When to Light or Shade, and When Not... Plants use light to
increase mass through photosynthesis. More mass usually means
higher quality and longer postharvest life. However, in many
cases, more light enters a greenhouse than a plant can use. In
the spring, extra light is great because it helps heat the
greenhouse. However, in the far south, or during the summer, we
often shade because this extra light heats a greenhouse above
what is desirable. We can see that our plants are not growing as
well; in addition, it’s often uncomfortably hot for us. In
recent years we have measured the effect of light, temperature
and carbon dioxide (CO2) on photosynthesis of many bedding and
potted plants. Using that data, we can make informed decisions
on when we should light, or conversely, when we should shade our
crops. This research has received support from the Floriculture
and Nursery Research Initiative and the American Floral
Endowment. In this article we will present some standards that
can be used for lighting or shad