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ReCLAYm Your Garden by Amending Compacted Clay Soil

Heavy clay soils – also referred to as “gumbo” soil – are a common occurrence throughout southern Alberta, and can often interfere with the growth of a healthy and productive garden. As a result, many Calgary gardeners have spent loads of time and lots of money trying to find the best way of fixing their clay-heavy soil.

Luckily there are a few ways to amend heavy clay soil and improve the health and vitality of your garden and its plants! As Calgary’s lawn care and landscaping experts, we have spent years discovering and refining the best techniques for fixing compacted clay soil. Now, we are more than happy to share with you what we have learned!

So fill up your stoneware coffee mug and put down your trowel – in this blog post, we’re sharing our top tips for loosening and amending clay-heavy soils in Calgary and throughout southern Alberta.

A Quick Primer on Clay Soil:

Photo of clay soil under a microscope.

All the clay soil in the world is made up of fine mineral particles that are typically smaller than .002mm (smaller than thewidth of a human hair). This small size is what makes clay soil smooth and sticky when wet (which is useful if you’re a sculptor, but not so much when its in your garden soil!)

In southern Alberta, the exact composition of clay soil varies, but it will have a high percentage of clay particles mixed with lesser amounts of silt, sand, and minerals.

“Gumbo soil”
AKA “Solonetzic soil”, is characterized by a heavy clay layer just below the topsoil. This layer causes root growth problems in plants due to swelling when wet, allowing for only to shallow-rooted plants that are vulnerable to drought.
– From “Farming Gumbo Soils”

While most Calgarians struggle with clay soil, having clay in your garden soil is not always bad.

Clay in your soil can have a range of beneficial and essential nutrients that help plants to thrive, including phosphorus, potassium, and magnesium. It can also help with water retention, reduce and/or prevent nutrient leaching, and can even help prevent soil erosion.

That said, having compacted clay soil is a different matter. Compacted clay soil can cause a bunch of issues for your garden. These issues include: poor drainage, lack of proper aeration, and restricted growth.

Left untended, compacted clay soil easily becomes a risk to the greater environment because it can increase the likelihood of erosion and runoff, contributing to flooding and soil depletion.

So why is so much of the clay soil in Calgary compacted?

The cause of much of Calgary’s compacted clay soil is a byproduct of our city’s success – expansion and development.

Photo of a large area of bare land being developed in Calgary with tractors, bulldozers, and diggers on it.
Suburban development in Calgary, circa. 2008ish.

When an area of land containing clay soil is developed, the soil gets compacted by heavy machinery and foot traffic. Once the development is finished, a common (and unfortunate) practice for developers is to simply leave the now compacted clay soil unaddressed.

So instead of fixing it right away, they simply spread a layer of topsoil over it in order to get a quick and easy grass-covered landscape.

It’s tempting to take the shortcut of simply covering compacted clay soil with topsoil, but it’s a poor choice for soil health and long-term sustainability.

How do you (effectively) fix compacted clay soil in Calgary?

Good things come to those who wait.

 While there is more than one way to deal with this issue, each method we talk about here will require 2 key ingredients:

Commitment + patience

There are 3 main ways of addressing and improving the quality of your compacted clay soil in Calgary.

One is to amend the soil itself. The other is to amend it by adding beneficial plants… and the third is to just do both!

Amending Your Clay Soil:

The Internet is full of recommendations for clay soil amendments, listing everything from horse poop to sand as the “best” way of making your clay soil workable.

Of the many, many soil amendment suggestions you will encounter, the 2 we recommend are:

  • Adding compost, such as composted manure or leaf mould compost.
  • Adding beneficial plants.

Using Composted Manure:

When it comes to amending your gumbo soil with horse, cow, or chicken manure, timing is… … … everything.


In order to get the most from manure, use composted manure that has been composted (or otherwise left to rot) for minimum of 6-8 months – ideally 1 full year. This gives it enough time to kill off any harmful microbes or bacteria, as well as to level off nitrogen and ammonia, both of which will harm your plants and garden beds when concentrations are too high.

Second, add your composted manure to the soil in the spring. One of the great things about composted manure is the nitrogen it provides for growing root systems – but nitrogen is very water-soluble.

Why springtime? Because if you add composted manure to your garden bed in the autumn then the rain and snow melt will cause the nitrogen to run-off or leach too far down for many plant roots to reach by the time growing season returns. (Learn more about this here.)

Third, be consistent. One application of compost might help a bit right now, but for impressive long-term results you need to regularly add compost over the span of several years.

If you decide to go with composted manure to amend your heavy clay soil then a rule of thumb is to add 7.5-10 cms (3-4 in) of compost on the existing soil and to very gently work it into the top layer.

Using Leaf Mould:

In case you haven’t heard, leaf mould is garden gold.

Photo of a pile of leaves being composted to make leaf mould.
To your garden, this is what a treasure chest really looks like.

Leaf mould serves as one of the most effective and sustainable ways of improving soil structure, enhancing water retention, and improving soil aeration. This creates an excellent growing environment for plants, allowing for better root development, better nutrient uptake, and better resistance to diseases and pests.

It’s made by decomposing fallen leaves that are left to naturally break down over time. As the leaves decompose, they release a wealth of nutrients that are essential for a plant garden. Microorganisms help break down the organic matter of the leaves and and facilitate its conversion into a slow, steady release of nutrients that result in healthier plant growth and more productive yields.

Photo of clay flower pots stacked to look like a couple sitting on a garden bench.
BFFs are awesome, even when they’re total potheads.

As if this wasn’t enough to make leaf mould your garden’s new BFF, we should let you know that it is also incredibly easy to create.

The recipe for making leaf mould yourself is:

  1. Collect fallen leaves: In the fall, gather the fallen leaves from your garden (and any neighbours who are willing to contribute to the cause). Avoid leaves that have been treated with pesticides or directly exposed to pet waste.
  2. Roughly shred the leaves: Breaking the fallen leaves into smaller bits helps speed up their decomposition process. (Helpful tip: Use a lawn mower or leaf shredder to get it done faster.)
  3. Make a leaf pile: This leaf pile is best placed in a low-traffic corner of your property where it can sit undisturbed while it transforms into garden gold. Ideally, this pile should measure about 1 meter tall by 1 meter wide (so, about 3 feet by 3 feet).
  4. Add water: Moisten the leaf pile so that it’s moist, but not soaked. This helps kick-start the decomposition process.
  5. Cover the pile: While you don’t have to cover it, it does help with the process. An old tarp or, even better, a layer of burlap will help the pile to retain necessary levels of moisture and heat.
  6. WAIT: Leave the pile to do its thing for 6 months to 1 year, or until the leaves have turned into a dark, crumbly substance that smells like a forest floor (rich, earthy, but not foul or strong & unpleasant).

And that is it! Once you have that deliciously dark, crumbly leaf mould you can apply it to your soil and watch as it works its magic.

Using Beneficial Plants:

Photo of flowering clover on a Calgary yard.
Can you spot the four-leafed clover here?

You can also add beautiful beneficial plants like clover or sunflowers to address your gumbo soil!

In fact, we recommend doing this in tandem with adding composted manure of leaf mould to your soil.

Why are beneficial plants so… beneficial?

These plants are known for their ability to break through hardpan layers and improve soil structure, making them a great addition to any garden that suffers from gumbo soil.

Photo of a plant's root system in the sunshine.One of the main ways beneficial plants improve compacted clay soil is though their roots systems. Beneficial plants tend to have deeper and more fibrous taproot systems. As these roots spread and grow, they create channels that allow air, water, and nutrients to flow more freely. This serves to improve soil structure, reduce compaction, and make it easier for more plants to grow and thrive.

In addition, plant roots release a variety of substances that change the physical and chemical properties of soil.

These substances include organic acids that make soil minerals more available to plants – in a way, making them more “digestible.”

Roots also release enzymes, sugars, and even hormones that help regulate plant growth and promote healthy microbiome diversity. This This leads to the on-going growth of more beneficial plants, which leads to further destabilization of the hardpan clay leyer.

In other words, beneficial plants amend compacted clay soils by improving soil structure, improving the microbiome, and releasing beneficial substances into the soil.

The best beneficial plants for clay soil in Calgary include:

Clover: A hardy, versatile plant that’s excellent for gumbo soil. It has a deep root system that helps to break through compacted layers. It’s also a nitrogen-fixing plant, meaning that it helps to balance nitrogen in the soil for greater fertility.

Black-eyed Susan: One of our favourite pet-friendly native plants, this wildflower is known for its ability to tolerate a vast range of soil types – including gumbo soils. Like clover, it has a deep taproot system, and it is great for attracting pollinators like bees and butterflies.

Photo of a honeybee landing on a light purple bee balm flower.
Bee balm’s flowers are beeee-yootiful!

Wild bee balm: Also called bergamot, this is yet another awesome, pet-friendly native flower that thrives in Calgary’s climate.As the name implies, bees love its delicate flowers. Humans also love this flowering beauty, and its leaves and flowers have been used for centuries as a culinary ingredient and in herbal medicines.

Sunflowers: In addition to deep taproots and fibrous root systems, sunflowers have a high nutrient requirement. This means that they help to draw nutrients up from deeper soil layers, making these nutrients more available to other plants in the vicinity.

In conclusion, your garden will thank you a million times over for addressing its hardpan clay layer and compacted clay soils! Whichever method you go with, know that you are never alone in this – we help make Calgary’s yards super, and yours is no exception! Let us know if you have any questions, or to take advantage of our years of experience to professionally manage your lawn care needs.

Why not let Superyards do your dirty work? Give us a call and learn how we can help make your lawn and garden the jewel of your neighbourhood! We offer seasonal lawn care service packages, as well as a variety of other options to make your yard Super.