Lot Lines – the Official Blog of Outdoor Design Group, Colorado Landscape Architects
Five Notable Noxious Weeds – The Staggering Reality at Hand
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.
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!
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!
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.
Work Cited:
(Photo1) – ODG Author
(Photo 3) – https://japaneseknotweedagency.co.uk/jkwa_faqs/can-japanese-knotweed-grow-in-or-damage-cavity-walls/
(Photo 4) – ODG Author
(Beck, 2013) ‘Principles of Ecological Landscape Design’ by Travis Beck. 2013. Published by Island Press.
(CO DOA, 2024) https://ag.colorado.gov/conservation/noxious-weeds/faq
(USDA, 2018) Poison Hemlock – https://www.ars.usda.gov/pacific-west-area/logan-ut/poisonous-plant-research/docs/poison-hemlock-conium-maculatum/
(NPS, 2009) – https://www.nps.gov/articles/field-bindweed.htm
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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Five Rules to Minimize Light Pollution from Your Landscape Lighting
Low voltage landscape lighting is a great way to add evening functionality to your home landscape, as well as highlight and enhance some of those landscape elements at night. But it’s also important to consider whether these light fixtures may be adding to the growing light pollution problem that is impacting our world more and more each day, or to be more exact, impacting each night.
What exactly is light pollution and why is it a problem? The International Dark-Sky Association defines it as: “The inappropriate or excessive use of artificial light – known as light pollution – can have serious environmental consequences for humans, wildlife, and our climate.” Light pollution keeps us from having the ability to view the stunning vistas of the night sky that have delighted and inspired our ancestors for millennia prior to the advent of artificial lights. But its not just stargazing that is compromised by nighttime light pollution. Artificial lights can harm wildlife such as insects, migratory birds, turtles and mammals, by disorienting them, distracting them so they are more easily preyed upon, or even disrupting migrations leading to exhaustion or starvation.
Light pollution has grown so much over the recent decades that researchers have concluded that “more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies. The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world’s land surfaces between 75°N and 60°S, 88% of Europe, and almost half of the United States experience light-polluted nights.” (https://www.science.org/doi/10.1126/sciadv.1600377#T1)
The International Dark-Sky Association lists the components of light pollution as:
Glare – excessive brightness that causes visual discomfort
Skyglow – brightening of the night sky over inhabited areas
Light trespass – light falling where it is not intended or needed
Clutter – bright, confusing and excessive groupings of light sources
The IDA has a list of 5 rules to consider when planning for landscape lighting:
1. Useful
Use light only if it is needed
All light should have a clear purpose. Consider how the use of light will impact the area, including wildlife and their habitats.
Consider using reflective paints or self-luminous markers for signs, curbs, and steps to reduce the need for permanently installed outdoor lighting.
2. Targeted
Direct light so it falls only where it is needed
Use shielding and careful aiming to target the direction of the light beam so that it points downward and does not spill beyond where it is needed.
3. Low level
Light should be no brighter than necessary
Use the lowest light level required. Be mindful of surface conditions, as some surfaces may reflect more light into the night sky than intended.
4. Controlled
Use light only when it is needed
Use controls such as timers or motion detectors to ensure that light is available when it is needed, dimmed when possible, and turned off when not needed.
5. Warm-colored
Use warmer-color lights where possible.
Limit the amount of shorter wavelength (blue-violet) light to the least amount needed.
And the International Dark-Sky Association has this summary that is a good mantra to consider if you want to keep your outdoor lighting from causing unnecessary light pollution: “Light where you need it, when you need it, in the amount needed, and no more.”
Our landscape lighting plans don’t have to make the light pollution crisis much worse than it already is. We can use landscape light judiciously around our properties. We can use fewer up-lights and more down-lights. We can keep the light level low and the light color warm. And we can use timing devices to turn off the brighter landscape lights when the pool party or garden fete is over, the guests have gone home, and we’ve gone inside for the night.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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14 Great Native Plants for Beginning Colorado Gardeners
Lately, it seems there has been an ever-growing buzz in the media regarding native plants. We here at Outdoor Design Group appreciate this budding interest in native plants, but we have a long-established love and interest in utilizing native plants in the landscapes we design.
The blooming enthusiasm for North American, as well as regionally specific native plants got us thinking about how to advise native plant newbies to get started with these plants in their gardens and landscapes.
If you’re not sure why you should include native plants in your Colorado landscape (or any landscape anywhere on earth for that matter), here are a few reasons:
- They’re adapted to the water, light, soil and temperature fluctuations and constraints of your area.
- They’re adapted to the animals and insects of your region, providing food & shelter for the native fauna, as well as being generally more resistant to browsing by insects and other animals.
- Utilizing them in your landscape design helps anchor your property in the ‘place’ of your region. Put another way: Why grow plants that can be grown in New York, London or Tokyo? Why not grow plants that show your interest and love of the region you live in?
This brings us to a quick list of the 14 Easiest Colorado Native Plants to include in your landscape.
Before we get to the list, we must mention one big caveat: the term “native” plant is somewhat subjective. What area is one referring to when they say, “native to a certain region”? North America? The Great Plains? The Rocky Mountains? The state of Colorado? Only within a 50-mile radius of your location? The native plants we are presenting on the following list are mostly native to the Rocky Mountain region, while some on the list are more broadly native to North America.
The other thing we should mention is that while native plants have various and obvious good reasons to be utilized in one’s landscape, there are many non-native plants that can be good and ecologically appropriate choices for a certain landscape as well.
It’s worth mentioning that even if a plant is native to your region or state, that doesn’t mean that these plants will do well in every situation your yard presents. For example, aspen trees are native to the state of Colorado and surrounding Rocky Mountain states, but only are they native to the mountains and foothills. Aspen trees often struggle on the hotter drier front range cities east of the mountains where Denver is located. And just because a plant is a “native” does not mean that it won’t perform like an invasive weed. An example of this is Virginia Creeper (Parthenocissus quinquefolia) which is a North American native vine but reseeds readily in many areas and can be difficult to remove.
It all depends on many factors! Now, on to our list of great native plants to grow in Colorado:
TREES:
– Blue Spruce (Picea pungens). Sporting a conical and classic Christmas Tree form, this evergreen tree has moderate water needs so should be thoughtfully placed if your property is hotter & drier. There are many cultivars to choose from. This is one evergreen tree that might do better in an irrigated lawn.
-Bristlecone Pine (Pinus Aristata). This is a tough pine tree that is native to higher elevations but can do well in some locations at lower elevations. It can have an irregular and shrubby form. Like most pines, it has low water requirements.
-Pinon Pine (Pinus edulis). The native range of this pine is generally southern Rocky Mountains of Colorado and New Mexico. This is a good pine tree for hotter and drier locations. Its form is somewhat bushy and rounded. And the nuts are edible!
-Cottonwood (Populus spp.). There are several types of cottonwoods to choose from. They are all tough and dependable, but they don’t live very long. And some varieties have a suckering habit. They prefer moist soils, and they grow fast. They can be messy as well, so best for informal areas or larger properties.
-Bigtooth Maple (Acer grandidentatum). One of the few maples that can survive drought type conditions. Related to sugar maples, this native of the Rocky Mountain region has orange-red fall color and is more adapted to Colorado’s alkaline soils so it shouldn’t suffer chlorosis like other maple trees. This tree maxes out at 20-30 ft. tall and is more shrub-like (with multiple stems) and not a classic shade tree shape like some more popular and common (but not suited for Colorado soils) maple trees sold in local nurseries.
SHRUBS:
-Currants (Ribes spp.). There are several native varieties of currants to choose from. One of our favorites is Crandall Clove Currant, Ribes odoratum ‘Crandall’
-Yucca (Yucca spp.). Yuccas are tough plants that are well adapted to most areas of Colorado and the surrounding states. Some species and varieties are less cold hardy than others. If you’re bored with the local native Soapweed Yucca, you could try Banana Yucca, Beaked Yucca or even Dollhouse Yucca. If you’re worried about the stiff spiky leaves, you could opt for Yucca filamentosa, which has spiky tips, but the leaves are less stiff. It is native to the Southeastern United States, so they’re less drought tolerant than other yuccas.
-Agave (Agave spp.). Agaves bring stunning architectural interest to the garden with their sword-like leaves. Most agaves that are native to North America are not cold tolerant enough to be grown in Colorado, but there are at least 3 species that can handle winter in greater Denver and other Front Range areas, as well as The Grand Valley on the Western Slope. Any areas that are at least USDA zone 5 or higher. As with cacti, keeping the agave roots on the dry side during winter will help them survive the cold. One of the cold hardiest Agaves is the Harvard’s Agave, Agave havardiana.
-Opuntia Cacti (Opuntia spp.). If you can get past the spines, you will be rewarded with amazing flowers in late spring. Not every Opuntia cacti variety is cold hardy enough for all of Colorado. But a few varieties are hardy to zone 5 and are great additions to your xeriscape, providing a stunning floral display in spring and interesting shapes and forms all year round. And if the spines are a roadblock to enjoying these North American natives, there are some cultivars with less spines. Cacti will be happier if their roots can be in mostly dry and well-drained soil throughout the winter.
Perennials & Ornamental Grasses:
– Native Blanket Flower (Gaillardia aristata). Blanket Flower is a wonderful North American native flower that provides eye-popping yellow, orange and red color when it blooms in late summer to early fall.
– Penstemon (Penstemon spp.). There are so many Penstemon cultivars and nativars to choose from, its hard to pick just one. Some live longer than others. Two of our favorite penstemons (how can we pick just 2?!?) are Penstemon pseudospectabilis, and Penstemon pinifolius.
– Desert Four-O’-Clock (Mirabilis multiflora). The Desert Four-o-clock is a low-growing perennial that is very drought tolerant. It grows and spreads fast during summer with a display of bright magenta-pink blooms, but it is an herbaceous perennial, so it “dies” back to the ground every fall, like peonies.
– Columbine (Aquilegia spp.). A classic perennial plant with many varieties to choose from. These plants generally do better in cooler & wetter conditions. It’s best to save them for the part sun / part shade areas of your property.
– Blonde Ambition Grama Grass (Bouteloua gracillis ‘Blonde Ambition’). This nativar, discovered by the late David Salman of High Country Gardens, has exploded in popularity, almost to the point of being overplanted. But it’s popular for good reasons. It is tough, drought tolerant and visually striking in the fall when it sends out its one-sided seed heads that catch the sunlight in the waning days of autumn.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.