Germination tests are usually conducted to assess the quality and viability of the seeds harvested. While still being an estimate and having certain limitations, it is a useful indicator that will help you identify seeds that have adequate germination rates and determine the planting value of a seed lot as well as its storage potential. Seeds that have been stored for several years can be tested occasionally to see if a potentially significant germination loss occurred during their storage. Low germination rates usually indicate that the energy reserves stored in the seeds are running very low, which will likely result in underperforming plants in the field. The germination rate can be tested using several methods, the most two common ones used by home gardeners being the soil germination and the paper tests.
Note 1: While most seeds of common vegetables germinate at an optimal temperature range of 20-25 °C, some will germinate best at lower temperatures. In some cases, these requirements may also be variety-dependent.
Note 2: Due to seed dormancy, certain lots of freshly harvested seeds that are tested in the fall might not germinate at all depending on the crop. This is a normal process and does not indicate that the seeds are dead and need to be discarded. If that occurs, let the seeds sit in storage over the winter to break dormancy, then conduct another test the following spring.
Soil Germination Test
A soil germination test can be run within a controlled environment such as a nursery using little material. In most cases, this solution is easier and more efficient than determining the germination rate through a paper test. The seeds that are tested must come from a sample that is representative of the whole seed lot. They will need to be checked, watered and counted every day (when seeds have germinated). It is an important step, as seeds are more vulnerable during their germination phase. Note that all germination tests must be labeled and recorded accordingly, especially when different varieties are tested simultaneously. As the germination capacity differs from a crop to another, the germination testing might take up to several weeks to be completed. A good general rule is to continue the test for at least 21 days, until all the seeds have germinated or the maximum predicted germination time for the variety has passed.
Instructions
- Step 1 – Select a seed sample of 30-60 seeds per variety;
- Some seeds such as beans might need to be mechanically scarified before planting. Scarification is a process designed to make the testa (seed coat) more permeable to water and encourage germination. It can be done by just rubbing the seed coat with sandpaper or nicking the seed with a knife.
- The more seeds you use, the more accurate the test will be.
- Step 2 – Plant them around 1.5 cm apart and at a depth twice the width of the seed in shallow furrows, in a seed tray or several egg cartons filled with potting soil or growing medium;
- The tray will need to be placed in an environment that is conducive to the germination of the seeds. Some seeds germinate best at lower temperature ranges (such as peas and spinach) while most normally prefer warmer conditions (eggplants and melons). Light is also an influential factor in the germination, with certain seeds (lettuce) depending more on its presence than others (onions). With experience and additional resources, optimal germination for each crop can easily be identified.
- In the tropics, grated coconut husk can be used as a growing medium as it holds moisture well and doesn’t contain weed seeds.
- Step 3 – Make a label indicating the variety’s name, test’s starting date, as well as the number of seeds and place it beside the tray;
- Step 4 – Check and lightly water the seeds every day;
- It is important to maintain a reasonably balanced soil moisture level as seeds might not germinate if the soil gets too dry or saturated with water for too long.
- Germination can be further encouraged by placing a wet cloth on top of the tray for the first three days of the test.
- Step 5 – Calculate the percentage of seeds that have germinated at the end of the test;
- When the test is over (21 days), the germination rate can be determined by counting the total number of seeds that have germinated, dividing it by the total number of seeds initially tested, and multiplying it by 100. For instance, if 30 seeds were tested but only 25 germinated, the germination rate is 83%.
Remember to keep a record of each step as well as the running count (with dates) of the dead and germinated seeds throughout the test.
Paper Test
The paper test is a suitable alternative when soil germination testing is not possible. It does, however, require close observation and careful attention as seeds might more easily dry out or mold using this technique. Similarly to a soil germination test, the seeds that are tested through a paper test must come from a sample that is representative of the whole seed lot. They will have to be checked, watered and counted every day (when seeds have germinated). All tests must also be adequately labeled and recorded. The paper test is deemed completed when, after 21 days, all the seeds have germinated or the maximum predicted germination time for the variety has passed.
Instructions
- Step 1 – Select a seed sample of 30-60 seeds per variety;
- Same note as with the soil germination test.
- Step 2 – Place them equidistantly (not closer than 1.5 cm) on a piece of absorbent, acid-free paper that has been moistened beforehand;
- Acid in paper can affect germination and should not be used.
- Ensure that the paper is not too wet as the seeds might mold.
- Step 3 – Once the paper is full of seeds, place a second moistened paper on top of the seeds and roll it up tightly to keep the seeds from moving and falling out;
- Step 4 – Place the paper in a location out of direct sunlight and wind, inside a partially closed plastic bag to allow air to enter;
- The bag can also be sealed all the way, provided it has holes in it.
- Step 5 – Make a label indicating the variety’s name, test’s starting date, as well as the number of seeds and tape it on the bag;
- Step 6 – Uncover the seeds and check twice daily, watering when needed to maintain dampness and prevent the paper to dry out;
- If a seed molds or looks rotten, count it as dead and remove it immediately to avoid adjacent contamination, which would compromise the entire test.
- Seeds that exhibit a full emergence of the first root can be counted as germinated and removed.
- Step 7 – Calculate the percentage of seeds that have germinated at the end of the test;
- Same note as with the soil germination test.
Remember to keep a record of each step as well as the running count (with dates) of the dead and germinated seeds throughout the test.
Germination Cabinet
Fluctuating ambient conditions such as temperature and humidity can be further reduced and controlled with both above-mentioned germination tests through the use of a germination cabinet (built out of a small kitchen cupboard). Parameters that are conducive to seed germination are optimized with the use of lights (incandescent for heat and/ or fluorescent for light) and foam (for insulation). Timers and thermostats can be added to the cabinet to give a greater degree of control over germination conditions.
Instructions on how to build a germination cabinet can be found in Appendix II – Building Tutorials.
Vigor and Limitations of Germination Testing
Being conducted within a controlled and favorable environment, germination tests may fail to provide accurate information regarding seeds’ field performance potential and might lead to an overestimation that doesn’t reflect the real seed vigor and quality. Indeed, germination testing only focus on the morphological emergence and development from the seed embryo of the plant’s essential structure over a predetermined period of time, often ignoring speed and uniformity; a prime element in the potential for successful stand establishment. Moreover, germination rates resulting from standard germination tests encompass any germinable seeds regardless of their germination speed or behavior. The germination percentage calculated is therefore a sum of strong and weak seedlings; the latter rarely performing adequately when exposed to environmental stresses associated with field emergence.
Seed vigor usually declines before germination is lost. Among the factors that will influence seed vigor are genetic constitution (susceptibility to diseases and mechanical damages), environmental conditions during seed development (seed maturity, soil maturity and fertility, postmaturation/preharvest environment), and seed storage. The main challenge of vigor testing has been to identify one or more quantifiable parameters that are common to seed deterioration. Testing seeds for vigor thus remains a complicated, non-standardized, and sometimes expensive process typically carried by laboratories.