Management of Glasshouses

New Zealand Journal of Agriculture, Volume 85, Issue 2, 15 August 1952, Page 109

Management of Glasshouses

By

R. R. WHITE,

Horticultural Instructor,

Department of Agriculture, Dunedin

THE management of glasshouses consists mainly of giving the plants a healthy environment. The correct amounts of light, fresh air, moisture, and heat should therefore be ensured and attention paid to the important aspects of glasshouse hygiene and disease control. Correct methods of seed sowing, pricking off, planting, and potting should also be strictly adhered to.

LIGHT plays an important part in plant life, enabling the process of photosynthesis to be carried out. However, too much light in the form of bright sunshine may prove harmful, especially to small seedlings and shade-loving plants. Some plants, however, require all the light available, although the heat effect may cause damage. Shading of the house helps to reduce light intensity and this can be achieved in two ways. Methods of Shading The first method is to apply a coat of whitewash or whiting to the outside glass surface. Such a mixture can be prepared by mixing whiting with cold water to form a thin paste to which is then added liquid glue as an adhesive. Though cheap, this method has the disadvantage of cutting the light down too much on dull days, and in districts where such days may be numerous plants tend to become drawn. More than one application may be necessary during the season, as shading is usually washed off by heavy rain or hail storms. In winter the shading has to be removed, as plants then require all the light available. This can be done by washing the glass with a solution of

caustic soda. At the same time unshaded glass can also be washed to remove any dirt, thus allowing as much light as possible into the house. second method of shading is with the use of blinds which can be raised or lowered as required on the outside of the glass. Though rather expensive for large houses, this method j s very useful for smaller types. The blinds can be made from scrim, canV as, or wooden slats. By pulleys and cords these can be rolled up when the sun is not shining. The scrim or canvas can be tacked to a wooden strip, fixed to the gable of the house, and a

wooden roller at the bottom. One end of the cord is fixed to the gable and runs down the glass round the roller and back to a pulley which is above the wooden strip and also fixed to the gable. From there the cord is brought back to the bottom of the house or by a small hole in the roof it can be run down inside the house and thus allow the raising and lowering of the blinds from within the house. By pulling the cord the blind may be rolled up. Wooden slats tin. x 3/16in. spaced tin. apart and attached to chandelier chains with bifurcated rivets make the best type of blind.

Roller blinds can be of use on frosty ■ nights, as they help to keep the frost off the glass and economise in heat where it is used in the house.

Ventilation

Ventilation is necessary to ensure a good,circulation of air round plants, especially where there is a'possibility of attack by fungus. During warm weather ventilators can be opened wide all day and partly at night. In houses with ventilators on either side of the gable only those on the lee side should be opened when a wind is blowing to prevent draughts. On hot windy days it is good practice to . close ventilators or nearly so, as the air inside the house becomes dry, causing too rapid transpiration in the plant and wilting and possible complete collapse.

Where heat is laid on in winter careful ventilation is necessary to prevent too much heat loss. Ventilators should only be opened on fine days, preferably when the outside air is warming up, and closed not too late in the afternoon to maintain . the temperature in the house. For cold houses the same course may be followed, except that closing of the ventilator in the early afternoon helps to trap any heat in the house caused by the sun.

Watering

Water enables plants to take up the necessary nutrients in the soil and so correct watering is essential. Overwatering should be avoided as it drives all the air from between the soil particles, thus depriving the roots of this necessity. Plants become wilted and as often as not more water is added, completely waterlogging the soil with resultant killing of the plants. The results of under-watering are known by all. No hard-and-fast rule can be laid down as to when to water, as this can only be determined by studying the condition of the soil. For well-established pot plants a fairly safe rule is to water them when the soil begins to leave the wall of the pot, filling the space between the soil and the top of the pot completely. With, seedlings the topsoil layer should never be allowed to dry out. Humidity can be maintained in the houses by “damping down” all walks and staging and also by using a fine syringe. Care of Heating Units In houses where heating units are used, economy in their use is the key to successful glasshouse cropping. Therefore they should be kept in first-

class order. The most important part - of any heating system is the boiler. It must be kept clean at all times so that it can produce the maximum heat for the fuel consumed. Many boilers are automatic and have a forced draught, The draught box must be kept clear of any debris and the combustion chamber requires periodic cleaning to remove clinker and ash. With oil burners a periodic check of jets and other equipment is essential Flues and heating surface require daily cleaning to remove soot and ashes, which can have an appreciable insulating effect. Where a thermostatic control is used this should be checked with a thermometer to see if it is operating at the correct temperatine. As the thermostat often cuts off the heater during warmer winter days, a good practice is to switch the thermostat out m order to have the water m the pipes hot. when temperatures begin to fall during late afternoon. Pipes that are . used solely for heating the air need to be kept clear of soil and debris to give as large a heating surface as possible to the air. They also require a periodic check to guard against air locks and possible leaks which may mean the loss of valuable hot water.

• Maintenance is essential for all houses and is best carried out when they are free of plants, in most cases during the winter. Any cracked or broken glass may .mean drips and cold draughts, while a thorough cleaning of the panes gives more light. Where blinds are used for shading they may be taken down, oiled in the case of wooden slat types,, or repaired where necessary. A coat of paint on all woodwork at least every 2 years adds to its life. ' < Pest and Disease Control To grow healthy plants greatest’ attention must be paid to all aspects of insect pest and disease control. Hygiene is the first essential. At no time should rubbish be allowed to

accumulate under a bench just because it cannot be seen. Such an accumulation is usually the first place from which diseases come, especially if it includes dead plants. Spraying and fumigation should be worked to a strict routine, thereby preventing disease rather than having to control it when it is rampant among the plants, Spraying should not be carried out h^ weather conditions are cold and d The ideal time is when the SD ’ will dry quickly on the leaves, gpray equipment should be thoroughly c fe ansed after use . Hot soapy water followed by two or three rinsings with clean cold water ensures the removal of residues in the sprayer. Fumigation is a good method of kill- . any insect pests within the house, T * adv antage of this type of control is that - t can be done last thing in the afternoon so that the house can remain h during the night, allowing the fumigant to have full effect. s , For good fumigation all possible care must be taken to prevent leakage of the fumigants. Draughts should be eliminated. A respirator should always be used . ft s good policy to have

another person standing by in case the operator is overcome by the fumes. The types of fumigants available are smoke producers, vaporising liquids, and gas-producing powders activated with water or acid. The last type includes the cyanides which produce the extremely poisonous hydrocyanic acid gas. They are dangerous and should not be used in glasshouses in heavily populated areas or by persons inexperienced in their use. Hydrocyanic acid gas may cause damage to plants. Use of Compost When plants are raised from seed a good compost is the first requirement. The best used are the John Innes composts and for seed sowing the one to use consists of sterilised loam 2 parts, sharp sand 1 part, peat or leaf mould 1 part (all by bulk) to which are added IJoz. of superphosphate or reverted superphosphate and foz. of carbonate of lime per bushel of mixture. Care must be taken when filling the seed box to have the soil firm but not packed too hard, with the soil surface level and about Jin. below the top of the box. The soil should then be watered thoroughly and the box left to drain. The seed can then be sown. To do this put the seed on a piece of cardboard or paper, hold it firmly in the hand, and tap it gently with the forefinger so that the seed falls off the paper slowly. At the same time the hand should be moved to and fro across the box to give an even distribution of seed. Practice can be gained by using sand, instead of seed. • The amount of soil covering the seed depends on the fineness of the seed. Very fine seed needs very little soil coverage, though coarser seed may need about Jin. As seeds germinate fairly rapidly in a glasshouse, a thick soil coverage is not necessary. This soil can be sieved on to the seed layer, a fine sieve being used, and then firmed gently with a wooden tamper. The box can then be covered with glass and brown paper or just brown paper; at the first sign of germination this can be removed to prevent the seedlings from becoming drawn. The next stage is pricking off into boxes. The John Innes potting compost is again the best to use for filling

the boxes. It consists of 7 parts of sterilised loam, 3 parts of peat or leaf mould, and 2 parts of sharp sand (all by bulk) to which are added ljoz. of dried blood, ljoz.- of superphosphate or reverted superphosphate, foz. of sulphate of potash, and foz. of carbonate of lime per bushel of mixture. As with the seed box the soil should be firm but not packed hard and the box . filled to within Jin. of the top. A suitable marker can be used to mark out the tray for plant spacing. The young seedlings are then lifted from the seed tray and inserted in the holes made by using a dibble. The soil is then ' firmed around the seedlings. Seedlings should be pricked off before they become too large, so that the rooting system is still small enough to sustain little damage. When the box

is filled with the required number of seedlings it can be placed in the house and watered thoroughly with a fine rose watering can, care being taken not to wash out any of the small seedlings. Before planting out in the glasshouse crops such as tomatoes the soil should be worked to a fine tilth and fertilisers added. The plants need to be firmed so that they cannot be lifted out and then watered if required. For potting the compost used is the same as for pricking off. Good fibrous loam is an advantage. The first essential is to use pots that are clean and properly crocked. A large crock is placed over the drainage hole in the pot bottom and covered with smaller crocks. These can be obtained from broken pots, of clean well-weathered coke and coke breeze can be used. Fibre can be placed on top of the crocks to prevent soil particles from falling down. Potting is best carried out on a bench. A three-sided bin is used for holding the soil, with the empty pots and plants on one side and the pottedoff plants placed on the other. Some soil is placed in the pot, it is firmed with the hand, and the plant is lifted from the box with a flat stick. The plant is then placed in the pot, held upright with the left hand, and the soil run in around it with the right hand. The soil is then firmed and more is added if necessary to bring the soil level to within -Jin. of the edge of the pot. The pot is then placed in the house and watered thoroughly. With pots, spacing is important as it prevents overcrowding and resultant weakness in the plants. For potting on the soil usually requires to be much firmer and a potting stick can be used. Except where root pruning is practised, all rooting systems should be disturbed as little as possible when potting off or potting on.