Updated: Sep 5
This article helps you create a beautiful outdoor space with responsible chemical use.
This article is presented with the following sections:
Background and the most dangerous chemical
Weed killer safety
How to effectively use low volume yard chemicals
Good turf management
Conclusion and Notes
1. Background and the most dangerous chemical
Let's start by describing the most dangerous chemical on the planet, which is regularly used on our yards. The human toll from this chemical is devastating.
How it harms us: It will coat a portion of our lungs in low concentrations, causing COPD-like symptoms such as reduced lung capacity and wheezing. (like emphysema) It will cause choking, complete airway blockage, and death at higher concentrations.
Death statistics: According to the World Health Organization (WHO), this chemical caused 236,000 deaths worldwide in 2019. This chemical is the 3rd leading cause of unintentional death in the world.
This chemical is composed of 2 atoms of hydrogen and 1 atom of oxygen in its stable state. You may ask, what is the street name of this highly dangerous chemical? It is commonly known as WATER.
You may be thinking - "Ha - you tricked me! Water isn't REALLY a dangerous chemical." Actually, water is very dangerous and certainly a chemical. I encourage you to separate your understanding of risk from your sense of familiarity. Just because something is familiar, does not reduce its risk. Conversely, just because something is unfamiliar, does not make it more risky. [i]
Here is my point: chemicals are tools we use to meet certain needs and desires. (what economists call "utility") Chemicals may have high or low utility, and utility is user-defined. Just because I find something useful, does not mean you will, and vice versa. Despite its danger, water has high utility for yard management and life in general. For many, other yard chemicals also may have high utility, especially for controlling weeds.
In general, chemicals often get an undeserved bad rap. This is for a few reasons:
There have been high-profile disasters involving chemicals. The gas/chemical disaster in Bhopal, India certainly comes to mind. This makes people naturally suspect when it comes to evaluating chemicals.
With their obscure-sounding atomic names, chemicals sound complicated and difficult to understand.
People are subject to both the dichotomy logical fallacy and the familiarity cognitive bias. As such, our brains naturally summarize complex topics into binary (good or bad) categories. Our brains are notoriously bad at taking an outside-in view necessary for robust understanding provided by statistics. Our brains are more likely to rely on individual inside-out stories like Bhopal. Since chemicals are both unfamiliar and seem complex, we tend to prejudge them in the unfamiliar "bad" category.
This article intends to help separate fear from knowledge, so you may use chemical tools to safely create and maintain a beautiful outdoor space.
2. Weed killer safety
In the context of useful chemical tools for the yard, besides water, allow me to suggest others. The general chemical category is called weed killers (WK). Weed killers can be segmented into a couple of helpful categories:
Selective - A WK that kills lawn weeds but does not kill the desired lawn grass. Please see the note for my favorite selective WKs. [ii]
Non-selective - A WK that kills all or most plant material. In particular, I am thinking of the complex chemical "glyphosate," with the street name Roundup.
I've been using glyphosate for about four decades. Roundup came to market in 1974 and its patent expired in 2000, so less expensive generic versions are now available. [iii] Glyphosate works by inhibiting certain plant-specific amino acids involved in the metabolic (energy conversion) processes. The inhibition creates a blockage in plant tissues and diverts energy and resources from other plant processes, eventually killing the plant. Think of it like slowly choking the plant, cutting off key energy resources, and diverting energy from other necessary processes. As an additional important point, these amino acids are only involved in plant metabolic systems, they are not relevant to animal/human metabolic systems. As such, the plant amino acid inhibitors will not directly impact people.
You may have heard that Roundup has been linked to cancer. Here, the evidence is mixed. There is some evidence to suggest a correlation, but not a causal link to some cancers including non-Hodgkin lymphoma (NHL). In general, these correlations were found only at very high concentrations, like people that had high contact exposure to Roundup. Think of insufficiently protected workers spraying Roundup from tanker trucks on large commercial farms. Also, some studies have shown no or weak evidence of NHL. In particular, a large 2018 study published by the Journal of the National Institute of Health showed no causal link to cancer. As a comparative frame of reference, according to WebMD, other potential cancer-causing agents include a) pollution, b) processed meat, c) alcohol, and d) ultraviolet rays. The point is - familiar activities like a) walking down a city street, b) eating bacon, c) drinking a beer, and d) being outside - seem less dangerous because they are familiar. Becoming more familiar with chemicals will help you safely get the most from them.
The glyphosate chemical formula is:
Notice the P at the end, this stands for Phosphorus. As a phosphonate, glyphosate inhibits a phosphate synthesis process. Ironic as phosphorus by itself is a plant fertilizer. In fact, if you keep fertilizer stored in your shed or garage, it will almost certainly have phosphorus. Phosphorus is the middle number in chemical percentages found in most fertilizers. 10-10-10 fertilizer has an equal 10% contribution of Nitrogen, Phosphorus, and Potassium. So depending on the chemical context, phosphorus can be a plant killer or a plant grower.
Overall, my belief is, if used carefully, glyphosate can be a helpful, low-health risk, and low environmental risk WK tool. Careful use includes:
Wearing gloves and covering impacted skin,
Quick water rinse of any skin coming in direct contact with glyphosate,
Glyphosate should be used for low-volume, household lawn care only... no high-volume farm use. Low-volume usage ensures safety for both humans and our environment.
3. How to effectively use low-volume yard chemicals.
Two primary lawn chemical classes are in scope for this article. That is non-selective WK and selective WK.
First, let's discuss weeds. Most people do not think much about weeds. They think of them as unwanted plant material. More specifically, weeds can be either plant-relative or location-relative. This means people may differ in what they consider a weed.
Plant-relative weeds: There are some northern U.S. perennial grasses, like bermudagrass, that are considered invasive weeds. In the southern U.S., bermudagrass may be suitable as the lawn. Location-relative weeds: Pachysandra is a relatively invasive ground cover, suitable for low-light areas. Located within its borders, pachysandra is a desired ground cover, outside its borders, pachysandra is a difficult weed.
Second, let's discuss borders. A border is the outer edge of a defined area that is intended for certain plants. The border is considered along 2 dimensions, which is
the perviousness of the border. (barrier or buffer) This indicates the extent to which plants outside the border can penetrate the border. And
the plant life type of the border (organic or inorganic). This indicates the extent to which the border is alive and impacted by WKs.
Borders are an important consideration in your weed control strategy.
Organic Buffer - This is often used as a buffer border between the woods and the yard. The problem with the woods maybe that it likes to grow in the yard. This may include weeds, vines, and other material perfectly suitable for the woods, but not desired in the yard. As an example, our yard backs up to the woods. I created a 6-foot organic buffer with my lawn. I maintain it by 1) periodically spraying selective WK on the grass, to control the weeds that creep in from the woods and by 2) periodically spraying non-selective WK on a small strip just into the woods. This keeps the scrub plants from accumulating as a lawn launch point for weeds. Since this is an organic buffer, I expect some weeds to creep into the yard, but I can stay ahead of them with this approach.
Inorganic Buffer - This is often used as a buffer border between distinct plants, especially when one is a more invasive grower, like Pachysandra. [iv] Since it is inorganic, the buffer allows a direct application of a non-selective WK to control any plants that grow into the buffer. Think of it as the Korean Peninsula DMZ for plants! As an example, I have a dry creek bed between a Pachysandra bed and a Hosta bed. While the Pachysandra does try to grow into the dry creek bed, it is easily controlled by periodic spraying of the non-selective WK.
Inorganic Barrier - This is often used as an impervious border between distinct plants, especially when both are invasive growers and both are close to each other. The barrier will not allow plants from either side to pass to the other side. By its nature, it does not require WK border maintenance. As an example, I have a Pachysandra bed bordered by my lawn. The hard barrier keeps the pachysandra and the lawn separated. I still need to maintain the lawn with selective WK, but I do not have to worry about the pachysandra invading the lawn. (Note: In the picture, there is a solid plastic barrier behind the rocks.)
4. Good turf management
The single most important attribute of a weed-free lawn is maintaining a thick stand of grass. This occurs for a couple of reasons:
Thick grass will naturally crowd out weeds. This occurs because weeds need light to grow from seeds. Thick grass will keep the ground in the dark and keep a new weed from being able to germinate or photosynthesize.
For the weeds that do get through the thick grass, a selective weed killer will defoliate the green stock but not directly kill the root system. The thick grass will keep the roots from regenerating leafy stock and ultimately die from lack of energy transfer.
Think of thick grass and selective WK as two important process steps in a reinforcing lawn growth loop. Maintaining a thick stand of grass is an ongoing, multi-year, building process. It includes regular seeding, fertilizing, weed control, aeration, de-thatching, and watering. Most selective WKs suitable for grass are defoliant based WKs, meaning, they work from the outside in to kill the weed. This means the weed's root stock may remain to produce another weed.
An interesting WK that is both weed selective AND operates systemically is called Tenacity. The active chemical in Tenacity is mesotrione. It disrupts photosynthesis in weeds by blocking enzymes needed for the photosynthetic process. An interesting result is that you know Tenacity is working because the weed turns pale and white. This is because the greenish color associated with chlorophyll is not able to be produced. By the way, mesotrione is based on a naturally occurring chemical called leptospermone as derived from the bottlebrush plant.
I was motivated because a thick stand of grass creates a barefoot lawn for you and your kids. It makes it inviting to run and play in the backyard. When our children were young, they played field sports like soccer and lacrosse. Our backyard was the family and friends' destination for field sports and fun!
Chemicals get an undeserved bad rap. With a little understanding and willingness to safely use chemicals, they can be a high-value, low-cost addition to maintaining a beautiful outdoor space. We have shown you how to think of different weed control types and how to implement smart borders for weed control. A thick stand of grass is the best deterrent to weeds in your lawn. Effective yard management, including the appropriate use of weed killers, is not hard and not particularly time-consuming. It is truly a case of “A stitch in time saves nine.” If you keep up with a regular program, a beautiful outdoor space awaits you!
[i] Our difficulty in perceiving the dangers of water relates to our naturally occurring Familiarity bias. If you have a choice between two options in your life or work — which one will you take? In a series of experiments, psychologists Chip Heath and Amos Tversky showed that when people are faced with a choice between two gambles, they will pick the one that is more familiar to them even when the odds of winning are lower. Our brains are designed to be wary of the unfamiliar. Familiarity bias is our tendency to overvalue things we already know. When making choices, we often revert to previous behaviors, knowledge, or mindsets. In the case of water, it is our very familiarity that causes us to underestimate its danger. Conversely, in the case of yard chemicals, it is our unfamiliarity that causes us to overestimate the danger. By the way, the literature for cognitive bias has grown substantially in recent decades. One of my favorite sources is Daniel Kahneman’s Behavioral Economics classic, Thinking, Fast and Slow.
[ii] My current favorite selective weed killers are:
3-way Max Turf and Ornamental
Quinclorac 1.5 L
These have proven to work for me in the Mid-Atlantic U.S. on a Tall Fescue lawn. 3-way and Quinclorac work on a broad array of post-emergent weeds. I tend to switch them up because they work a little differently. Tenacity and Sedge Ender I use on tough weeds, like Nutsedge and Crabgrass. I find Momentum is particularly helpful for sedges. Tenacity works on some sedges as well. By the way, the grassy looking weed that grows taller than the rest of your grass is a sedge. When available, I buy my selective WKs at Amazon. I have had mixed results with the selective WKs purchased from the big box home improvement retailers (like Home Depot and Lowes). By the way, Tenacity is the brand name of the chemical mesotrione. Amazon has other, less expensive products using mesotrione.
[iii] Technically, glyphosate and Roundup are not the same. Glyphosate is one of the main active ingredients in Roundup, but not the only active ingredients. There is also a non-selective defoliant in Roundup. There is an interesting reason for the extra ingredient. When Monsanto first started test marketing Roundup, the only active ingredient was glyphosate. Initially, it was not accepted well in test markets. This occurred because glyphosate is a slower-acting systemic WK. It can take 2 weeks or more for the plants to "show" like they are dying. In effect, glyphosate kills from the inside out. This was frustrating for consumers as the delay caused them to wonder if the treatment was working to kill the weed. To resolve this marketing problem, Monsanto added a fast-acting defoliant. The defoliant is generally unable to kill the plant, but it will quickly show the results of yellowing and wilting leaves. In effect, the defoliant acts from the outside in. While the defoliant showed the appearance of a dying plant, it was the systemic glyphosate that was actually getting the job done.
[iv] Understanding ”invasiveness” is very important. Pachysandra spreads with shallow (4-6 inches) underground rhizomes. These are root-like, tuberous appendages that spread to create new above ground leafy stock. So, the barrier or buffer approach mentioned works well to contain the pachysandra. Keep in mind, native plants tend not to be invasive, mainly because of a millennia or more of evolution to create stable plant symbiosis. Introducing non-natives, like Pachysandra, may be problematic if not managed well.
Another particularly invasive non-native is bamboo. Bamboo is very cool and creates an attractive hedge. The bamboo canes are also nice for other purposes, like a fishing pole.
Bamboo is extremely invasive. It’s rhizomes are very aggressive and can burrow through many barriers. Also, the rhizomes can jump to the surface and go over a low barrier.
Personally, I do not have bamboo in my yard. If you are up for it, here is my bamboo containment strategy:
1). Dig a hole 3 feet deep and about 3 feet in diameter. 2). Buy a thick, hard plastic planter. At least 60mm thick. Just over 3 feet high. The diameter should be just smaller than the hole. 3). Cut the bottom out of the planter, set in the hole. Important, planter should be a couple inches above ground to cut down on the above ground bamboo rhizome jumping. 4). Fill planter and surrounding hole with loamy dirt. 5). Plant bamboo within planter area.
This “should” create a sufficient barrier to hold the bamboo. Watch it though. Trim back any rhizome jumpers. Also, periodically check the hard plastic containment field. If containment is breached, you should remove and replace the planter barrier ASAP.
This is like playing with fire. Think of yourself as a vigilant fire handler!
Here is some bamboo advise from Ari Novy, U.S. Botanic Garden executive director and botanist:
“If it’s listed as invasive by your local species council, then don’t plant it. But if you absolutely must plant a colonizing bamboo, then you must build an underground mechanical barrier, in the form of a metal or concrete wall, says Novy. “The wall needs to extend at least 2 feet below and up to 6 inches above the soil because these [rhizome] runners sometimes jump onto the surface of the soil to colonize.”