Seeds and Germination

With many experimental technologies (and a likely equal number of environments that are being used to grow crops), germination is a very important place to begin some trials to optimize yields. Also, noting that seeds are generally a significant cost, plant performance that does not waste growing space or seed is related to profits as well.

If we keep records of our plantings, we often concern ourselves with the final product and ignore the impact of germination on optimizing yields per unit time and cost for final product.

Germination performance, often referred to as vigor, depends on the seed (source, quality and variety), seed treatment (dormancy and scarification), environment (moisture, temperature and light) and the need for stem elongation. Genetics has the largest impact on germination, so you might wish to trial several varieties of the same species.

Seeds come from many places, including outside the United States. For instance, imported lettuce seeds come mostly from Australia and Chile, although they come from Holland and the United Kingdom as well. Typically, seeds are harvested and then marked for the season in which it is to be planted.

Distance traveled is not likely to be a factor in quality unless the seeds became moist (begin germinating or rotting), too hot (possibly sterilizing them) or too cold (inducing dormancy). Most seeds can last for several seasons when stored in a dry (less than 6% moisture), dark location at the proper temperature (typically 41°F).

Tropical plant seeds often vary considerably in their tolerance of desiccation. (Indeed, the text for seed germination is quite thick reflecting the many types and needs of seeds.)

When buying in larger quantities (lb.), the label has the date when the germination percent was determined. The determination of this percent was done under laboratory conditions engineered to get high numbers. This is no guarantee of performance under your conditions. However, hydroponic results often exceed these percentages to the advantage of the grower.

Seeds come with a variety of treatments, most often pesticides and pelleting. Pesticide-free seeds are generally available, but caution should be used to ensure a disease is not present on the seeds that will damage the more mature crop. If seeds are stored for some time at low moisture and sealed to remove oxygen, pests cannot survive. Pelleting is an aid to handling that might also provide nutrients.

Germination will reflect growing with proper conditions, so one must learn what is best for the variety being grown. Seed companies typically publish these results, but usually for soil conditions. By experimenting, you can derive the interpretation of these recommendations to performance with your own growing system.

Before planting, be sure that there is not a requirement for a treatment to release the seed from dormancy (e.g. strawberries require some time in the freezer). Also, prepare your labeling scheme and a map of location so that the records of your trials will be accurate. Be sure to plant with very similar conditions to ensure a good comparison. The following are the conditions to consider:

• Moisture – Be sure that the maintenance of moisture is similar via covers and regular replenishment, if applicable. Note that the contact a seed has with the growing medium will determine the moisture it receives.
• Light – Be sure that the presence of light or dark is similar. Some seeds require a short burst of light or continuous light for best results. I use a set of squares moving from transparent to translucent to opaque (nested inside each other as covers for seed germination).
• Duration - Experimentation with covering for different periods will give differing stem length that can ease harvesting.We typically remove covers just prior to, or at the presence of, cotyledons (first leaves).
• pH – Seeds have a range they find acceptable and this should be similar for all being compared.
• Density – Although little allelopathy (impact of natural herbicides produced by plants to enhance their competition with other plants) is of concern during the first few days to impact germination, your germination tests can also help determine optimal densities for future yields. In our experiments, there is an optimum where too many or too few hurt yields.

Table I. Seed weight and longevity for home garden vegetables

• Seeds, The Yearbook of Agriculture. 1961. Stefferud, A., Editor. The United States Government Printing Office.
• Handbook for Vegetable Growers. 1960. Knott, Joe. John Wiley and Sons, Inc.
• Vegetable Growing Handbook. 1979. Splittstoesser, W.E. AVI Publishing, Inc.

Table II. Germination data for home garden vegetable seed

• Minimum percent germination to federal standards
• Handbook for Vegetable Growers. 1960. Knott, J.E. John Wiley and Sons, Inc.
• Seeds, The Yearbook of Agriculture. 1961. Stefferud, A., Editor. The United States Government Printing Office.