Do Seedlings Need Light Before They Sprout?
Seeds, when they come to us in seed packages, are dormant. For a plant to grow from the seed, that dormancy has to be broken. Some seeds break dormancy when their seeds get wet. Some require that fire or pressure break their husk. Others require light.
Light Versus Dark
The light requirements for seeds vary widely. Some seeds need light to germinate. Other seeds will germinate only in darkness. Still others seem to have no preference and will germinate in either light or darkness if their temperature and moisture requirements are met. Some seeds — meadow sage (Salvia pratensis) and tufted saxifrage (Saxifraga caespitosa), for example — require light to germinate if you attempt to grow the seeds immediately after harvesting them. If you hold the seeds over the winter, however, they loose the light requirement and will germinate in darkness.
A seed’s need for light is tied to a pigment called phytochrome, which exists inside most plants. Photochrome reacts chemically to light. This pigment is involved in plants growing upward to seek light. It is what determines that plants that grow in low light get longer and more spindly than plants grown in enough light. When light hits light-sensitive seeds, the photochrome inside the seeds reacts, causing the seed to break dormancy and sprout.
Seeds that Need Light
According to Norman C. Deno, author of “Seed Germination: Theory and Practice,” swamp plants typically need light to germinate. Woodland seeds also often need light as do many weed seeds. That’s why when you cultivate to get rid of weeds, others pop up as soon as they receive enough light to grow. Vegetable seeds that need light to germinate include dill (Anethum graveolens), lettuce (Lactuca sativa) and some peppers (Capsicum annuum). Coleus (Solenostemon scutellarioides), snapdragon (Antirrhinum majus) and Shasta daisy (Leucanthemum Leucanthemum x superbum) are among the flower varieties that need light to germinate.
Planting Seeds That Need Light
The general rule of thumb is to plant a seed no deeper than its length. Seeds that need light to germinate must be planted shallower than this, however. One method is to sow the seeds over the surface of the soil. Using your hand or the back of a trowel, gently press the seeds into the soil so the tops of the seeds remain uncovered. If the seeds are tiny enough that they are likely to blow away, you can sow them on the surface of the soil, sift a fine layer of compost over the top and water the compost. Doing so will hold the seeds in place while allowing light to penetrate.
Do Seedlings Need Light Before They Sprout?. Seeds, when they come to us in seed packages, are dormant. For a plant to grow from the seed, that dormancy has to be broken. Some seeds break dormancy when their seeds get wet. Some require that fire or pressure break their husk. Others require light.