Choosing a suitable type
Nearly all gardeners, whether beginners or experienced growers will readily understand that a greenhouse, no matter how small, will offer a great deal of help and indeed pleasure. When space and finance are very limited, a small lean-to preferably situated against a south wall of the house can be used to great advantage for growing decorative plants throughout the year and, during the summer, supplying the family with tomatoes.
There are many other types of greenhouse available which can be delivered in easy to erect sections. Some made almost exclusively of wood and others of metal, the latter have perhaps a small advantage over the wooden variety as they can easily be extended with an extra section should this be required. In some cases the greenhouse is designed to have either a brick or wooden wall extending some two or three feet from ground level below the glass. This type is most suitable if pot plants placed on shelves are mainly to be grown, but if tomatoes or other plants are to be grown from the ground it would be wiser to choose a house where the glass begins at floor level. The main requirement of a greenhouse is adequate light and when deciding which particular one is most useful, the positioning should also be considered. It should of course not be too close to any overhanging trees and should be as near to a supply of water as possible. If heating is to be added either at the time of erection or later, this should also be considered as early as possible since the type of heating chosen may necessitate electric cables which naturally should be within reasonable reach of the main supply.
There are then two main types of house, firstly the lean-to and secondly the span-roof variety, both highly useful for all general needs whether it be starting offearly in the year for later, or simply for growing plants which need that little extra protection for decorative purposes.
The type of staging required in the house will of course depend largely on the size of house decided upon, and whether plants will be planted in pots or directly into the ground. It would be advantageous to have removable slatted shelves which can be taken away and stored during the tomato growing season and easily replaced later in the year for winter flowering plants and bulbs.
If permanent shelves are to be fitted the supporting legs should be strong enough to allow for the heavy weights which must be carried when the boxes or pots are finally put into place. Having decided on the type of support necessary, the top surface can be of wooden slats. This, when covered with a layer of shingle, will allow the water to drain away properly from boxes and pots at the same time retaining useful moisture which will keep the atmosphere in the house sufficiently damp during the hours of sunshine.
If space will allow, a small shelf near the roof will be useful for boxes of seedlings which should be placed as near to the light as possible and for storing pot plants out of the way during their resting period.
It is possible to heat the greenhouse in many ways, some using solid fuel or gas boilers heating water which is then piped round the house. This is the way most favoured by commercial growers and is of course efficient. It is however rather expensive and alternatives can be found such as electrically heated wall mounted tubes and fan heaters which, if coupled to a thermostat, are not necessarily expensive to run and give good results. It is also possible to buy a paraffin oil heater which will be sufficient to keep the frost out of a greenhouse during the winter months. It should be borne in mind that only an oil heater made specifically for greenhouse use should be used as they are carefully designed to reduce the harmful fumes to a minimum and usually have side tubes to distribute the heat evenly. This type of heater is often fitted with a water tray which stands above the heater and helps to increase the humidity during heating hours. Care should be taken to keep the appliance clean and clear burning however as plants do not take too kindly to strong paraffin fumes.
A thermometer should always be found in a heated greenhouse so that an eye can be kept on the situation and the heat regulated to allow for as even a temperature as possible. By far the most efficient thermometer is a “maximum-minimum” type which records not only the highest temperature reached during the day but also the lowest during the night. Small metal pins are inserted into the double tubes during manufacture which are pushed in either direction by the mercury and are left behind as indicators when the temperature changes.
All growing plants need air and sufficient ventilation must be available in greenhouses to allow for this and to cool the temperature during the very hot part of the day. Care should however be taken to close the ventilators early enough in the day so that some of the day’s heat can be retained in the house during the night. Only during the very hottest part of the summer should it be necessary to keep the ventilators open all night.
During the hot weather it will be necessary to give some shade to the roof of the greenhouse so that plant leaves are not scorched up by the temperature rising too high. This can be done in several ways, undoubtedly the best being roller blinds which can be quickly regulated when the need arises. These are unfortunately rather expensive and an adequate alternative can be fairly cheaply made with hessian tacked along wooden laths. The other alternative is to coat the roof area with a solution sold for this purpose which resembles distemper. This method of shading works well and the solution can be easily washed off after the heat of the summer has passed but does have the disadvantage that it is not possible to regulate the amount of shade needed from day to day.
To maintain the best conditions in the greenhouse for growing most plants, the humidity of the air must be carefully watched, and the staging, walls and floor of the house sprayed with water from time to time during the summer to make the necessary moisture available. This should of course never be done during the winter in a cool greenhouse as naturally too much dampness around with no evaporation taking place will lead to disease.
Seed and potting
The type ofused for planting seeds and later for potting up the small seedlings is of great importance. It would be useless to simply take a bucket of soil from anywhere in the garden and use this for the greenhouse, or in fact any other potting elsewhere. A carefully prepared, balanced compost which has been sterilised against and is
weed-free should be used and this can be bought from any garden suppliers or seedsmen. The most generally useful type is called “John Innes Compost” which is specially mixed from loam, peat and sand in the most satisfactory quantities and has the addition of certain fertilizers which are necessary to promote healthy growth. A similar compost can of course be mixed at home but since large quantities are not usually required the saving concerned would not seem worth the trouble.
Seeds should be planted in either wooden seed trays as illustrated or in flower pots which of course can be bought in both the usual clay, which incidentally need soaking before use, or plastic. Whichever container is chosen the main necessity is for ample drainage. Bought seed boxes have gaps left between the boarded floor and flower pots have at least one drain hole at the bottom. This is essential as the water must have freedom to drain away naturally. This should be helped with pieces of broken flower pot, called crocks, placed along the gaps in the box and placed over the holes in the flower pots. Be careful to put these crocks with the curved side uppermost so that they do not obstruct the drain away.
The box or pot is now ready to receive the compost which should be put in and firmed lightly with a suitable piece of wood. Although the soil must be firmed it should not be rammed down too tightly as the young roots from germinating seeds will have difficulty in penetrating down.
The container should be filled to approximately h inch from the top, and if the soil is not moist enough the pot or box should be lowered gently into water until the moisture seeps up to the top. The seeds should now be sown thinly and covered with a very thin layer of fine compost. A piece of glass can now be put over the planted container and, having labelled it clearly with the name and date planted, finally cover with a piece of newspaper to cut out the light and encourage germination. Each day the glass should be removed and wiped clean of condensation and replaced. The moment the first seedling has appeared remove both glass and paper as by now as much light as possible is needed.
When the seedlings have begun to grow their second pair of leaves it is time to transfer to other boxes or pots in smaller quantities so that they have room to expand and grow into healthy little plants. Similar preparations should be made to the container as described in thesection but now each seedling is lifted out of its position with the help of a small piece of wood, a small labelling peg is ideal for this job, and replanted into the new box with at least 2 inches space between each seedling. Care should be exercised so that the delicate little roots are not damaged during transfer. When each box has been filled it should be watered with a can fitted with a fine rose to settle the soil around the roots.