Seed quality is the cornerstone of High Mowing Organic Seeds. Everyone here at High Mowing works in some way to grow, trial, sell, or ship well-adapted organic seed of wide varietal selection that germinates well. Our success depends on clean seed.
The seed cleaning process at High Mowing is two-tiered. We clean seed crops in the field before they come inside for germination testing and further cleaning in the seed cleaning room. For growers interested in seed production, field cleaning is really important. Field cleaning for both dry and wet seeded crops requires little additional farm infrastructure. With some screen material (1/2 inch, ¼ inch, or window-sized) and lumber from the hardware store, box screens can be made. Field cleaning attempts to isolate everything that resembles seed in size and weight. With screens and fans, we do a thorough cleaning to remove all light chaff and light non-viable seed. Screening and winnowing are repeated until the seed appears mostly free of foreign matter.
After field cleaning, seed comes inside. Our in-house lab first conducts a “dirty” germination test. The dirty germination helps determine the extent to which the seed needs to be cleaned. If a dirty germination test returns results of only 50% there are probably lots of nonviable seed in the lot.
We grow and clean relatively small lots of seed, so our cleaning equipment is tiny compared to the grand grain cleaning operations throughout the Midwest and Western states. At our scale, smaller cleaners do the same job and maintain good seed quality. We use a couple of different tools to clean non-viable seed from living seed. The cleaner we use depends on the crop and amount of seed to be cleaned. We have a few types of mechanical cleaners – primarily we use two Clipper-type cleaners and an Oliver gravity separator. We also have a spiral cleaner to separate round, viable seed such as our brassica crops from flatter, lighter (dead) seed.
Clipper seed cleaners are old technology—tried and true. Clipper has produced seed cleaning equipment since the mid 1800s. The Clipper at first glance seems complicated. However, after watching it work, it becomes remarkably intuitive. The Clipper uses two different sized screens that shift back and forth. The top screen separates out large foreign matter, allowing viable seed and smaller matter to fall through to the next smaller screen. Small inert matter falls through the bottom screen, leaving anything that is a similar weight and size to the seed. The seed shakes down to a chamber that air blows through. The fanned air separates light, nonviable seed from the viable seed. Viable seed falls into a container at the bottom of the machine. This process is usually repeated a few times to ensure that the seed is thoroughly cleaned.
On the Clipper, everything is variable. We use dozens of different sized screens depending on crop type. The amount of air fanned through the Clipper can be controlled with precision. The Clipper is a very refined version of the field winnowing method mentioned in a previous article which uses a box fan, a square bucket, and three large plastic totes. Our seed cleaner, Craig, keeps meticulous notes regarding screen sizes and air flow used for crop types and even individual lots.
We also clean with an Oliver Laboratory gravity separator. The Laboratory model can sort up to 500 lbs of dry seed per hour. The gravity table separates out light-weight nonviable seed as well as heavy foreign matter, like rocks, from the viable seed. The table shakes and blows air through the bottom of the table to distribute matter of different weights to different parts of the table. Light, nonviable seed and chaff sifts to the bottom of the table. Rocks and other heavy foreign matter gather at the top of the table. The table shakes into partitions that lead the light, heavy, and mostly viable seed into segregated containers.
As with the Clipper, the controls on the Oliver are highly sensitive and can be dialed in for precision. Craig, our seed cleaner, has learned the subtle nuances of our seed cleaning machines over the past six years. To offer the cleanest seed possible we require all of the parameters of precision for which these machines were designed. Craig finesses the Clipper and Oliver like Picasso with brush in hand, each stroke removing chaff, rocks, and dead seed from living, viable seed.