Do Seeds Need Light or Dark to Germinate?


seeds and hand lying on compost

Most seeds prefer to germinate in a wholly dark environment. However, some species, including some flowering plants, like at least some light to successfully incubate. It is, in fact, safe to say that different plant species require varying light conditions to activate favorable seed germination.

What is Germination?

Germination is the process a plant seed or spore has to go through to produce a living, growing, breathing seedling. It is much like a revival of metabolic systems after a period of dormancy.

You can break down the process of germination into three consecutive phases:

Phase 1 – Imbibition

During imbibition, a sleeping seed can is forced into life by the introduction of moisture. The seed coating swells and softens, allowing for the seed to germinate.

The process may be aided artificially by soaking seeds in warm water overnight or wrapping them in moist paper, toweling and covering with a plastic film. By following these tips, it will create a humid atmosphere that is conditionally appropriate to sprouting.

In some situations, scarification or stratification is necessary to coax reluctant seeds into the procedure.

Phase 2 – Interim (lag)

Viable, dormant seeds house healthy, living embryonic tissue and stored food resources needed to germinate. The interim, or lag phase of the germination process, sees the activation of the seed’s inherent biological and metabolic processes. The seeds themselves start to respire (breath), accesses and absorbs the stored nutrient cache, and produce protein.

Phase 3 – Radicle and Root Emergence

To complete the sprouting process, cells inside the seed now extend and divide to form the primary root or radicle of the seed. The radicle will lead to the emergence of the seedling from the soil and then anchor the structure to the earth, simultaneously absorbing moisture.

This process differs slightly depending on whether the seedlings raise cotyledons (seed leaves) above the soil (epigeous) or require them to stay snuggly below the earth (hypogeous) during the exercise.

At this point, seedlings break through the surface of the earth and start maturing into adult specimens.

What Do Seeds Need to Germinate Successfully?

Seeds need moisture, light, the right soil temperature, oxygen, and sunlight to germinate. Let’s take a closer look at each.  

hand sowing seeds into cell tray

Moisture

During imbibition, seeds absorb proximate water and start to sprout. However, too much water can rot the root and damage the embryo inside, leading to the seed’s failure to bud. As a rule of thumb, a fifty to seventy percent of moisture content ratio to field capacity is optimum to successful sprouting.

Light

Some species of flora are particularly fussy about perfect light conditions when germinating.

Some plant variants such as asparagus, beans, beets, and carrots opt for a dark, humid germination experience, while broccoli, cauliflower, and peppers, to name a few, prefer a fraction of light when growing.

These conditions are also suitable to some greenhouse perennials, epiphytes such as ferns and orchids, and some grass varieties. Covering seeds with a light sprinkling of moist soil should do the trick in most instances.

Temperature

Soil temperature plays a significant role in successful seed development. Most examples will only sprout when the weather is uniquely suitable. However, the minimum and maximum temperature requirements of different plant genera vary widely in this regard. You can evaluate soil temperature by inserting a soil thermometer three to four inches into the soil and reading.

In some cases, trees and shrubs will only sprout if seeds had been exposed to cold stratification, either artificially or in their natural habitat.

To regulate higher temperature demands, horticulturists sometimes use germination mats to ensure optimal temperatures and uniform propagation rates.

Air/Oxygen 

Seeds are said to germinate better in fully aerated, fine-textured soil. As seeds need to absorb oxygen to breathe, tightly packed, dense soil does not allow for the smooth exchange of involved gases in this regard. Carbon dioxide build-up in the soil can suffocate fragile seeds, leading to low germination ratios.

To aerate soil sufficiently before planting, gardeners add organic materials such as compost or dead plant matter into the topsoil. After they’ve added this, they will continue turning it over, employing manual manipulation. You can also use peat moss and perlite successfully.

Why Do Seeds Sometimes Become Dormant?

A seed is said to be dormant when it is not germinating or developing. It is essentially resting and waiting for the right conditions in which to reactivate.

So, why do seeds become dormant in some instances?

fingers sowing lettuce seeds

Exogenous Dormancy

Exogenous dormancy refers to the seed being inactive due to factors external to the seed embryo. It includes influences limiting water absorption, mechanical resistance to emergent radicles, or limited oxygen supply outside the seed casing. 

Endogenous Dormancy

Dormancy is regarded as endogenous when the embryo is unable to participate in germination and is underdeveloped or immature (morphological dormancy).

Conditional Dormancy

  • Innate dormancy refers to a seed that is inactive despite suitable germination conditions. As an example, the practice of after-ripening seeds requires a period of dry storage before the kernels develop the ability to sprout.

Similarly, an impenetrable seed coat could affect water penetrating, and germination starts. Thus, the seed coat effectively prevents oxygen and water from permeating the seed because it has built up hard, impenetrable layers.

In some instances, chemical inhibitors such as abscisic acid, phenolic acid, and cyanogenic chemicals inside the seed prevent the development and induce dormant sleep. Chemical dormancy happens when the seeds are exposed to extreme, hostile germination conditions.

The process shuts down after initial water absorption. Chemical dormancy can be circumvented by leaching seed or employing cold, moist, or fire scarification. Adding nitrates to the soil in the case of cultivated crops may similarly alleviate the problem.

  • Enforced dormancy occurs when environmental considerations are inadequate. This includes oxygen levels, available light, moisture, and optimum temperatures suitable to the particular plant seed type. 
  • Induced dormancy, also called secondary dormancy, becomes applicable when seeds fail to germinate due to essential soil, moisture, light, and temperature conditions being regarded as unsuitable.

Are There Advantages to Seed Dormancy?

Yes, there are a few advantages connected to seed dormancy, they are:

  • Seeds sometimes remain dormant to ride out bad weather conditions
  • In tropical and dry areas, dormancy protects against damage incurred through drought conditions
  • The storing of grain for future consumption is much more successful if seeds remain dormant
  • Plants protect their existence by staggering germination over a period of time. This ensures the survival of the species in inclement weather or destruction by means of ingestion by hungry herbivores.

Can I Grow Vegetables and Flowers from Seed?

Growing plants from seed are straightforward and an excellent way to get your gardening schedule on track for the season. However, knowing what you want to do and how to do it is very important.

  • The first step is to set your goals. When will you need your seedlings to be ready? Will the weather be favorable at that time? Remember that not all plants (vegetables, shrubs, or otherwise) flourish in the same conditions. Consult a planting almanac to guide your seeding choices.
  • Seeding requires the use of the correct receptacles. Containers should be at least two to three inches deep and have sufficient drainage to allow for excess water seepage. You can often recycle discarded household containers to meet these requirements.
  • The planting medium is of vital importance. Select an appropriate sterile, free-draining mix for the task. Moisten the mixture and pack solidly into seed trays.
  • Read embedding instructions on seed packets to plant according to proper conditions. Some seeds need only be scattered on top of the medium, while others should be covered or buried deep. Be sure to source healthy, organic seeds from reputable retailers.
  • Moisten or mist newly planted seeds to aid germination. Cover the seeded receptacles with plastic or domed lids to ensure that the correct light- and temperature conditions are being adhered to.
  • Water seeds regularly but guard against over-saturation of the soil. Apply a liquid fertilizer as deemed necessary and provide for ample circulation of air.
  • Once your seeds sprout, move the seedlings into the light, preferably facing south. Rotate the pots regularly to ensure even, upright growth and substantial, controlled exposure.
  • Before transferring seedlings into the soil out of doors, harden them to climactic conditions by placing them in a sheltered outdoor site for a few hours a day. After about ten days, they will be ready for the great outdoors.
hands sowing seeds into metal pots

So, Do Seeds Need Light or Dark to Germinate?

Although it is generally believed that dark conditions promote more consistent seed germination, a selection of flora prefers the presence of solid light to aid sprouting.

For example, Begonia, Primula, Petunia, and Coleus are pro light, while Phacelia, Calendula, and Allium spp. are inhibited by light when germinating.

Rudyard Kipling has said, “Gardens are not created by singing ‘Oh, how beautiful, and sitting in the shade.” Life begins when you start a garden. So, put in the hard work and enjoy the rewards.   

Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

Recent Posts