To Spray or Not to Spray -- Garden Site Prep and Reviving Biodiversity

4/6/2020

In a recent newsletter I shared with folks a plan to DIY prep garden spaces over the summer, just in case nurseries and landscapers had to shut down this spring and could not reopen until later in the summer or fall. Autumn may actually be the best time to plant -- with less weed competition, more steady rains, and cooler temps that reduce both human and plant stress during install.

I mentioned that in considering lawn removal or bed prep, herbicide may be needed to kill grass or to make repeated controls over extremely weedy areas. For the latter, you want to kill off the current vegetation, allow weed seeds to germinate and reach several inches tall, then kill off again and again; performing this regimen helps exhaust the weed seed bank, a bank that would otherwise ruin the aesthetics of the design, impede establishment for plants you do want (and paid good money for), as well as reducing management time the first year or two when weeding will take up 99% of your garden life. [A note on weeding post planting -- it's best NOT to use chemical control if you can avoid it since you might damage "good" plants or harm wildlife. However, pulling weeds simply brings new weed seeds to the surface. Clipping or mowing weeds before they bloom will reduce weed seed production and may be the best method of weeding as the garden establishes.]

What ensued after the newsletter were many emails, some using swear words, pleading with me to not recommend the use of any herbicides for any reason at all. I can not make that kind of sweeping recommendation at this time. And if you are willing to hear me out, here's why:

The selective use of some herbicides are essential to controlling invasive weeds. Prairie and woodland conservationists know this, and herbicide used selectively (to target specific species and specific plants or stands of plants) is critical to reviving diverse habitat for wildlife and ecosystem function.
Herbicide for lawn removal is not only inexpensive, but less polluting (one common chemical may also be less toxic than common organic treatments). To remove lawn effectively one would need a sod cutter, a machine that spews out noxious chemicals. More importantly, sod cutters also increase soil disturbance, which is the very last thing you want in prepping a garden site. That newly-opened soil now has exposed weed seeds ready to take off like gangbusters. When you spray kill a lawn you are leaving the dead lawn in place, which helps control weeds and reduce erosion by acting as a mulch layer. Sure, you could smother the lawn in cardboard and wood mulch, but doing so impedes air and water transfer to / from the soil, reduces soil moisture, increases pests, and makes the planting (and sowing) of a designed meadow garden significantly harder. In other words, don't sheet mulch.
Using an herbicide one time to prep a landscape for a sustainable, biodiverse, ecologically-thriving landscape is worlds apart from millions of commodity farm fields where a monoculture exists and demands multiple sprays year round for decades. Using an herbicide formulation in the home landscape that targets only foliage -- one that is not a pre-emergent -- reduces the impact of the chemical on wildlife, as does following product directions for factors like temperature, wind speed, and time of day
If you are an older individual, someone with sudden fatigue syndrome, have a bad back, or are in some other way physically limited by how much you can do, employing an herbicide can be a god send. Same goes if you have limited financial resources that can be better used on procuring plants, because the more plants you have the more sustainable and manageable the space will be -- aka green mulch.
I'm not an apologist for the wholesale slathering of our nation in pesticides, fungicides, and herbicides, or the large corporations who buy the government to increase profits while our planet's health deteriorates. I know our food and water is poisoned. I am as angry and horrified as the next person. However, the strategic and careful use of herbicides to revive ecological function and biodiversity in the urban environment (and reduce another chemically-dependent monoculture called lawn) is an essential component to sustainable design that actually protects the environment; from invasive weeds getting a foot hold to reducing site erosion, herbicides are an important tool among many. Each site is different, each landowner is different, requiring nuanced approaches tailored to each circumstance. No matter which method you choose to create a native plant garden for wildlife inspired by your local ecoregion, it's important to carefully consider the benefits and drawbacks of each method, including time, cost, labor, pollution, and long-term management goals.

In summary, the benefits of spray killing lawn or weedy beds to prep for a new garden are:

Less soil disturbance
Fewer weeds
Minimizes erosion
More affordable (and don't solarize -- it kills soil life and produces plastic waste)
Less physically demanding
Results come sooner (which means fewer weeds, less erosion / runoff, etc)
More ecological benefits sooner

In the end we ALL have the same goal -- to revive wildness wherever we can while being wise stewards of nature in the places we live, work, and play. We will get there. We have to .

Post Script ---- In reply on various social media channels, a common refrain from folks has been that wood mulch is a stupendous weed inhibitor. First, wood mulch has to be re-applied every 1-2 years, and if you apply it too thickly it's simply a topsoil layer that weed seeds love to germinate in. On clay you don't want a thick mulch layer otherwise the soil drowns, which means the mulch is so thin weeds still have an easy go and / or it washes away into storm drains.

Second -- and more importantly -- wood mulch inhibits self sowing and plant spread. We want our garden plants to spread ASAP in order to create both an ecological community and to out compete weeds (not to mention slow erosion, sequester carbon, shade / cool our homes, etc). Wood mulch keeps plants in a perpetual state of establishment -- a common refrain espoused by landscape architect Thomas Rainer. In my design practice, we often use a combination of plugs and seeding to create a dense, layered bed quickly, something wood mulch would negate. Working with plants in this way certainly requires greater knowledge about how plants act together in communities, as well as their life cycles above and below the soil line, but learning about them in this way is worthwhile and pays massive dividends. What did nature do before the timber industry invented wood mulch in the 1970s and 80s? Plants. Plants. Plants.

22 Comments

Jennifer Lauruol link

4/7/2020 05:54:41 am

To get rid of lawn c, all you need is lasagne mulch, soil cover and seed. See Charles Dowding no-dig methods on YouTube and online.
We are so late with rewilding, and evidently still haven't learned the lessons of human folly and hubris.

If Nature wanted Glyphsate, it would have evolved naturally

Benjamin

4/7/2020 10:50:11 am

Glyphosate was not mentioned in this post. There are many herbicides out there -- some more dangerous than others (especially if folks don't follow directions). As for lasagna mulching, please link to the article in the above post about water / gas transfer, pests, and drying out the soil. Also consider that many folks who are as physically able might not be able to lasagna mulch.

Zuni

4/7/2020 11:20:29 am

I agree with all but the lawn suggestions. Use of herbicide for lawns is purely cosmetic. Pristine lawns are unnecessary and unsustainable. Use best management practices for turf (if you must: aerate, overseed, mow at correct length...)

Benjamin

4/7/2020 11:23:02 am

This post is not about maintaining lawns but removing them with herbicide. The less lawn we have the better in most cases.

Tim Boland

4/7/2020 04:37:43 pm

I think you should mention, if they are out there, non-monsanto products that could be used. The company is so bad in its governance and human rights abuse, its hard to use their products and I feel it supports their corporate actions.

That said, its impossible to take the pressure of invasive weeds without drastic measures. We will end up with a homogenous weed flora with little co-dependent biodiversity. Its quite a challenge!

James McGee

4/9/2020 09:42:31 pm

I’ve seen plots created as a comparison between an area that was sprayed, to kill smooth brome, and an area that was not sprayed. Several years after seeding both areas, with the same mix at the same density, the number of prairie plants in both treatments was the same. Although, the unsprayed area continued to have more smooth brome. I’ve also seen cool season grass pastures that were burned and seeded. No herbicide was broadcast sprayed to kill the lawn grasses composing these pastures. However, several years later these areas had developed into good prairies.

My point is … you don’t have to spray lawn grasses with herbicide to restore ecosystems. The native plants mostly grow taller, shade out the lawn grasses, and win over time. Fescue being an exception in some cases. Spraying to kill lawn grasses before planting is usually more about aesthetics than necessity. Although, some would argue that when gardening, aesthetics is a necessity.

The above being said, I use herbicides all the time. However, I use them to control things that are too large to be pulled out of the ground and are real ecosystem killers like common buckthorn and bush honeysuckle.

I still don’t understand your wholesale aversion to mulch. Yes, just like with herbicides a lot of people use mulch inappropriately. However, mulch is how nature controls weeds. A prairie has a layer of weed suppressing thatch if it has not been burned. A woodland has a layer of duff and small twigs.

To prepare a garden bed, or control weeds in between plants in a developing garden bed, I use chopped up deciduous leaves. I either get them from the landscaping companies that my neighbor’s hire or from my own yard. The landscape companies love to give me their leaves because it saves them from making a trip to the compost facility. I pile the leave about a foot deep and by the time they have decomposed in early summer the lawn grass is dead. All that survives is a few dandelions that I dig out. I get enough chopped leaves each year to smother an area as large as I would want to plant. It takes planning for where you will want to plant next year. However, smothering grass with chopped leaves is not difficult. Please give this method a try.

Benjamin

4/10/2020 08:40:31 am

My wholesale aversion to wood mulch is that 1) you can't seed in it and 2) it keeps plants in a state of establishment for a longer period of time, thus reducing ecosystem function in the early years (not to mention weed suppression). Wood mulch is over used and creates an aesthetic that is unsustainable. Wood mulch covers the ground where 75% of our native bees nest, making it impossible for them to nest. But I also understand wood mulch is a way for mow / blow firms to generate more steady income and repeat business.

As for converting lawn to meadow (not so much a deigned garden but something wilder), you know I did that in my backyard: the lawn was already stressed, though, from years of no fertilizer or watering, so competition from seeds and plugs was easier. And in this case you are right, the natives out competed the lawn 90%. In a thicker lawn with much less seed to soil contact -- and sunlight for the seed to get -- it'd be much, much harder to create the necessary competition. But, again, using a synthetic herbicide is ONE TOOL AMONG MANY, used in both landscape design (converting from a monoculture) AND in habitat management to curtail invasive weeds that would otherwise create a monoculture in restorations.

Lynne

4/10/2020 10:32:13 am

Benjamin, it is a simple matter to rake away wood chips to add seed; however, I prefer using straw mulch in areas that are to be seeded such as vegetable gardens. As for your second point, it is unfounded. Please review
Wood chip mulch - Washington State Universitys3.wp.wsu.edu › uploads › sites › 2015/03 › wood-chips
just as an overview. Wood chips do not slow the establishment of soil microbes. And if used over properly prepared (ie weeded) soil, they are quite effective at suppressing new weed growth while maintaining soil moisture. It is much easier to pull weeds in wood chip mulch than in bare soil or inorganic mulches. A review of the scientific literature will support the use of wood chips..

Benjamin

4/10/2020 10:40:52 am

Lynne -- Once you pull that wood mulch where do you put it? If you're going to sow prairie seed why did you install mulch in the first place? And I did not mention soil microbes, did I? Mulch slows the spread of plants to fill the ground and out compete weeds, especially those that self sow -- that was the argument. As for pulling weeds I don't recommend it: that simply brings more weed seeds to the surface and creates a new pile of soil for weed seed to blow into and establish on. And what if you are not physically able -- or don't have the time -- to pull weeds? If you have a weedy site to begin with, the whole reason to do a spray, let weeds grow, spray regimen is to exhaust the weed seed bank to reduce future problems after planting (like garden failure or added expense -- it's MUCH harder to take care of a weed explosion after planting). In any case, for prairie style gardens I design, I suggest clients mow the beds if we deem weeds are a major issue; this prevents weeds from flowering and setting seed.

James McGee

4/10/2020 05:48:04 pm

I forgot you direct seeded into lawn in your backyard.

As for “you can’t seed into it (mulch)”, I think this could be done if the mulch was not too thick. Just last weekend I dug up first and second year purple coneflower (Echinacea purpurea) from wood mulched areas in my front yard. I put these plants in plug trays and small pots to grow on for a plant sale or to give away. When I planted Carex craweii plugs under my down spout, I put wood mulch around them. The plugs have filled in the entire area. The wood mulch is still present under the sedge’s leaves, but I only see it after I burn. The wood mulch smolders until I spray it with the hose. In a few more years it will decompose and be gone. I also have Carex pensylvanica spreading in an area where I put down wood mulch.
The original plant has expanded in diameter considerably.
Interestingly, it has formed new small clumps about a foot from the original plant.

Depending on how thickly mulch is applied, it does not necessarily eliminate the ability of seedlings to establish. It takes up space, so seedlings have less places to establish. This is not all together bad. Less seedlings, mean less weeds. Especially small seeded weedy species which are most likely to be prevented by mulch. I admit, it also can mean less seedlings of desirable plants. However, sometimes less is more. If you have less plants competing for the same resources, they tend to grow larger and be healthier. Also, the negative space occupied by mulch is not evaporating water which is a plus for seedlings trying to get down that first root.

I have not seen ground nesting bees making nests in my gardens. However, I can’t imagine a thin layer of wood mulch would stop them. It sure does not deter yellow jackets from making nests, which love wood piles or forest soils developed from wood decomposition.

I like wood mulch during the development stage. It gives a garden a more formal look and helps prevent erosion until the native plants get established.

James McGee

4/10/2020 06:27:24 pm

My experience with my park district mowing weeds (sweet clover) is it actual causes more weeds the following year. I believe this is because the perennial native plants are weakened. If mowing is done for enough years, at the right time, it can significantly reduce populations of certain weeds in big dense patches, so they are more manageable. However, removing them root and all is usually best if possible. The window where monocarpic weeds can be selectively cut, without again flower, is so small not much can be done during this period. Selective cutting typically only works for annuals and biennials.

In contrast, if you remove a weed root and all it won’t come back. That is … unless you miss getting some of the root. However, if you work at it over time you will get it all. The one big exception to this is field thistle (Cirsium arvense). You’ll never get all the root of field thistle without a back hoe and causing way too much soil disturbance.

Digging up weeds has worked great for me. When I dig up weeds, I count the number of weeds I remove. Each year the native plants fill in more and there are less weeds. I know there are less weeds because I’ve recorded the numbers to back this up.

I know everyone says soil disturbance promotes weeds. In my experience, if you have mostly weeds and you disturb the soil you will get more weeds. Whereas, if you have mostly long-lived perennial plants and you disturb the soil only as much as is necessary to remove the weed then each consecutive year you will have less weeds.

Mandi

2/24/2021 03:39:51 pm

Fascinating post and discussion. Something I wrestle with myself. On the topic of woodchips/mulch I wonder/worry in the prairie setting how it impacts/changes the soil composition. I used a thick layer of mulch in my yard (no cardboard) and planted directly in it. The plants are thriving. It has certainly inhibited reseeding for the first 2 years. I've now raked it back a bit and now things are starting to reseed and naturalize a bit. I can tell you've made a well researched decision with your choose to use herbicides. Thank you for your well thought out contributions to our ecosystem.

Benjamin Vogt

2/24/2021 04:18:02 pm

Here to serve, Mandi! :) It's yet another complex topic riddled with human emotion because, I suspect, gardening is such a personal and activistic act (think I made that word up). I have a section on this in my forthcoming book that began as one paragraph but ballooned into eight, precisely because of this post and conversation.

Nomi

1/12/2022 11:20:54 am

I was in the "no pesticides ever!" camp, until I moved and my new garden contained perennial sow thistle.

No amount of careful removal of the delicate rhizomes from the soil was enough to eradicate it. It regenerates from the tiniest nub.

"Eco" weed killers such as iron sprays had zero effect. Hand pulling was not an option.

The area was shaded enough that solarizing failed to heat the soil hot enough to cook the rhizomes dead.

Sometimes the judicious use of herbicides is the only option sort of taking a backhoe and completely removing the soil from a wide area.

Ximo

1/31/2022 01:48:21 pm

You could also leave silage tarp with the white side up for a whole growing season. It takes time and is not great for the soil, but it will kill even the worst perennial weeds. The soil will recover as the meadow establishes.

Naomi

1/31/2022 01:54:33 pm

A good option in a backyard. Unfortunately, this is a front yard and my neighbours would strangle me if they had to look at a tarp for an entire growing season.

Karen link

7/25/2022 09:40:06 pm

Thank you for sharing this.Our raspberry garden was overrun by thistle. I hate losing the raspberries, but it's a 50 year old victory garden. Time to wipe it out and do some raised beds.

Susan

1/24/2023 09:35:36 pm

Hello Benjamin. I am currently reading your book “ Prairie Up” can you recommend a few specific herbicides to use to remove unwanted weeds? My “lawn” is mostly weeds. I’m excited to get started. I was hoping to be planting this spring but it sounds like I might need to wait until Fall if I want to eradicate ALL the weeds, correct? Thank you for any additional input!

Mari

2/7/2023 10:10:24 am

As an add-on to Susan's question about specific herbicides you might recommend (with gratitude!) - what do you think about the possibility of applying the herbicide then covering with plastic, as an added measure to protect insects that might contact the patch and to provide some summer solarization?

Benjamin

2/7/2023 10:16:54 am

How will the herbicide dry? Plus the stress of sunlight on the plants will help them absorbs more. Then you have herbicide on the plastic. And you still have plastic waste which we REALLY need to stop yesterday. Firm believer in ends justify the means here.

Front Range Wild Ones link

6/13/2023 11:11:41 am

Some of our members use a the lasagna technique (smother grass with cardboard & deep mulch), or some have used manual sod cutters (those half moon shaped edgers) to remove sections of grass to compost without the need for a gas sod cutter or chemicals, which also works great.

Lisa

9/14/2023 09:17:16 am

It’s inappropriate to talk about the relative toxicity of herbicides as you have done here. Glyphosate is never used apart from formulations which enable it to stick to the plant and penetrate cell walls. Also, there are varying mechanisms of toxicity. Acute effects are important, but glyphosate is a genotoxin. So chronic exposure can be carcinogenic. A glyphosate based herbicide will kill bugs and amphibians with direct contact. And it’s been shown to disturb the gut microbiota of bees. The chemical industry continues to cultivate a lot of misunderstanding about this product. And remember, our EPA doesn’t evaluate pesticide formulations for safety, only the chemical that the industry claims is active.

The environment cost of manufacture, packaging and distribution of these products should also be weighed into the calculation of best practices. No one would deny that killing acres of weeds using herbicides is less labor intensive than some other methods. But is the end product the only goal? Is speed and ease of use the metric by which we should proceed?

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