Seed Cleaning

Successful revegetation projects rely on the use of high-quality seed. Seed harvested mechanically or by hand will include a mix of stems, leaves, chaff, seed or fruit appendages, nonviable seeds, and seeds of nontarget species. The extraneous materials must be removed to ensure a quality product and to improve uniform dispensing through seeding equipment. Seed cleaning (also called processing or conditioning) improves seed lot purity and quality, reduces pathogen and pest infestations, decreases seed lot volume and related storage costs, and facilitates management of seed moisture levels to improve the duration of seed viability in storage.

Equipment is available for cleaning the generally highly uniform seed of agricultural and horticultural species. With experience and some ingenuity, operators can adjust or modify equipment to produce a quality seed product for many native species. The large number of native species, their diverse fruit and seed structures, the wide variation in dispersal unit sizes within and among populations of a species, and the lack of research or practical experience with cleaning many natives, however, often necessitate creative approaches to cleaning seeds efficiently and effectively. A major concern is avoidance of seed damage that can reduce viability, germination, and seed longevity. Additionally, the cleaning sequence should retain the full range of target seed variability within the seed lot to maintain genetic diversity.

Careful observation of each seed lot is essential for selecting the appropriate sequence of steps and associated equipment for cleaning it. The cleaning process generally begins with separation of the target fruits or seeds from inert material. This is followed by extraction of the seeds from their fruits or appendages. Cleaning devices are available that separate seed by density, length, width, thickness, shape, color, and other characteristics. Finishing to remove fine debris is often accomplished using devices such as air screen separators. Several machines and repeated operations may be required to obtain acceptable purity for some seed lots.

Some native species and seed lots present seed cleaning challenges, some collectors and producers own only the most commonly used seed cleaning devices, and natives are often collected or grown in small lots. Careful examination of each seed lot can enable the operator to select the best equipment for cleaning each seed lot and suggest needed modifications for addressing specific problems. For small lots, sieves, corrugated rubber mats, and other inexpensive materials have been utilized for manual seed cleaning.