Influence of Daily Light Integral On Coleus Morphology and Leaf Variegation

Coleus (Solenostemon scutellariodes (L.) Codd) is an ornamental foliage plant valued for its colorful variegation patterns.  Cultivars of coleus are able to tolerate a broad range of light conditions.  However, the leaf variegation that coleus is valued for has been noted to change depending on the amount of light in which it is grown.  Successful coleus sales rely on a combination of dramatic coloration and dense growth habit.  To our knowledge, the exact light conditions required to promote these characteristics have not been determined.  Therefore, two cultivars of coleus, ‘Kong Red’ and ‘Wizard Coral Sunshine’, were grown under four daily light integrals (DLI) (10.0, 5.8, 3.8, and 2.9 mol·m^-2·d^-1) to determine the optimal light level for production.  ‘Kong Red’ and ‘Wizard Coral Sunshine’ coleus grown under a DLI of 2.9 mol·m^-2·d^-1 exhibited reduced leaf areas of 66% and 63%, respectively, compared to those grown under a DLI of 10.0 mol·m^-2·d^-1. The number of leaves per plant followed the same trend, decreasing 64% in both cultivars when comparing those produced under the lowest and highest DLI treatments.  Percent non-green area per leaf decreased by 18% for ‘Kong Red’ and by 23% for ‘Wizard Coral Sunshine’ produced under 2.9 mol·m^-2·d^-1 compared to plants grown under 10.0 mol·m^-2·d^-1. Overall, both cultivars exhibited a more dense growth habit and greater degree of variegation (relative percent of non-green area per leaf) when grown under the highest DLI.  Therefore, we recommend growing these two cultivars under a minimum DLI of 10.0 mol·m^-2·d^-1.