The objective of every seed treatment is to boost seed performance in one or more of the following ways:
- protect or eradicate seedborne pathogens from soilborne microorganisms,
- improve ease of handling and accuracy of planting (minimize gaps in plants or the need for thinning of plants, particularly when mechanized planters are utilized), and
- improve germination rates.
In conventional cultivation, seed is often treated with chemical fungicides which minimize seed and seedling losses as a result of seedborne and soilborne attack.
Seed Protectants for Organic Farmers
Most seed protectants are not an option for organic farmers; however, there are some seed treatment methods, such as priming, pelletizing, and the use of hot water or NOP-compliant protectants, that could be used by organic gardeners to improve seed performance.
“…priming, pelletizing, and the use of hot water or NOP-compliant protectants, that could be used by organic gardeners to improve seed performance.”
Specific crops are better options for seed treatment option due to the traits of the seed (small or irregularly shaped) or the designated cultivation system. 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 production.
All-natural Seed Treatment options
Priming or Soaking
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 very thick or thin plant stands.
“Primed seed … germinates faster and more uniformly”
Priming results in earlier plant establishment, which can aid in fending of the attack of damping-off pathogens to which germinating plants are particularly vulnerable. Priming is usually performed in conjunction with a pelleting process to protect the primed seed, which has a shortened life expectancy.
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 once it gets wet.
Seed Health Treatments
This is a broad category of treatment options that includes hot water, biological and plant extracts, bleach disinfection, and biologicals (microbes). These treatment options can improve seed and seedling health by getting rid of seed-borne microorganisms from the seed or protecting germinating seeds from attack by soil-borne pathogens.
Warm water treatment
The typical procedure consists of:
1) soaking/warming the seed in 100 ° F water,
2 )warming the liquid the seed is soaking in for 20-25 minutes, depending on the crop species, in a 122 degree soak.
3) chilling the seed for 5 minutes in cold water, and
4) quickly drying.
It’s important that you take these instructions very literally and be precise in your temp and timings since the seed embryo could be killed in hotter water or the disease incompletely eliminated in colder water. I took all of these temperature and timings for the different crops from this helpful page here.
Broccoli, Mustards, Kale, collards, Turnip, Carrot and Cauliflower: soak at 122 degrees for 20 minutes
Cabbage, brussel sprouts peppers tomatoes: soak at 122 for 25 minutes
CAUTION: 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. The procedure is described in detail in resources cited below. Some companies do their own warm water treatment option or will custom hot water treatment method upon farmer request.
If a lot is not treated by the company and no testing has been done for pathogen detection, producers may conduct their own warm water treatment with a home set-up. If the producer treats the seed him/herself, it should be noted that the company’s liabilities are null and void. Only fresh seed of high vigor should be subjected to hot water treatment option, as old seed or seed of low vigor may respond poorly to the stress of the treatment option and have reduced viability.
Warm water treated seed should be used within one season; the storage life of the seed may be reduced by the treatment option. For more information see the Ohio State University Extension Fact Sheet Hot Water Treatment method of Vegetable Seeds to Eliminate Bacterial Plant Microorganisms in All-natural Production Systems
Plant Extracts and Plant Oils
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.
Bleach (sodium hypochlorite) can be used to surface-disinfect seeds as an alternative to hot water. Bleach will eliminate microorganisms on the seed surface but will not eliminate pathogens beneath the seed coverings
Biological Seed Treatment Methods
Biological seed treatment methods, alone or in conjunction with soaking, priming and pelleting processes, may have potential in some situations for improving plant health. In studies evaluating the efficacy of these microorganisms as seed treatment methods or drenches, results have been inconsistent.
Products that are currently commercially available include Kodiak (Bacillus subtilis, Bayer CropSciences), Mycostop (Streptomyces grieseoviridis, Verdera), SoilGard (Gliocladium virens, Certis), T-22 Planter Box (Trichoderma harzianum, BioWorks), Actinovate (Streptomyces lydicus, Natural Industries, which novozymes acquired, and Riznate (Genesis Ag).
The purpose of any seed treatment is to improve seed performance in one or more of the following ways: 1) protect or get rid of seedborne microorganisms from soilborne microorganisms, 2) optimize ease of handling and accuracy of planting (reduce gaps in stand or the need for thinning of plants, particularly when mechanized planters are used), and 3) improve germination rates. Most seed protectants are not an option for all-natural producers; 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 purely natural growers to improve seed performance.
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 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. Bleach will eliminate microorganisms on the seed surface but will not eliminate microorganisms beneath the seed surface.