Seed must go through several tests to ensure quality prior to sale. (Photo: Shutterstock).

We are told to read labels and instructions on just about everything we purchase whether it is a new cell phone, food or pesticide. This is also the case with seed. If you purchase your seed from a reputable dealer, then you can be assured that the information on the package and the seed in the package meets certain requirements. You may have noticed the information on the seed bag but didn’t know what it meant. State law, federal law and either Association of Official Seed Analysts (AOSA) or the International Seed Testing Association (ISTA) manage seed testing requirements.

Seed must go through several tests to ensure quality prior to sale. Once seed has been harvested, collected and cleaned to remove unwanted materials and weed or other crop seed, a representative working sample is removed for testing. If this sample is not representative, then all information gained from testing is suspect. The AOSA in their “Rules for Testing Seeds” define how samples are to be taken.

Standard tests that are performed on seed samples are purity and germination. In a purity test, the submitted working sample is divided down into two portions – the purity and the noxious samples. The purity sample consists of at least 2,500 pure seed units (a unit can either be a single seed such as a cucumber seed, a multiple seeded capsule such as a beet, or multiple grass seed floret). This portion is sorted through by hand to separate out the pure seed from inert material such as rock, plant stems or leaves, weed seeds and other crop (such as wheat in squash seed or corn in bean) seed. In the case of a grass mix, the individual species are also separated out. All portions are weighed and the percentage of each is calculated and recorded. The noxious sample must consist of at least 25,000 seed units. This sample is only examined for any weed seed that it contains with particular emphasis placed on any noxious weed seed. The federal government and each state have a list of weed seeds not permitted in any seed sold or it may put a limit on how many of the weed seeds it allows per pound of desired seed. This is the reason why obtaining a representative sample is critical. All of this information is placed on a certificate and usually on the seed packaging. It often looks like this:

• Kentucky Bluegrass 50%
• Annual Ryegrass 25%
• Creeping Red Fescue 21%
• Inert material 2%
• Weed seed 1%
• Other crop 1%

Germination tests are the next test. In this test, 400 pure seed units are pulled from the sample and placed on media and placed in a germinator. Depending on the type of seed, the media on which it is placed varies along with the temperature, light or dark conditions and the length of time the test is run to optimize germination. Tables have been developed listing species and the optimum media type, temperature and test length for the most commonly tested species. Germination tests are repeated if all the seed is not sold in one year. If the germination falls below a certain percentage, the seed lot must not be sold.

What you might also see on the label is PLS (Pure Live Seed). This is the percentage of pure seed units in a seed lot that have the potential to germinate and produce viable seedlings. It is calculated by multiplying the percent germination by the percent pure seed and dividing by 100.

It is not possible to remove all weed seed from seed lots but through cleaning and testing, the weed seed is minimized. So next time you purchase seed, take time to read the label.

By Sharon Bokan, Colorado State University Extension Boulder County. Sharon is the Small Acreage Coordinator at Colorado State University Extension Boulder County. For more information, call 303.678.6176, e-mail or visit