What do Admirals, Commas, Question Marks and Tortoiseshells all have in common? No, it’s not a love letter written by a shipwrecked seafarer on a desert island.  These are all butterflies that are commonly found in the southern Great Lakes region and they, along with a few interesting moths, all use members of the nettle family (Urticaceae) as host plants. 

Many of us are familiar with that not-so-lovely burning sensation when we inadvertently brush a bare leg or an arm against some Stinging Nettle (Urtica dioica).  This happens because the stems and leaves are covered with a lot of tiny, brittle, needle-like hairs called trichomes that easily break off when touched. At the base of these hairs is a potent mix of histamine, acetylcholine, serotonin and formic acid. And it is this chemical mixture that provides the stinging sensation that can last anywhere from a few minutes to a few hours, depending on your sensitivity level and the size of the dose you get.  

Stinging Nettle is not native to our region – it is naturally found in Europe, Asia and North Africa. Fortunately, we have several members of Urticaceae that are native to the southern Great Lakes region that we can grow in our gardens as host plants, and some of these are even non-stinging if you really don’t want to get stung.  

Nettles and Relatives in the Garden 

Stinging Nettle (Urtica dioica) 

Let’s start with the non-native Stinging Nettle. You COULD choose to grow this though personally I find it pops up unwanted in my garden without any help. (Apparently it makes a great cooked green, tasting a lot like spinach and loaded with vitamins A and C – the sting is removed with cooking – but always read up on the potential side effects before eating any wild plants). If you really want this plant, consider growing it in containers to help prevent its spread as it grows vigorously from rhizomes and can quickly overtake a garden. Deadheading can reduce the likelihood of seeds, which can remain dormant in the soil for decades. 

This plant typically grows from 3-7 feet tall and 1-3 feet wide. It thrives in full sun, but will also tolerate a fair bit of shade (in my garden, it happily grows in full shade under large walnut trees). It’s not fussy about soil type and likes anything from very moist to relatively dry soils. 

Canada Wood Nettle (Laportea canadensis) 

There are many similarities between our native Canada Wood Nettle and Stinging Nettle – including the sting they both give when you brush against them. One of the easiest ways to tell the two apart is that Canada Wood Nettle has alternate leaves whereas the leaves of Stinging Nettle are opposite. Also, Canada Wood Nettle prefers moist, shady woodlands and doesn’t like hot, dry sunny sites.  

Canada Wood Nettle grows 2-4 feet tall with a 1-3 foot spread. It will tolerate deep shade if sufficiently moist. Self-fertile, separate male and female flowers are inconspicuous and appear in the summer. Male flowers are shorter, less than 1/8″ across, with 5 white to green petals. Female flowers are loose and lacy with 4 green sepals that resemble curly leaves in longer clusters. These are clustered at the top of the plant. Like Stinging Nettle, this plant spreads readily by rhizomes.  

False Nettle (Boehmeria cylindrica) 

Also sometimes referred to as Smallspike False Nettle, Swamp Nettle or Bog Hemp, this is our stingless native. It has opposite leaves (like Stinging Nettle) and gets up to 5 feet tall in full to partly sunny, damp to average soils.  

Because it doesn’t have stinging hairs, this is a great choice as a filler plant in moist, shady gardens as it remains green and leafy well into the fall. 

Clearweed (Pilea pumila) 

One of my personal favourites in the nettle family, Clearweed gets its name from its smooth, translucent stems, which to me are almost jewel-like. Also called Canada (or Canadian) Clearweed, Dwarf Clearweed, Coolweed and Green-fruited Clearweed, this short(ish) cousin of nettles ranges from 6 inches to 2 feet tall – in my southwestern Ontario garden in sandy loam soil it usually tops out at around 1 foot in height. It prefers part shade, but I’ve seen it growing in full sun to full shade as long as the soil is at least moderately moist. Like False Nettle, it also has no stinging hairs.    

A Note on Urticaceae 

All the plants listed here are wind pollinated, so you won’t see much pollinator activity around them.  And all are purportedly edible, though with varying degrees of palatability. Some sources claim, for example, that neither Clearweed nor False Nettle are edible, while others suggest they are. If you decide to try some on your plate, do your research first. For me, I’ll just leave all mine for the caterpillars.  

Who doesn’t love to see a majestic butterfly flit through the garden, alighting on newly opened flower buds for a sip of nectar, then watch as it explores what else you have to offer. If you’re really lucky, you may even get to see it lay an egg or two on the underside of a leaf. Although most folks do know by now the relationship between Monarch Butterflies and Milkweed, surprisingly I met someone a few weeks ago that saw monarchs nectaring on his Purple Coneflower and wondered why he never saw them laying eggs on it! He didn’t realize that they ONLY lay their eggs on members of the Milkweed family. 

Monarchs aren’t the only butterflies (or moths, for that matter) that have very particular tastes. Although some species of Lepidoptera are generalists – meaning their caterpillars will eat many different kinds of plants, what a lot of folks don’t realize is that most butterflies and moths do not lay their eggs on just any plant. They require very specific species of plants if they are to successfully multiply their numbers.  

This month’s article will be the first in what I hope will be a series of articles about host plants – which plants host which butterflies and/or moths – and a brief description of what you need to grow those plants to make your yard a nursery for many beautiful butterflies and moths. I shall start with my own favourite butterflies, the swallowtails. 

Swallowtail Butterflies 

In the southern Great Lakes region, we are home to 9 species of Swallowtail Butterfly, according to Rick Cavasin  (https://www.ontariobutterflies.ca/families/Papilionidae) one of which – the Midsummer Tiger Swallowtail – he indicates has only recently been described. In today’s article I will cover the two most common ones that I regularly see in my southwestern Ontario garden. I will provide photos of the butterfly and its caterpillar, as well as photos of some of its host plants along with some basic facts about growing these plants. Over the coming months I will look at a few more of the swallowtails, then perhaps go on to some of our other butterflies, if sufficient interest exists. 

Black Swallowtail (Papilio polyxenes)  

This black beauty is a challenge to photograph because it rarely sits still. Even while nectaring its wings are constantly aflutter. The caterpillar of this butterfly feeds on plants in the carrot family. Many vegetable gardeners are accustomed to seeing it on their dill and parsley plants, and even on their carrots or celery, and if you don’t mind sharing your produce, this is a great way to attract them. 

The native host plants for Black Swallowtail Butterflies include Golden Alexander (Zizia aurea), Cow Parsnip (Heracleum maximum), Purplestem Angelica (Angelica atropurpurea), Sweet Cicely (Osmorhiza claytonia) and Canadian Honewort (Cryptotaenia canadensis). 

Golden Alexander (Zizia aurea) 

• Zizia aurea is a full to part sun perennial that likes moist to dry, sand to clay soils. It is an early flowering plant in the garden, with blooms starting in early May and often blooming right through to the end of June. (On a personal note – the first year I grew just a single Golden Alexander plant, I had 7 Black Swallowtail caterpillars on it!) 

Cow Parsnip (Heracleum maximum) 

• Heracleum maximum is the tallest member of the carrot family in North America, often reaching heights of 6-8 feet. It is a relative of Wild Parsnip and Giant Hogweed, and like those plants its sap can cause sun rashes or blisters. It grows in full to part sun, in just about any moist but well drained soil. 

Purplestem or Great Angelica (Angelica atropurpurea) 

• Angelica atropurpurea is another giant in the garden, often getting up to 7 feet tall or more. This short-lived perennial likes full to part sun and wet to moist clay or loamy soil, or sandy soil with lots of decaying organic matter.  As with Cow Parsnip, if you choose to grow this plant be careful to avoid getting the sap on your skin. 

Sweet Cicely (Osmorhiza claytonii), Aniseroot (O. longistylis) 

• Osmorhiza claytonia and O. longistylis are plants for full to part shade. They tolerate most soil types and like average moisture soils. They get about 2 feet tall and bloom in May and June.   

Canadian Honewort (Cryptotaenia canadensis) 

• Another shade plant, Cryptotaenia canadensis, starts flowering in June and can continue right through to September, and though its flowers are quite small and delicate they often put on a lovely show because of the sheer number of blossoms. This perennial can get up to 2 or even 3 feet tall in average moisture, rich, loamy soil. 

Giant Swallowtail (Papilio cresphontes)  

The Giant Swallowtail gets it common name for a good reason – with a wingspan up to 4½ inches (113 mm) – it is the largest butterfly in Canada. Its caterpillar, unlike the colourful caterpillar of the Black Swallowtail (which the uninitiated often confuse for a Monarch caterpillar), looks exactly like a bird dropping on a leaf. Its disguise is so convincing that these caterpillars don’t even bother to hide under the leaf. You will almost always find them sitting on the top of the leaf, as if the bird had just pooped and flown on. 

The Giant Swallowtail’s host plants are mostly members of the citrus family – the leaves of orange, lemon, lime and grapefruit trees. Fortunately, we have two species that it uses here in the southern Great Lakes region – Hop Tree and Northern Prickly-ash (both of which member of the citrus family). The fact that Prickly Ash is related to oranges is obvious as anyone who has tasted the berries can tell you – it’s like biting into concentrated orange rind. 

Hop Tree (Ptelea trifoliata)  

• The Hop Tree goes by many common names – Wafer Ash, Stinking Ash, Swamp Devil’s Bit, Water Ash, Wing Seed and even Shrubby Trefoil. This is a small tree/ large shrub, getting 15-20 feet tall and spreading just as wide. It likes just about any kind of soil in full sun to full shade. It even makes a good potted shrub – just make sure your pot is large enough. The Hop Tree is monoecious, often producing male, female, and perfect (bisexual) flowers on the same shrub. 

• The first time my Hop Tree flowered (in June), I couldn’t figure out where the lovely fragrance was coming from. Once I did, I regularly altered my path so I could come near the blossoms for a whiff of perfume. But it must be one of those fragrances (like the taste of Cilantro for some) that you either love or hate – how else would it get the common name Stinking Ash?!? 

Northern Prickly-ash (Zanthoxylum americanum) 

• Northern Prickly-ash is a very thorny shrub that can get 15-20 feet tall, though the only place I’ve seen it in the wild (the alvars of Prince Edward County, near Kingston, Ontario) the shrubs were typically around just 5-7 feet high. Not a great choice for a small yard as it can spread aggressively by root suckers, but these can be controlled by either pruning them as they appear, or by planting the shrub in a barrel sunk into the ground.  

• Prickly-ash does best in full sun, in well drained, average soils. It produces small, inconspicuous green flowers in the spring, but these are beautifully aromatic and attract many bees. Even the leaves have a lemony smell when crushed. In late summer, the fruit ripens to a reddish orange. Another common name for this plant is Toothache Plant, because eating the berries will numb your mouth, but you will need both a male and a female plant to get berries. ` 

Next time: Eastern Tiger Swallowtail and Spicebush Swallowtail 

So far in this series on garden soil, I have looked at soil texture, pH, and organic matter in your soil and their impact on plants. In this, the final article in the series, I will discuss soil moisture and nutrients, and why these things even matter. 

Water 

Some of our native plants need dry, well drained soils. At the extreme end are plants like Prickly Pear Cactus (Opuntia spp). Because these plants have evolved strategies to retain water and have lost their mechanisms for eliminating excess water, too much water will cause the plant to drown because it is not able to get enough air to the roots. In cactus, in particular, too much water will lead to rotting roots because they do not have the ability to fight of moisture loving fungi and bacteria.  

We all know that plants need water to grow. How much they need (or will tolerate) depends on a variety of factors, not the least of which is the conditions under which they evolved.  

At the other end of the spectrum are aquatic and semi-aquatic plants. Plants like Soft Bulrush (schoenoplectus tabernaemontani) will quickly desiccate and die if left out of the water because they have no mechanism to retain moisture (such as the thick walled cells often found in plants like cacti). But why don’t they drown? In order to get the necessary oxygen down to the roots that are in waterlogged soil, these plants have specialized cells, called aerenchyma, which form tubes to conduct air down below the water level. 

But most of our native plants fall somewhere between the two extremes. In average garden soil, there will be periods that the soil is very wet, such as after the spring thaw and after a period of rain, and times when the soil is quite dry. The moisture retaining capacity of the soil, as we saw in the first two articles in this series, has to do with soil texture and the amount of organic matter present. And if you grow plants that are suited to the soil conditions in your garden, they will easily tolerate these variations in soil moisture. 

We know plants need water, but what role does water actually play in plant growth. For starters, water is essential for photosynthesis. Photosynthesis is the plant’s superpower – being able to convert water (H₂O), carbon dioxide (CO₂) and sunlight into nutrients for the plant, then discarding the excess oxygen (O₂) as a waste product – which is very convenient for oxygen breathers like us. During photosynthesis, water provides the hydrogen (H) atoms required to make glucose (C₆H₁₂O₆) – the simple sugar that serves as the primary source of energy for the plant. 

Water also dissolves nutrients – both organic and inorganic – in the soil, making them available for uptake by the plant’s roots. It is also the medium through which the glucose and soil nutrients are distributed to various parts of the plant. 

Finally, water also plays a role in the plant’s structure and shape by creating a constant pressure, called turgor, on cell walls. When a plant doesn’t have enough water, the cell walls contract, causing the wilting that we see in plants that need watering. If allowed to remain dry for too long, the cells reach a point where they can no longer reabsorb the water and the plant dies. 

Matching your plants to the appropriate soil moisture can be a tricky task. Fortunately, most of our native plants are very forgiving and will tolerate short periods outside of their moisture comfort zone. After all, we have dry years and wet years, as well as those crazy years than bring a pile of rain followed by two months of drought. If plants couldn’t cope with these vagaries, we’d have very few plants. 

Plant Nutrients 

There are 17 nutrients that are essential for plant growth and these can be divided into two categories: macronutrients – those nutrients that are used in large amounts – and micronutrients -those that are used in small amounts by the plant. The macronutrients hydrogen, oxygen, nitrogen and carbon contribute to over 95% of a plant’s entire biomass. Micronutrients are present in plant tissue in quantities measured in parts per million. Carbon, oxygen and nitrogen are all absorbed from the air, while the other nutrients (including H in the form of water) are primarily taken up from the soil through the plant’s roots. 

Each of these nutrients plays an important role in the plant’s growth. We’ll first look at the role of the three principle components of fertilizers – Nitrogen, Phosphorus and Potassium (N, P & K) – followed by a quick look at the other macronutrients. 

NPK 

Nitrogen is used by the plant to create amino acids, the building blocks of protein, and is used by chlorophyll in photosynthesis to convert sunlight into energy for plant growth, among other roles. Insufficient nitrogen can result in leaf yellowing and stunted growth.  

Nitrogen is a water-soluble element that is primarily available to the plants from soil water in the form of nitrite (NO₂-), nitrate (NO₃-), or ammonium (NH₄+) ions. Bacteria in the soil convert nitrogen gas into ammonia, which plants can use. Lightning also converts atmospheric nitrogen into ammonia and nitrate, which enter the soil with rain. When plants and animals die, or when animals excrete waste, the nitrogen in their organic matter returns to the soil. Compost, which is primarily the excrement of soil organisms, is a great source of nitrogen. 

The primary role of Phosphorus in plants is storage and transfer of energy produced by photosynthesis for growth and reproductive processes. It is necessary for seed germination, photosynthesis, protein formation, flower and fruit formation, and is particularly important for good root development. Without adequate phosphorus, plants will be slow to mature, will have poor flowering, will drop flowers and fruits prematurely, and their growth will be stunted.  

Phosphorus in its mineral form is not readily available to plants – it requires bacteria to convert it to a plant available form. Ideally, soil pH should be in the range of 6-7.5 – soils more acidic or alkaline than this will result in P becoming bound to other elements in the soil and not available for plant use. Chicken and horse manure, bone meal, fish emulsion and rock phosphate (used in the manufacture of organic fertilizers) are all good sources of phosphorus for plants. 

Potassium plays a vital role in photosynthesis and regulates water usage by the plant. It has also been shown to improve disease resistance in plants, improve the size of seeds, and enhance fruit quality. Insufficient K can result in leaf yellowing between the veins of leaves and curled or scorched leaves. Potassium is very mobile in the plant, and plants move it to the younger, needy tissue when it becomes limiting. As a result, potassium deficiency first shows up as a mottled chlorosis of the older leaves and eventually the leaf edges become brown. 

Potassium is mined as Potash (cool fact: the world’s largest potash mines are in Saskatchewan) and wood ash. Manures, compost and other organic materials are also potassium sources, even though the concentration of potassium in them is pretty low, but these materials are typically applied generously enough to contribute a sufficient amount of K. 

The Other Macronutrients 

Sometimes called “secondary nutrients”, the elements of carbon (C), hydrogen (H), and oxygen (O) are absorbed from air and water, while Magnesium (Mg), calcium (Ca) and sulphur (S) are taken up from the soil. 

Carbon, in addition to its role in the formation of glucose for the plant, is an essential building material that gives strength to cells. Adding organic matter, such as manure or decomposing plant parts (rich in carbon– or the browns in compost), to the soil surrounding growing plants is an effective way to provide C for the plants. 

Hydrogen, made available from water during photosynthesis, in addition to being used to form glucose molecules, plays a key role in plant respiration, and recent research suggests that hydrogen also plays a role in mitigating plant stress as well as promoting root growth. 

Oxygen is used by plants in cellular respiration – to break down food molecules and release energy for growth. In addition, the amount of oxygen available to a plant’s root cells affects its growth rate, water and nutrient uptake, as well fruit yield and quality. 

Magnesium plays a critical role in the production of chlorophyll and is a key driver in photosynthesis. It is also involved in the transportation of carbohydrates from leaves to actively growing tissues of plant roots, shoots and reproductive organs. A deficiency of Mg can reduce root or shoot growth, and potentially seed weight, and can appear as yellow bands between the leaf veins. Although Mg is normally sufficient in most garden soils, if necessary, supplemental Mg can be added through compost, Epsom salts (magnesium sulfate), or dolomitic lime.  

Calcium is an important structural component of cell walls. It is necessary for cell growth and division, and influences water movement in cells. In some plants, calcium is required for the uptake of nitrogen. Calcium is found naturally in most limestone-based soils but can be supplemented with crushed eggshells, ground oyster shell or dolomite lime. Calcium can also help to neutralize acidic soils. If Mg levels are sufficient in the soil, adding extra calcium could lead to soil toxicity and cause further problems. If in doubt get a soil test done. 

Sulphur also plays a key role in photosynthesis and the formation of chlorophyll, and in the production of plant proteins. It is also a great tool to help acidify soils for those acid loving plants like blueberries. Sulphur deficiency can resemble N deficiency – leaves can become light green or pale yellow due to the lack of chlorophyll production. Manure, compost, and decomposing plant matter are all sources of sulfur for the garden. 

To learn more about nutrients (and nutrient deficiencies), check out the following websites, or simply google the subject. 

https://nsnewfarmer.ca/wp-content/uploads/sites/5/2018/02/Nutrient-Deficiency-Guide.pdf

https://extension.arizona.edu/sites/default/files/2024-08/az1106.pdf

Summary 

Most soil conditions across the world can provide plants adapted to that climate and soil with sufficient nutrition for a complete life cycle, without the addition of nutrients as fertilizer. In fact, here in the southern Great Lakes region, we are blessed, for the most part, with great nutrient rich soils. When growing native plants, adding additional fertilizers or compost will often simply result in tall, lanky plants that fall over in the garden. And, speaking from experience, it can take several years for the excess nutrients to be used up. So unless you are trying to grow plants in an industrial wasteland, it is highly unlikely that you will need to add extra nutrients to a native plant garden. The deep roots of many of our native species are able to tap the depths of the soil and find all that they need. 

But it is also important to do your homework on the moisture needs of the plants you are growing, and plant those with high moisture needs together and those that like it drier separately. In this way you will greatly increase your success in the garden, and provide habitat and food for many insects and for those that rely on them. 

Happy Native Plant Gardening. 

Let me preface this piece with the caveat that I am not trained as a soil scientist (though I did take a couple of university soils courses many years ago). Nevertheless, as a gardener I am always working with soil, and I’ve been curious enough to do some more research over the years.  

In any good book on growing plants, you are likely to come across terms such as clay-loam, soil alkalinity, humus, topsoil, etc. Understanding what some of these terms actually mean, and how they relate to your gardening, will help you to be more successful at growing your native (or other) plants. 

First off, some definitions. 

Texture: refers to the size of the soil particles (this is not the clumps of soil you may see in your garden, but the elemental particles that make them up). Soil scientists have determined that there are 3 basic soil particle sizes – Sand, Silt and Clay – and these combine to form 12 soil types that you would typically see in gardens (more on these later).  

Sand is made up of ground minerals and rocks that are rounded or irregular in shape. These range in size from 2 mm down to 0.05 mm in diameter and feel gritty when rubbed between your fingers. 

Silt particles are between 0.05 and 0.002 mm in diameter and feel a bit like flour when dry. 

Clay particles are extremely small – less than 0.002 mm in diameter. In fact, they are so small that you can really only see the individual particles through an electron microscope. We often refer to clay soils as “heavy”. (One suggestion for this term is that plowing clay soils takes 2 to 4 times the tractor power to pull the plow through it as in “light” sandy soils.) 

The Implications of Texture 

If your soil is mostly sand, you cannot form a ball of it when it is wet – it will just crumble and fall apart. This is because the large particle size of sand results in large air gaps between the particles and thus water doesn’t have a strong enough bond to hold the particles together. Although these gaps allow water to enter easily, it also lets the water flow right through. As a result, sandy soils dry out quickly.  

Some plants have adapted to sandy soils – Big Bluestem (Andropogon gerardii) and Prairie Smoke (Geum triflorum) are just two examples – and thus will typically not do well in wetter areas with heavier soils. By the same token, plants that have evolved in wetter areas, especially in clay-rich soils, are unlikely to survive in sandy soils. This is, in part, because without moisture retaining mechanisms, their roots will simply dry out. 

At the other end of the spectrum, clay particles are so small that the air spaces between them are extremely tiny. Often, water will just puddle on top of clay soils and take ages to drain away. (This is why they use clay to line ponds and landfills.) However, water will eventually soak into the pores and because of the physics of water molecules and soil particles, the clay will actually “hold onto” the water for a much longer time.  

Anybody who has walked through wet clay can attest to the fact that wet (even damp) clay sticks tightly to boots, shovels, etc. One impact of this characteristic is that clay soils readily compact and compacted soils do not allow roots to penetrate easily. 

To test if you have clay soil, wet a small lump of it and press it between your finger and thumb and try to form a ribbon of soil. In pure clay, the small clay particles will stick tightly together and you should be able to press out a ribbon a few centimeters long. This Ribbon Test is used by soil scientists to get a quick idea of the soil texture. 

Just as some plants have evolved in sandy soils, so too have some evolved in areas of heavy clay. Cardinal flower (Lobelia cardinalis) and Swamp Milkweed (Asclepias incarnata) are two that come to mind. 

Everything in Between 

Soil scientists have developed a Soil Texture Triangle which, once you learn how to read it, will allow you to identify which of the 12 soil types you have based on the clay, silt and sand composition of your soil. 

Let’s say you get your soil tested and it comes back that you have 45% sand, 20% clay and 35% silt. Where these 3 lines cross on the triangle indicates your named soil type – in this case, loam. (The angle of the numbers indicates which line to follow.) 

If you want to determine your own soil texture, one method you can use is what is called a jar test. 

• Start by getting a shovel full of soil from your garden (you can take samples from different areas, if you want, to get a general feel for your entire yard though it is unlikely that there will be significant differences in an area as small as a town lot). Make sure you take your sample at least six inches (15 cm) down – not just off the surface – as you want to get a complete picture of your soil.  

• Sift your soil to remove debris, rocks and large organic matter and fill a clear jar about 1/3 full of this “cleaned” soil.  

• Add water almost to the top of the jar and add a small amount of water softener or liquid dish soap. Put the lid on the jar and shake vigorously for a few minutes until the soil/water mixture is a uniform slurry. Let the mixture stand for 48-72 hours for the soil to settle out (it will separate out into layers with sand at the bottom and clay at the top).  

• After the mixture has set for a couple of minutes, you can mark the side of the jar with a black marker. This represents the sand component. 

• After the mixture has set for about two hours, mark the side of the jar. This represents the silt layer. 

• Finally, after 2-3 days, the clay will finally have settled out and you can mark that level. 

• Using a ruler, measure the depth that each layer makes up. To calculate the percentage of each element, divide the height of that element by the total height of the soil in the jar.

With this information, you can now determine which plants will like the soil you have in your garden. After that, you can determine light and moisture levels to narrow down your selection. 

Values from my yard’s soil sample: Total soil = 42 mm

Sand = 21/42 = 50%, Silt = 15/42 = 36%, Clay = 6/42 = 14%

Reading these values of the Triangle, we find that my soil is classified as loam (and very close to being a sandy loam).

Next Month – Beyond Sand, Silt and Clay – Organic Matter, Loam, Soil pH and other magic 

Most people reading this article will have, at one time or another, faced the prospect of removing a section of lawn in order to create a new garden – whether that be specifically for a native flower bed, for a vegetable patch, or for some other good reason. Today I want to discuss some of the pros and cons of the various methods of getting rid of the grass that I have experienced in my quest to grow something besides lawn. In particular I will look at the following 5 methods… 

1. Herbicides 

2. The “Lasagna” Method 

3. Tarp 

4. Solarization 

5. Removing the Sod (with shovel or mechanical sod lifter) 

Herbicide (Glyphosate) 

Let me start this section with the confession that, in the early days of gardening, I DID use RoundUp (i.e. Glyphosate) to kill off the sod, but I no longer use this method (see *Note at the end of this article on my feelings about Glyphosate).  

Roundup is very effective at killing sod. It is also very easy. The best part of it is that it is relatively quick – spray your patch of grass this weekend, and next weekend start lifting the dead sod (it can take up to 2 weeks for some of the plants to turn brown, but they will be dead. Glyphosate is drawn down into the roots of the plant via the sap stream in the leaves, where it prevents the roots from absorbing nutrients from the soil. The big advantage is that if you don’t dig out all the roots, it won’t matter.) 

However, RoundUp is expensive, hard to get (in some cases), and carries a huge stigma. It also has the distinct disadvantage of potentially killing off good plants through spray drift. Another drawback is that if you accidentally step on a sprayed patch, you leave footprints of dead grass across your lawn as you walk back to the house. (Ask me how I know this – d’oh!) That makes it pretty obvious that you have used Glyphosate to anyone who visits (at least until the dead spots fill back in). 

And, although the sod is now dead, you still have to rototill it up or dig it out before you can plant your new garden. I would only recommend this method if your patch of lawn is heavily infested with bindweed or some other equally deep-rooted invasive species that you won’t be able to easily remove with the other techniques. 

The Lasagna Method 

The lasagna method of gardening is often used in the preparation of vegetable gardens. This is because the materials used will create a rich, moisture retentive garden soil that may be too rich for native plants. However, if you are developing a garden in a new subdivision where all the topsoil has been removed, or on land that was once a gravel pit, this method might work for you. 

The trick with the lasagna method is to lay down a layer of cardboard or newspaper first. This helps to smother the grass (these materials will decompose in a year or less and become part of the soil). You then cover it with layers (like a lasagna) of mulch, lawn clippings, compost, etc. to make a rich, fluffy soil to plant into. The process can take a year for the layers to break down enough to become soil, so it is a long term process. 

A great advantage to this method is that you don’t have to physically remove the sod. And you can plant right into the decaying mulch. (Don’t do this if the mulch is actively working and is hot – you could burn off the sensitive plant roots.) 

The big disadvantage is that it can take the better part of the year to decompose enough to safely plant into – depending on weather, depth of mulch, etc. 

Tarps, Old Carpet or Cardboard 

Similar to the lasagna method, in that this method starves the sod (and weeds) of light and moisture, a tried and true way to kill grass is to cover it with some form of dark barrier. The main drawback to this method, if you’re an impatient gardener, is that it can take months to ensure the grass and weeds are all killed.  

Cardboard will work, though it might be a tad of a challenge to keep it from blowing around or getting shifted from foot traffic. Adding some mulch to weigh it down brings you back to the lasagna method but, if your land is stony, you could use rocks to keep it in place. Cardboard will eventually deteriorate, and if you don’t plan to leave it in place and plant through it (cutting holes for each plant), then it can be pretty messy to lift for disposal. 

I have used old carpet – someone had put rolls of it out for garbage pick up and I just scooped it up and took it home. If there is a carpet store near you, they will likely be glad to give you carpet they’ve ripped out of someone’s house – it will save them from taking it to the dump. The carpet was quite effective at killing off the grass under a large maple tree and it did not have to be weighed down with anything as it was quite heavy enough to resist any unwanted movement – especially after it had been rained on. The hard part was cutting up the old, smelly, rotting carpet to dispose of it – small chunks at a time – with my household garbage once it had done its job.  

Tarps work well. They have the advantage of being lightweight and easy to handle, and they come in various sizes (and colours). They do need to be weighted down (with stones or bricks) or pegged. The drawback is that they are pricey and UV rays will eventually break down the plastic if it is left in full sun for the better part of a year.  

A much more frugal option is to go to your local lumber yard and ask for the plastic tarps that cover the lumber piles. These are normally just thrown in the garbage when a new shipment of lumber comes in. My local lumber yard chuckled when I asked if I could have a couple, but they gave them to me for free. If you’re lucky, you may get some that don’t even have rips or holes in them. And the bonus: you can cut them to fit any shape garden without worrying about ruining a perfectly good tarp. 

Like other methods of smothering the grass, you will probably have to leave the covering on the lawn for several months to effectively kill unwanted weeds. Some of the very persistent plants (like bindweed, etc) may even survive tarping – especially if they are well established in your lawn. 

Solarizing 

Solarizing is similar to the tarp method, but with the use of clear plastic sheets that magnify the sun’s rays to kill the grass. Proponents claim this can effectively kill off the sod in a couple of months. It is a method I have NOT tried, so I only have their word for it. Nor do I know how effective it is on those deep rooted weeds like bindweed. But if your future garden area is small, you can buy clear plastic (sold as vapour barrier in the hardware store) at a relatively reasonable price. 

Shovel, Mechanical Sod Lifter 

My preferred method of sod removal these days is a flat-bladed shovel. This is because I enjoy the physical aspect of digging, I have a flat-blade shovel (so it doesn’t cost me anything), and my soil is a nice sandy loam that is easy to dig.  

With my shovel, I simply dig a small v-shaped trench around the perimeter of the new garden bed, then shove the blade under the grass and flip it up. I then toss the sod clump into the wheelbarrow to be dumped (grass side down) in a back corner of the yard where the grass then dies – leaving a pile of topsoil for use when and where I need it. The drawback is that this is a slow process and can be very hard on the back. The good part is that you can dig out any deep roots as you come across them.  

I’ve never tried an actual sod lifter, either a manual one a powered one, but really these are just more sophisticated versions of the flat shovel.  You can usually rent manual lifters or powered sod lifters, depending on your budget and the size of the garden area, at most of your typical tool rental places. 

The End Results 

Ideally your efforts will result in a garden that is free of grass and weeds, ready to plant into. You may have to rototill if you are in heavy clay soil or you may do like I did and simply add a layer of woodchip mulch to keep moisture and soil organisms in place, thereby letting nature loosen the soil for you. In the end, you should have a wonderful new garden bed that is ready to go. 

Happy Native Plant Gardening. 

PS – My Thoughts on Herbicide Use (this may be controversial for some!) 

*Note – I do not have a problem with the judicious use of Glyphosate, in small amounts, for very specific plants – especially for invasive, poisonous or extremely deeply rooted plants (like bindweed). Round up is broken down in the soil by soil bacteria within a few days. The bacteria use it as a food source (Kanissary, et al., 2019). “Glyphosate’s half-life in surface waters after forestry spraying in Manitoba was less than 24 hours. In soils, glyphosate undergoes microbial degradation to the metabolite aminomethylphosphonic acid (AMPA), which is slowly degraded to carbon dioxide and simple inorganic compounds” (Gov’t of Canada, 2015). 

For those who believe salt, vinegar and dish soap are a better option, I suggest you do some unbiased research. That home remedy will kill off the above-ground part of the vegetation only (it is a contact herbicide and works by killing whatever it comes in contact with), but not the roots, so most perennials will just re-grow. In the meantime, you will have poisoned the soil for microbes, earthworms, etc., killing off those important soil fauna (Enroth, 2020). If you believe that this is a chemical free way to kill plants, remember that salt is the chemical sodium chloride and vinegar is acetic acid, and in sufficient quantities to burn off plants, these chemicals will also kill soil micro- and macrofauna. Research has also shown that acetic acid in great enough concentration to effectively kill plants (5-10%) is “incredibly harmful to humans. Any contact with the skin and eyes causes irreversible corrosion and damage, meaning gloves and goggles are a must when using vinegar herbicides” (Enroth, 2020). In fact, even at these high concentrations of acetic acid it is really only effective at killing very young (less than 2 week old) seedlings and some young annual species (Smitth-Feola & Gill, 2022). 

Equally as problematic, it will kill any frogs or toads it happens to land on (Enroth, 2020). For herbicides to be approved in the first place, they have to be shown to target only plants, usually by attacking specific plant parts at the cellular level, like the chloroplast which animals and other organisms lack. Neither salt nor vinegar are approved as herbicides because they impact both plants and animals that they come into contact with (Pelliccia, 2024). A good friend accidentally spritzed a toad while using the concoction. She noticed right away and washed the toad off, but it died anyway.  

I am not condoning the wholesale use of herbicides to remove lawn. Quite the contrary. But if it is used carefully and in small quantities, it can be a very safe and effective solution for problematic weeds. 

References 

Enroth, C. 2020. Home Horticultural Remedies. University of Illinois Urbana-Champaign, Illinois Extension. https://extension.illinois.edu/blogs/good-growing/2020-05-22-home-horticultural-remedies  

Government of Canada. 2015. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Glyphosate. https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-glyphosate.html  

Kanissery, R, Gairhe, B, Kadyampakeni, D, Batuman, O and Alferez, F. 2019. Glyphosate: Its Environmental Persistence and Impact on Crop Health and Nutrition. Plants. doi: 10.3390/plants8110499 

Pellicia, S. 2024. Salt & Vinegar on Weeds? Save it for the Chips! Washington State University/Washington Dept of Natural Resources. https://foreststewardshipnotes.wordpress.com/2024/06/12/salt-vinegar-on-weeds-save-it-for-the-chips/  

Smith-Feola, D. and Gill, S. 2022. Vinegar: An Alternative to Glyphosate? University of Maryland Extension, https://extension.umd.edu/resource/vinegar-alternative-glyphosate/