Agriculture Reference
In-Depth Information
Soil blocks with sprouted lettuce seedlings.
Light
Plants evolved with needs for light intensity that match the
output of the sun, which provides light that is so intense that
merely looking at it can permanently damage the eye.
Naturally, seedlings grown inside also need an intense light
source that can provide enough light without also making so
much heat that plants get burned.
With the exception of certain flowers, most plants do not need
light to germinate. In fact some plants, like those in the
brassica family, may have their germination inhibited by
light. But once the first plant parts emerge above the ground,
all plants need light to grow. In most of North America and
Europe, there is not enough sunshine coming through even a
south-facing window to adequately start seedlings during the
winter months when most seed starting takes place, so a
source of artificial light is required. Selecting an artificial
light source should be based on an understanding of the
plants' requirements.
Plants require light of various wavelengths or colors for
various purposes. Red wavelengths, for example, regulate
dormancy, seed production, and tuber formation, whereas
blue wavelengths stimulate chlorophyll production and
vegetative growth. Violet wavelengths affect plants' tendency
to turn toward a light source. The best light sources for
starting seedlings, then, should generate a wide spectrum of
light wavelengths that encompass both the blue and the red
ends of the spectrum.
