This term signifies the raising of plants in inert materials which conduct water to the plant but are devoid of all plant nutrients. Nitrogen, phosphate, potash and other necessary nutrients and trace elements must be continuously or regularly supplied to plants in aqueous solution.
A small-scale arrangement is quickly and easily put into operation. A flower pot withholes, or a seedbox, is filled with cither pumice gravel, vcrmiculite or perlitc, and stood in a watertight tin or similar receptacle. The is sown in the vermiculite and watered with a suitable plant nutrient solution; any excess drains into the tin, and is drawn up by the porous vcrmiculite as and when required.
It is only when this method is used on a larger scale, in a coldframe for instance, that its real advantages become apparent. The first task is the removal of the old soil from the frame and its partial replacement with a thin layer of sand arranged in such a way as to allow a fall of 1-2 inches towards the middle, or one corner. Next, the entire floor and sides (up to a height of 6-8 inches) of the frame are lined with a sheet of polythene. To facilitate free, a brass or copper plate fitted with a pipe flange is securely glued to the polythene sheet at its lowest point; a heated nail or ‘knitting needle neatly cuts the polythene to fit around the outlet flange, to which in turn is attached a rubber tube sufficiently long to hang down outside the frame. To prevent the growing medium, still to be put into the frame, from blocking the water outlet, it is first covered with a bottomless jar or tin. The growing medium, whether pumice gravel, vermiculitc, or perlite, is sieved with a ¾-inch mesh; the larger particles are then used to fill the lower portion of the frame, the fine particles to top it up to a height of 4%-6 inches.
Pumice gravel, a natural, porous and volcanic mineral, is ideal for this purpose. Though it is always moist, it does not retain excessive water.
Its porosity, and the air space between the particles, favour gooddevelopment. Vermiculite and perlite are both exfoliated minerals, also light and porous, but with less or no air room between the particles.
Provided the frame area is no larger than 10 square feet, a semiautomaticdevice is easily arranged. A bucket with a capacity of 4 ½ —6- gallons (5 ½ —8 us gallons) is connected to the rubber tubing and filled with plant nutrient solution. On lifting the bucket, the solution flows into the growing medium and is absorbed; when the bucket is lowered, the excess fluid flows back into the bucket. The liquid requirements of frames of more than 10 square feet would necessitate a liquid which, when full, would be too heavy to lift; the alternatives are by hand with a fine-rosed can and permitting any excess to drain away, or installing a pump.
One or other of the generally available proprietary brands of completely balanced liquid manures are suitable for making the plant nutrient solution, although its analysis should be checked first. A few additional drops of phosphoric acid may be necessary to adjust the pn around 5-5 to 6-5 (slightly acid). Correct pH values are easy to determine, either with a pH meter or with one of the specially prepared test papers.
Frequency of watering can vary from once a week to once every second day, depending entirely on the weather, and duration and strength of sunshine. Watering must cease completely during the autumn, and can only be resumed in the spring, when the warmer weather returns.
Frames should be closed during periods of rain to prevent the nutrient solution from being leached out, while moisture losses due to evaporation are easily made good through extra watering. To guard against fusarium, a fungicide watered over the whole of the frame area once every four weeks proves beneficial. The nutrient solution must always be renewed at regular four-weekly intervals; any old solution which may be left is best discarded.
Sowings can be made as early as February, March or April.are sown in shallow drills and covered with a layer of vermiculite inch thick. The space between rows need not be wide, as the nutrient solution is able to provide for a larger number of plants even if , Hemerocallis, or alpines are sown at the same time – all of which will do equally well under the same conditions. Normal treatment along the lines of the usual coldframe culture is all that is necessary, but frames should be kept closed after the seed is first sown; once germination has taken place, shade and ventilation are essential to prevent the temperature inside the frame from rising too high. The advantages of soil-less culture are as follows: 1. Healthy growth in a clean growing medium 2. Satisfactory, quick, high germination 3. Controlled fertilizer application of selected plant nutrients 4. Consequent strong and quick development 5. No losses due to fungi 6. No worms, insects or slugs 7. No weeds or weeding, therefore no physical damage to 8. Impossible to water to excess because of porous growing medium 9. Therefore first-class development 10. Exceptionally easy to lift without damaging
The same growing medium can be used again, but must first be disinfected with formalin, once the seedlings have been removed. The formalin solution should be left in situ for several days, and then well washed out of the growing medium, prior to its being air-dried.
The same method is also used forwork; it is clean, simple, labour-saving, and capable of producing seedlings which flower as early as the second year.
Recent experiments and trials in the United States have established that good aeration of the growing medium is essential for successful germination and seedling development; the better the aeration and drainage, the better the germination and seedling growth. This in itself is yet another recommendation for soil-less culture.