Self Sufficient Greenhouse Gardening

The greenhouse is ideal for year round fruit and vegetables and also for anybody wanting to grow plants for selling on. Apart from the three standard types of greenhouse – the span or ridge, three-quarter span, and lean-to, recent years have seen the introduction of the circular house and the modification of the span types, often producing irregular designs.

The span type is an independent structure standing alone and the best for all-round purposes. Many of these are now produced with glass to the ground, instead of the traditional style with low walls of brick, concrete or wood. These walls help to preserve heat and do not allow the same violent changes of temperature as the all-glass house. Plastic is sometimes used as a glass substitute but must be regarded as of temporary value only.

Wood greenhouse gardening

Apart From cost, an important decision to make is whether the framework should be wood or metal. Wood is warmer, easier to repair and better for fitting shelves. Against this, wood needs to be painted or oiled if red cedar is used. Type of wood is also important. Teak is strong and durable but expensive. Redwood or red deal is much used and is easier to work.

Whitewood is cheaper but it is not fully weather resistant and sometimes splits. Western red cedar is particularly durable. If used unpainted, it should be dressed annually with linseed oil.

Straight grained oak is very durable and to lessen expense, it is now often used in conjunction with steel. The use of white lead paint inside helps to preserve wood and reflects light.

Metal

Steel and aluminium greenhouses are quite widely used, the latter material being easier to shape. Aluminium alloys are reasonably strong and provided they are well and firmly sited, they are satisfactory and in spite of their light weight, will stand firm. Points to watch for when selecting a metal greenhouse are absolute rigidity and provision for expansion and contraction without glass breaking or air leakage. Metal sashes are not glazed with putty; they need an elastic sealing compound. Steel needs painting, aluminium does not.

Concrete

Concrete greenhouses are also widely used. Less elegant than wood or metal, they are strong and durable especially since the concrete is usually reinforced with wire rods or frames.

Whatever type of greenhouse you decide to buy, make sure that all parts work properly, Ins ill-lilting joints, doors or ventilators can lead to trouble.

Guttering and down pipes should be provided to prevent water pouring off the roof and down the wide panes, as well as snaking it possible to store rain water in butts lir cisterns.

Choosing your Greenhouse

Buying a greenhouse is an investment, not only because it increases the value of your property but because of the all the year round pleasure it will give.

Since there are many kinds of greenhouse available, in various sizes and. Made of different materials it is important to choose I he one that will best suit your needs. This will depend on a number of factors, including the site available, the plants you intend to grow and the price.. Price will govern the size, although it is wise to buy the largest house you can afford to begin with.

It is a mistake to buy a greenhouse without lust deciding on what plants are to be grown in it. If you want to grow grapes or melons as well as ornamental plants it is no use choosing an 8 x 6 ft. greenhouse. The so-called Dutch light houses provide plenty of light and, in summer, they can accommodate tomatoes followed by chrysanthemums in autumn. Winter lettuce can follow and other forced vegetable crops could succeed the lettuce.

For pot plants such as cyclamen and primulas and for raising bedding plants, the usual span roof greenhouse is ideal. A structure with a brick or wood base allows for staging but if you want to grow tomatoes or chrysanthemums, or lettuce on one side where they will need full light, it is possible to buy a type with glass to ground level-or to have one side with staging and one with glass to base.

If you are concentrating on orchids there are special houses for these plants. They are fitted with extra ventilators and often with two-tier staging, the idea being to stand the Plants on the top lath staging, covering the lower staging with pebbles or old coarse ashes which are kept moist to provide the required humidity. A lean-10 house is useful for a vine, peach, or nectarine, while staging can be erected to accommodate colourful plants.

Make sure whatever type of greenhouse you buy is provided with ample ventilators of the right size. Ensure there are ventilators on both sides of a span greenhouse so drat there is always one side against the leeward wind.

Siting the Greenhouse

It is advisable to put the structure where it receives the maximum amount of sunshine, especially in winter. Avoid overhanging trees, because they cast shadows, and shed leaves and other deposits which can easily dirty the glass. Ideally the situation should be within easy reach of a water supply.

Avoid ground which becomes wet in winter and, wherever possible, choose a site where good paths can be made and which is not too far from your house.

The traditional alignment for a greenhouse is north to south, since in this position there is both a warmer and cooler side to the house. Some gardeners prefer an east to west siting, on the grounds that more light reaches the house. At all costs avoid windy situations, especially those exposed to north or east winds for these will bring draughts and some loss of heat, especially if north winds blow directly into the door. For preference, a lean-10 should face south.

Erecting the Greenhouse – The Foundation

A proper and permanent foundation is of paramount importance. Most greenhouse manufacturers supply a ground plan which must be strictly adhered to. A simple way of making a satisfactory foundation is to take out a 10-in. Deep trench 1 ft. wide, with vertical sides. In to this is built a brick footing. Concrete blocks for footings and walls are also satisfactory. Cultivated ground needs stronger foundations since it is more likely to sink.

If the superstructure is to rest on brick walls the top of the concrete foundation must be 6 in. below ground level. If electricity is to be used lay the cables before the concrete is put in.

A solid or concrete floor can be made, but a soil base is an advantage, as it allows some crops to be grown in the ‘floor’. In winter the soil can dry out, in summer it will help to maintain a humid atmosphere.

Glazing

When putting in the glass, it is advisable to use putty for bedding it on the glazing bars. If the structure needs a coat of paint or preservative, put it on before the framework is glazed.

Glass should be dry when used. If wet, the panes stick together and they break more easily in cold weather. Make sure the woodwork can be securely fastened to the foundations so that subsequently, there is no movement as could occur in windy, exposed positions.

Plastic is sometimes used as a substitute for glass but is certainly not of the same value. Glass is easier to clean and the full quality of light is transmitted. Polythene or plastic houses are useful for providing summer protection and giving dappled light. While it does not break in the same way as glass, plastic needs renewing from time to time.

Heating Methods

Hot Water

The hot-water method is very satisfactory, since an evenly distributed warmth is produced without creating a dry atmosphere. However, it involves stoking at least twice a day, with regular cleaning and ash disposal and the right kind of coal and coke must be used.

Electricity

Electrical heating is time and labour saving and requires no boiler or fuel storage. With thermostatic control a predetermined temperature can be maintained, provided the right heaters have been chosen and there are no power cuts. There are various ways of using electricity for heating:

(1) By a wire grid over which air is blown by a fan.

(2) By a convector heater designed to produce warm air without a fan. Rapid warmth is produced, although distribution is not so even.

(3) By radiating tubes, plates or strips.

(4) By immersion heater used for hot-water pipes.

Soil warmth can also be produced by electric cables. This is used to provide bottom heat for propagating seeds or rooting cuttings and does not substantially increase air temperature.

Paraffin

These heaters are widely used and, provided high quality heating oils are used, there is little danger of poisonous fumes. This means keeping the burners clean so that incomplete combustion does not release harmful gases. For large houses, heaters with outside chimneys should be used. For small houses there are several portable models available which need little attention other than refilling. Choose one producing a blue flame which results from complete combustion of the oil.

Manufacturers usually indicate how long a heater will burn with one filling. More important, is how much heat is produced. Heat is lost through ventilation, but stagnant air encourages fungoid diseases and other disorders, and particularly with paraffin heating, a crack of ventilation is always needed, except during the severest weather.

What can be grown in a greenhouse largely depends on the temperature that can be maintained. At one time, in large private gardens, a range of houses was to be found, starting from the cold house and passing from the cool to the intermediate and hot or stove house. Today few gardeners can afford more than one greenhouse.

While many greenhouse owners like to specialize in particular types of plant, those less experienced, usually prefer to cultivate a range of plants. This means that one has to grow plants which need similar conditions.

Types of Greenhouse

The Cold Greenhouse

This is one which ix never heated by anything but the sun and d colourful display can be had without any artificial heat. In extra cold weather, some protection can be given by blinds which can be pulled down or let up at will. Outdoors, many plants are killed by winter dampness  – if taken indoors they come through bad weather unscathed.

Where space is scarce the staging can be erected in tiers. Slatted wood is useful in that 11 allows air to circulate round the pots, helping to avoid atmospheric dampness in winter. Unfortunately, it also encourages pots to dry out quickly in summer.

The best plan is to place corrugated or asbestos sheeting over the staging and cover it with small shingle or stone chips. In summer the shingle can be kept damp to provide humidity, while from late autumn onwards, through winter it can be allowed to dry.

The Cool Greenhouse

This is one where a minimum night temperature of 40°-45°F (4-7°C) can be maintained. This must be controlled, which means adequate ventilation. It is, perhaps, plants in smaller greenhouses that suffer most when air conditioning is wrong, especially if sufficient ventilators have not been provided. Fresh air is important but when the air vents are opened, this naturally lowers the temperature but equally important, it moves the stagnant dank air, leading to the buoyant atmosphere so vital for plant health.

The Intermediate or Warm House

A winter night temperature above 48F (8 C) will allow a wider range of exotic plants to be cultivated. Such houses are usually sited where the benefit of all available sun is felt.

It pays to install automatic ventilation which acts according to outside weather conditions and inside temperature. Costing not ling to run, it is easily fitted.

A Hot (or Stove) House

This is one where the winter temperature never falls below 60°F (16°C). As it is fairly expensive to run not many amateur gardeners can afford a house of this type. Except for the temperature difference and the fact that a wider range of tender plants, including many orchids, can be grown, the inside arrangements and attention needed, are the same as for the warm greenhouse.

Plants to Grow

In the Cold Greenhouse

The success of plants in the cold greenhouse largely depends on the choice of the right kinds and the way they are looked after., There are distinct advantages in being able to provide just enough heat to keep the temperature falling below freezing point in winter. Failures are often due to overwatering in winter. In frosty weather, plants should be kept on the dry side.

Many alpine plants can be grown successfully in the cold house, where they can be raised from seed. These include: Aster alpinus, aethionemas, aubrietas, campanulas, dianthus, gentians, primulas, saxifrages and miniature cupressus.

Many bulbs do well as the protection provided leads to unblemished blooms. Among these treasures are crocuses, irises, including the Dutch varieties ‘Wedgwood’, lavender; and ‘Princess Beatrix’, yellow. Dwarf irises are specially good, including I. danfordiae, yellow; and I. reticulata, violet, and its many forms. Narcissus, early tulips, fritillarias, liliums, scillas, tritonia and the early gladiolus produce a bright display. Cypripedium calceolus is handsome in flower. It likes a limey soil. Early flowering shrubs grown in pots taken in the greenhouse in I kcember or January, soon produce a showy display. They include daphne, Erica carnea, lOrsythia, prunus and spiraea, while HeIleborus niger, the Christmas rose, responds well.

In the Cool Greenhouse

It is fascinating to see how quickly many exotic plants become acclimatized and grow in a cool greenhouse.

  • Daisy-flowered plants raised easily from seeds, such as arctotis, dimorphotheca, gazania and ursinia, will bloom continuously. Gerbera jamesonii has long lasting huge brilliant orange-amber flowers.
  • Erica hyemalis the Cape heath has long, white-tipped pink bells, while there are species with red, orange and yellow flowers. Gardenias, daphnes, epacris and daturas are handsome shrubs.
  • Hoya bella, the wax flower, is flesh-pink. Ipomoea or morning glory, easily raised from seed, is in shades of blue. Jasminum primulinum, yellow; Lapageria rosea, rich pink waxy bells; Passiflora caeruka, the Passion flower; and Thunbergia alata, orange with a black throat are all interesting.
  • Foliage plants are indispensable. They include Lippia citriodora, the lemon-scented verbena, caladiums with beautifully spotted and veined leaves; Eucalyptus globulus with grey-green foliage; Grevillea robusta; Maranta leuconeura, with leaves curiously marked and spotted; Saxifraga sarmentosa, fine for hanging baskets. Ferns and palms can be grown for temporary use in the living room.
  • Climbing plants can be grown in pots or planted in the greenhouse border. Among these are bougainvillea with brightly coloured mauve bracts in summer; Clematis armandii, an evergreen with white flowers; Cobaea scandens, a fast climber of which seed is sown in March.
  • Carnations are among the important cool greenhouse flowers. Their cultivation is described later..

Fruit in the Greenhouse

Although there are specially constructed greenhouses for the cultivation of fruit, few amateur gardeners are likely to buy a greenhouse solely for this purpose.

What can be grown depends on the space available and the amount of time that can be spared.

Propagation

Greenhouse and frame plants are propagated from seed or various types of cuttings. Seed sowing is often the easiest method although many plants must be propagated by cuttings, division, or off-sets.

By seeds

  • The majority of seeds germinate in a temperature of 60-65°F (15°-18°C) but it is not necessary to keep the whole greenhouse to this required minimum. A propagator heated independently, can be used for seeds and cuttings.
  • Many seed failures are due to the use of unsuitable compost. Destructive damping-off diseases frequently result from the use of poor soil. This is why the John Innes seed compost has proved such a blessing.
  • Whether trays, pans or boxes are used the compost should be evenly compacted without being made hard. Thin sowing is essential. Very fine seeds such as those of begonias and gloxinia: need not be covered but merely pressed into the surface soil. Larger seeds should be lightly covered. After watering place the boxes or pots in a propagator and cover them with glass and paper. Once the seedlings appear remove the paper and glass, taking care to keep the surface soil just moist.
  • Early pricking out of seedlings is necessary. Keep the pricked out seedlings shaded for a few days until they are established. As the seedlings develop they will need potting up. Stein etittings Many plants raised from seed can be increased from stem cuttings. These are usually made from young shoots or shoot tips. Only really healthy plants should be propagated and the cuttings should have Iwo or three joints. Remove the lowest leaves and sever the stem cleanly just below a joint. The best results are obtained when the cut t ings are inserted around the edge of pots tilled with a moisture-retaining but fairly open mixture. Water in the cuttings, then place them in a heated propagator or in a polythene bag, closing it with a rubber band, but keep the plastic off the cuttings.
  • When the plants have rooted the propagating case should be gradually ventilated so that they become accustomed to greenhouse temperatures. Cuttings with hairy leaves are liable to damp off and should be rooted on the open bench where they should be shaded to reduce transpiration.

Leaf Cuttings

  • Some plants, notably peperomias and saintpaulias, can be increased by leaf cuttings. Use healthy mature leaves and trim them so that the stalk is up to 1 in. long. Insert them in compost so that the leaf blades just touch the soil.
  • Rex begonias are treated rather differently. Slit the main veins in several places. Then weight or peg down the leaves. Roots and plantlets will develop where the cuts are made.

Stem Sections

  • Ficus, dracaenas and some other plants can be propagated from stem sections. The dormant bud in the leaf joint will develop into a good plant.

Leaf-bud Cuttings

  • These consist simply of a leaf situated centrally on a piece of stem about in. long complete with a dormant bud.
  • August and September are good months for the job since plants will be in full growth.
  • Among plants that respond to this treatment are aphelandra, pilea and ficus.

Division

  • Some plants such as chlorophytum and maranta can be divided in spring.
  • Many bulbous plants multiply naturally by forming offsets which can be detached and potted separately.

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