When purchasing common or certified seed, ensuring mechanical seed purity is critical. A seed analysis certificate can be requested from reputable seed processors and suppliers before purchase is finalized, and prior to any blending of seed-lots into a mix (Figure 7.2). These certificates give important information about weed seeds present, inert material, germination, and pure live seed (PLS). They are used to establish the grades of both pedigreed and common seed. They also provide the necessary information if a seedlot needs to be tracked back through the system. In the case of pedigreed seed, a seed lot could be traced back to the registered grower, field, and name of the field inspector in the event of a problem.

A seed analysis certificate will be attached to many seed lots, and will be a requirement for seed imported to Canada. At a minimum, labs will report federally listed noxious weeds, and some labs may also report results based on regionally listed (i.e., state or provincial) noxious weeds. Listed noxious weeds may be specific to the jurisdiction where the seed analysis is conducted. A second seed analysis can be ordered and paid for by a customer, with the request to list every weed species detected at any level. This would be extra insurance against the potential introduction of unwanted species, and is advisable for special seeding projects in sensitive areas where a high level of ecological integrity must be maintained.

It is possible to have seed custom cleaned to a higher standard with a “0” tolerance for particular weeds. This may be difficult to do depending on the species and the specified weed seeds. But in some cases seed cleaning plants can improve results by double running and adding extra screens if they are adequately compensated. Suppliers may also be able to find an alternate lot of the desired species with no undesirable contaminants.