Lily is conventionally propagated by scaling: scales are detached from bulbs and kept in moistened vermiculite. These scales regenerate new bulblets. In micropropagation, scale fragments cultured on a medium under sterile conditions, regenerate new bulblets. We examined various aspects of lily micropropagation. Because the size of bulblets strongly influences the performance in the field, we focussed on bulblet weight, which strongly depended on the position in the scale from where the explant was taken (on average heavier bulblets from basal and middle explants). The formation of new vascular tissue within the explant played a role. Mild abiotic stresses (like heat, drought and anaerobiosis) administered during bulblet growth increased the growth of bulblets by 20-65%. We also developed novel methods to reduce contamination during initiation of bulblets in vitro. We found strong evidence that low CO2 levels during tissue culture (caused by the consumption of CO2 by active photosynthesis and the closure of tissue culture containers) is detrimental for the development of the bulblets.