In German Patent Publication (Open Application DE-25 54 108), a planter has been described in which a valve plate is carried by a lever arm articulated to a wall of the planter and having a free end provided with a float responsive to the liquid level in the root compartment of the planter.
With lowering of the liquid level in the root compartment, the float drops and lifts, via the lever arm, the valve plate from a valve seat so that liquid from the reservoir can flow into the root compartment and thus a substantially constant liquid level can be maintained therein.
This system has several difficulties. For example, for various types of plants, different liquid levels are required for maximum growth and it is frequently necessary to vary the liquid level in accordance with seasonal water requirements for the various plants. Adjustment for these conditions is not possible with the conventional device just described in a convenient and efficient manner. For example, if a variation is required in the liquid level for any reason, the planter must be disassembled and the float replaced by one of a different shape or type.
In a further embodiment of the system described in the German Patent Publication DE-OS 25 54 108, level control is provided, but here the level control requires an airtight sealed reservoir which is difficult and expensive to fabricate and which creates problems when the reservoir must be refilled.
In another German patent document (Printed Application) DE-AS 23 64 868, a planter has been described in which the root compartment is so provided that the maximum liquid level in the planter always lies below the root compartment and the liquid transport is effected by a tube extending through the root compartment and using capillarity and liquid conductivity characteristics of the tube. The refilling of the reservoir is effected through the interior of the tube which has an inner flange defining a valve seat for a float provided in the tube. The float acts as a check valve preventing overfilling of the planter. The float is also provided with a rod which can extend out of the upper end of this tube so that the change in liquid level in the planter can be monitored by watching the descent of this rod. In this construction as well, there is no way to conveniently vary the liquid level in the planter or in the root compartment and, indeed, in this system as well there is no way to maintain the planter liquid level substantially constant by automatic refilling from a reservoir.