Growing mediums

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loam composts Special growing mediums have been developed for container-grown greenhouse plants, and the more important ones are described in this chapter. For over JO years the John Innes composts have been used by commercial growers and amateur gardeners alike. The name John Innes is taken from the research station where they were formulated after years ot investigative work. The formulations provide horticulturists with various growing mediums to cover every greenhouse activity, from seed sowing through to final potting. All these formulations are based on the use of good loam. They have stood the test of time, and composts made up to the original formulae are available at most horticultural stores and garden centres.

There are, however, many garden

ers who prefer to mix their own composts and the brief description here will provide guidance as to what is entailed. Kettering loam is a medium heavy loam, and while tins is ideal it is not readily available in all parts of the country and a similar loam may have to be used instead. The term 'loam' here means the top 75 to loo mm (3 to 4 in) of a grass field. After cutting, the sods are placed grass downwrards in a rectangular stack about 1.5 m (4$ ft) square. The stack is watered well while it is being built, and a layer of rotted farmyard manure or similar is spread at i 50 mm (6 in) intervals throughout. The stack is finished off at a height of 1 to t .5 m {3 ft to 4 \ ft) and a polythene sheet is placed over the top to keep off excessive rain, After some six months the stack may be used as required by slicing down one face with a spade and putting the loam through a riddle. The result is a fibrous soil which to the experienced gardener looks good, feels good, and even smells good! However, it may unfortunately contain pests and diseases injurious to plants, as well as weed seeds. For these reasons it has to he partially sterilized at a temperature not exceeding K2 C {180 F) with no part of the 'cooking' being below 71 C (163 F). This is best done in a small electric sterilizer which passes steam through the loam, killing all the harmful organisms in about an hour. The 'cooked* loam may be used after two weeks. !t is then mixed with peat, a coarse sand or grit, lime (chalk), and a base fertilizer in the following proportions (by volume): john innes seed COMPOST 2 parts loam 1 part peat t part coarse sand To each bushel (0.04 cu m) of this mixture is added 20 g (j oz) chalk and 40 g (l^ oz) superphosphate.

Above left Three popular potting composts pest-based, peat and sand and loam-based Right The flower grower can have cotour m the greenhouse all the year round

Peat Base CompostGreenhouse Seedling Pots

Plant pots end seed containers are made in a variety of materials for different uses john innes potting compost No. I 7 parts loam 3 parts peat 2 parts sand To cach bushel (0.04 cu m) of this mixture is added 20 g oz) ehalk and 115 g (402) of John tnnes Base Fertilizer (a mixture ofhoof-and-horn meal, superphosphate, and potassium sulphate) which is sold ready for use. J.I. Potting Compost No. 2 is the same as No. 1 but with an extra 11 $ g (4 oz) of Base Fertilizer: Potting Compost No. 3 is the same as No. i but with an extra 230 g (8 oz) of Base Fertilizer. Do not mix too large a quantity at any one time: it is best used within six to eight weeks.

All composts need to be kept where they will not be contaminated by weed seeds, soil, already used compost, or unclean pots; harmful bacteria from these sources can quickly infect the sterilized compost. It is highly desirable to establish a clean {sterilized) area in the greenhouse and to make it a rule never to move used pots, seed trays, and so on into the area until they have been thoroughly washed and allowed to drain. Too often, equipment is carefully sterilized - and then left to collect weeds and disease organisms. It is little wonder that gardeners who treat their equipment in this way often complain that expensive composts have failed to produce healthy plants, loamless composts In recent years loamless composts based on mixtures of peat and sand or on peat alone have become increasingly popular. Their attraction stems from the fact that the ideal loam is difficult to obtain, the sterilizing process is laborious and costly, and the weight of readymade J.J. composts leads to high carriage costs. The components of loamless composts are sterile to start with and the composts are considerably lighter in weight. The amateur gardener should buy such composts ready-mixed, for peats and sands vary and not all are suitable for seed and potting mixtures.

Gardeners accustomed to using loam-based composts will initially find peat/sand composts more difficult to manage. They need to he moist to start with, and it they dry out they are difficult to re-wet. Also, because they are light in weight, tall plants can more easily tip or be blown over along with the container m which they are grow ing; this can be overcome by putting .1 little J.I. compost in the bottom of the pot to weigh it down.

Seeds germinate more rapidly in peat and peat/sand mixtures than in loam composts, and the light, open texture of such mixtures seems also to suit many mature plants - most proprietary growing bags are filled with them. Feeding of container-grown plants needs to begin earlier with loam less com posts than with loam composts. On the other hand, there is no need to line the bottom of pots with crocks if peat/sand composts are used, and they are specially suitable if plants are to be watered by capillary action for example, by means of a tray of moistened sand placed under the pots.

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