Common Lawn Weeds in Western Montana and What They Mean

Why do weeds show up in my lawn?

Because there is room for them. MSU's MontGuide on maintaining lawns says plants considered weeds tend to grow in disturbed areas with bare ground or thin turf, or where there are issues like compacted soil, so you can prevent weeds by keeping the lawn healthy: adequate water and fertilizer, and aerating or overseeding thin areas with an appropriate grass. Colorado State University Extension lists what encourages lawn weeds: mowing too short or not often enough, fertilizing too much, too little or at the wrong time, and over- or under-watering.

MSU also makes a point that is easy to forget: it is often not necessary to control every weed, and many plants considered weeds provide ground cover and food and shelter for animals and beneficial insects. CSU says a completely weed-free lawn is neither practical nor environmentally sensible.

Can weeds tell you what is wrong with the soil?

Sometimes, with caution. University of Florida IFAS Extension's publication on weeds as indicators says certain weeds can reflect moisture, pH, fertility, light or compaction, but that one or two weed species are not diagnostic on their own; heavy infestations, or several species that favor the same condition, are what suggest a cultural practice should change. UF also notes some weeds thrive in many conditions, and that a soil test is the only reliable way to know pH.

Florida's weed flora differs from Montana's, so we use UF's framework rather than its full lists. The patterns below come from Montana and Rocky Mountain extension sources where possible. For a soil test, see our sibling guide to soil testing for Montana lawns.

What does clover in the lawn mean?

Usually low nitrogen. CSU's PlantTalk on white clover says that as a nitrogen-fixing legume, clover is often found in lawns that have not been adequately fertilized with nitrogen, and that regular fertilization, especially fall nitrogen, helps reduce it. CSU also notes some people want clover for its nitrogen and its value to pollinators, while others remove it, sometimes because a family member is allergic to bee stings.

If you do want it gone, CSU says pre-emergent crabgrass preventers will not control it, and that post-emergent products containing dicamba, triclopyr and MCPP/MCPA provide good control, applied when clover and grass are well watered and temperatures are below 85 degrees F. Our guide to fertilizer rates and timing covers the fall feeding that does most of the work.

What do patches of different-looking grass mean?

Grassy weeds are often a watering signal. MSU says weeds such as annual bluegrass and rough stalk bluegrass thrive under frequent, light watering. CSU's PlantTalk on roughstalk bluegrass describes it as a lighter grass that spreads by runners into large patches, especially in lawns kept on the wet side and in shade, and turns purple or red then brown in summer heat, even with generous irrigation. CSU says no selective herbicide removes it from a bluegrass or ryegrass lawn.

Coarse clumps a foot or two across that green up early in spring are usually pasture-type tall fescue, according to CSU, and can be dug out or spot-killed and reseeded. Spreading, coarse mats in late summer may be crabgrass, but CSU notes that much of what people call crabgrass is something else; in late winter and early spring the common grassy weeds are perennials such as quackgrass, tall fescue and bromegrass.

Is crabgrass a problem in Montana lawns?

Less often than people think. CSU explains that crabgrass, goosegrass and foxtail are annuals that germinate from seed in April, May or June, spread through summer and are killed by frost in September or October. CSU's weed timing note adds that a couple of hard frosts kill summer annuals such as purslane, knotweed, pigweed, crabgrass, goosegrass, barnyard grass and foxtail, so fall herbicide treatments for them are unnecessary and wasteful.

Prevention is the tool for annual grasses: CSU says a pre-emergent applied in early to mid April (in most of Colorado) prevents germination, but cannot be used on newly seeded or sodded lawns or in garden areas. For western Montana, the right date follows soil warming, which our sibling guide to frost dates in Missoula and the Bitterroot helps you judge.

What about dandelions and plantain?

Dandelions are a thin-turf weed. MSU's 2025 weed post on dandelions says large patches where turf used to be are a problem that usually extends beyond the dandelions, and that dense, healthy turf outcompetes them. University of Minnesota Extension adds that dandelions can indicate compaction. UF's compacted-soil table also lists dandelion, prostrate knotweed and annual bluegrass. Our dedicated guide to dandelions in Montana lawns covers timing and control in detail.

Plantain shows UF's caveat in action: broadleaf plantain appears on UF's lists for both alkaline and acidic soils, so it tells you little about pH on its own. CSU groups dandelion, plantain, clover and thistle as the most common broadleaf lawn weeds and says perennial broadleaf weeds are best treated from early September to early November.

Which lawn weeds are hard to get rid of?

Field bindweed and creeping bellflower top the list. CSU's PlantTalk on bindweed says this deep-rooted perennial in the morning glory family quickly takes over malnourished lawns and lawns with drought stress or poor sprinkler coverage, and that proper fertilization, uniform irrigation and mowing at 2.5 to 3 inches can substantially reduce it over a couple of years. CSU says pre-emergent herbicides are useless against it and 2,4-D alone is largely ineffective; three-way mixtures with dicamba or dichlorprop give moderate to good control, and quinclorac is highly effective.

Creeping bellflower is an escaped ornamental. MSU's 2022 weed post describes blue to purple bell-shaped flowers on unbranched stems, and a root system of creeping rhizomes that form carrot-shaped taproots, extending over 12 inches deep. It is often found near older homes. MSU says control takes at least two years: digging and sifting soil to 12 inches and removing any regrowth within 10 days, or repeated herbicide applications over several seasons. MSU names glyphosate (non-selective), clopyralid, triclopyr and dicamba as effective, and warns not all are approved for lawns or gardens. Several native bellflowers look similar, so MSU stresses identification first.

Are any common lawn weeds legally noxious in Montana?

Yes. The Montana Noxious Weed List linked from the Montana Department of Agriculture's noxious weed page (effective June 21, 2019, the most recent list the page links when we checked) places Canada thistle, field bindweed, oxeye daisy, spotted knapweed, houndstongue, St. Johnswort and whitetop in Priority 2B: weeds abundant in Montana and widespread in many counties, where management requires eradication or containment where less abundant, prioritized by local weed districts. Cheatgrass is listed separately as a Priority 3 regulated plant, not a noxious weed.

Dense turf is the best defense; CSU's bindweed note says bindweed and other common weeds do not like the competition of a dense, healthy, well cared-for lawn. Lists and local priorities change, so confirm with your county weed district. Our Ravalli County noxious weeds landowner guide explains obligations in the Bitterroot, and cheatgrass and dry grass as fire fuel covers the field edge.

Should I spray the whole lawn or spot-treat?

Spot-treat in most cases. CSU's PlantTalk on broadleaf weeds says to treat only individual plants or infested spots, that broadcasting over the whole lawn is not desirable, and that liquid spot treatments are generally more effective than weed-and-feed products. MSU recommends mechanical removal (hand-pulling, hoeing or digging) before weeds set seed, and bagging plants that may have mature seed in the trash.

Because no single product kills all weeds, CSU says you need to know which weeds you have before choosing one. CSU's general timing guidance is to spray between 65 and 85 degrees F, not when it will exceed 85 degrees within 24 hours, in calm conditions, and not when rain is expected within 24 hours. With any herbicide or insecticide, the label directions are the law: the product has to be labeled for lawns, and the label sets the rate, timing and re-entry rules.

Weed control from HJ

We are licensed for fertilizer, weed control and pesticide application. Our fertilizer and weed control program starts with identifying what is actually growing, treats spots rather than blanketing the lawn, and fixes the thin turf underneath through aeration and overseeding and recurring lawn care. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call (406) 215-7319 or request a free estimate.

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