A Glasshouse in the Flower Garden

New Zealand Journal of Agriculture, Volume 101, Issue 1, 15 July 1960, Page 94

A Glasshouse in the Flower Garden

By

J. P. SALINGER,

Horticultural Advisory Officer (Ornamentals), Department of Agriculture, Wellinqton 3

INTEREST is increasing in the construction and use of glasshouses in the flower garden both for propagating plants and for growing plants tor ornament. A glasshouse is essential for gardeners specialising in plants such as orchids, and the more tender plants like begonias, while it can also provide flowers and foliage for decorating the home during w j n | er 3 3

BEFORE building a glasshouse the gardener should decide whether it is to be solely for propagating, for growing a range of plants, or for cultivating specific types such as carnations succulents, and orchids. Possibly the house may be used to grow some grapes or tomatoes in summer as well as flowers, though this is not particularly desirable, as the cultural conditions for the two types of crops are somewhat different. Usually it is better to have a house

which can be used for various purposes, as though in the beginning the gardener may specialise, he frequently becomes interested in a wider range of plants. A gable roof g i asshoU se should have the ridge running north and south or north-east and south-west. If a lean-to house is constructed, the longest glazed side should face north . In many gardens there may be only limited areas where a house can be built. The glasshouse must be away from trees or

buildings which throw shade from the advisable tQ S proSd^ larly to the south and possibly to the. north. To the north trellis or a hedge can ,^ e some distance from the IXes ° 0 ? where the house will be placed need not be level, as this can be overcomeby J suitable foundations. The soil inside the glasshouse, however, should be level. If the ground is much higherat 01 ? e side ° f the ? e His advisable J° P lac a drain between this higher land and the w all of the glasshouse, Probably the lean-to glasshouse is the cheapest and easiest to build, if there is a suitable back wall, such as; a garage or potting shed. Temperatureand; humidity tend to change morerapidlj m a lean-to glasshouse and forgeneral purposes gable roof types aremore satisfactory. Construction of gable roof and lean-to glasshouses is given in Depart-

ment of Agriculture Bulletin No. 373, “Glasshouse Construction” (Is. 6d.). A very simple glasshouse with limited use can be made from secondhand material such as windows and glazed framings. It is advisable always to fix a gutter and spouting to a glasshouse to keep the foundations dry and prevent water seeping into the house. Main Requirements A glasshouse is built to protect plants from wind, heavy rain, frost or snow, intense heat and sun and should provide a more equable and suitable climate for the plant. To achieve this light, ventilation, heating, and water are required. It is most valuable if electricity can be provided to the glasshouse for heating and for light for working in winter. Light The house should be painted both inside and out with white or aluminium paint to get the greatest reflection of light in winter. In summer, on the other hand, shade will be required. Permanent materials such as blinds made of laths fixed either inside or outside can be used or shading can be temporary by painting the glass with whiting or similar materials, or black polythene may be attached in strips to the inside of the glazing bars. Ventilation Ventilation is most important at all times, but especially in summer. Usually the vents are placed at the ridge, but this can be improved by placing vents also at the base where there are low glass sides or at the eaves with high glass sides. Additional ventilation can be obtained by having vents at the ends and for this purpose louvres are most useful. Where the gardener cannot alter the ventilation during the day an extractor fan fitted at one end of the house will assist, especially if it is operated by a thermostat. If a door is left open for ventilation an insect-proof screen in the door frame is advisable to keep out animals and insects. Heating Depending on the location of the house and the types of plants grown, heating will be required in winter to be almost continuous or to provide against frost. Hot water heating is seldom used now, as electric heating is convenient and efficient, and kerosene heaters provide frost protection. Probably the cheapest method of heating is to use a combination of kerosene heaters and electricity, using electricity to provide an even temperature and kerosene heaters for additional heating in really cold weather. Many of the plants grown in glasshouses are almost hardy and only need frost protection, with a minimum tern-

perature of 40 degrees F; in sunny areas in warmer parts continuous heat is seldom required. However, for propagation of plants from seeds or cuttings temperatures of 60 to 70 degrees F are desirable. A part of the bench area can be set aside and if necessary boxed in and covered with a glass or plastic frame light. Heating to this part, is best supplied by low voltage galvanised

wires attached to a transformer, the loading being between 7 and 10 watts per square foot. Alternatively high voltage plastic covered cables of definite lengths for a specific area of bench can be laid down to give the same loading. The cables should be laid in damp sand, gravel, or scoria, allowing 2 in. of medium above and below the cable. The pots or boxes are then placed on this.

Atmospheric heating on a permanent basis by electricity can be carried out by having “Pyrotenax” cables fixed on framework to the side walls or under the benches, by tubular heaters, usually 60 watts per foot run, attached to the walls or bench supports, or by fan heaters, usually of 1 or 2 kilowatts. The wiring of these heaters should be thoroughly waterproof. All electric heaters are most economical if thermostatically controlled. Before electric heating is installed the electricity supply authority should be consulted. All mains wiring must be carried out by a registered electrician. In all glasshouses heat loss can be reduced without affecting light transmission by lining the- interior of the glazed sides and part way up the roof with clear or white polythene sheets of .0015 in. gauge. The sheets should be attached to timber members with staples or drawing pins and with a cardboard “washer” between these and the sheet. In metal constructions it is advisable to fix wooden laths to the members and fix the sheet to the laths. Water An adequate water supply is necessary. A stand pipe from the main is best actually in the glasshouse, as such water is never too cold for glasshouse use. Alternatively rain water can be collected from the roof and stored in a tank in the house with an overflow leading outside or a small tank should be kept in the house. It is not convenient to enter and leave the glasshouse frequently to draw water from outside. If the water is from an artesian bore, it may be too cold and it is advisable to run the water into a tank in the glasshouse to allow it to reach the temperature in the house before use. Tanks in the glasshouse should be so placed that they can be emptied easily and cleaned out regularly and should be covered to keep out plant leaves and other rubbish. Paths Paths should be of a dry, firm material, preferably concrete, but reinforced metal flooring or a layer of shingle is also satisfactory. Frames A few frames outside both on the sunny and shady sides of the glasshouse or standing apart are a useful adjunct to the glasshouse. If fitted with glass and shades of laths or scrim, they can be used for hardening off plants in spring and for growing or ripening off plants in summer; in autumn pots of bulbs can be plunged in them before being brought into the glasshouse to flower. Growing the Plants Most plants will be grown on benches in the glasshouse; a few grow better planted in the soil or in

specially made-up beds. This applies particularly to carnations and the larger succulents and gerberas in the coldest areas. A few permanent plants like lapageria and hoya grow better when planted in the soil and even if the house has benches, provision can be made to lead the main stems up through the bench. Most gardeners wish to grow as many plants as possible in their glasshouses so benches may be placed at various levels. It is advisable to have one wide bench at a height of 2 ft 8 in. to 3 ft where plants can be propagated or groups of plants grown in the same conditions. Additional space can be provided by having ■ other benches in tiers and even by having narrow benches at one end and a single bench suspended from the ridge if the house is high enough. Alternatively, hanging baskets may be suspended from the roof. Benches should be of solid materials and if they are permanent, the supports can be of metal or of timber set on concrete. Benches are frequently of slats, but growing conditions are better with a material such as asbestos sheeting surfaced with shingle or scoria or similar materials. Provision should be made to drain such benches. Consideration could be given to making a small part of the bench a permanent plunging area for pot plants. For this a low wall of a single layer of bricks set on edge can be built on the bench and filled with sphagnum moss or peat and the pots plunged in this material. This method reduces the watering required. . The space beneath the benches is suitable for Rex begonias, maidenhair fern, selaginella, and other shadeloving plants. ROUTINE MANAGEMENT A glasshouse grower aims to obtain a good “buoyant growing atmosphere”, which it may be said is one which is comfortable for human beings to work in; for instance, a cold damp atmosphere in winter or hot, dry air in summer is unsuitable both for plants and the gardener. The ideal conditions will only be achieved by a combination of heating, watering, ventilation, and shading. For instance, in sunny weather even in winter the temperature of a glasshouse will rise appreciably and this will tend to stimulate growth. As a high temperature is not desirable in the glasshouse at this time, a little ventilation on the leeward side of the glasshouse may be needed. ' Spring In spring the winter flowers will be passing their best and most plants making new growth. The glasshouse will probably be full of boxes of germinating seeds and seedlings. Conditions can be variable with a bright sunny day followed by a cool, frosty night

or the weather may be grey and humid. Where a range of plants are being grown it is best to divide the glasshouse into sections for propagating, growing-on, and drying off.

The propagating section should be in a warm, shady part, as seeds and tubers such as gloxinias mainly require warmth and moisture and little light. Once the seeds have germinated they may be moved to the growing-on part, though immediately after pricking-off they will need to be shaded for a short period. Similarly the tubers will need more light as the shoots develop. All permanent pot plants which have been overwintered will be placed in the growing-on area. Woody plants such as fuchsias which have been cut back will be making new growth on the older wood and most foliage plants will also be growing away. All these plants require maximum light, a fair amount of. water, and only a moderately warm atmosphere. During late spring ' these and other plants will require repotting either into the same sized pot with fresh soil or into larger pots. The plants should be shaded for a few days after repotting. In the drying-off section, which is a small part of the glasshouse in the warmest drying position, probably at the north end, plants such as cyclamen, freesias, and hyacinth should be placed to complete their growth before they are placed outside or in a frame. If frost is expected, a stove should be lit or the electricity switched on before the house temperature falls too low; normally when it is at 45 degrees F. Summer In summer the temperature in an unshaded glasshouse will be very high. At such times the atmospheric conditions are improved by shading, adequate ventilation, and damping down by spraying the benches and paths with water as well as watering the plants. Plants are growing vigorously and so require regular and frequent watering. They will also need to be moved from one bench to another as they grow to allow each plant sufficient room and to place those plants which require more shade and cooler conditions in the coolest part of the glasshouse, normally the south end. Watering can never be a routine operation and the best way to tell whether a plant requires water is to lift the pot. If it feels proportionately light in weight, water is required. If it feels very heavy, it will not require water and the pot drainage may be blocked. Quick .growing plants or plants with heavy flower heads such as primulas or begonias will require neat and careful staking. Dead heads and old

leaves should be removed-and taken from the house. The ventilators can be left open night and day unless the weather is cold. Pests, especially aphids and red .spider mite, can build up quickly and .should be promptly controlled by insecticides in aerosol form or as smoke fumigants. Fungous diseases such as grey mould (botrytis) indicate that conditions in the glasshouse are too damp and cold. Damping down should be reduced and a slightly drier atmosphere maintained. Diseases such as powdery mildew are more prevalent under hot, dry conditions and these can be overcome by more frequent damping down and by additional shading and ventilation. Plants will require regular feeding and soluble fertilisers or liquid manure are best, but should be used only when the soil is already moist. Autumn In autumn plant growth will be slowing down. The weather may be warm, but frosts can be expected in bright, clear weather. Temporary shading should be gradually removed. Plants will still require water, but less than in summer and less damping down will be required. Feeding should be reduced and then stopped completely. Plants such as primulas and cyclamen and winterflowering begonias which are expected to flower should gradually be brought to a sunny part of the glasshouse and plants which are becoming dormant may be placed in a more shaded position. Plants such as carnations which are raised from cuttings taken late in spring should gradually be given more light and will still need regular watering, as they will continue to grow during winter. Autumn is not a good time for sowing seeds in the glasshouse. It is best to wait until late winter or spring. If it is possible, on a fine day the house should be cleared of plants and the whole of the interior thoroughly washed down with a dilute formalin solution —1 pint in 5 gallons of water—and then washed with clean water. Many fungus spores will be eradicated and the house can be cleaned generally. Every effort should be made to ensure that the plants when returned to the glasshouse are free of pests and diseases. Old flower heads and yellowing leaves should be removed, the outside of the pots scrubbed free of algae and moss, and the soil surface lightly worked up. The surface material on the benches should be raked over and added to, if necessary. The water tank should be emptied and cleaned out. If plants are grown permanently on the floor of the house, it will be pos-

sible only to scrub the house down. A household detergent should be added to the water and the plants covered with sacking or , similar material. Winter During winter, with cooler temperatures and less light, plants will be growing slowly. Watering and damping down, if required, should be done in the early part of the day so that the atmosphere is drier by the evening. Some ventilation will still be required on warm sunny days on the leeward side or through the end ventilators. The heating system should be checked regularly to see that it is working satisfactorily; kerosene heaters should be kept clean. Flowering plants should be placed in the sunniest part of the glasshouse and can be brought into the home. When returned to the glasshouse they should be placed in a more shaded place until they have again become accustomed to glasshouse conditions. Seeds of plants which require a long growing period should be sown in July or August for pricking off in spring.