Got Cheatgrass? Take action: Invasive grasses can fuel hotter and more frequent wildfires in our communities!

March 19, 2022

When the Marshall Fire raced through eastern Boulder County in December, were you taken by surprise? The wildfire wasn’t burning in the mountains, or in a forest, or even during traditional “fire season”, and yet nearly 1000 structures burned down in just a few hours! Subsequent investigation revealed that the main culprit in getting things going was simply dry grass set aflame amidst intense winds. As it spread, the fire then preheated the already desiccated fuels in its path (including homes) and quickly ignited them in rapid succession.

This fact, that dry grass fuels wildfire, should be a wake-up call for all of us, mountain residents or not. It is something that we all need to take seriously if we wish to make our communities safer from the threat of wildfire. Be aware, also, that the major player on the grass-fueled wildfire scene around here is often the noxious weed, cheatgrass (CSU fact sheet here) Also known as Bromus tectorum, or downy brome, if it is on your property it is bad news.

This exotic weed, originally from Eurasia, aggressively invades both disturbed areas and existing meadows. It has become widespread in many of our mountain communities over the years. It competes annually with our native grasses and wildflowers and has little to no value for our wildlife. You and your pets are probably familiar with its annoyingly spiky seed heads that burrow into clothing and pet fur.

But how does cheatgrass infiltrate and degrade our native plant communities? It gets a head start by germinating in the fall or early spring. By summer it has already set seed, turned brown and dried out, creating a dense carpet of fuel. This dry thatch represents an extreme fire hazard, double that of the surrounding vegetation. If it burns hot, interspersed native plants can literally be incinerated in place. And adjacent homes next?

So what steps can be taken to reduce the wildfire risk in our home ignition zones and beyond,, especially from flammable invasives like cheatgrass? 

First stop: Prevention! 

When creating defensible space around your home, have this as your goal: a 30ft-belt of well-maintained lawn or native meadow. Sparsely scattered or grouped trees and shrubs (well-pruned), or rocks and hardscaping are fine in this zone too. It should stretch from your buildings to any continuous forested area. Keep the grass mown short (4” for turf, 6” for natives) and irrigated (if a lawn) so it cannot carry an encroaching fire further towards your home.

Most of us aren’t fully there with the green belt yet though. So It is important for us to check that some of what’s growing in this zone isn’t actually cheatgrass. To do this, get familiar with identifying cheatgrass (Jeffco factsheet here) and scrutinize your property for it. If you have no cheatgrass yet, congratulations! Stop it from getting a foot in the door by keeping soil disturbance (and fertilizer) to a minimum (cheatgrass thrives on high nitrogen levels). Encourage the growth of a carpet of native grasses and forbs that will crowd interlopers out. And be vigilant.

Second stop: Eradication!

If you find cheatgrass on your property, you want to get rid of it, and sooner rather than later.. 

By hand. Pulling or tilling young plants may be feasible for small patches if done before seed set, especially if in ornamental beds or turf. However, be aware that the soil disturbance may promote a new flush of germinating seeds later in the season. These will need further removal. Since cheatgrass seeds remain viable in the soil for up to seven years, this repeat procedure may go on for a while. 

Don’t mow. Unfortunately mowing cheatgrass in larger areas is not effective since the plants will still set seed if even only a few inches tall. Grazing only works when the plants are small and palatable.

Kill seed sprouts. A very effective option for stopping cheatgrass growth and spread is use of a pre-emergent herbicide. Such a product can prevent the germination of cheatgrass seed for multiple seasons. Rejuvra is the poster child pre-emergent already being used with great success in Colorado’s open spaces and beyond. It does not harm existing plants or wildlife. Check out this video to learn more. Where cheatgrass is present within existing native vegetation, Rejuvra will deplete its seedbank and allow the natives to bounce back and thrive. If cheatgrass is the sole plant cover in an area, a combination of replanting with native grasses and preventing cheatgrass germination may be needed.

So, don’t despair at the prospect of cheatgrass invading your (or your neighbor’s) idyllic mountain retreat! There are a variety of solutions you can implement yourselves to reduce fire risk and improve the health of your landscape. You can also request the help of a professional who works in this field. Such a person should be able to help you with cheatgrass control, and with the management of any other noxious weeds such as thistles, mullein, knapweed or toadflax.

Lucy Bauer is a PhD ecologist and owner of the local business, Fireweed Ecological Services LLC, that specializes in vegetation management. She is happy to help property owners with any problem weed issues by phone or email, free on-site consultations, or even a community presentation. She is also a fully licensed and insured herbicide applicator in the state of Colorado.