As we move into August many growers are preparing to plant. Here are some general comments about ginseng seed and seeding rates that growers should keep in mind before planting.
Seed viability
When preparing seed for planting, make sure to avoid temperature fluctuations between storage and seeding, such as seed being left in a hot vehicle or sitting in a cooler for prolonged periods. It is suspected that these temperature fluctuations may be responsible for delayed germination that has been seen in some fields. This is especially true for late seeded crops, where air temperatures may be cooler and more fluctuations can occur.
Seed viability (is it alive?) can be checked using the ‘tetrazolium’ test. It is a colorimetric test that must be done by someone experienced in this technique. It will not tell you if the seed will germinate in the 1st or second year. Check with your agriculture supplier or consultant to see if they do this test.
One measure of germination may be the embryo size. If the embryo is about 1-2mm long then there is a good probability that it will germinate in the first spring. If it is smaller, then it may germinate in the second spring. To check the embryo, split the seed along the axis and look for the small, comma-shaped developing plantlet at the edge of the seed.
Seed viability tests can also give some indication of the level of seed disease. Low viability may indicate issues with seed disease that may spread to viable seed before germination. Separate out disease seed. Seed harvested from gardens that were stressed by disease or weather conditions (e.g. high heat and low moisture) over the past few years could have lower viability and higher disease levels. Adjust seeding rates based on seed viaibility.
Dry seed: We are sometimes asked about survival of dry seed. Seed as dry as 10-11% moisture can survive. However, before planting, dry seed must be soaked in water to replenish the lost moisture.
Sizing seed: There are 4 main sizes of ginseng seed. Your seed will be a mix of these. They will fit standard seed sorters for small, seed 4.4-4.8 mm in diameter (Ciommercial grade 11-12); medium, seed 4.8-5.2 mm in diameter (Commercial grade 12-13); large, seed 5.2-5.6 mm in diameter (Commercial grade 13-14); and extra-large, seed 5.6-6.0 mm in diameter (Commercial grade 14-15). Research has shown that small and extra large seed have the lowest emergence. The best emergence is from medium to large seeds. Research has also shown that seed size is directly related to embryo size. In the case of small seeds, low emergence in the first year may be because of delayed emergence.
Delayed germination: Occasionally, some or all seed may not germinate until the second year. The reasons for this are not fully understand, however when ginseng seed germination is delayed it is often a matter of temperature fluctuation. It seems like most of this occurs when the seed is being handled, either before storage or before and during seeding. Take care to avoid temperature fluctuations when handling seed for any length of time.
Growers who would like to monitor seed temperatures during stratification might want to consider purchasing data loggers. These will take temperature readings at intervals specified by the operator. Most scientific and crop monitoring equipment suppliers carry these instruments.
Seeding rates: Studies have shown that ginseng self thins over 3 years to between 80-100 plants/m2 and over 4 years to between 35 and 70 plants per m2, regardless of the initial seeding rate or plant stand in year one. Research has shown that the more crowded the roots are in the first year of development, the smaller the individual roots will be. Additionally, crowded gardens will be more prone to both foliar disease, due to a thicker canopy and less air flow, and root disease, because pathogen more readily between roots. Consequently, a thicker garden may require more pesticide applications which may offset any potential benefits of higher yield.