About restoring dryland prairie grass in open spaces....

Dryland prairie grass provides vegetation for a more wildlife-friendly environment on open space that was previously in agricultural use or is no longer in a natural state. Broomfield is currently in the process of restoring prairie grass at several open space areas.  

Typically, prairie grasses take three to five years to get established. The process requires patience and persistence, especially since growing prairie grass depends on rainfall and temperature factors that are not possible to control. Broomfield works closely with a grassland specialist and also discusses ideas with neighboring communities undertaking similar efforts to gather best practices for restoration. 

Step 1 Weed Control

The first phase of work involves weed control to prepare for the grass seed. Weeds deplete the soil of moisture but do provide some protection from erosion.  There are two methods of weed control: clean cultivation and chemical fallow.   

Clean cultivation entails repeatedly undercutting the weeds to allow for as many “waves” of weed seed as possible to germinate so they can be killed. This depletes the potential for weeds to grow and allows more moisture to be retained in the soil since the weeds aren’t there to use it up. Another procedure, deep cultivation, brings up soil from a depth where there is often valuable soil moisture. If done in a dry period, this soil moisture then evaporates. So, the preferred technique in prairie grass restoration is the shallow, clean cultivation method using undercutting, because it kills weeds with a minimal loss of soil moisture. 

Despite best efforts to reduce weed seed prior to planting, once the grass seedlings appear, weeds will poke up, too. Common bindweed and other deep-rooted perennial plants will often persist for many years. The good news is that, within five years after the grassland is seeded, the native grasses will likely out-compete the weeds and dominate the site. However, since weeds are persistent, the need for at least some weed control will continue.  

Step 2 Sowing the Seed

The second phase of work is to sow the grass seed.

The following seed mix was used at The Field and alongside the trails at Broomfield County Commons Open Space:

% of Seed per #: Percentage of Seed per Pound
PLS/ac:  Percentage of Live Seed per Acre

These grasses were selected because they are drought-resistant and low-growing. Two different seed mixes were used at Broomfield County Commons along the drainage area south of the athletic fields to accommodate the wetland area and salty soils.   

Step 3 Maintenance

Just like any revegetation project, once the grass is seeded, maintenance becomes important. Until the germinated grass seeds have established a competitive stand of grass – usually in the first and second years after planting – the grass will be mowed periodically to reduce the weeds. The weeds serve as cover to the emerging native grasses but need to be cut while the grasses are in the establishment phase. This lets sunlight get to the grasses, and insures that the grasses get adequate moisture to survive. Mowing actually limits the competition between the grasses and the weeds, especially important since broadleaf herbicides cannot be applied during the first year as they would kill the grass seedlings, too.  

Step 4 Tracking the Growth of the Drought-Resistant Grasses

Over the next five years, Broomfield will track the establishment of the prairie grasses at The Field and Broomfield County Commons. Below are links to a sequence of pictures for each site at several key locations over time. Getting drought-resistant grasses established and growing well takes time, especially on dryland sites like the Field and Broomfield County Commons. It cannot be emphasized enough that this is a slow process.