APPENDIX 11
PREPARATION OF LEONARD JARS
The modified Leonard jar assembly (Figure A.11) consists of a 700 ml capacity beer bottle with the lower portion cut off. This bottle is inverted into a heavy glass jar (reservoir), 1 l minimum capacity. The mouth of the bottle should be 23 cm above the base of the reservoir. The growth medium (sand or vermiculite) in the bottle is irrigated by a centrally positioned cotton wick running the length of the bottle and extending out of the mouth and into the reservoir containing the nutrient solution. Various types of wick material have been used with Leonard jars, e.g. braided cotton lantern wicks, cotton rope, strands from cotton mop heads, coiled cotton wool, braided or twisted nylon rope. New wick materials should be tested for their ability to conduct water and their compatibility with plants. Generally, a 12 mm cotton rope is adequate and easy to obtain.
Place approximately 50 cm of wick material in the bottle with about 10 cm extending out of the mouth. A small amount of absorbent cotton stuffed into the neck of the bottle will aid in securing the position of the wick, and prevent the growth medium from settling in the reservoir. Wick material of cotton rope should be boiled in water and squeezed dry prior to use. This removes air trapped in the wick and improves water conductivity.
While holding the wick in a central position, fill the bottle with growth medium (well-washed river sand or horticultural grade vermiculite). Pack the medium to minimize air spaces. Sand is easier to pack when dry. For vermiculite, it is more convenient to pack when wet. The vermiculite should be soaked overnight and the water drained off prior to packing into the bottles.
Position the bottle in the reservoir. The bottle should fit firmly on the rim of reservoir. Moisten the growth medium in the bottle by adding 150200 ml of the Nfree nutrient solution. Allow the nutrient solution to saturate the medium and the excess to drain into the reservoir. Fill the reservoir with 800 ml of the nutrient solution. Use 1600 ml if the reservoir has a 2 l capacity. Wrap the bottle and jar assembly with white or brown moisture-proof paper and secure with rubber bands at critical points along the jar. Tape may also be used. Aluminum foil wrapping may be used if it is inexpensive and available. Cap the open end of the bottle with either aluminum foil or wrapping paper. Hold the assembly by the reservoir when moving it.
Sterilize the complete assembly and nutrient solution by autoclaving for 1.52.0 hours at 121C and 15 psi. For convenience, cool the assembly in the autoclave overnight.
Figure A.11. The Leonard jar