Factors Affecting Germination

- Heather Jerrett / Delia Gillen

Seeds are living organisms held in a state of suspended animation or dormancy. There are many factors that can affect the viability of seeds, including moisture, air, temperature, and light. In an ideal situation and environment, every single seed we planted would grow into a seedling, but as we all know, that doesn’t normally happen. We’ve written up a short article to help explain some of the factors that affect seed germination, and to also explain High Mowing Organic Seeds’ standards for seed viability.

Although dormant, seeds are still slowly respiring and using food reserves within. When the right environmental cues wake the seeds up they begin to germinate and emerge from their hard seed coat. There are four major factors that are affect germination:

Moisture: A dormant seed only contains 10-15% of water and is essentially dehydrated. The seed has to absorb water in order to become active. It is imbibed by the seed coat and enzymes within the seed become active and functional, metabolizing stored food reserves. The embryo then begins to swell. The softened seed coat ruptures as the seed grows too big for its encasement and germination has commenced. The seed leaves or cotyledons are now apparent. Photosynthesis does not begin until the true leaves are developed and at this point in development the seedling is still surviving on its own food reserves.

Air: In the dormant condition the seeds respiratory rate is very low and so oxygen is required in very small quantities. But for germination, oxygen is needed in large quantities. The seeds obtain oxygen that is dissolved in water and from the air contained in the soil. If soil conditions are too wet, an anaerobic condition persists, and seeds may not be able to germinate.

Temperature: Germination can take place over a wide range of temperature and is specific to individual crop types, and can be specific to varieties. The optimum for most crops is between 65-75°F, but exceptions do apply. For example lettuce germinates best at 65°F and can be inhibited at temperatures over 68°F while peppers and eggplants prefer warmer temperatures around 80°F and will not germinate well at cooler temperatures. If your soil is too cold or too hot, your seeds may not sprout. Check your seed packet to find the best temperature needed for your seeds.

Light: Light has varied effects on germinating seeds of different plants. Some seeds need light for germination, while in some seeds germination is hindered by light. Most wild species of flowers and herbs prefer darkness for germination and should be planted deep in the soil while most modern vegetable crops prefer light or are not affected by it, and are planted shallowly to allow small amounts of light to filter through the soil.

Seed Depth When Planting

Seed size usually is a good indication of how deep to plant your seeds, which usually corresponds to how much light they need. The general rule of thumb is to plant your seed at least as deep as the seed is long. Certain seeds need light to germinate and shouldn’t even be covered with any soil! Check the back of the seed pack for specific information on how deep to plant your seeds.

Why didn’t my seeds germinate?
When seeds fail to emerge from their shell there are a few things to consider. Have all the seeds failed? If this is the case, more than likely it is an environmental condition. Seeding too deeply, planting in cold soil, too much or too little water, improper soil preparation, and birds or rodents are the most common causes for environmental conditions that prevent seeds from germinating.

When germination is poor it is most likely a degradation of seed quality, and the seed has begun to die. Seed death begins as soon as the seed is mature and viable. In general seeds hold high germination rates for 2-3 years falling no less than the 80% range. Once seeds hit about 75% germination they start to loose the ability to germinate quickly.

Outdated seeds will not germinate properly. Most seeds have a shelf life of only one to two years if kept in a cool dry place over winter. When planting seeds, be sure to use the freshest seeds available to you. The best way to store leftover seeds is in an air tight glass jar in the refrigerator with a little bit of powdered milk wrapped in a paper towel to absorb the excess moisture.

How does High Mowing Organic Seeds test for germination?

At High Mowing, as part of our quality control program, we are constantly testing our seed germination rates every 3, 6, or 9 months, depending on the crop type.

Crops such as onions and soybeans tend to lose their germination value quickly, so we test these seeds every three months. Other crops such as squashes and lettuce retain their germination vigor for quite a long time, so we test these crops every six months. Some crops such as tomatoes can remain viable for over ten years! Therefore we test tomato seed every 9 months.

Our seed packaging is continually being updated with current germination information. Federal guidelines for inter-state sale require germination testing every nine months. There are also federal guidelines that mandate how germination standards must be maintained. For example, to legally sell pepper seed, you only need to have a minimum germination of at least 60%, with a germination test done in the past nine months. Obviously a 60% germination rate is not acceptable for many of our customers, so we have created our own in-house guidelines. High Mowing Organic Seeds only sells seed with a minimum germination of 80% for most vegetables (there are exceptions) and a minimum between 60-70% germination for most flower and herbs.

All of our in-house standards exceed the federal minimums.