TURFGRASS MATH
Pure Live Seed : Does it Really Matter ?
By Cale A . Bigelow , Ph . D .
Rapid establishment of a dense , persistent turf from seed relies on planting a viable optimal target seedling density . Target seeding rates , however , vary by individual species and seed size . For example , spreading grasses such as Kentucky bluegrass with smaller but numerous seeds per pound have a lower suggested seeding rate ( e . g ., 1-2 pounds / 1,000 ft ²). By contrast , bunch-type grasses such as perennial ryegrass possess large but less numerous seeds per pound and , in turn , have a higher suggested seeding rate ( e . g ., 6-9 pounds / 1,000 ft ²).
Seeding rate guidelines have been developed over decades of research and practical observations , and take into account factors such as seed size , growth habit , the presence of seed hulls , seed age and additional considerations ( such as if one is planting on bare soil or into an existing turf ). Other factors may include target planting date , soil temperature at seeding , the availability of water to keep the seed moist during the germination process , and sometimes even differences in soil texture ( e . g ., seeding into a sandbased rootzone , etc .).
Ultimately , there are numerous sources for seeding rate guidelines ( See table below from Columbia Seeds or visit Seed Research of Oregon at https :// www . sroseed . com / technical-specs / seeding-specifications ). While subtle differences may exist , in general , published guidelines are similar with the goal of rapid , healthy establishment .
Once a target seeding rate is determined , there is another important but often overlooked factor that must be considered if you want to achieve your target planting density . This is referred to as pure live seed ( PLS ). In other words , what percent of the desired species in the seed bag is actually viable and most likely to establish under optimal field conditions ? In simple terms , PLS is the percentage purity of a given species / cultivar multiplied by the percentage germination . For example , if a given turfgrass species listed on a seed label contains 95 % purity and has a lab-tested germination rate of 90 %, the PLS would be equivalent to 85.5 % PLS .
95 % purity x 90 % germination = 85.5 % PLS
18 SportsField Management | May 2024 sportsfieldmanagementonline . com