Imagine a shade tree that’s free, never needs water and will never die. Too good to be true? Yes, it is.
This is known as The Tree of Heaven (Ailanthus altissima) and it’s a widely distributed noxious weed. The ensuing text presents five noteworthy noxious weeds growing on Colorado’s Front Range. As evident with these five weeds, the public attitude towards weed management must evolve to reflect the staggering reality at hand – invasive plants have spread globally and some of these plants have very particular adaptations that are highly detrimental to native ecosystems, naturalized ecosystems and (even) human health. Landscape architects, property owners and the public must respect noxious weed classifications in order to confront the problem.
Bindweed in a recently installed commercial landscape. Westminster, CO. Credit in work cited (photo 1)
What’s a weed? The simple answer is that one man’s weed is another man’s treasure. This topic is stacked with semantic complexities. The term ‘weed’ is used to subjectively describe undesirable plants. This definition is flimsy – like a plastic bag blowing in the wind. An ecological interpretation contends that most weeds are ruderal species, which appear in high-productivity environments with high levels of disturbance (Beck, 2013). They pop up when conditions allow & devote all energy to seed production. These plants colonize disturbed land & are eventually overtaken by larger species. Weeds that mature into shrub or tree form are merely invasive. Invasive plants are introduced into an environment where they did not evolve. They are highly successful, to the point where they outcompete native plants. In other words, they found a new home with similar conditions to their old home. Invasive plants range from ruderal weeds to large shade trees and they are highly influenced by location & climate. What’s invasive in California will probably not be invasive in New Hampshire, though some noxious weeds are adaptable enough to span vast geographic regions. ‘Noxious weed’ is a legal term that cuts through layers of ambiguity. If it’s a noxious weed, then, yes, it’s a weed – and you should eradicate it! The State of Colorado considers noxious weeds to be:
Aggressive invaders that are detrimental to the economy & native ecosystems.
Plants that can poison livestock.
Carriers of detrimental insects, diseases & parasites.
Plants that are detrimental to the sound management of natural or agricultural ecosystems.
The spread of plant material by sea-faring Europeans during the 18th century was a landmark shift in global ecology. Previously, plant populations were very localized. Now days, mass disturbance and plant migration have imperiled native ecosystems – as demonstrated by the flowing weeds, which are all non-native, invasive & noxious But first, a few mentions are in order.
Noxious weeds are classified by the government as a matter of policy.
They are classified as type A, B, C, with A being the most harmful.
Noxious weed management requires specialized knowledge and techniques.
Noxious weeds are highly adaptable and competitive due to adaptations picked up from their native habitat over thousands of years.
They lack natural controls from their native habitats (insects, pathogens, etc.).
Noxious plants come in all forms: annual, perennial, vine, shrub & tree.
The remedy for non-noxious weeds is a non-lazy individual with two hands, two feet & the ability to visually differentiate.
Most non-noxious weeds DO NOT require an herbicide! Just pull them before they flower.
Type A noxious weeds are designated for eradication by the Colorado Department of Agriculture (CO DOA, 2024). These next level super weeds include Japanese Knotweed (Reynoutria japonica) – one of the most invasive plants in the world. It was taken from the slopes of a Japanese volcano and brought to Europe during the mid-1800s. It has spread worldwide and has been found in at least 12 Colorado counties. The plant is so prolific that it can grow through asphalt and even into buildings. Why? Because it adapted to the extreme conditions of its natural environment – volcanic islands. It has adapted to massive disturbance and is the first plant to recolonize the volcanic moonscape post-eruption! If you have this plant.. refer to expert advice for removal. Godspeed!
(Left, 2) Japanese Knotweed in its native habitat and (right, 3) its new habitat. Photo credits in work cited (photos 2 + 3).
Type B weeds are included in Colorado Department of Agriculture noxious weed management plans – which intend to eradicate/contain/suppress their continued spread. Russian Olive (Elaeagnus angustifolia) illustrates this category in Colorado. Like other invasive plants, it was installed with legitimate intentions, windbreaks in this case, but it quickly became detrimental to the native environment. Often found in riparian zones up to 8000’, Russian Olive is highly adaptable – it is tolerant of shade and poor soil. In Colorado, they stress native riparian zones, outcompeting cottonwoods and willows (CO DOA, 2014).
Type C weeds are included in state noxious weed management plans, but their elimination is not a goal. Instead, outreach and education are program goals. Prolific urban weeds in our region are typically Type C and include the Tree of Heaven, Field Bindweed and Poison Hemlock – among others. These plants are widespread and their complete elimination is impossible. If you live in the Denver metro area, you have seen them. The Tree of Heaven (Ailanthus altissima) is the quintessential urban trash-tree. Originally from China, this highly adaptable tree can grow 9 feet in a single growing season up to mature heights of 40-50’. If cut, the tree responds with a myriad of suckers (cut off one head and five grow back). It unsurprisingly produces thousands of seeds and also spreads by rhizome. It can be eliminated with the application of glyphosate to a freshly cut stump. Another worthy mention goes to European Field Bindweed (Convolvulus arvensis) – the ultimate yard pest. It is thought to have originated as an imported seed contaminant (NPS, 2009). Also known as morning glory, it is highly adaptable and aggressive. It’s ubiquitous white flowers can be found growing within your bluegrass lawn, flower beds and anywhere else with soil, light and water. It’s a perennial vine that reproduces via seed and creeping roots (NPS, 2009). Much like the Tree of Heaven, Bindweed does not like glyphosate and 2-4-D, but this method only works while the plant is actively growing. Best of luck getting rid of this one.. The final type C noxious weed killed Socrates and is known as Poison Hemlock (Conium maculatum). It’s highly adaptable, but prefers riparian areas, producing thousands of seeds from white flowers. There’s enough coniine within 6-8 leaves to invoke respiratory paralysis and death (USDA, 2018). Other mammals are also at-risk including canines and livestock. On the Front Range, it is found in thick stands with carrot-like leaves and white flowers. It can be eliminated by chemical and mechanical means. Be sure to wear PPE if interacting with this plant! It is highly toxic!
Tree of Heaven stand. Photo credit in work cited (photo 4).
So, what do we do about it? The prevention of noxious weeds by homeowners and commercial property managers requires knowledge and effort. If the government considers a plant noxious, it should be eradicated before it flowers and disperses 180,000 seeds that last for 100 years (Mullein!). It doesn’t matter how pretty you think it is. Weeds, regardless of their classification, thrive with neglect. At the most basic level, human development is disturbance and disturbance generates weeds. Limit disturbance as much as possible and preserve native habitats. Be careful with imported fill; it might be stacked with weed seeds! Pay attention and guide your landscape in the right direction. Learn how to eradicate these plants. It’s not as simple as you might think. Many of these plants have extensive root systems that will reshoot in perpetuity. Herbicides are massively overused, yet they are an extremely useful tool in this fight. Use them sparingly and safely! We’ve significantly altered the earth and it’s our responsibility to mitigate the damage! At the end of the day, just be glad you don’t have Japanese Knotweed growing through your floorboards.
Landscape architects (LAs) are part of the problem and the solution. LAs manage a larger scope than just plants, but typically develop plans to replace existing vegetation with proposed vegetation in accordance with code, client, budget, site, etc. Intentions are benevolent, yet ideas turn into plans, which turn into commercial shopping centers, homes, parks and so on. Landscape architects, in a sense, perpetuate ecological disturbance, opening the door for colonizer species (aka: Weeds). Of course there’s a plan to avoid this, which is one reason landscape architecture exists in the first place. It’s critical for LAs to identify existing noxious weeds on a project – so they can be eliminated before breaking ground. Many noxious weeds have deep roots, allowing them to survive extreme disturbance (like a construction project). Landscape Architects employ a myriad of techniques to manage plant competition and succession. They are highly trained individuals, but more can be done. They can advocate for limited disturbance to native landscapes. They can design native landscape zones on the site periphery. They can stipulate proper maintenance for native grass. With landscape architecture, this goes beyond noxious weeds. Are business incentives and ecological stewardship mutually exclusive?
* This was not written by an ecologist, policy maker or certified pesticide applicator. Nor was it written by an official landscape architect. Seek expert advice elsewhere before making any drastic decisions! Your local CSU Extension Office is a good place to start.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
Outdoor Design Group is based in Arvada, Colorado – this blog concerns the Great Plains and Western United States. A previous blog post – wonderfully written by Julie O’Brien – traced the origins of the “green carpet”. The ubiquitous American lawn. It’s important to note that the green carpet exists in multiple forms. It’s a literal thing and a cultural construct. Most Americans associate homes with green lawns regardless of the prevailing environmental conditions. The lower 48 of the USA receives between 5” – 120” annual precipitation. Established Kentucky Bluegrass (KBG) requires about 26” of precipitation during the growing season. Our collective perception of the green carpet must incorporate prevailing environmental conditions!
Within the confines of this blog, the term ‘native grass’ refers to grass species found on the Great Plains prior to western settlement; to understand the applicability of native grass, refer to the map below. The eastern half of the United States receives 30 – 70” per year; the western half gets 5-30” (with exceptions in the Pacific NW). Denver sits on the dry half with 15” annual precipitation. Landscape is all about place, and our place is pretty dry. Our native flora have adapted to the prevailing conditions, yet the same cannot be said for the green carpet!
Sown native grass shines in low-traffic applications. Once established, it needs no supplemental water or fertilizer. It is not soft and fluffy. It needs full sun and doesn’t tolerate heavy foot traffic. If planted in your front yard, there is a high probability that at least one neighbor will vehemently dislike. Yet it’s a solid solution for covering low-use space. After all, you need to do something with any given patch of earth – so weeds don’t run amok. Semi-arid climates such as ours render large-scale KBG nonsensical. It requires excessive irrigation, fertilizer and herbicides, while contributing zero ecological value. Native grass isn’t a silver-bullet; it’s a tool in the toolbox that’s applicable to many areas.
There are myriad factors to consider with native grass. First off, it doesn’t have to be native! Secondly, many species are sold by container. While many viable grass species are endemic to the Great Plains, other well-adapted varieties come from elsewhere in the world. Either way, native grass species have deep roots, grow relatively tall and are not available as rolled sod. They are typically sown by seed, and in some cases installed by plug. It’s difficult to establish and there’s an ongoing maintenance requirement. Ample moisture is required during the first season and an underground sprinkler system is recommended. Temporary (above ground) irrigation can also be used. Weed management is critical. Certain weeds (especially bindweed) must be addressed BEFORE installation! Ongoing weed management will be required! Native grass is not easy. If you’re willing and able, you’ll be rewarded.
There are many cool & warm season grasses to choose from – that differ in terms of height, texture & cold-tolerance. On the shorter side, buffalograss and blue grama are proven options. Taller options include little bluestem, big bluestem, switchgrass, western wheatgrass, sideoats grama & tufted hairgrass – in addition to many more. You might consider several varieties of water-thrifty turf as an alternative to native grass. Options such as Dog Tuff, RTF Tall Fescue & Tahoma 31 Bermudagrass.
This is not an installation guide. Contact your local agricultural extension for more information. Seed suppliers such as Pawnee Buttes and Arkansas Valley Seed are also great resources. Most western residential and commercial landscapes have a place for KBG – the key is scale; not overdoing it. Native grass isn’t for everyone, nor is it perfect for every landscape – yet it’s severely underutilized!
Written by Matthew Whiteman
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
With recent news headlines (https://abcnews.go.com/US/happen-colorado-river-system-recover-historic-drought/story?id=98475953) warning of the extreme drought conditions hitting the western U.S. and the region that makes up the Colorado River basin, cutting water use has become top of mind for many citizens and leaders in Colorado and beyond. One city in Colorado has approved a plan to cut water use in the face of this historic drought, and this plan is raising some eyebrows and generating its own headlines due to its potential impacts.
In the summer of 2022, the city council for Aurora (Colorado’s third largest city), approved restrictions on high water turf lawns for all new construction. Originally proposed by Aurora mayor Mike Coffman, all ten members of the city council voted to approve the new ordinance which limits the amount of turf lawns in new developments and golf courses. (https://www.denverpost.com/2022/08/23/aurora-limits-grass-lawns-golf-courses-water-usage/)
The ordinance prohibits water guzzling turf lawns in common areas, medians, curbside landscape and front yards. In back yards, lawns must be equal to or smaller than 45% of the area, or 500 square feet, whichever is smaller. However, an exception was included to allow front yard turf lawns for residences whose backyards are too small to fit the 45% or 500 square feet threshold.
Perhaps most importantly, the ordinance restricts turf from being used merely for decorative purposes in common areas unless it is for use in “active or programmed recreation areas.” The skinny strips of lawn often found in older commercial developments which are inefficiently irrigated as water over-sprays wastefully on to nearby walks, streets and parking lots, will hopefully become a relic of the past.
Wasting water in a parking lot.
Considering that the typical high-water lawn needs 25″ of water annually to look good and green, and Aurora (as well as most of the front-range urban corridor of Colorado) only receives 15″ of natural precipitation all year, reducing or eliminating non-active or un-programmed turf lawns is a very easy way to reduce urban and suburban water use.
This is why another recent headline grabbing story regarding reducing turf lawns was welcome news. In June 2022, the State of Colorado passed a bipartisan-sponsored measure that will encourage property owners across the state to ditch their water-wasting turf lawns (https://leg.colorado.gov/bills/hb22-1151).
The legislation is intended to use state funds ($2 million) to financially incentivize the voluntary replacement of irrigated turf with water-wise landscaping. The bill, HB22-1151, requires the Colorado water conservation board to develop a statewide program that would distribute funds to various “local governments, certain districts, Native American tribes, and nonprofit organizations” for lawn replacement programs. Those funds could then be used to pay property owners to reduce their landscape irrigation by transitioning away from high water turf lawns, towards more climate appropriate landscape treatments. The funds could also go towards expanding some existing programs that already pay property owners to replace water-thirsty lawns, about $1 to $3 per square foot of removed sod. Most of these rebates are only offered in cities in Colorado and not unincorporated areas. One goal of this legislation is to broaden this type of program to other areas in the state.
An example of a water saving landscape renovation at a multi-family property in Aurora, CO.
While $1 to $3 per square foot of removed sod may seem generous, there are reports of some landowners in California getting lawn replacement rebates up to $6/sf. (https://www.cnn.com/2022/08/19/us/california-drought-lawns/index.html). Interestingly, some of the rebate programs in California also require installation of rain barrels as well as turf lawn replacement. That is an intriguing idea for rebate offering entities in Colorado to consider, especially since rain barrels only became officially legal just a few years ago.
Researchers at Colorado State University estimate that landscapes account for at about 55% of the total annual water use for a typical single family home in Colorado.
Typical Colorado household water use; CSU extension
And most of this goes towards lawn irrigation. In the city of Denver for example, it’s estimated that nearly 25% of the city-wide entire annual water consumption is sprayed on high-water turf lawns. (https://denverite.com/2019/05/06/denverites-can-use-120-million-gallons-a-day-to-water-their-lawns/) Considering that lawns are only irrigated about half of the year or less in Colorado, that is a lot of water that could easily be saved if more lawns were changed into climate appropriate landscape treatments.
Let’s hope that the recent passage of Aurora’s lawn restriction as well as HB22-1151 helps usher in a more water conserving and water conscious future in Colorado and other states in our drought prone region. This won’t translate into a complete disappearance of high-water turf lawns. However, for the sake of our rivers, aquifers and reservoirs, it means that these water-hogging green carpets must be used wisely and judiciously in the designed landscapes of the future.
Example of beautiful low-water groundcover alternatives to high water turf lawn.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
Once upon a time, there was a castle guarded by soldiers. Enemies obscured by the trees would sneak close to the castle, so the soldiers reduced the threat by removing the trees. Without the trees, the land filled in with grasses, thyme, and chamomile. Animals began to graze in these new fields, keeping the plants low. The soldiers could see clearly across the land, and the sheep were fat and happy. The castle prospered, and everyone who visited wished their land could be so grand. The other land owners cut down their trees and filled in their land with grasses. The smell from the grazing animals wasn’t ideal, so they brought in men to cut the grasses low instead.
The “green carpet” surrounding the finest castles and estates in the 16th & 17th century became a status symbol, and planted the seed for the sod lawn we’re all familiar with today.
In the United States after WWII, automobile technology and availability took off. With the open road ahead of them, well-to-do folks left the cramped urban conditions of the cities, moving outward to new suburban neighborhoods.
Planners like Frederick Law Olmsted and Abraham Levitt gave the people sprawling neighborhoods, with acres of lush green grass. With the popularity of the 2-day weekend on the rise, homeowners indulged in their green Edens. This ignited a new chapter for the centuries old status symbol of the turf lawn – now repurposed for mini-golf and lawn bowl rather than spying enemy invaders and feeding livestock.
“No single feature of a suburban residential community contributes as much to the charm and beauty of the individual home and the locality as well-kept lawns” – Abraham Levitt
Ingrained into the new vision for the American Dream, well-kept lawns became the golden standard. With an estimated 30 to 40-million acres of the United States serving as an irrigated sod lawn today, this status symbol is butting heads with our resources and priorities.
The cold hard truth about lawns are that they are a water hog, high maintenance (what other non-food-production plants do you cut weekly, fertilize seasonally, and treat with chemicals?!), lawns are a food desert for animals & insects, and they do nothing for our groundwater while the water runoff often pollutes creeks and streams with high nitrogen fertilizers, causing harmful algae blooms. All of that lawn maintenance also creates air pollution and noise pollution from mowers, blowers, and trimmer equipment.
A renovation project where Outdoor Design Group helped our client reduce their turf lawn.
But lawns can be great in the right location!
This is where “active-use” vs. “passive-use” spaces come into play. Lawns can be very durable, and are amazing for active children and pets. Maintaining a lawn to play and entertain on is a lovely idea. Kentucky Bluegrass has been a popular turf choice for decades, but climate suited alternatives like Dog-Tuff Buffalo Grass, Bermuda grass, or “steppable perennial lawns” made up of creeping thyme or clover can serve the same purpose as high-water turf lawns with fewer drawbacks. While choosing the right type of lawn for your environment is a start, reducing the overall amount of lawn is still the key to a progressive and sustainable landscape. Maintaining any type of lawn on the side or front of your house where no-one ever spends their time is wasteful for you, your wallet, and the environment.
Steppable groundcover used with other perennials, step stones and mulch.
Consider ditching the golf-course-quality front-yard peacocking and save that neighborly competitiveness for the holiday light display. Instead, beef up your shrub beds, add some neat planters, and opt for native seed mixes that include drought-tolerant grasses & wildflowers. Keep your lawn only where you will use it, and plant a nice tree just west or south of it to keep it cooler and healthier during hot sunny days.
A front yard filled with a diversity of ornamental grasses, perennials, shrubs, landscape rock and mulch.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
Today’s photo is a recent view of a portion of one street median renovation we designed in Lakewood Colorado. We designed several landscape plans for this renovation project, consisting of many miles of existing street medians in that city, that are slated for renewal. It was an interesting and challenging project to work on, and the city staff were great to work with. We look forward to seeing how these designs grow and flourish over time!
Landscape median in Lakewood, Colorado
Before renovation photo of the same median as above, but with camera looking north.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
