Author: Dianne DeLongchamps
How do I control crabgrass and dandelions in Colorado bluegrass lawns?
For crabgrass, CSU Extension gives northern Front Range homeowners a date: apply pre-emergent by mid-April. For dandelion control , CSU puts the best window for treating perennial broadleaf weeds at early September to early November. Underneath both, lawn density does the heavy lifting, thick turf denies both weeds the opening they need.
These are the two weeds we get asked about most across Fort Collins, Windsor, and Timnath. At Clean Air Lawn Care we formulate our own bio-based weed blend, Moose Juice, for the clover, dandelions, and other weeds that keep showing up in Northern Colorado yards. It goes down alongside natural pre-emergents, paired with our non-toxic organic fertilizers and Luke’s mowing standard: 3 inches minimum, 3.5 in July and August. No synthetic herbicides. Both weeds are opportunists that move into thin, stressed turf.
When should I apply crabgrass pre-emergent in Northern Colorado?
CSU Extension’s PlantTalk 1541 is specific:
“Apply preemergent products by mid-March in Pueblo and Grand Junction, by early April in the Denver metro area, and by mid-April in the northern Front Range.”
Fort Collins, Windsor, and Timnath are the northern Front Range. Mid-April. That’s your outside edge.
CSU adds an adjustment: “Sites that warm earlier in the spring like southern exposures and turf near sidewalks should be treated earlier than these dates.” The strip along a south-facing driveway warms weeks ahead of the middle of the backyard. That’s why crabgrass shows up along hard edges first.
CSU frames it from the germination side too. Crabgrass germination “generally begins when surface soil temperatures reach 55 to 60 degrees F”, not the 50-55°F figure that circulates widely, and “Along the northern Front Range, it can germinate from mid-April to mid-May.” CSU recommends applying “preemergence herbicides two to four weeks before” germination begins.
So the working window here is late March into early April, with mid-April as the deadline. Earlier on warm southern exposures and near concrete.
A pre-emergent applied in May lands on already-germinating crabgrass. And the window stretches to mid-May, so one early application has a long tail to cover.
When is the best time to kill dandelions?
Most people have this backwards. Spring is when dandelions are loud. Fall is when they’re vulnerable.
CSU: “The best time to apply a general-purpose broadleaf herbicide to control perennial broadleaf weeds such as dandelion, plantain, and clover is early September to early November.”
CSU sets expectations: “Multiple herbicide applications may be necessary to completely control difficult perennial weeds, including dandelions.” One pass in one autumn isn’t usually the whole story.
Does mowing or pulling get rid of dandelions?
Mowing. Not at all. Because it grows from a basal rosette that is lower than a mower blade can reach, mowing will have no effect on dandelion control. You remove the flower and leave the plant.
Hand-pulling, at least the casual kind. UC IPM: “Removing dandelions by hand-pulling or hoeing is usually futile, unless done repeatedly over a long period of time, because of the deep tap root system.”
That taproot is “most commonly found in the top 6 to 18 inches of the soil,” and that’s why partial pulls fail: “Sections of the root as short as 1 inch are also capable of generating new plants.” Snap it at four inches and you’ve left behind a plant.
Hand-pulling isn’t useless. It works with a weeding tool, in soft ground after watering, repeated over a long stretch. Most of us don’t sustain that, which is why density is the real control here.
How does mowing height help control crabgrass?
CSU puts turf health first: “The best way to control crabgrass and related annual grassy weeds in lawns is to maintain healthy grass with proper seeding, mowing, watering and fertilizing, and judicious use of herbicides.”
University of Minnesota Extension puts a number on it: “Raising mowing heights to at least 3 inches reduces the amount of sunlight that reaches the soil, reducing crabgrass seed germination.”
Three inches. That’s the floor we give every customer, 3.5 in July and August. We didn’t set it because of crabgrass, but the height that protects turf through heat is the same one that shades out germinating crabgrass seed. Vertical edging helps too, clean hard edges without scalping the strip where crabgrass most wants to start.
CSU’s published mowing band is 2 to 3.5 inches in PlantTalk 1515 and 2.5 to 3 inches in Fact Sheet 7.202. Our 3-inch minimum is our own standard, at the top of theirs. CSU is clear on going low: mowing under two inches “can reduce drought and heat tolerance, and cause a higher incidence of insect, disease and weed pest problems.”
Everything else that thickens turf works on both weeds at once: overseeding thin areas in CSU’s mid-August to mid-September window, relieving compaction so roots can build, and watering 1 to 2 inches a week across two to three deep waterings. Why Is My Lawn Thin or Patchy?
Our natural weed control: https://cleanairlawncare.com/services/natural-weed-control/
Luke jokes that dandelions are Colorado’s unofficial state flower, given how often we get asked about them. But the thing we keep coming back to is that a thick, well-fed lawn handles both of these better than any single application ever will. If you’ve been fighting the same weeds year after year, let’s talk about what’s happening underneath — that’s usually where the fix lives.
Clean Air Lawn Care Northern Colorado is owned by Dianne, Paul, and Luke DeLongchamps — a family business serving Fort Collins, Windsor, and Timnath with organic lawn treatments and solar-powered electric equipment.
