What Is Inert Material On Seed Tags And Why You Should Avoid It

You're ready to take your lawn from patchy to perfect with a grass seed that's great for overseeding. Or perhaps you've finally made the decision to enhance the number of butterflies and native bees that visit your garden and replace your lawn entirely with a wildflower meadow. Whether you're purchasing a bag of lawn seed or a wildflower mix, knowing how to interpret the information provided on the label is vital if you want good germination rates and good value for money. Inert material, also called inert matter, is one of the most important percentage values listed on a seed bag label (usually it's near the bottom with weed seed percentages). The term denotes anything mixed into a bag, or lot, of seeds that won't grow — think broken seed, chaff, soil, sterile florets, fungus bodies, stones, wood shavings, empty seed hulls, sand, sticks, corn cobs, or sawdust. You can't avoid it entirely, but you should try to find seed bags with as little inert material as possible.

Inert material percentages have appeared on seed labels for well over half a century. Its government-regulated inclusion is mentioned, for example, in a circular produced by the California Agricultural Extension Service way back in 1949. The classification has stayed relevant for so long because it's an indispensable measurement in determining seed purity. Why? The more inert material you have in a bag of seed, the less true, viable seed it contains. And the less actual seed you have, the patchier and pricier your lawn, wildflower meadow, or crop harvest will be and the more you'll pay for that seed.

Bulk seed is packaged for sale by the grower, and it isn't as pure as certified seed, which has been tested for purity factors like the quantity of weed seed and percentages of inert material. Sorting seeds to determine viable seed percentages — that is, whether it contains an embryo and endosperm — is a labor-intensive process done in laboratories by hand and using specialist equipment. High percentages of inert material are a warning sign that a bag of seed contains minimal live seed and lots of filler. A seed lot with high purity is the opposite. Only buy seed with 4% or less and up to 15% (excluding fertilizer coatings) of inert material as a rule of (green) thumb.

Keeping a close eye on your garden budget and, in turn, looking for tricks to increase seed germination rates for a flourishing garden or lawn? Use inert material percentage to cost-compare seeds. For example, you could subtract the inert material percentage from the weight of seed packets you find online or in-store, giving you the live seed weight. Then, divide the price by the answer to compare the price per weight across brands and determine the best deal. Seed labels also list pure live seed (PLS) percentages, and a low PLS rate means higher rates of other materials. Use this figure to work out how many bags of seed you need to cover an area — called seeding rate. Hate math? The University of Wisconsin-Madison's Team Forage Division of Extension has an online calculator to help you work this out using the PLS percentage.

Knowing inert material percentages is so vital to seed purity that states require it on labels for all seeds sold and regulate — by law — the amount a bag can contain. For example, under Arizona law, seed labels must contain no more than 10% inert material (with limited exceptions for some species). Georgia seed law excludes coatings, pelleting material, fertilizer, and mulch from the inert material percentage, whereas the USDA Natural Resources Conservation Service considers coatings part of it. New York State has different inert matter labeling requirements for different types of seed species. Although each state has unique and self-determined seed labeling requirements, inert material percentages should always be listed on the label, or, in a pinch, you can infer the inert material percentage from the pure live seed (PLS) percentage.

Note, too, that inert material can be a positive addition to seeds. Treated seeds might be coated in everything from fungicides to fertilizers to pesticides, or a bag of seed might contain mulch, clay, or walnut shells to help aid in seed broadcasting and hand sowing. Though these additions serve a purpose, they may contribute to a higher inert material percentage and still need to be considered when comparing costs. Likewise, don't get the inert material listed on a seed bag label mixed up with any inert material you add after purchase — for example, if you purposefully mix small seeds with sand before sowing (or with perlite, wet sand, sawdust, or cottonseed hulls ... the list goes on) to help it spread further and more evenly.