Only through the research and refinement of the grain crops is it possible that each bushel of wheat equal 60 pounds; milo, 56; oats, 32; soybeans, 60; etc. Native grass seeds, on the other hand, because of their relative popularity don't have the benefit of decades of research and refinement and therefore cut and dried standards. (See Table 1, Suggested Standards.) The paradox is that if the native grass seeds we're used to working with did have those standards they would be as far removed from native as corn or wheat. Native grass seeds are variable from year to year in their unharvested quality. Conditioning (cleaning) can help to mediate the peaks and valleys but the general quality will fluctuate with the quality of the unharvested seed. Native grass seeds should always be bought on the basis of pure live seed (PLS).
PURE LIVE SEED EXPLAINED
In order to determine the PLS percentage of any given lot of seed it must be tested. (Unlike quality standards, there are procedural standards for native seed testing. The theory being that each lot of seed tested at however many testing labs will have similar results. Results which could also be repeated at the same lab.) Testing reveals the purity, which when added to the other crop, weed and inert percentages equals 100% of the sample. Testing also determines the germination rate. Pure live seed discounts for the inert material (any non-seed item; stems, leaf parts, etc.), weed seeds and other seeds which are not the specified crop and any seeds which do not germinate under the specified conditions. Pure live seed is calculated by multiplying the purity by total live seed. Total live seed is determined by adding germination and hard seed or dormant seed. Take a look at the following example.
| PURITY |
65.40% |
GERMINATION |
75% |
| OTHER CROP |
.10% |
HARD SEED |
|
| WEED |
.10% |
DORM SEED |
12% |
| INERT |
34.40% |
TOTAL LIVE SEED |
87% |
| TOTAL |
100.00% |
|
|
PURITY X TOTAL LIVE SEED/100 = 65.40% X 87%/100 = 56.898% PLS
For each bulk unit of seed, 56.898% is pure live seed.
BUYING NATIVE GRASS SEEDS-THE INSIDE SKINNY
Now that you know about pure live seed it should be easy to call or drop by your seed supplier and know exactly what you're getting. After all a PLS is a PLS, right? Well.... not necessarily so. Not all pure live seeds are created equal. Before you buy you should be informed as to what makes some pure live seeds different than others. Ask questions about the analysis and you can get some indication as to whether you are getting good PLS or marginal PLS. (I stress indication, this is not scientific, but based on experience.)
ANALYZING THE ANALYSIS
Every bag of seed should have an analysis tag attached or you should be given a copy of the seed analysis when you purchase native grass seed. A seed company is required by law to list the following items on the analysis tag.
| PURE SEED |
GERMINATION |
| CROP SEED |
HARD SEED |
| WEED SEED |
DORMANT SEED* |
| INERT MATERIAL |
DATE OF TEST |
| NOXIOUS WEEDS |
ORIGIN |
*Dormant seed is not required but it may be listed and Total Live Seed reported as Germination plus Dormant.
Let's take a closer look at each one of the components. Each one can tell you something about the seed, sometimes revealing problems.
PURE SEED (PURITY)
Purity is the amount of actual seed in a sample. Generally, the higher the purity the better the overall quality of the seed. Usually purity by itself doesn't reveal much but when considered with germination, might tell you something about the seed. During cleaning, material is removed to increase the purity of the seed. Low purity with high germination could indicate a by-product of the cleaning process. Low purity with low germination could also be a by-product. It is possible that high purity with low germination is old seed. In any of these cases it doesn't mean you don't want to buy the seed but you should expect to buy it at a discount.
CROP SEED (OTHER CROP)
Examples of other crop in native grasses would be any other native grass seeds which are not the specified crop as labeled when the sample was submitted. Any "other crop" which is greater than 5% is listed as part of the purity and the lot is then changed from the specified crop to a mixture. For example if big bluestem were submitted for analysis and a purity exam showed 6% indiangrass, the seed sample label would be changed from big bluestem to big bluestem/indiangrass mix. Germination is also performed on those "other crops" in excess of 5%. Other crops less than 5% are listed but not germ tested. The only thing to be concerned about is that fescue (argh!) is also other crop. If other crop percent exceeds 1% inquire about what the other crop is.
WEED SEED
There are three types of weeds: Prohibited noxious weeds, those which cannot be present in any amount; Restricted noxious weeds, those which can only be present in less than specified amounts and Common weeds, those whose cumulative total cannot exceed a certain percent. (See Table 2) Seed conditioners are required by regulation to report the percent of weeds in each batch of seed and specifically name any restricted noxious weeds in excess of specified amounts. The amounts vary from state to state. If you are interested in obtaining a list, contact your State Department of Agriculture. Be inquisitive of any weed content above 1% and suspicious of any high percentage of weeds with no declared noxious weeds.
INERT MATERIAL
Small stems, leaf parts, dirt clods, insect parts, etc.-any non seed item is inert. Inert is conversely related to purity. When purity is high, inert is low and visa versa.
GERMINATION
Germination is the seed which when treated by the recognized and accepted standard for germination, sprouts. (The method of germination testing varies from species to species.) Germination is expressed as a percent of sprouted seed from a known amount of seeds.
Germination is pretty straight forward. High germination rates indicate good quality seed and probably good vigor seedlings.
Be wary of low germ seed. Low germination seed might indicate one or more of several problems, possibly related to the storage, handling or conditioning of the seed. The bottom line is that low germination seed can mean low vigor seedlings. But what is low germ seed? Remember I said earlier, native grass seeds are variable from year to year. When determining whether a seed lot has low germination it should be compared to other seed lots of the same species and variety and those should be from the same year's harvest. If seed lot A whose germination rate was 50% were compared to others of the same species and variety but harvested in another year whose average germ were 85% you would think you had a bad lot. However compare seed lot A to seed harvested in the same year and the average germination rate was 55% you'd know there was nothing to be concerned about. If the germination rate seems low ask your supplier how it compares to other seed lots. To confuse the issue low germ seed is not always bad seed. In one instance that I'm familiar with; low germ, low purity switchgrass seed was sown onto fescue CRP pasture and has resulted in a reasonable stand of switchgrass. Typically this type of material can be picked up for next to nothing and could be an economical way to treat a waste area (construction borrow pits, strip pits, etc.). However don't use it on areas where you are depending on production.
HARD SEED
Hard seed is used to refer to legume seeds and is firm seed which did not sprout or become disfigured during the germination process.
DORMANT SEED
Dormant seed is seed which did not sprout under the specified conditions but sprouted after additional treatment or stained when treated with tetrazolium. Tetrazolium (TZ) is a chemical which stains live tissue. Native grasses have dormant seed rather than hard seed.
Ask how much dormant seed there is. High total live seed rates indicate good seed but may contain a high dormancy rate. Although dormant seed is still good seed it could put a lot of undue stress on you, waiting for it to sprout. Dormancy comes in two types; short term and long term. The influences of soil moisture and temperature will sprout short term dormant seed during the first growing season. Long term dormant seed requires both those influences plus time-one or more seasons may be necessary. Unfortunately there is no way to tell from the seed analysis how much is short term and how much is long term. If a seed lot has over 20% dormant seed, you should ask if there is another lot with lower dormancy. (Usually the chaffy grasses aren't too susceptible to this. Switchgrass is notorious for dormancy. Try to buy year old switchgrass seed if available.)
TOTAL LIVE SEED = GERMINATION + DORMANT SEED
OR GERMINATION + HARD SEED
Many times germination and total live seed are used synonymous with each other. Technically they are not the same. Total live seed is the sum of germination plus hard seed or dormant seed, depending upon the species. Total live seed is used to calculate pure live seed. All seed analyses should indicate germination and hard seed or dormant seed separately if any hard or dormant seed exists.
DATE OF TEST
A seed analysis is useless without a test date. Obviously things like purity, crop, weeds and inert are not going to change over time but germination and dormant or hard seed can change dramatically. Each state has a maximum allowed time period since the last test. The test date restriction is set by each state, therefore there are several different limitations depending upon which state the seed is sold in. Nine and six months are the most common maximum limits. Always check the test date and only buy seed that has been tested within the time limit of your state, check with your State Dept. of Agriculture.
The test date, in some cases can tell you something about how old the seed is. Native warm season grasses are harvested during late summer through fall and early winter. Conditioning usually take place during fall and winter months. Seed samples are submitted for testing soon after cleaning. If you were to buy native grass seed in December and the test date showed the analysis was performed in July you would know the seed was harvested during a previous year and was not the current year's crop. It is still within the allowed time restriction so there is no real reason to be concerned. There is one instance in which you should be aware. Be cautious of seed purchased in the fall with a test date near the 9 month limit. That seed has been carried over the summer since the last test and could have gone through some significant changes (germination drop) if not stored properly. Ask how the seed is stored. If your supplier doesn't keep it in some sort of controlled storage and the original test reports low germ, do not buy that seed. Low germ usually means low vigor and if the seed has lost germination over the summer you could be buying a sack of dead seed. Ask for a new test or wait until new crop is available. In contrast, if the seed showed a high dormancy rate it is most likely that a portion of the dormancy has "broke" and as a result would give a better initial stand.
ORIGIN
The state the seed was grown in will be listed as the origin, but may be misleading. Cave-in-rock switchgrass genetically originates from southern Illinois but can be grown nearly anywhere east of the Rockies. If grown in Pennsylvania the tag would read: ORIGIN: PA. Is it's true origin Pennsylvania? For non-varietal native seed origin would be used to identify local seed, which may be important for some projects. Usually the state of origin is not specific enough for those projects. Ultimately you would have to ask the supplier for a more specific location.
COMING TO YOUR SENSES
The first reaction most people have when they see native grass seed is, "Where is the seed, that's just a bunch of trash.". The seeds of the chaffy grasses, big bluestem, indiangrass and little bluestem are so unique, without experience, you can't tell if the seed is true to the stated purity. However, if you haven't succumbed to a severe attack of hay fever you can use the sense of smell to identify a problem. If the seed smells musty or moldy it has probably been stored improperly or it is old seed. Call your supplier and inform them of the situation. They should offer an explanation or an exchange. If you are not satisfied with the explanation ask for a copy of the original seed test signed by a registered seed technologist. >From the test apply some of the information you have just read to determine if it is current crop or old seed. Most generally current crop seed, which smells musty, if planted will still stand up to test. Be sure not to carry any of the seed over to plant next year. Old seed which smells musty should be avoided. Commonly the germination is unpredictable.
IN A NUT SHELL
If you just can't quite put all of this together just follow these basic rules. Always buy native seed on the basis of pure live seed. Do not buy untested seed or seed "out of test". Do not buy low quality seed at 1st quality price and if you are depending upon production, ask about dormancy. It is best to buy from a reputable dealer or someone you trust. If your supplier can't or doesn't want to answer any of the questions I've suggested - Shop elsewhere!
TABLE 1: SUGGESTED RANGE OF STANDARDS FOR 1ST QUALITY CURRENT CROP NATIVE GRASS SEED.
| SPECIES |
PURE SEED
RANGE (%) |
TOTAL LIVE SEED
RANGE (%) |
MINIMUM PLS |
| Big Bluestem |
60 - 90 |
50 - 90 |
30% |
| debearded |
70 - 95 |
50 - 90 |
35% |
| |
| Indiangrass |
70 - 98 |
50 - 90 |
35% |
| debearded |
90 - 98 |
50 - 90 |
45% |
| Little Bluestem |
40 - 70 |
50 - 90 |
20% |
| debearded |
60 - 80 |
50 - 90 |
30% |
| |
| Sideoats Grama |
65 - 90 |
50 - 90 |
33% |
| |
| Switchgrass |
90 - 99 |
65 - 90 |
58% |
A reputable dealer should be able to supply seed near the upper range of purity in most years. Germination and dormancy are variable from year to year and the conditioner has little control over total live seed rates.
TABLE 2: EXAMPLES OF SOME TYPICAL WEEDS.
| Prohibited Noxious |
Restricted Noxious |
| Canada Thistle |
Giant foxtail |
| Johnson grass* |
Buckhorn |
| Field Bindweed |
Dodders |
| Quackgrass* |
Horse nettle |
| Russian Knapweed |
Cocklebur |
*Each state develops its own list of Prohibited and Restricted noxious weeds. Weeds listed as Prohibited in some states may be Restricted in others.
