With cooler weather upon us, now is a good time to begin planting some heat-intolerant vegetables. For those who like to propagate their own plants, it’s also a good time to begin germinating seeds.
There are three conditions that must be met for successful germination to occur. First, the seed must be viable (the embryo must be alive and capable). Second, the seed must have favorable internal conditions (no chemical or physical barriers). Third, there must be favorable environmental conditions.
The germination process begins when water is absorbed by the dry seed. Essentially, this is an awakening stage where various biological systems are reactivated during cell hydration. The practical significance is that it is necessary to maintain adequate moisture levels once the germination process has begun. Temporary drying can result in the death of the germinating seed. Moist soil is generally all that is needed to begin germination.
The second stage of germination involves the translocation of stored food to the growing points of the embryo. The third stage consists of expansion of the growing points until the seedling emerges from the soil. In addition to moisture, these stages also require a supply of oxygen. The practical significance is that the germination media must be loose, crumbly and well aerated. One should avoid heavy, wet soils.
Temperature is probably the most important environmental factor that affects germination and controls subsequent seedling growth.
For many plants this range would fall between 80 and 90 degrees Fahrenheit. The practical significance is that you can significantly improve germination percentage and growth rate during these cool winter months, especially if you live up mauka, by placing seed flats/pots in warm locations, such as indoors, near a sunny window or on top of the fridge.
You may be surprised to learn that most seeds do not require light to germinate. Lettuce seeds are the most notable exception; conversely, seeds of some species of allium and phlox are inhibited by light.
To summarize, once the germination process has been activated by the absorption of water, seeds need a constant supply of moisture and oxygen in a moderately warm environment.
Not maintaining an adequate, continuous moisture is the most common source of failure. There are a few handy techniques to overcome the moisture problem and eliminate the need to remember to water your seeds. Some flats come with clear plastic lids that snap on and prevent moisture from evaporating. This can also be done with clear plastic wrap stretched over container tops. Just be sure to leave several inches of clearance above the media for the emerging seedlings.
The covering should be removed as soon as germination occurs because the high humidity inside is conducive to fungal diseases attacking the succulent sprouts.
A less common moisture-retention method, sometimes used on slow-to-germinate palms, is placing them in sealed plastic bags filled with moistened perlite and stored in a warm place indoors. Again, you don’t have to remember to water them, which is helpful if the seeds take three to four months to germinate.
Soaking seeds before planting to initiate the germination process can shorten the time required for seedlings to emerge. This treatment is useful with seeds that are slow to germinate or are hard and dry.
It should be mentioned that some seeds have impervious seed coats that severely inhibit germination. Water absorption can be improved by first scarifying these seeds — breaking or scratching the seed covering enough to make it permeable. This is commonly done with koa seeds in Hawaii.
Ty McDonald is a University of Hawaii College of Tropical Agriculture and Human Resources Cooperative Extension agent and Master Gardener coordinator at the Kona Extension Office.
