Seeding Rate Considerations
Utilizing proper seeding rates at the time of establishment is critical to producing a functional turfgrass stand that will develop to maturity as quickly as possible. Compared with other turf management inputs, high quality seed is relatively inexpensive on a cost per acre basis. Seeding at rates that are less than optimum will result in an open turfgrass stand of low shoot density, creating a less functional surface that encourages weed invasion. Seeding at less than the recommended rate, therefore, is not an effective cost saving strategy because mangement need and associated cost will increase over the long term. In most circumstances, seeding at excessive rates will result in a stand containing a high number of small, immature (juvenile) plants. These will be slow to develop into mature and robust adult plants which are more tolerant of environmental stresses such as heat, drought, cold, and wear. Therefore it is important to avoid the temptation to seed at excessively high rates (i.e. "more must be better" mentality) which can delay or postpone turf stand development. Recommended seeding rate ranges take into account several factors such as seed size and number, growth habit, and minimum purity and germination differences that exist among species.
For recommended seeding rates by species, refer to Table 1 below. For recommended seeding rates for seed mixtures, refer to the Turfgrass Selection: Species and Cultivars chapter of our Professional Turf IPM Guide.
Seed Size and Number
Large seed varieties such as ryegrass and tall fescue require higher seeding rates than small seed varieties like bentgrass and bluegrass. There are fewer seeds per pound with large seed varieties requiring higher rates to achieve a sufficient number of plants in the stand.
Species with a spreading type growth habit (stoloniferous or rhizomatous, Table 1) such as creeping bentgrass and Kentucky bluegrass have a greater capacity to spread laterally than bunch type grasses such as tall fescue and the ryegrasses. For example, seeding spreading type grasses at less than recommended rates can over time yield a uniform, dense turf but this will take a longer period of time to achieve. Seeding rates for bunch-type grasses that are too low will produce turf with a clumpy, non-uniform, and open appearance that will likely require later overseeding to improve density. The minimum acceptable seeding rate, thefore, is more important when seeding bunch-type grasses.
Purity and Germination (PLS)
Seed of lower purity and germination has to be seeded at higher rates to compensate for lower Pure Live Seed (PLS) content. For example, to sow Kentucky bluegrass determined to be 76% by weight PLS at the recommended rate of 2 lb. per 1,000 ft2 (from Table 1) the following adjustment could be made to account for PLS using the example below. No seed is 100% Pure Live Seed (100% purity and germination) but normally is measurably less than 100% depending on the species minimum purity and germination (see Table 1). Some adjustment in seeding rate using PLS as described in Example 1 may be needed, especially if seed quality is low or when germination rate is expected to be low because of age and/or poor seed storage conditions. Refer to our Understanding a Turfgrass Seed Label fact sheet for more information on purity, germination and PLS.
Expected Field Survival
It is important to further understand that not all PLS which is technically capable of germinating should be expected to survive the germinating environment in the field, which is typically less than ideal. Any factors that contribute to high seedling mortality (death rate) would be expected to reduce the number of plants that will survive to maturity in a turfgrass stand. Actual field germination and survival may range from as high as 95% to as low as 50%. Under ideal field conditions for germination 95% survival can be expected, but with good field conditions an approximately 70% survival rate may be expected. Therefore if seedling survival rates are expected to be low because of poor conditions for germination, higher seeding rates will be required to compensate. Seeding rates in Tables 1 and 2 are given as ranges to allow for such conditions. For example, if seed bed preparation and post planting care are expected to be near ideal, then lower rates can be used. If good or less than ideal conditions are expected, then the high end of the seeding rate range is recommended.
If exceptionally poor conditions for germination and seedling survival are expected, then seeding rates should be adjusted above those rates given in Tables 1 and 2. As a general rule, seeding rates should be increased by approximately 50% to compensate for poor conditions. Factors or conditions that may contribute to poor germination and seedling survival include:
- poor soil: drainage (excessive, poor), pH, nutrient deficiency, compaction, salinity.
- improper seedbed: inadequate or excessive soil firming, excessive tilling, rocks and debris at soil surface, poor seed/soil contact or coverage, inadequate or excessive mulch, steep grades (slopes) that contribute to soil erosion.
- less than ideal seeding time: late spring/early summer mortality (drought and heat stress, weed competition, and disease); late fall/ early winter mortality (winter desiccation, frost heaves, unfavorable temperatures).
- inadequate post-planting care: not enough or too much soil moisture (irrigation), improper mowing and fertilization practices.
Generally, the better the conditions for seeding (soil type, seedbed, time of year) the less seed will be required. Late summer is the preferred period for turfgrass establishment because warm soils promote rapid germination and turfgrass development, and the long favorable time for growth (2 to 3 months) that is expected prior to the onset of winter stress is a time of reduced weed competition.
|Species||Growth Habit||seeds per/lb||seeding rate lb/1000ft2||minimum purity %||Minimum gemination %||MINIMUM Pure live seed %|
|colonial||stoloniferous||8,723,000||0.5 to 1.0||95||85||80.75|
|creeping||stoloniferous||7,890,000||0.5 to 1.0||95||85||80.75|
|kentucky||rhizomatous||2,177,000||1.0 to 2.0||90||75||
|rough||stoloniferous||2, 540,000||1.0 to 2.0||90||80||72.0|
|red||various||546,000||4.0 to 6.0||95||80||76.0|
|tall||bunch||227,000||7.0 to 9.0||95||85||80.75|
|annual||bunch||227,000||7.0 to 9.0||95||90||85.5|
|perennial||bunch||227,000||7.0 to 9.0||95||90||85.5|