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weed seed percentages

Inert matter is typically described as a percentage of the weight of the entire seed bag. According to the United States Department of Agriculture, a bag of grass seed suitable for cultivation should contain no more than 15 percent inert matter. This ideal percentage depends somewhat on the type of plant you’re growing, so some plants may still thrive with a higher percentage of inert matter.

Depending on the size of the inert matter in the seed bag, growers may encounter problems when sowing seeds, when harvesting full grown plants, or both. Inert matter such as pieces of stem or unthreshed seed clusters can become trapped in seed drills and spreaders, for example. A good rule of thumb is to purchase seeds with as little inert matter as possible.


If you’re starting plants from seed, the full-grown plants will only be as good as the quality of seeds from which the plants were grown. For this reason, understanding the quality indicators listed on a seed tag is an essential part of growing healthy, mature plants. Part of the requirements for a seed identification tag is to describe the amount of inert matter in the seed.

If you’d rather not have to remember the different ideal percentages for every type of plant you grow, consider purchasing certified seed. A seed is considered certified when it has low percentages of inert matter, weed seeds, and seeds of other crops, but high degrees of genetic purity, germplasm identity and germination ability. Purchasing certified seed not only sidesteps the problems associated with inert matter but can help ensure good crop yields and germination as well.

Inert matter, in the context of seed identification tags, refers to dirt, sand, stones, sticks, glumes, stems, broken seed and other miscellaneous non-seed items that have made their way into the seed bag. These items are referred to as inert because they don’t contribute anything to seed germination, crop yield, or other growing concerns. But the inertness of these materials doesn’t mean that they shouldn’t be of any concern to home growers.

The following label properties and their references are listed in the same order as they would appear on the bag of seed:

Purity– This is the % by weight per bag of the particular species of grass seed. In the sample label, the purity of the creeping red fescue is 49.17%. If the whole bag weighed 100 lbs., then 49.17 lbs. would be creeping red fescue.

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For this reason, if a rate of 2-4 lbs. of seed is recommended for 1,000 square feet of bare ground, then it is wise to go with the higher rate, as not all of the 2 lbs. of seed will germinate.

Typical layout of a grass seed label. Note that only one cultivar- Transition 2400 variety of ryegrass, is listed. The other seed varieties are not identified as to which cultivar they are.

Being able to understand the information on a grass seed label will help in selecting a high-quality seed. All mixes and blends of grass seed are not of the same quality, but all seed labels must list certain information which will enable the buyer to decide whether that particular seed is of a quality suitable for their needs. It may not be necessary or practical to use a high-quality seed in all situations, but the information on the label will still be useful.