Respiration rate increases during germination. The medium in which the seeds are sown should be loose and well aerated. If the oxygen supply during germination is limited or reduced, germination can be severely retarded or inhibited. Other plants germinate best in the dark. These include calendula, centaurea, annual phlox, and verbena.
Some plants germinate in either light or dark conditions.
Seed catalogs and seed packets often list germination and cultural information for particular plants. When sowing light-requiring seeds, sow them on the soil surface. Supplemental light can be provided by fluorescent fixtures suspended 6 to 12 inches above the medium for 16 hours a day. Media A wide range of media can be used to germinate seeds. With experience, you will learn to determine what works best for you.