Categories
BLOG

do seeds need light to germinate

Do Seeds Need Light to Germinate & Grow?

By: Anna Roberts

Seeds contain the material needed to grow into a plant, but they need certain conditions met for germination, or the beginning of the growth process, to occur. Generally speaking, seeds do not need light to germinate and begin to grow, but plants do need light to make food later in their life cycle. Some exceptions exist, so you should check the labels of individual flower and vegetable seeds to determine whether or not light is needed.

Requirements

Seeds need water, nutrients and warmth to germinate. It is best if the soil is evenly moist because too little water will prevent the seeds from germinating and too much water can cause the seed to rot. Nutrients come from the soil, which should be properly fertilized. Different plants require different soil temperatures to germinate, but most seeds fall in the range of 40 to 104 degrees Fahrenheit. If you do have seeds that require light for germination, they are usually planted by sprinkling them on top of the soil so they remain exposed to light.

  • Seeds contain the material needed to grow into a plant, but they need certain conditions met for germination, or the beginning of the growth process, to occur.
  • Generally speaking, seeds do not need light to germinate and begin to grow, but plants do need light to make food later in their life cycle.

Germination

Seeds are packed with all the nutrients the baby plant needs to sprout and reach the surface of the soil without the aid of light. The plant’s roots extend from the bottom of the seed to absorb moisture and nutrients and the stem pushes its way up to the surface of the soil to reach light and air. Germination is complete once the plant reaches the surface. Until that time, the plant relies on the nutrients stored in the seed for survival. Germination may take from days to months.

Early Growth

After a new plant has germinated, reached the surface of the soil and formed its first leaves, it can begin making its own food. Light is a key ingredient in photosynthesis, the process by which plants make food for energy to grow. If a young plant is not exposed to sufficient light when it has used up all of the nutrients in its seed, it will have very unhealthy growth or not survive at all. A tall and spindly plant indicates insufficient light during the early growth stages.

  • Seeds are packed with all the nutrients the baby plant needs to sprout and reach the surface of the soil without the aid of light.
  • The plant’s roots extend from the bottom of the seed to absorb moisture and nutrients and the stem pushes its way up to the surface of the soil to reach light and air.

Photosynthesis

Plants use a green pigment called chlorophyll to convert carbon dioxide, nutrients, water and sunlight into sugar. Plants can’t use sunlight alone for energy. It is the chlorophyll that allows the plant to convert ingredients into a usable form of chemical energy. The plant’s leaves are packed with cells that perform photosynthesis, which releases oxygen as a byproduct.

Seeds contain the material needed to grow into a plant, but they need certain conditions met for germination, or the beginning of the growth process, to occur. Generally speaking, seeds do not need light to germinate and begin to grow, but plants do need light to make food later in their life cycle.

Seeds that Need Light for Good Germination

Starting seeds is not complicated, but you do need to know what conditions the seeds you’re planting need. Many gardeners are unaware that some seeds require light to germinate and covering them with soil will inhibit their sprouting.

There’s a general seed planting rule that says you should plant a seed to a depth that is three times its thickness. That means fat bean seeds should be planted one to three inches deep and tiny carrot seeds should barely be covered. Most seed packets will take the guesswork out of the process and tell you how deep to plant the seeds. It’s a good idea to follow these recommendations because a seed that is planted too deeply might not have enough stored energy to push itself above the soil line.

There’s an exception to every rule, though. Some seeds need the stimulus of light hitting them before they will break dormancy and start to germinate. Very often it is seeds that self-sow that require light. These plants, such as balloon flower (Platycodon grandiflorus) and poppies, drop their seeds on the soil and they germinate where they land. They sprout in response to environmental factors, including having the light hit them.

Seeds That Need Light to Germinate

There are several seeds that germinate best when they are exposed to light. If these seeds are covered in soil, chances are they will remain dormant and not sprout until conditions improve.   It seems counterintuitive not to bury seeds, but these seeds should only be pressed onto the surface of the soil and kept moist to germinate. They include:

  • Ageratum
  • Balloon flower
  • Begonia
  • Browallia
  • Coleus
  • Columbine
  • Gaillardia
  • Geranium
  • Impatiens
  • Lettuce
  • Lobelia
  • Nicotiana
  • Osteospermum
  • Petunias
  • Poppies
  • Savory
  • Snapdragons

Seeds That Will Germinate With or Without Exposure to Light

While most plants that self-sow in your garden are able to germinate without being covered with soil, that doesn’t necessarily mean they absolutely need light. Some plant seeds are indifferent to light exposure and simply need to make contact with soil, whether it is underneath them or covering them. Flowers such as alyssum and cosmos will self-seed during their current growing season as well as the next one, whether or not they are exposed to light.   Other seeds that will germinate uncovered include:

  • Alyssum
  • Aster
  • Balsam
  • Cole Crops
  • Celosia
  • Cosmos
  • Cucumbers
  • Dianthus
  • Eggplant
  • Marigold
  • Melons
  • Pepper
  • Squash
  • Tomato
  • Zinnia

Although the seeds listed above do not require a covering a soil, you will probably get better germination if you follow the recommended planting depth because it will be easier for you to keep them moist and safe from hungry birds.

Keeping Seeds Moist When Exposed to Sunlight

Being able to sow seeds on the surface of soil makes planting easier, but keeping them moist until germination can be difficult since they are exposed to more than just light. Animals, wind, heavy rain, and digging gardeners can all disturb or remove seeds from your garden. If you are growing your seeds in flats or containers, you can cover them lightly with plastic wrap, plastic domes, or tuck them inside of clear plastic bags. They will still be exposed to sunlight, but they will not dry out as quickly as if they were left open to the elements.  

For seeds directly sown outdoors, another option is to cover the seeds with a thin layer of fine vermiculite, a naturally occurring mineral with water-holding properties. Vermiculite is porous enough to let the light shine through while retaining enough water to stay in place and keep the seeds and soil under it moist. It can usually be found near seed-starting supplies; look for finely ground horticultural vermiculite, as other types are not suitable for gardening.

This may all sound complicated, but most seed packets will tell you exactly what you need to know. And remember, seeds have been sprouting for millennia without a lot of fuss––it’s just nice to give them the best chance possible by providing them optimal conditions so they can thrive.

Some plant seeds need exposure to light to germinate and should not be covered with soil. Here are some tips for starting seeds that need light.