Groeimetingen bij de tulpebol = Growth measurements on the tulip bulb

Tulips did not require a specific soil, if pH was not below 6.5 and water supply was sufficient. Influence of weather conditions was studied by comparing bulb production in different years and areas. Low temperatures after planting and during winter, a gradual increase in spring, sunshine in April and early May, were most favourable. Cold during May and June caused some extension of growth and increased bulb productions.Records of daily weather conditions and growth yielded no correlation with radiation and temperature and with precipitation, except after drought. Increase in circumference was positively correlated with the length of period with a limited evaporation and transpiration. Growth therefore took place during the night while dry and hot days decreased bulb size.In conclusion the most favourable conditions for bulb production were an early winter and a long cool spring, and circumstances limiting transpiration of the crop. Of these environmental conditions only evaporation could be influenced and for this purpose shelter belts of conifers were recommended