Down with Downy Brome

Downy brome in rock mulch before it dies and casts its seed

After the spring moisture we received, many landscape plants have decided to green up after all. So have the weeds. One you may have noticed is downy brome (Bromus tectorum), also known as cheatgrass. Now is the time to remove it so you prevent it from becoming a worse problem.

How do you know if you have downy brome in your yard?

This time of year, you’ll notice its silvery drooping seedheads waving gracefully in light summer breezes. In suburban neighborhoods, I notice downy brome as a problem mostly in rock mulch. It can become a seemingly overnight pest even in the most well-kept landscapes. Here’s a three-minute video that shows you what downy brome looks like.

Its leaves are initially green, but as the plant dries out, it will first turn purplish, and then straw colored. You’ll also notice the sheaths, or the parts of the leaves right above ground level, are covered with hairs. This is why it’s called “downy” brome. But why is downy brome such a bad weed?

It spreads.

Each plant produces a lot of seed. Imagine you have a rock mulch area with a few downy brome plants and you let them go to seed. There’s a very good chance you will have a much worse downy brome problem the following year. The seeds spread by wind, but they’re also spread by animals and neighborhood walkers.

It outcompetes desirable plants in unwatered areas.

Downy brome grows from seed each year. Unlike most plants, it germinates in the fall and overwinters as a semi-dormant 1-2 inch tall plant.

Notice the purple tones on the leaves close to the base of the plant.

In spring, while other plants are still dormant, downy brome emerges from winter as an actively growing plant. It takes advantage of any spring moisture to rapidly grow to its full size. It then produces seed before hot summer weather sets in.

Because it’s bigger than other plants in early spring, it uses all the available soil moisture. This leaves little or no soil moisture for other plants to grow. This is why downy brome is also known as “cheatgrass.” It cheats other plants by leaving the soil dry. In Colorado parks and natural area, it has become a major problem because the native plants cannot compete with it.

It’s flammable when dead.

Once warm summer weather arrives and downy brome dies, it becomes a major fire hazard. Because it’s so good at outcompeting other plants, it often grows in large patches. If it happens to catch on fire, it burns readily and allows fire to move quickly through an area.

If you live in an area that is at risk for wildfire like a foothill community, it is surely worth the effort to work on removing downy brome from your property.

How do you get rid of downy brome?

If you have a small amount, the best thing to do is to weed it by hand before it turns brown and casts its seed. Don’t put this task off for too long. Do it now. Luckily, it pulls out very easily, so grab a trash bag, put on your gardening gloves, and rip it out. Throw away any plants you pull.

The good news is hand pulling downy brome is usually a once-per-year task. If you attack it now, there won’t be any new plants until late fall.

Keep in mind that even if you pull all you can find now, it may take a couple of years of intensive weeding to get all the plants germinating from seed still left in the soil.

If you’ve got a major problem, you can use chemicals to help. You can sprinkle a weed preventer in rock mulch in late summer to kill any germinating seedlings. You can also watch for the tiny plants in early April, then spray them with a weed killer with the active ingredient “glyphosate.”

What about string trimming it?

It seems like it would be a good option, but it can be problematic. Here’s why.

There’s a very short window when string trimming will work. If you string trim too early, downy brome will survive the string trimming since most of its leaves are short. Then it will flower and set seed as a short plant. If you string trim too late, you’ll simply scatter all of the seed around your landscape. You’ll have a bigger problem the following year.

If you want to string trim, wait until the stems of the flower heads are as long as their going to get but the seed has not yet begun to form. Mid-flower is the best time to string trim. If you do it then, it’s unlikely it will flower again before it dies. However, this approach takes a keen sense of timing to get right.

In summary, for many Front Range Communities, we are still within the window of opportunity to put a dent in downy brome patches. So take action and look forward to a future of weed-free rock mulch!