TYPES AND MATERIALS FOR PLANT CONTAINERS
The material must not yield phytotoxic substances harmful to the crops. The material must be sufficiently durable, which means that it must last the whole culture-period, but also can take the transport to different commercial links and the transport over long distances from grower to consumer. It must be taken into consideration that container grown plants can be kept a fairly long time in the retailer business, so that the durability must be covering the whole period to the very end. The material must be good-looking, i.e. it is to be understood that the material must not spoil the saleability and if possible add something to it. The material must be rather cheap and it should be water-tight. Different materials will be discussed in the following.
- Iron in thin plates is cheap, especially when used containers can be applied, but it has a very distinct drawback that the cans are normally cylindrical, which makes pulling of the plant without disturbance of the root very difficult. In U.S.A. a method of making the cans conical before potting or a procedure with cutting the can with the can opener directly before planting procedure, is used. Iron is not sufficiently durable in thin plate qualities and as it rusts, it will be unesthetic for containers if a painting or rust protection is not carried out.
- Clay is cheap and ceramic containers are very good, but the breaking in frost will be of disadvantage in northern areas. The heavy weight will give too great freight expenses and there is also unwanted big water loss through the clay walls. They are not recommendable for this purpose.
- Concrete can be used for large containers. But for small ones it will have the same disadvantages as for clay and is of no interest. Big containers can be made of two half cylinders kept together with a wire. At delivery the wire is cut and the plant can be taken out with intact root ball. The two half cylinders can be used again. The principle seems to be good for large plants and for this purpose the heavy weight of the concrete will be valuable as a ballast for the plant during cultivation.
- Fibrous materials with or without impregnation can be taken into use provided that the tenability will be long enough to cover the cultivation periods, but when planted out will be decayed in the soil. Such material as cardboard, peat, and cellulose, canvas, jute and woods. Normally these containers cannot stand long transport from the growing area and this naturally diminishes the application. The large variation