Temperature adjustments are often necessary to increase or decrease, the rate of growth of chicons in order to produce the best quality product. Watertight trays generally 1 m 2 are fabricated using wood or steel. A 4 cm outlet hole at the midpoint and as close to one edge as possible receives a telescoping plastic pipe fitting which can be extended downward into the tray below. Flow level in the top and succeeding trays is controlled by protruding the telescoping plumbing above the bottom to the desired level. This provides a 5 cm depth of flowing solution to the packed roots in the tray below.
Sufficient headroom is provided to allow space for the chicons to grow.
Stacking of the trays is such that the outlets are opposed to each other, thus providing a labyrynthian flow through the stack. Stacks are therefore in multiples of two trays and typically are 8 high, making for efficient utilization of vertical space. An upward drift in pH may occur during forcing attributable to the uptake of anions and efflux of hydroxyl ions and maybe monitored and adjusted periodically by additions of nitric or sulfuric acid to maintain a pH near 7.0. Nutrient depletion may also be monitored by measurements of solution conductivity and periodically adjusted by additions of fertilizer solution concentrates. Advanced forcing operations consist of computer assisted monitoring and adjustment of temperature, pH, solution conductivity and fertilizer injection.