Cuttings are most likely to form roots if: (i) they have plenty of leaf; (ii) they are exposed to strong light; (iii) they have a rooting medium that is biologically and nutritionally inert; and (iv) they are kept in a 100% humidity. These conditions are met in a simple apparatus called a mist propagator. When the cuttings have plenty of leaf, and plenty of light, they can manufacture all the carbohydrates they need in order to grow roots. But they must be kept moist until they are able to produce enough root tissue to absorb water from the rooting medium. The rooting medium must be biologically and nutritionally inert to prevent rot-causing fungi and bacteria from attacking the cuttings.
The mist propagator consists of a tray containing the rooting medium. A good rooting medium is polystyrene granules mixed with sand in a ratio of about 4:1. If polystyrene granules are not available, use plain sand, or sand mixed with vermiculite or perlite. The tray is enclosed in a tent of transparent plastic film, and it may be exposed to full sunlight, at least for part of the day (photo in preparation). A domestic humidifier is used to continuously pump a fine water mist into the tent. Alternatively, a hand sprayer can be used every hour or so during the day, in order to keep the inside of the mist propagator permanently moist. A more simple apparatus consists of a plastic bag tied over the top of a flowerpot and supported by sticks (photo in preparation).
Under mist propagator conditions, potato cuttings will form roots in 5-10 days (photo in preparation). They can then be transplanted into pots of soil, and protected by a plastic bag cover for a few days. Once they are growing vigorously, they can be transplanted into larger pots or into the field.
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