Seed Treatments

Untreated seeds are rarely used by commercial growers. Many growers use F-1 hybrid seeds >> that are more expensive than the open-pollinated seeds used in the past.

Many growers are willing to pay more for treated seeds to ensure the best possible stand establishment.

Pesticide applications are one of the more common seed treatments used today. A light coating of fungicide is usually applied to the seed surface. A brightly colored dye is sometimes added as a reminder that a fungicide has been applied. Systemic insecticides have also been used as a seed treatment for certain crops.

Inoculation of legume seeds with rhizobium to improve nitrogen fixation after germination is another common treatment.

• Coating and pelleting are two widely used seed treatments, particularly with small-seeded species. Coated seeds have a thin layer of material such as clay or diatomaceous earth added to make the seeds larger but not to change the overall shape. Seeds are coated to make them easier to handle, to deliver chemicals, to improve soil contact, or to inoculate seeds with microbes The exact composition of coating material is a carefully guarded secret by the companies who develop them. Pelleted seeds have been coated until they are round. This makes seeds easier to handle and plant, particularly when planters that utilize belts with pre-punched holes of a specific size are used. To make identification easier, coated seeds are often color-coded, so cultivars or types are not mixed at planting. One successful pelleting treatment splits upon hydration and does not pose a barrier to radicle growth or limit oxygen availability to the seeds.
• Film coating is another recent innovation. Many coating materials are very dusty. However, film coatings are made of the same materials used by the pharmaceutical industry to coat pills. These coatings are water soluble but dust-free.
• Pregerminated seeds, particularly celery, have been marketed by some companies in Europe. One company marketed pregerminated celery seeds in the United States briefly during the mid-1980s, but they are no longer sold in this country to my knowledge because ttheyare very perishable.
• Fertilizer treatments should not be applied to seeds, such as legumes, that are sensitive to high salts. However, some seeds are relatively tolerant of salts and additions of very small quantities of fertilizer with a low salt index can boost early seedling growth. Research suggests that some matric priming materials, such as diatomaceous earth, boost early seedling growth because mineral nutrients are absorbed by the seed.
• Synthetic seeds >> derived from tissue culture and coated in gelatinous material have been developed but are expensive, difficult to ship, have a short shelf-life, and are excessively variable for commercial use. Current research has focused on developing synthetic seeds that are desiccation tolerant and can be handled like other seeds. Although progress has been made in developing desiccation-tolerant synthetic seeds, it is unlikely that they will be commercially available for many years.

• Primed seeds have been subjected to a controlled hydration process followed by redrying. Generally, priming reduces the time to germination and may improve the seed’s ability to germinate under temperature or moisture stress. Priming does not usually improve the viability of poor-quality seeds. Peppers, tomatoes, and lettuce show a greater response to priming than some other types of seeds. Since the seed law does not require that primed seeds be labeled, they seldom are. Some seed companies advertise seeds as “vaporized” instead of calling them primed.
• Precision-sized seeds are often available and have been carefully sorted so all seeds are the same size. Sized seeds often have greater uniformity of germination. In many cases, large seeds are sold at a premium, because they are often more vigorous and may produce more uniform emergence. Some growers prefer sized seeds to get more uniform placement when belt seeders are used. It is possible to buy seeds spaced at a specific interval on tape. The tape is buried in the ground and dissolves when wetted.

• “Seed tapes” are used mainly by home gardeners. Seeds are embedded in water-soluble tape for ease of planting.