In Denver, as elsewhere in Colorado, many varieties of grass are well suited to grow. Most are cool-season varieties, which include perennial ryegrass, tall fescue and Kentucky bluegrass, the most widely used turfgrass in the state. Warm-season grasses like buffalograss are also an option, and most lawns actually contain a blend of grasses.
Seeding is a relatively inexpensive way to establish a lawn. Seed cool-season grasses in late summer; the best time is roughly from August 15 to September 15. Plant warm-season grasses in May or June. If you are reseeding unhealthy or bare patches in your lawn after the winter, you can do so in early spring.
Sod is more expensive than seed, but has an advantage in that it provides an almost instant lawn. You can lay sod any time during the growing season. Avoid planting too late in fall, because roots need to establish before they freeze. And if you sod in summer, water three times per day for the first two weeks.