The successful micropropagation of woody or herbaceous perennial plants is often limited by large losses which occur as plants are transferred from culture to soil. Poor photosynthetic capability may be partly responsible for losses at this stage. Results show that growth irradiance, CO 2 and carbohydrate in the growth medium are all factors which combine to affect the development of photosynthetic capability in vitro. Low capacity for the photochemical dissipation of excess light energy is primarily a result of endproduct inhibition of photosynthesis by accumulated leaf carbohydrate, and results in plants being extremely sensitive to photoinhibition. Manipulation of carbohydrate in the growth medium and growth irradiance may result in increased photosynthetic capability of plants transferred to soil, and can increase survival. This appears to be a result of increased energy supply for growth during the first few days ex vitro. Manipulation of carbohydrate in the growth medium and growth irradiance also affect growth morphology. In particular, root production in woody material can be affected, and can have a significant effect on nursery survival.