and may be rooted in full sun. Many plants may be propagated by cuttings in a mist bench that would be difficult to root otherwise.

Control of Pests and Diseases

Because the atmosphere in a greenhouse is warm and humid, pests and diseases breed and spread rapidly. Be scrupulous about hygiene. Remove and burn faded flowers, and discoloured or diseased leaves. At the first signs of a disease or pest take action at once, and apply the appropriate control measures – a spray or a fumigation of the house with insecti-cidal or fungicidal smoke pellets.

Check plants two or three times a week. Turn leaves over here and there as pests and diseases often attack the underside of the leaf. Look too into the heart of young shoots; pests love to cluster down among a tuft of young tender foliage. Sometimes in such cases an aerosol spray is most effective in penetrating among leaves or shoots.

Keep the staging and floor of the house free of green slimy algae by watering the surfaces with an algicide recommended for the purpose. Keep pots clean too, and stir the surface soil in the pots frequently to prevent mossy growth establishing itself.

Staking plants is something that should always be done in good time. If, for example, freesia flower stems bend over and become ‘kinked’ they will not flower. Staking plants in peat-based mixtures is always more difficult than with loamy mixes, but there are now special wires which may be clipped to the pot and to a cane to keep it upright and rigid in peat.

Dust on plant leaves can be a killer, so spray the foliage on warm days with clear water, 01 sponge large leaves occasionally.

As mentioned elsewhere, light is more important than heat in winter and the early months of the year. So clean the glass of frames or greenhouses every few weeks with warm water containing a little household detergent.

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