Primer On Seed Dressings
The objective of every seed treatment is to enhance seed performance in one or more of the following means:
- improve germ rates. In conventional cultivation, seed is frequently dressed with synthetic fungicides which minimize seed and seedling losses due to seedborne and soilborne attack.
- eliminate seed-borne microorganisms or protect from soilborne microorganisms, and
- optimize ease of taking care of and reliability of planting (reduce gaps in stand or the need for thinning of plants, particularly when mechanized planters are utilized),
Most seed protectants are not necessarily an option for certified organic growers; however, there are some seed treatments, such as priming, pelletizing, and the use of hot water or NOP-compliant protectants, that can be used by certified organic farmers to boost seed performance.
Certain plants are superior prospects for seed treatment due to the nature of the seed (irregularly or small shaped) or the designated production system (conventional versus organic). For instance, pelleted seed is useful in head lettuce production due to the need for accurate seeding, but is less beneficial for dense sowings of looseleaf lettuce in bed cultivation.
All-Natural Seed Treatment Options
Primed seed has absorbed just enough water to dissolve germination inhibitors and activate the early stages of germination. Primed seed is therefore in a suspended state of growth, so it germinates faster and more uniformly over a broader temperature range, reducing the likelihood of thin or very thick plant stands.
A seed pellet is a coating, usually of clay mixed with other inerts, that streamlines the size, shape, and uniformity of a small, non-round seed such as those of lettuce, carrots, onions, and many herbs and flowers. Ideally, the pelleting materials are somewhat permeable to oxygen and absorb water quickly so that the pellet splits immediately upon hydration.
Seed Health Treatments
This is a broad category of treatment options that includes warm water, biological and plant extracts, bleach disinfection, and biologicals (microbes). These treatment methods can improve seed and seedling health by eliminating seedborne microorganisms from the seed or protecting germinating seeds from attack by soilborne microorganisms.
Hot water treatment
The use of hot water treatment option to eliminate seedborne diseases, particularly those caused by plant pathogenic bacteria, is well-established. While the technique does not work for large-seeded vegetable crops, it has proven effective for brassicas, carrots, peppers, and tomatoes, and, to a lesser degree, celery, spinach, and lettuce.
Pro tip: While there are some general guidelines that put the heat around 120 degrees F and the time around 20 minutes to complete the priming and cleaning of the seeds, try experimenting a little bit as some seeds may prove more sensitive to heat than others.
Hot water treatment can cause a reduction in vigor over time, so hot water treated seed should not be kept for longer than a season. Only fresh seed of high vigor should be subjected to hot water treatment method, as old seed or seed of low vigor may respond poorly to the stress of the treatment method and have reduced viability. Hot water treated seed should be used within one season; the storage life of the seed may be reduced by the treatment method.
Oils and Plant Extracts
Evaluating plant extracts and oils as seed treatment options is a new research area so there is currently little data on their efficacy. Plant oils such as thyme, cinnamon, clove, lemongrass, oregano, savory, and garlic show some potential to suppress damping-off, and thyme oil is in use in Europe as a seed treatment option. Pure soybean or mineral oils have been shown to reduce storage molds of maize and soybean. Further research on the disease suppression potential of these oils is necessary to determine the viability of essential oil-based seed treatment protocols.
Bleach can be used to surface-disinfect seeds as an alternative to hot water. Bleach will eliminate pathogens on the seed surface but will not eliminate pathogens beneath the seed coat.
Biological Seed Treatments
Biological seed treatment options, alone or in conjunction with priming and pelleting processes, may have potential in some situations for improving plant health. In studies evaluating the efficacy of these microorganisms as seed treatments or drenches, results have been inconsistent.
The purpose of any seed treatment method is to simply to improve the seeds’ performance in one or more of the following ways:
- get rid of seedborne microorganisms or protect from soilborne pathogens
- optimize ease of handling and accuracy of sowing (reduce gaps in stand or the need for thinning of plants, particularly when mechanized planters are used), and
- improve germination rates
Most seed protectants are not an option for all-natural producers; however, there are some seed treatment methods, such as priming, pelletizing, and the use of hot water or NOP-compliant protectants, that can be used by all-natural growers to improve seed performance.