Purchasing the highest quality seed possible is always a good investment. Poor establishment resulting from improper cultural practices will negate the monetary investment in purchasing high quality seed. However, poor quality seed will almost never result in a well-established lawn no matter how good the cultural practices.
Purchasing high quality seed can be easier by understanding a few basic terms on the grass seed label. See Table 5.2 for an example seed label. All labels must provide information about the grass seed purity, its germination potential, crop seeds present, weed seeds present, noxious weeds present and inert components in the package.
Table 5.2. Example Seed Label (company and variety names are fictitious)
WILL-GROW SEED COMPANY
Lot No: 1234-B Test Date: month/year
|44%||Arctic Creeping Red Fescue||85%|
|31%||Blue Ribbon Kentucky Bluegrass||80%|
|9%||Wilson Chewings Fescue||85%|
|12%||Gopher Perennial Ryegrass||90%|
|Noxious Weed Seed: None found|
Purity is the percent by weight of pure seed, crop, weed, and inert ingredients in the package. These percentages added together should total 100 percent. Purity is concerned only with quantity, not quality. That is, not all seeds present in the package are capable of growing. The term pure live seed is the calculated amount of seed that actually has the capability to germinate and, given favorable conditions, continue to grow. It is determined by multiplying the purity percentage by the listed percent germination on the label. For example, 31 percent Kentucky bluegrass (purity) multiplied by a germination percentage of 80 percent equals 24.8 percent. This is the percentage of Blue Ribbon Kentucky bluegrass variety that one would expect to grow under optimum germination conditions. It should be apparent that one would always seek to purchase grass seed with the highest germination percentage possible.
Table 5.3. Calculating Pure Live Seed (PLS)
Percent of Purity x Germination Rate = Pure Live Seed per pound of seed mix
Calculation for Blue Ribbon Kentucky Bluegrass (from Table 5.2):
31% ÷ 100 = 0.31 Purity
80% ÷ 100 = 0.80 Germination
0.31 (Purity) x 0.80 (Germination) = 0.248
0.248 x 100 = 24.8% Pure Live Seed (PLS)
Calculation for Gopher Perennial Ryegrass (from Table 5.2):
12% ÷ 100 = 0.12 Purity
90% ÷ 100 = 0.90 Germination
0.12 (Purity) x 0.90 (Germination) = 0.108
0.108 x 100 = 10.8% Pure Live Seed (PLS)
Now calculate the two remaining turfgrass varieties in Table 5.2:
Artic Creeping Red Fescue: [0.44 (Purity) x 0.85 (Germination)] x 100 = 37.4% PLS
Wilson Chewings Fescue: [0.09 (Purity) x 0.85 (Germination)] x 100 = 7.65% PLS
Germination is the percentage of seed that will germinate and grow in an ideal laboratory environment during a prescribed length of time. Since field conditions rarely ever duplicate these laboratory conditions, it is especially important to purchase seed with the highest germination percentage possible. As noted above, this is the percentage used in the determination of pure live seed.
Crop is the percent by weight of seeds normally considered to be grown as an agricultural crop, including hay. This can include other types of grasses that may be undesirable in a lawn situation. This percentage should be as close to zero as possible.
Weeds refers to the percent by weight of all seeds in the package that are not otherwise listed in pure seed or crop. It is not required to identify these weeds or how many there are since this is on a percent by weight basis. For example, 1 or 2 large seeds of a weed would pose no particular threat to the new lawn. However, some tiny seeds that weigh very little, such as chickweed, can account for many thousands of weed seeds distributed over a 1000 ft2 of lawn area. This percentage should always be as low as possible.
Noxious weeds are listed as the number per pound not as percentage per pound. Noxious weeds are weedy plants considered by individual states to be very difficult to control and could pose hazards to humans, livestock and the environment. While this is often more of a problem in farm crop seed, one should always purchase grass seed without the contamination of any noxious weeds.
Inert is the percent of material contained in the package that will not grow under any condition. Broken and damaged seeds, chaff, and empty seed hulls are just some of the more common inert material included. Obviously, this percentage should be as low as possible.
Considering Seed Weight vs. Seed Count
The Federal Seed Act requires that grass seed be listed on the label by weight and that it be separated into two broad categories: fine-textured grasses and coarse-textured grasses. However many of the grasses vary significantly in their respective seed sizes and consequently vary significantly in the number of seeds per pound.
A more accurate description of the grass seed contents contained in a package is to list their percentage by seed count rather than percentage by weight. For example, large seeds (such as those of perennial ryegrass) are quite heavy and take only about 250,000 seeds to make one pound.
On the other hand, Kentucky bluegrass is much smaller and therefore a much lighter seed by weight than perennial ryegrass. In fact, Kentucky bluegrass requires from 1 to 2 million seeds depending on variety to make a pound. Table 5.4 contains the number of seeds per pound for several common lawn grasses.
Table 5.4. Ranges for the Number of Seeds per Pound for Several Cool-Season Lawn Grasses
|Creeping bentgrass||5-8 million|
|Kentucky bluegrass||1-2 million|
|Fine-leaved fescue||400 to 500 thousand|
|Perennial ryegrass||200 to 250 thousand|
Table 5.5 illustrates how to calculate seed count.
Table 5.5. Calculating Seed Count using Example Seed Label (Table 5.2) Seed Mix
Purity (Table 5.2) x Seed Count (Table 5.4) = seeds per pound of variety (cultivar) in the seed mix
Example Blue Ribbon Kentucky Bluegrass:
31% x 1,000,000 to 2,000,000 = 310,000 to 620,000 seeds per lb in mix
Example Gopher Perennial Ryegrass:
12% x 200,000 to 250,000 = 24,000 to 30,000 seeds per lb in mix
Now calculate the two remaining turfgrass varieties in Table 5.2:
Artic Creeping Red Fescue: 44% x 400,000 to 500,000 = 176,000 to 220,000 seeds per lb in mix
Wilson Chewings Fescue: 9% x 400,000 to 500,000 = 36,000 to 45,000 seeds per lb in mix
Calculating the actual amount of seed for each variety or species will give a more realistic description of what is actually contained in any seed mixture or blend. Depending on the intended use of the seed mix, additional varieties or species can be added to better match the site conditions.
In the upper Midwest, Kentucky bluegrass, fine fescue, and some of the perennial ryegrass cultivars are recommended. However, before a seed mix is selected, carefully evaluate your site and note potentially troublesome areas. See Table 5.6 for information on selecting the proper grass seed for your site.
Table 5.6. Guidelines for Selecting Grass Seed
First Things First: Right Seed - Right Place - Right Function
- Like most aspects of landscape plant selection, choosing the right plant for the desired location is of utmost importance for long-term plant health. In addition, when choosing turfgrass varieties, blends or mixes, it is very important to match the intended use of the lawn area with the proper types of grasses. Following are some examples to help you match appropriate turfgrasses with intended function:
- Full-to-partly sunny conditions with minimal traffic or wear, low-to-moderate inputs intended: 60% to 70% Kentucky bluegrasses, 20% to 30% fine fescues, ~10% perennial ryegrass.
- Full-to-partly sunny conditions with moderate-to-high levels of traffic and/or wear, moderate-to-high inputs required for rapid recovery: 75% to 85% Kentucky bluegrass; ~15% to 20% perennial ryegrass.
- Shaded for a portion of the day or receives partial shade all day with minimal traffic or wear, primarily a dry shade: 65% to 75% fine fescue; 25% to 35% Kentucky bluegrass (shade tolerant cultivars); ~10% perennial ryegrass.
- Shaded for a portion of the day or receives partial shade all day with minimal traffic or wear, typically a moist shaded area: 30% to 40% fine fescue; 25% to 35% Poa trivialis*; 20% to 30% Kentucky bluegrass (shade tolerant cultivars); ~10% to 15% perennial ryegrass.
- Full sun-to-very light shade, little to no inputs intended: 70% to 85% fine fescues; 10% to 20% common Kentucky bluegrass; 5% to 10% perennial ryegrass.
- Be a little cautious when adding perennial ryegrass to a mix. Research has shown that a 50/50 mix of Kentucky bluegrass to perennial ryegrass results in a stand that may be dominated by perennial ryegrass even though there are many more seeds of bluegrass than perennial ryegrass in the mix.
- Because of the seedling vigor of annual ryegrass, it is sometimes used in general-purpose seed mixes; but almost never in mixes for "elite" or "premium" turf.
* Poa trivialis is a lighter green and more horizontally growing form of bluegrass. Those that do not prefer this type of color and growth habit should select a seed mix that does not contain this species.
For more about purchasing grass seed see:
Proceed to Seeding Rates and Planting Methods.