Historically, lawn seed included clovers and other legumes which provided nitrogen to the associated turfgrass; however, increased reliance on herbicides and altered aesthetic preferences have resulted in an emphasis on uniform, green turf monostands. A return to clover inclusion has the potential to increase the sustainability of low-input urban grasslands by providing pollinator forage, enhancing or extending green cover and competitiveness, reducing additional nitrogen requirements, and providing visual appeal. Most research on clover inclusion in turf has focused on white clover (Trifolium repens). Alternative clover options for use in cool-season turf have not been as widely tested. This study evaluated fertilized (9.76 g N m-2 yr-1) and unfertilized Kentucky bluegrass grown as a monoculture or in mixtures with individual clover species. Clover species included white, rose (T. hirtum), crimson (T. incarnatum) and strawberry (T. fragiferum) clovers seeded at 65 PLS m-2.
The objectives of this study were to evaluate 1) Kentucky bluegrass/clover mixtures for persistence, quality and competitiveness and 2) how nitrogen fertilization impacts mixture quality and composition. A 100-point quadrat was used to evaluate weekly percent cover of turfgrass, clover and weeds. Any weeds present were identified but not removed. Pictures were taken weekly with a light box and analyzed for quality (1-9 scale; 6 is minimal acceptable quality) using Turf Analyzer software.
Results/Conclusions
All clovers established well, though crimson clover struggled to recover from the initial mowing (10 cm) after reaching foliage height >30 cm during establishment. During the first season (Fall 2019), unfertilized crimson and rose clover mixture quality was lower than turfgrass monostands. White and strawberry clover mixtures maintained similar or greater quality than monostands but rarely achieved minimum acceptable quality.
Clover dominated stand composition (>50% stand) in mixtures except in fertilized crimson clover mixtures. Fertilization increased grass cover except in white clover mixtures. Weed competition in clover mixtures was similar to or less than fertilized and unfertilized turfgrass monostands, respectively. Tall fescue (Festuca arundinacea) was the most prevalent weed (60% of all weeds present).
Variations in leaf color can impact quality ratings but these variations, along with the flowers, can add visual interest to an urban grassland. White and strawberry clovers exhibit dark green color; crimson clover is a yellow-green color. All three are prolific flower producers. Rose clover vegetation is gray-green and often displays red watermarks. Rose clover did not flower in Fall 2019.