produces what are known as cultivars. A cultivar is a cross-breed of two different varieties of grass and aims to combine certain traits taken from each individual breed. This creates a new strain which can be very specialised, suited to a particular environment, such as low water, low light or low nutrient. Cool season grasses Cool season grasses start growth at , and grow at their fastest rate when temperatures are between and , in climates that have relatively mild/cool summers, with two periods of rapid growth in the spring and autumn. They retain their color well in extreme cold and typically grow very dense, carpetlike lawns with relatively little thatch. Bluegrass (Poa spp.) Bentgrass (Agrostis spp.) Ryegrasses (Lolium spp.) Fescues (Festuca spp.) Feather reed grass (Calamagrostis spp.) Tufted hair grass (Deschampsia spp.) Warm season grasses Warm season grasses only start growth at temperatures above , and grow fastest when temperatures are between and , with one long growth period over the spring and summer (Huxley 1992). They often go dormant in cooler months, turning shades of tan or brown. Many warm season grasses are quite drought tolerant, and can handle very high summer temperatures, although temperatures below can kill most southern ecotype warm season grasses. The northern varieties, such as buffalograss and blue grama, are hardy to . Zoysiagrass (Zoysia spp.) Bermudagrass (Cynodon spp.) St. Augustine grass (Stenotaphrum secundatum) Bahiagrass (Paspalum spp.) Centipedegrass (Eremochloa ophiuroides) Carpet grass (Axonopus spp.) Buffalograss (Bouteloua dactyloides) Grama grass (Bouteloua spp.) Kikuyu grass (Pennisetum clandestinum) Grass alternatives Carex species and cultivars are well represented in the horticulture industry as 'sedge' alternatives for 'grass' in mowed lawns and garden meadows. Both low-growing and spreading ornamental cultivars and native species are used in for sustainable landscaping as low-maintenance and drought-tolerant grass replacements for lawns and garden meadows. wildland habitat restoration projects and natural landscaping and gardens use them also for 'user-friendly' areas. The J. Paul Getty Museum has used Carex pansa (meadow sedge) and Carex praegracilis (dune sedge) expansively in the Sculpture Gardens in Los Angeles. Some lower sedges used are: Carex caryophyllea (cultivar 'The Beatles') C. divulsa (Berkeley sedge) C. glauca (blue sedge) (syn. C. flacca) C. pansa (meadow sedge) C. praegracilis (dune sedge) C. subfusca (mountain sedge) C. tumulicola (foothill sedge) (cultivar 'Santa Cruz Mnts. selection') C. uncifolia (ruby sedge) Grass seed for shade Grass seed mixes have been developed to include only grass