This invention relates to a method and an apparatus for hydroponically growing plant sprouts.
There are known a lot of methods for growing plant sprouts in soilless media. Hydroponics is one such method in which a plant is supported by a bed disposed on or above the surface of water, optionally containing nutrients, with the roots of the plant passing through the bed and extending into the water. Several beds for hydroponics have thus far been proposed such as (a) shaped bodies, such as plates and trays, formed of a close celled, synthetic polymeric foam material, (b) shaped bodies prepared by molding a mixture of close celled, synthetic polymeric foam particles and a vegetable organic material, (c) plates formed of a mixture of a close celled, synthetic polymeric foam particles, open celled, synthetic polymeric foam particles and scrabs, and (d) perforated sheets or wire nets mounted on buoyant frames. These hydroponic beds, however, are not quite satisfactory in practice.
The bed of the aforementioned type (a) has a very small bulk density and is floatable by itself. However, since the floatable shaped body per se has no water permeability, it is not possible to sow seeds of a plant directly thereon for germination. Thus, the shaped body is processed to form relatively large perforations or apertures on which seedlings are transplanted. Alternatively, the perforations are covered with water absorbent materials such as pebbles, sand, and peat moss, in which seeds are sowed. In either case, it is not easy to maintain a suitable humid growing environment throughout their growth.
The second, type (b) bed is suited for the germination of rice seeds. Since the vegetable organic material, which serves both as a binder for the shaped bodies and a fertilizer for the plant, is soluble in water, they are broken upon harvesting and cannot be reused.
In the hydroponic plate of type (c), the close celled foam particles serve to provide the plate with flotage, while the scrabs and the open celled foam particles serve as a water absorbent. The scrabs additionally function as a fertilizer for the growth of the plant. Thus, the mixing ratio of respective components is very important in that it has a great influence upon the moisture environment necessary for the germination of seeds and the growth of the germinated sprouts. Although the availability of the three components as waste materials is one of the merits of the type (c) bed, the use of waste materials makes it difficult to adjust the mixing ratio to a predetermined range because of the lack of uniformity in quality of the waste materials. Moreover, with the type (c) bed, the roots of sprouts extend into the pores of the open celled foam particles and the softened portions formed by the rot of the scrabs and entwine with each other. In harvesting, therefore, the matured sprouts are cut near the roots and the roots remaining in the bed must be allowed to rot in order to reuse the bed. In addition, because the type (c) bed, which contains scrabs and rot roots, is liable to become infected by germs, it is not suited for the culture of clean plant sprouts which are generally eaten as raw. For the same hygienical reason, the type (c) bed is not suited for indoor use, especially of homes.
The bed of the above-described type (d) is designed so that when it is floated on the surface of water, the pad of a perforated sheet or wire net is positioned just above the level of the water. Seeds of a plant are spread on the pad for germination. In this case, although the distance between the pad and the surface of water is maintained substantially unchanged at an early stage of growth of the sprouts, the pad will be submerged as the sprouts grow higher, i.e. with the increase in weight of the sprouts. Therefore, it becomes necessary to lift the bed on a suitable support to keep the sprouts in a suitable growing environment.