The seed’s temperature is raised to 18 to 20°C in steps of about 1 to 2 degrees a day. After that, the grower maintains a constant temperature and ensures good ventilation throughout the sprouting period.
The potatoes are kept in the dark until they have formed sprouts of a few millimetres to half a centimetre. At this stage the sprouts are vulnerable to damage.
| Physiologically very young seed potatoes may benefit more from a sudden drop in temperature than from a heat shock. Keeping the seed potatoes at a low temperature for a short time after the wound healing period (for example 3°C for two weeks) may shorten the dormant period of certain varieties. |
As a result of the pre-sprouting the tubers have a large number of sprouts. During the planting, great care must be taken to ensure that the tubers are not damaged, to prevent the loss of sprouts. It is for this reason that the tubers must be hardened off. This is done by placing the tubers in a light, cool, well ventilated area for at least a few weeks.
A drop in temperature and exposure to daylight will slowdown the growth of sprouts while the tuber’s development continues. This will initiate the development of leaves, stolons and roots and the formation of chlorophyll. The sprout will consequently remain relatively short and firm.
A low light intensity will already slow down the growth of sprouts. The greater the lightintensity while the tubers are being hardened off, the f rmerthe sprouts will be.
Besides trays, suspended bags can also be used. This system saves labour in the pre-sprouting and hardening off of the tubers and the filling of the planting machine. Many growers of ware potatoes use an intermediate form, which involves placing open bags outdoors in windows.
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