Panax ginseng C.A. Meyer was grown in raised beds at Mosgiel, New Zealand (Lat. 45° 51S Long. 170° 22E) at 2, 8, 20, and 36% of ambient irradiance. Mean root weight at planting was 2.0 g. Plants began to emerge on 29 September 1994 with a median emergence date of 15 October 1994. Seventy‐seven percent of plants emerged; emergence probability was strongly associated with bud size. Half of the roots that failed to emerge survived until autumn and doubled their bud size during summer. Root death was associated with low root weight. Leaflet area was well predicted by leaf length or width. On leaves bearing five leaflets, relative areas of the three leaflet size classes were 1:4:5 allowing whole plant leaf area to be predicted accurately from the central leaflet area, even when some leaflets were missing. At plant harvest in April, mean final root weight was 5.5 g. Final root weight was strongly associated with initial root weight, but for any given initial root weight, final root weight was lower and increased less as initial root weight increased in the low light treatment (2%) than in other treatments. Leaf area was also strongly associated with initial root weight, and for any given initial root weight, leaf area was lower and increased less as initial root weight increased in the high light treatment (36%) than in other treatments. Leaf area per plant was 61 cm2 in the high light treatment (36%) compared with an average of 116 cm2 in the other treatments. Even after accounting for the association of initial and final root weight, there was a positive effect of leaf area on final root weight. Final bud length was positively associated with final root weight, but for any given final root weight final bud length was greater in the low light treatment (2%) than in other treatments. Leaf senescence occurred earlier the higher the irradiance. Chlorophyll fluorescence Fv/ Fm ratios, measured in January, were 0.763 at 2% irradiance, significantly (P < 0.05) greater than values for plants at 8 and 20%, which were not significantly different. Fv/Fm at 36% irradiance was 0.646, significantly (P < 0.01) lower than in the other treatments but indicative of only mild photoinhibition. Low leaf area, mild photo‐inhibition, and shorter leaf duration at the highest irradiance (36%), appear to have been balanced by higher rates of photosynthesis, resulting in similar root growth in 8–36% of ambient irradiance.