2.2. Explant sampling time
Sampling time is also an important factor affecting the culture of herbaceous peonies. P. lactiflora ‘Zhong Sheng Fen’ buds should be harvested in November to December (100% sprouting and 90.0% differentiation) and March (100% sprouting and 92.7% differentiation), while buds selected in September to October have the poorest response (47.2% sprouting and 44.4% differentiation), assessed after all explants were plated on half-strength MS medium containing 0.5 mg l−1 BA and 1 mg l−1 GA3 ( Guo, 2001). Zhang (2006) claimed that P. lactiflora (P. suffruticosa ‘Jin Huang’ stock) stem tips should be sampled from November to March and that, if prior to November, buds would not be able to completely differentiate while buds that already germinated after March would be more difficult to sterilize.