The Grass Seed Tag, Read Line by Line

Why this matters

Overseeding is one of the few services where the customer pays now and judges in six weeks, and the seed tag decides more of that judgment than the aerator does. A cheap bag with a low germination figure and a high other-crop number can put fewer live seeds on the lawn than its weight suggests and plant clumps of coarse grass that will be there for years. The tag is a regulated label printed in a fixed format, so every bag on the shelf can be compared in a minute once you know which lines carry the weight.

Overseeding method and timing belong to 'Overseeding Techniques for Cool-Season and Warm-Season Lawns' and 'Fall Core Aeration & Overseed'. This card is the tag.

Who makes the tag say what it says

Seed sold across state lines is labeled under the Federal Seed Act and its regulations at 7 CFR Part 201, administered by USDA. Seed sold within a state is labeled under that state's seed law, which most states have written in close agreement with the federal format. State law also sets two things that vary: the list of noxious weed seeds (and which are prohibited outright versus restricted to a stated count), and how old the germination test may be at the point of sale. The test-age allowance is commonly on the order of nine months for ordinary packaging, with longer allowances for seed in sealed moisture-proof containers; your state department of agriculture publishes its figure.

The tag, as printed on the bag

An illustrative mock of a tall fescue blend with a little Kentucky bluegrass, laid out the way most lawn seed tags are.

 LAWN SEED - TALL FESCUE BLEND        Lot TF-2291
 ----------------------------------------------
 PURE SEED  VARIETY / KIND              GERM
  31.60%    Variety A tall fescue        90%
  31.50%    Variety B tall fescue        90%
  25.40%    Variety C tall fescue        85%
   9.80%    Variety D Kentucky bluegrass 80%
 ----------------------------------------------
   0.30%    Other crop seed
   1.35%    Inert matter
   0.05%    Weed seed
            Noxious weeds: none found
 ----------------------------------------------
 Test date: 08/25    Origin: OR
 Net weight 50 lb    Labeler name and address

Read across a row and down a column. The pure seed column and the three lines below it add to 100%: 31.60 plus 31.50 plus 25.40 plus 9.80 is 98.30, and 0.30 plus 1.35 plus 0.05 is 1.70. If a tag does not add to 100, you are misreading a line.

What each line means

Variety and kind. The kind is the species (tall fescue, Kentucky bluegrass). The variety (or cultivar) is the named selection within it. A tag that says "tall fescue, variety not stated" (often printed VNS) is legal and tells you nothing about disease resistance, color or texture. Named varieties let you look up performance in turf trial data, such as the National Turfgrass Evaluation Program's. "Kentucky 31" is a common older tall fescue, coarse in texture, and a frequent source of clumpy-looking patches in an otherwise fine lawn.

Pure seed (percent by weight). The share of the bag's weight that is seed of the named kind and variety. It says nothing about whether that seed is alive.

Germination (percent of the pure seed). The share of the pure seed that sprouted under standard laboratory conditions in the test. Some tags split it into germination plus dormant or hard seed, which is seed that was alive but did not sprout during the test period; the total is the figure to use. Germination falls as seed ages, faster in heat and humidity, so the figure is only as good as its test date.

Other crop seed. Seed of crops or grasses other than those named. In lawn seed this is where unwanted grasses hide: bentgrass in a fescue lawn, orchardgrass, timothy, sometimes bermudagrass in cool-season seed. Even a fraction of a percent is a lot of seeds, because grass seed is small and a pound of it is hundreds of thousands of seeds or more. A premium lawn blend often states 0.00% here, and that line alone is worth reading before price.

Inert matter. Chaff, broken seed, dirt, seed coating material. Coated seed carries a large inert figure because the coating is counted here; that is not a defect, but it does mean less seed per pound.

Weed seed. Seed of plants the seed law treats as weeds. Some labs and states count annual bluegrass here; in others it may appear under other crop. Either way it matters on a lawn.

Noxious weeds. Weeds named on your state's noxious list. Prohibited noxious weeds are not allowed in seed sold in that state at all; restricted noxious weeds are allowed up to a stated count per unit weight and must be named with their count on the tag. "None found" is the line you want.

Test date. The month and year the germination test was done. This is the line that ages.

Origin and lot. Where the seed was grown and the lot it came from. Write the lot number on the work order; it is how a germination complaint or an off-type grass gets traced.

Pure live seed: the number that is actually planted

The tag gives pure seed and germination separately. The share of the bag's weight that is live seed of the kind you want is their product, called pure live seed (PLS):

PLS % = pure seed % x germination % / 100.

For a blend, work each line and add. From the mock tag:

• Variety A: 31.60 x 0.90 = 28.44
• Variety B: 31.50 x 0.90 = 28.35
• Variety C: 25.40 x 0.85 = 21.59
• Variety D: 9.80 x 0.80 = 7.84
• Total PLS: 28.44 + 28.35 + 21.59 + 7.84 = 86.22%

So about 86 lb of every 100 lb in this bag is live seed of the four named grasses. The other 14 lb or so is dead or dormant seed, other crop, inert matter and weed seed.

Worked example: two bags for one overseed

A crew lead is pricing an overseed of 8,000 square feet of thin tall fescue lawn after core aeration. Two bags are offered. Bag 1 is the mock tag above. Bag 2 is a cheaper contractor mix: tall fescue, variety not stated, 85.00% pure seed, 80% germination, 2.50% other crop, weed seed 0.40%, test date 14 months ago.

Step one: the rate on the bag. Bag 1's directions give an overseeding rate; say 4 lb per 1,000 sq ft (illustrative; the real figure comes from the tag or the bag's directions, and from your own overseeding standard). That rate was written for Bag 1's own seed, so it carries Bag 1's PLS inside it.

Step two: live seed per 1,000 sq ft from Bag 1. 4 lb x 0.8622 = 3.45 lb of PLS per 1,000 sq ft.

Step three: Bag 2's PLS. 85.00 x 0.80 = 68.0%.

Step four: how much of Bag 2 delivers the same live seed. 3.45 lb PLS / 0.680 = 5.07 lb of Bag 2 per 1,000 sq ft. Check it the other way: 5.07 x 0.680 is 3.45. That is about 27% more product by weight (5.07 against 4.0 lb), so a lower price per pound has to beat that margin before it is cheaper per live seed.

Step five: the job totals. At 8,000 sq ft (8 thousand-square-foot units), Bag 1 is 4 x 8 = 32 lb. Bag 2 is 5.07 x 8 = 40.6 lb, which is most of one 50 lb bag either way.

Step six: what else goes down with it. Other crop seed in the job: Bag 1, 32 lb x 0.30% = 0.10 lb. Bag 2, 40.6 lb x 2.50% = 1.0 lb, roughly ten times as much. Weed seed: Bag 1, 32 x 0.05% = 0.016 lb; Bag 2, 40.6 x 0.40% = 0.16 lb, again about ten times as much. On a lawn that has just been aerated, every one of those seeds has a seedbed.

Step seven: the test date. Bag 2's test is 14 months old. Its real germination today is likely lower than the 80% printed, and in many states it may be past the allowed test age for sale; ask the supplier for a current test or do not use it. Bag 1's test date has to be inside your state's allowance on the day the seed goes down, not just the day it was bought; a bag that was current in spring can be stale by a fall job.

Decision. Bag 1. Bag 2 needs 27% more weight for the same live seed, plants ten times the other crop and weed seed, and has a germination figure nobody can rely on.

What would change the answer. Coated seed, where much of the weight is coating: its PLS is lower by design, and its own label rate already accounts for that, so compare live seed, not pounds. A spring overseed on a lawn that will get a pre-emergent shortly afterward: the seed tag is no longer the main decision, because many pre-emergents prevent desirable seed from establishing too; the label of the pre-emergent product governs the interval. A warm-season lawn overseeded with perennial ryegrass for winter color: the rate is much higher and the other crop line matters less, because the rye is temporary.

Habits that keep a tag honest

• Read the tag on the bag you are opening, not the one on the shelf last season. Lots change.
• Store seed cool and dry, off the trailer floor. Germination drops faster in a hot trailer than in a climate-controlled shop.
• Keep a photo of the tag with the job record, next to the lot number.
• Do not mix bags in the hopper without working the combined rate; two partial bags with different PLS figures give a rate neither tag supports.

References

• Federal Seed Act and its regulations at 7 CFR Part 201 (USDA), for seed sold in interstate commerce
• Your state's seed law and noxious weed seed list (state department of agriculture), including the germination test-age allowance
• See related: Overseeding Techniques for Cool-Season and Warm-Season Lawns; Fall Core Aeration & Overseed
• National Turfgrass Evaluation Program (NTEP) trial results, for comparing named varieties