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The photosynthetic daily light integral (DLI) dramatically increases during the spring when the majority of bedding plants are commercially produced. However, the effects of DLI on seedling growth and development have not been well characterized for most bedding plant species. Our objectives were to quantify the effects of DLI on growth and development of Celosia, Impatiens, Salvia, Tagetes, and Viola during the seedling stage and determine whether there were any residual effects of DLI on subsequent growth and development after transplant. Seedlings were grown in growth chambers for 18 to 26 days at 21 °C with a DLI ranging from 4.1 to 14.2 mol·m^–2·d^–1. Average seedling shoot dry weight per internode (a measure of quality) increased linearly 64%, 47%, 64%, and 68% within this DLI range in Celosia, Impatiens, Tagetes, and Viola, respectively. Seedlings were then transplanted to 10-cm containers and grown in a common environment (average daily temperature of 22 °C and DLI of 8.5 mol·m^–2·d^–1) to determine subsequent effects on plant growth and development. Flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola occurred 10, 12, 11, 4, and 12 days earlier, respectively, when seedlings were previously grown under the highest DLI compared with the lowest. Except for Viola, earlier flowering corresponded with the development of fewer nodes below the first flower. Flower bud number and plant shoot dry weight at first flowering (plant quality parameters) decreased as the seedling DLI increased in all species except for flower number of Tagetes. Therefore, seedlings grown under a greater DLI flowered earlier, but plant quality at first flowering was generally reduced compared with that of seedlings grown under a lower DLI.

The photosynthetic daily light integral (DLI) dramatically increases during the spring, but effects of DLI on seedling growth and development have not been characterized for many species. We quantified the effects of DLI on growth and development of Celosia, Impatiens, Salvia, Tagetes, and Viola during the seedling stage and determined whether there were any residual effects of DLI on subsequent growth and development after transplant. Seedlings were grown in growth chambers for 18–26 days at 21 °C with a DLI ranging from 4.1–14.2 mol·mol·m^-2·d^-1. Average seedling shoot dry weight per internode (a measure of quality) increased linearly 64%, 47%, 64%, and 68% within this DLI range in Celosia, Impatiens, Tagetes, and Viola, respectively. Seedlings were then transplanted to 10-cm containers and grown in a common environment (average daily temperature of 22 °C and DLI of 8.5 mol·m^-2·d^-1) to determine subsequent effects on plant growth and development. Flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola occurred 10, 12, 11, 4, and 12 days earlier, respectively, when seedlings were previously grown under the highest DLI compared with the lowest. Except for Viola, earlier flowering corresponded with the development of fewer nodes below the first flower. Flower bud number and plant shoot dry weight at first flowering decreased as the seedling DLI increased in all species except for flower number of Tagetes. Therefore, seedlings grown under a greater DLI flowered earlier, but plant quality at first flowering was generally reduced compared with that of seedlings grown under a lower DLI.

Commercial greenhouse growers often produce bedding plants from midwinter to early summer, and thus crops are grown under a wide range of environmental conditions. Despite bedding plants' high economic value, the interactions of temperature and photosynthetic daily light integral (DLI) on growth and flowering have not been determined for many bedding plants. We grew celosia (Celosia argentea L. var. plumosa L.) and seed impatiens (Impatiens wallerana Hook.f.) in glass greenhouses in a range of temperature (15 to 27 °C) and DLI (8 to 26 mol·m^-2·d^-1) conditions to quantify effects on growth and flowering. Growth (e.g., plant dry mass at flowering) and flowering characteristics (e.g., time to flowering and flower bud number) were modeled in response to the average daily temperature and DLI by using multiple regression analysis. Rate of progress to flowering (1/days to flower) of celosia increased as temperature increased up to ≈25 °C and as the average DLI increased to 15 ·mol·m^-2·d^-1. Impatiens grown under a DLI <15 mol·m^-2·d^-1 flowered progressively earlier as temperature increased from 14 to 28 °C, whereas temperature had little effect on flowering time when plants were grown under the highest DLI treatments. Number of flowers and flower buds at first flowering increased in both species as temperature decreased or DLI increased. Shoot dry mass at first flowering followed a similar trend, except celosia dry mass decreased as temperature decreased. The models developed to predict flowering time and plant quality could be used by commercial growers to determine the impacts of changing growing temperature, growing plants at different times of the year, and providing supplemental lighting.