Grass seed production is a specialized form of agriculture focused on cultivating the plant to maximize the yield and purity of its reproductive structures. The industry is concentrated in geographically distinct regions, notably the Willamette Valley in Oregon, which leads global production of cool-season grasses like perennial ryegrass and tall fescue. European countries such as Denmark and Germany also contribute significantly. Producing high-quality seed is a multi-year commitment involving precise field establishment, specialized crop management, meticulously timed harvesting, and rigorous post-harvest quality control.
Field Establishment and Crop Management
The journey begins with selecting a field free from weed seeds, as contamination is costly and difficult to remove later. Preparing the land involves cultivating the soil to create a fine, firm seedbed, which encourages successful germination and establishment.
Farmers use specialized planting equipment, such as grain drills, to sow the seed at a low rate. This is often around 25 to 30 pure live seeds per linear foot in rows spaced approximately 36 inches apart.
The goal of low-density planting is to encourage the grass plant to tiller heavily and focus energy on producing seed heads, not dense leaf growth. For perennial species, the crop is a long-term investment requiring management over multiple seasons to maintain viability and yield.
Management involves carefully scheduled fertilization, particularly nitrogen application, timed to stimulate seed head development without promoting excessive vegetative growth. Weed and pest control are paramount to ensure the genetic and physical purity of the final product.
Cultivation between rows is a common practice, sometimes paired with specific herbicide applications to target competing plants. Fields must also undergo official inspections to verify the genetic integrity of the variety and check for prohibited noxious weeds.
Harvesting Techniques
Timing the harvest is the most critical decision, as the window for optimal seed collection is often narrow, lasting only a few days for some species. The crop must be harvested when the seed heads are mature enough to contain viable seed but before the seed begins to shatter due to wind or over-ripeness. Growers test maturity by checking the seed’s moisture content and stage of development, aiming for the medium to hard dough stage.
Two primary methods are used for harvesting: swathing and direct combining. Swathing involves cutting the crop when the seed moisture is still relatively high (around 35–50%) and laying it in a windrow to cure and dry in the field for several days. This method is preferred for grasses that shatter easily, as it allows the seed to after-ripen while minimizing loss.
Once cured in the windrow, a combine harvester fitted with a pickup attachment collects the material. Alternatively, direct combining involves harvesting the standing crop later, once the seed has dried naturally to a lower moisture content, often below 30%. Combines are typically modified for grass seed, requiring adjustments to the internal fan speed and sieve settings to prevent the lightweight seed from being blown out. The result is a raw, uncleaned bulk material containing straw, debris, and the newly collected seed.
Seed Processing and Quality Assurance
The raw material must undergo extensive conditioning to transform it into a marketable product. Initial processing involves drying the seed below 14% moisture content to prevent heating, molding, and loss of germination during storage. This is achieved using specialized drying floors where the seed can be turned and monitored for even drying.
Physical cleaning separates the pure seed from inert matter, chaff, broken seeds, and weed seeds. Cleaning plants utilize sophisticated machinery, including air-screen cleaners and gravity tables. Air-screen cleaners separate materials by weight and size, while gravity tables separate seeds of similar size but different densities, ensuring only the heaviest, most viable seeds remain.
A strict quality assurance process follows physical cleaning to verify the seed’s performance and purity, which is legally required for commercial sale. Laboratory testing includes a Purity Test (determining the percentage of pure seed, inert matter, and weed seeds) and a Germination Test (measuring the percentage of seeds capable of producing a normal seedling, indicating viability).
These two metrics calculate the Pure Live Seed (PLS) percentage, representing the true planting value of the seed lot. Once the lot meets regulatory standards, it may be treated with protective coatings or fungicides, and then packaged for distribution. Over 390 conditioning plants in the Willamette Valley alone perform these services, preparing the high-quality seed for global distribution.