Hydroponics: Raising plants from seed
Most vegetables that can be raised from seeds can be started off by using either the flotation technique or the aggregate culture technique.
A clean plastic seed tray, divided into sections by vertical panels, is then part filled with a perlite layer evenly spread over the base. The tray is placed where the seeds are to germinate, before tap water (at room temperature) is very carefully poured into the box so that the perlite layer floats.
These chemicals can all be obtained from a fertilizer or garden chemical supplier, from an industrial chemical supply house, or even from a chemist or garden centre.
You will find that adding the super-phosphate produces some sediment at the bottom of the container in which you mix the ingredients; ignore this when pouring out the solution.
Fertilizer pellets are added before seed is sown. Seeds are then carefully placed on the perlite which is moistened from the water below and then covered with finely granulated cork or bark to discourage algal growth and keep out light. The tray is then covered with glass or plastic, and kept warm and dark. The, which tend to be more fleshy than -grown plants, are transplanted in the normal way.
Sand or aggregate method
Clean seed trays, plastic for preference, are evenly filled with aggregate and levelled and watered with nutrient, then the seeds are sown on the surface. A thin covering of fine aggregate or sand is scattered over the seed. The tray is then placed in a warm place, and covered with glass or plastic in the usual way.
The seed trays, which should have drainage holes about 0.5 cm (3”) in diameter drilled in the base, can be watered as necessary by standing them in containers holding nutrient solution. It is a good idea to cover the drainage holes with nylon gauze to prevent them becoming clogged with aggregate. It is also wise to put a layer of larger gravel or even stones at the bottom of the tray, for most efficient drainage.
After germination, the plants are treated in the normal way. The seedlings, which tend to be slightly more tender and brittle than soil-grown ones, can be more easily lifted out if the trays are immersed to the rim in water just before easing the seedlings out.
Seedlings which are to be grown by nutrient solution (true hydroponic) culture are carefully transferred to a cradle of wire mesh filled with wood wool or similar material. This material must always be kept moist. The level of nutrient solution is then raised so that the developing roots of the seedlings are in the nutrients. As the plants grow the nutrient solution level is lowered to leave a 1 cm (2”) air space between the cradle and solution. This air space is left so that the roots can obtain enough oxygen. As the roots of the plant grow, reduce the amount of the nutrient solution somewhat until the air space is 5 cm (2”).
The nutrient solution requires regular changing every 7-10 days and should be topped up with tap water (at room temperature) in hot weather to replace that lost by evaporation.
With aggregate culture methods, the basic technique is similar, whichever method of irrigation is used. Where trays orare used, one end is raised slightly to make drainage and washing easier. Suitable containers are filled, levelled and firmed with aggregate.
Before planting, the aggregate is watered, and the seedlings are planted in the usual manner. The aggregate should be watered about two to four times a week, and aerated for an hour or two after each watering by draining the nutrient solution into the reservoir. Pour the solution back onto the aggregate after aeration.
If using surface watering methods, take care not to disturb the aggregate if possible. The nutrient solution should be renewed every 7-10 days. After draining off the old solution, flush the aggregate thoroughly with clean water before adding fresh solution, which should be at the same temperature as the old solution.
Other operations are similar to those involved in soil culture, but the time scale is usually considerably shorter. Temperature, ventilation, shading and syringing are much the same, but spacing can be a good deal closer. Provided other conditions are satisfactory, soilless culture methods enable plants to obtain all the moisture and food they need at close spacing, which would be difficult or impossible in most soils. One of the main differences between soil culture and hydroponics is the method of support for plants, because the root anchorage of crops grown by hydroponic culture is less firm than that of crops grown in soil. Gravel and other aggregates do not provide enough support for stakes. It is essential to support plants from above, for example by tying them loosely to wires stretched between posts inserted into the soil alongside the containers.
Check the pH of the water supply every three or four days: a pH of between 5.0 and 6.0 is needed. Occasionally tap water has a rather higher pH than this, but this can be corrected by adding dilute sulphuric acid to the water, very slowly and carefully (never add water to acid).
The pH of your nutrient solution may tend to drift towards alkalinity, especially with a new tank, and this should be corrected in the same way.
Pests and diseases
Prevention and control measures forare basically the same as for soil culture, and sprays used according to the manufacturer’s directions should present no great difficulties.
The most common problem is likely to be the growth of algae, although this is usually more unsightly than harmful. Provided that the containers and aggregate are sterilized after each crop, algae should not present too much of a problem. However, if you do have this problem, a solution of 10 g of copper sulphate in 18 L (4 gal) of water, sprayed onto the surface once or twice should check the growth of algae. Proprietary chemicals for the control of algae are also available.
Choice of crops
Given reasonable care and attention, most fruit and vegetable crops can be grown using water culture methods, but, , and tree fruits are not as easy as some crops.
However, aggregate culture is a different matter: theoretically any crop that can be satisfactorily grown in soil can be grown in aggregate media. In practice, the best choices for the amateur are salad crops and strawberries.