David M. Kopec, Extension Turfgrass Specialist
Selection of the proper turfgrass variety for a lawn, based on the site and intended use is the major consideration for successful performance of a lawn. If you have selected a turfgrass which will be established from the seed, the next question is to acquire the seed for planting. In order to better understand what's in the "seed bag," you should be able to read the "seed tag." The seed tag is a legal document which contains important information about the integrity and condition of the varietie(s) and other materials sold to you as the final product. For seed that travels from state to state, Federal Seed Act (FSA) requirements must be met which requires the following information.
1) Seed Lot Number: (used for permanent identification).
2) Kind of Seed: (accepted or common crop name). Examples: perennial ryegrass, tall fescue, common bermudagrass.
3) Percent Pure Seed: This is the amount of seed by weight for each variety. This includes the name(s) of the variety or varieties included. If no variety is claimed, then VNS (variety not stated) appears on the tag.
4) Other Crop Seed: This includes either other un-named varieties of the desirable turfgrass species, or other species of other grasses or crop seeds. This can be up to 5% by weight of the seed bag.
5) Weed Seed: This is the percent by weight of the seed bag which contains either noxious weeds, and/or other weed seeds. If noxious weeds are present, then usually strict limits are imposed as tolerance limits.
6) Inert Matter: This includes the amount of non-seed materials by weight. Soil particles, broken seeds, awns and short stems are items included in the percent inert matter.
Note: The amount of pure seed, other crop seed, weed seed and inert contents equals 100%.
Quality of the Turf (Crop) Seed Itself
The seed tag also bears information regarding the germination capability of the seed, which is tested under strict laboratory conditions for each species.
The percent germination indicates what percent of the actual seed itself will germinate (under optimum conditions). The date (month and year) of the germination test is included on the seed tag. For seed which travels as interstate commerce (essentially all our cool season turf grasses are from other states) the germination test information is applicable for a period of five months after the test month. For in-state seed produced in Arizona (bermudagrass) the germination test is valid for nine months.
Special seed treatments (if applicable) must be noted on the tag as well. These treatments include any chemical or temperature treatments to break seed dormancy (potassium nitrate/cold storage, etc.). Any fungicide treatments to the seed would be included here as well.
If the variety has an application for, or has received a PVP (Plant Variety Protection) certificate, this too appears on the tag.
Blue Tag Certified Seed
This is the highest quality seed available. In order for turfgrass seed to achieve blue tag status, the following conditions must be met.
1) Fields have been planted with either approved foundation or breeder seed, or established with certified planting stock.
2) Variety is worthy of certification, or describable by the originator.
3) Production fields meet sanitation standards and are grown with proper isolation distances (from other plants of the same species).
4) The production fields have 0.03% or less off type plants.
5) Minimum standards for purity are met.
6) Other grass contamination limits are met.
These conditions when met, insure the buyer that the best quality seed is available to them.
Pure Live Seed - - The Rest of the Story
When following seed rate guidelines for turf (next issue), it is important to take into consideration the actual amount of seed which can be expected to germinate.
Two components of information on the seed tag allow you to do this. These two items are (1) % pure seed, and (2) % germination. If the seed is 90% pure, then the remaining 10% is not seed at all. If the germination is 85%, then on average 8.5 out of ten seeds will germinate. The remaining 1.5 out of ten seeds, will not germinate. In order to find out how much "good seed" will at maximum "germinate", you must calculate the PURE LIVE SEED (PLS) INDEX. To do this, simply multiply the % purity times the % germination.
From our discussion example above...
PLS = % purity X % germination
( 0.90 ) X ( 0.85 )
= 0.76, or 76%
This means that 76% of the product by weight will germinate, under the best conditions. So a 50 lb. bag of perennial ryegrass seed will have a PLS content of 38 lbs. Knowing this, the actual amount of seed required must be adjusted for the PLS content.
For example, a 3000 square foot lawn is to be overseeded at 20 lbs./1000 ft2 with annual ryegrass. This quickly figures to a convenient 50 lbs. of seed required. But, since the PLS content is 76% (0.76), we must now adjust and calculate how much of the actual product we need.
50 lbs. divided by 0.76 (PLS) equals 66 lbs.
We now need 66 lbs. of seed which has a PLS index of 76%, to seed 3000 ft2 of turf at the 20 lb seed rate.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.