Climate change

What are the factors that determine seed germination?

When you buy your packet of squash seeds each spring, you plant them in the ground, and expect plants to sprout! It seems like an easy process, but there’s a lot of plant physiology going on. Besides the current weather conditions, the seeds’ history, and their parents, play a role in how well they germinate. You might even be aware that seed packets are labeled with an expiration date. Let’s talk about what are those top factors that affect seed germination.

light orange butternut squash in garden with blue sky

Planting a seed, tending to plants, and yielding some home-grown vegetables is quite satisfying. But, what goes into seed germination? Variables like temperature, moisture and oxygen are important. Credit: Justin O’Dea

Seeds are designed to spread throughout the environment and grow into new plants through the process called seed germination. This process causes a seed to sprout. As seeds absorb water, stored food materials become hydrated. Enzymes in the seed become active, producing energy for the growing seed. The root (or radicle) is the first part of the seedling to emerge. It is the first indication of that a seed is viable, meaning it is possible for it to grow into a healthy plant. Roots provide all the necessary nutrients, minerals, and water for the growing shoot. Cotyledons are the parts that form into the first leaves of the seedling. So now, the plant is capable of obtaining energy from sunlight to do photosynthesis in order to make its own food. A few conditions must be present in order to properly germinate a seed.

Hand with puple glove holding germinating seed with tweezers

The root, or radicle, is the first plant part to emerge from a germinating seed. Credit: Kevin Hudson

Temperature

Environmental conditions must trigger the seeds to grow. Among them, temperature plays the major role. Some plants require moderate to high temperatures, but others may need cold temperatures. For an example, spinach needs cold – if temperatures are 77°F, you’ll only get about half the amount of seeds to germinate than their ideal temperature of 59°F. But, coriander seeds will double their germination rate if the temperature is 77°F (vs the same 59°F). Germination temperature for vegetable crops such as beans, cucumber, okra, tomato, and pepper fall in the range of 60-85°F. Radish, cauliflower, lettuce, cabbage, and carrot need low temperatures, typically in the range of 45-70°F. So the ideal temperature depends on the plant species.

Moisture

Moisture essentially brings the seed back to life. When the seed fills with water in a process called imbibition, it activates enzymes to initiate the germination process. On the other hand, too much water can cause seeds to rot instead of developing into a seedling. So, suitable moisture is needed to get the best results.

Oxygen

Like humans, seeds also need to breathe. Most seeds will not germinate under waterlogged conditions, because water is taking up all the air space in the soil. So, proper drainage is important to supply enough oxygen to the growing seeds. Aeration by plowing or mixing the soil can increase the available oxygen to grow. This is why getting your soil texture right before planting can really help with your yields. Adding in some compost and making sure your garden is appropriately drained can help in this regard, too.

Containers of just-sprouted soybeans showing that some seeds germinate (four leaves per container) while others don't (two leaves)

The soybean plants on the left germinated at more than double the rate than the seeds on the right. Credit: Chathurika Wijewardana

Seed depth

On your package of seeds, there are instructions for how deep to plant your seeds. This is another area where optimal depth will depend on the plant. Small seeds typically need to lay on top of the soil for successful germination. Because of their small size, they only have stored food for a limited period of growth. If we put small seeds in too deep, lack of oxygen will limit seed germination, or the seedling will finish its food reserve prior to reaching the soil surface. On the other hand, large seeds need a deep planting location so that roots can grow deeply for proper anchorage.

In your home garden, when you start planting your seeds (vegetables, flowers, or any kind of herbs), the two most important things that you want to achieve are maximum germination and fast germination rate. However, due to some natural factors and environmental limitations you may have to put an extra effort to achieve the best possible results. These are some tips you can use to achieve the highest germination rate:

  1. Always plant seeds that are for that particular year. If you feel tempted to use seeds purchased in a previous year, do a germination test first (see bottom of linked page).
  2. Choose the ideal planting time, as noted on your seed packets. The ideal planting temperature range will be listed.
  3. Some seeds stay dormant and take a long time to germinate until they have enough moisture to grow. Pre-soaking the seeds before planting (usually overnight, on a wet paper towel), can help.
  4. If you haven’t had any luck germinating seeds soon after sowing on your outdoor seed bed in the past, you can begin planting seeds indoors. By doing so, you can protect your plant from any damages like wind, frost, or drought and later you can move the seedlings outdoors to continue to develop.

Answered by: Chathurika Wijewardana, Mississippi State University

To see a video of Dr. Wijewardana in action and read about her work, visit  https://www.crops.org/about-crop-science/at-work/chathurika-wijewardana

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

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