Taller grass, deeper roots
The single biggest change most Denver lawns need is a higher mower deck. Colorado State University’s extension experts and the state’s landscape contractors recommend cutting Kentucky bluegrass to 2.5 to 3 inches, and raising the deck to 3 or 4 inches in dry stretches. Most mowers roll out of the store set lower than that.
Height matters here more than it does in a wetter place. A taller blade of grass shades the soil, so it loses less water to the sun and the wind. It also grows a deeper root to match, and a deep root is what gets a lawn through a July week with no rain. Short grass does the opposite: shallow roots, hot soil, and bare patches where the weeds move in.
The one-third rule
Never take off more than a third of the blade in one mowing. Cut a 4-inch lawn to 3, not to 2. Taking more than that shocks the plant, and it spends the next week recovering instead of growing roots. In May, when bluegrass and fescue are growing fastest, that can mean mowing twice a week, which is tedious and also correct.
A sharp blade is the other half of the rule. A dull blade tears the grass instead of cutting it, and the torn tip browns and dries out. If the lawn looks faintly grey two days after mowing, the blade is dull. Sharpen it in spring and again in midsummer, or keep a second blade and swap.
Water by the rules
Denver Water’s summer rules run from May 1 to October 1 every year: no watering between 10 in the morning and 6 in the evening, when most of it evaporates, and a limit on how many days a week the sprinklers run. In a normal year that limit is three days. In 2026 the utility declared a Stage 1 drought and cut it to two assigned days a week, so check the current rule before you set the controller, and check again if the summer turns dry.
Fewer, deeper waterings beat a daily sprinkle. The goal is to wet the soil 6 inches down and then let the top dry, which is what trains the roots to go deep. New sod or seed is the exception, and the utility issues a short-term permit for establishing it.
Leave the clippings
Clippings left on the lawn aren’t thatch. They’re mostly water and they break down in days, returning nitrogen to the soil. Bag them only when the grass was wet or too long and the clippings sit in clumps, and then compost them rather than sending them to the landfill.
Edging and trimming finish the job: a clean line along the walk and the beds, and the trimmer run along fences and posts the mower can’t reach. Blow the clippings back onto the lawn, not into the street, where they wash into the storm drains.
A season at a glance
- April. First mow once the grass is growing. Sharpen the blade. Set the deck to 3 inches and leave it there.
- May and June. Mow often, twice a week if it needs it. Start the sprinklers under the summer rules, deep and infrequent.
- July and August. Raise the deck to 3.5 or 4 inches. Mow in the morning or evening, not in the heat. Expect some browning in a dry spell; it recovers.
- September. Best month to seed thin spots and fertilize. Keep mowing.
- October. Last mows a little shorter, down toward 2.5 inches, before the first hard freeze. Blow out the sprinklers.
Mow high, cut a third, water deep and early. The rest is edging.