Crafting the Ideal Soil for Raised Garden Beds

By founder Bryant Mason

One of my biggest challenges since I launched my business in 2012 has been finding the ideal soil for raised garden beds. Prepare yourself for a detailed history of Urban Farm Co soil…how riveting!

The process I’ve gone through attempting to create an ideal soil mix has been so complex and difficult that it’s led to some of the fastest learning I’ve experienced over the past three years. The science behind soil quickly becomes complicated and variable, which is simply a reflection of the beauty and complexity of the incredible natural world under our feet.

To take a step back, why is soil so important? I often wonder why I’m not focusing all of my attention on marketing, scalability, networking, my revenue model, and all the other traditional entrepreneurial things.

Soil is by far the most important component in farming and gardening.

1. Soil directly determines the yield, or amount of food, you get from your garden in a season. And yield is the traditional metric in farming and gardening!
2. Soil determines the nutrient density of the food. You can literally influence the vitamin, mineral, protein, and essential oil content of your food by how you amend your soil.
3. When vegetables are healthy by living in healthy soil, they also taste better (shown with a measurement called brix).
4. Soil determines how much pest and disease pressure you have in your garden. If you grow healthy plants, they have the immunity to fight off pests and diseases.

So why soil? The success of my business rests on how successful our customers are long-term. How delicious and nutritious the vegetables are. I’m a believer in the product.

What’s the point of building a business if what you’re delivering isn’t the best that it can possibly be? Why promote gardening if the food coming out of gardens isn’t the highest quality possible? Where is the craftsmanship of a product if perfection isn’t the ongoing goal?

Good soil sounds simple to achieve, but it’s not.

Understanding the science behind soil is coupled with limited supply chain options when blending a soil mix on the Front Range. With limited good sources of organic matter, a lack of high-quality micronutrient sources, and low-humus topsoil, life is hard. If none of that means anything to you, read on.

Right now, there are a few options for garden soil.

The first is to garden in the ground instead of in a raised bed. I call this the Iowa method. With this approach, you’re tasked with amending the existing ground year after year until it’s able to grow healthy plants. Having seen soil in hundreds and hundreds of Colorado backyards, this approach can work well if your existing soil is good, but most of the time new gardeners are faced with unbelievably poor existing soil (non-expandable clay put in before their house was built, rocky mountainous slopes, or dense clay soil saturated with chemical fertilizers and herbicides from years of bluegrass).

Option two is to garden in raised beds—obviously our bias for the above reason.

The traditional two approaches are to get bagged soil from a garden center, or to get bulk “Planters Mix” from any landscape company.

Both of these are bad options for healthy nutrient dense growing. Here’s why…

Bagged Soils

Bagged soils do not contain real mineral topsoil. They’re composed of a peat moss or coco coir base, then amended with various goodies from compost to perlite. The reason it doesn’t have soil in it is because of weight. Topsoil weighs 3-4 times more than peat moss or coco coir, and it’s just not financially efficient to ship something that heavy around the country to different Home Depot’s and garden centers.

However, we believe that topsoil—even if it’s really clayey—is actually a great thing! Consistent moisture is very important to maintain healthy and consistent plant growth, and clay holds water much better than peat or coco. Soilless mixes go through a constant wet-dry flux in the Colorado climate, stressing plants and decreasing plant health. Clay particles also hold on to plant nutrients, while peat/coir mixes leach the majority of their nutrients within a couple years, requiring gardeners to heavily amend or replace them altogether. Mineral topsoil usually contains all or most of the small micronutrients (trace and rare earth minerals) needed for truly healthy plant growth—some people say up to 64 different minerals for true plant health. Plants need a few parts per million of boron to synthesize vitamin B12, for example. Peat moss doesn’t have all of those minerals like topsoil does, so growing truly healthy and nutrient-dense plants is an uphill battle in a soilless media. Plus, it says something that plants have evolved for over 400 million years growing in mineral soil, with good structure, consistent moisture, a spectrum of micronutrients, and…clay! And finally, filling a 4’x8’ garden bed—or ten of them—with bagged soil is exorbitantly expensive.

Bulk Landscape Soils

Another option is to buy a bulk “Planter’s Mix” from a landscape supply company. The base of these mixes is topsoil, which is great! However, even though some clay is a good thing, Colorado bulk topsoils have way too much. Everyone knows the issues with too much clay – in short, it decreases the “fun” component of gardening.

The best way to break up and open up clay soil is by adding Calcium and/or Carbon. Colorado soil is typically high enough in calcium, but doesn’t have enough carbon. The best way to get carbon into the soil is through organic matter. Compost is the most common source of organic matter. So large landscape companies put loads and loads of compost into their topsoil to break up the clay, and they sell it very inexpensively as “Planter’s Mix.” Planter’s mix actually grows plants pretty well, especially if you get a lucky low salt batch. But there’s one gaping problem…every industrially produced compost in Colorado has a shockingly high potassium content. After a lot of research, I’ve found that this is because of the feedstocks that are used to make the compost. Most of the compost are made from biosolids (composted human waste), manure from industrial feedlots, or municipal food waste. All of these sources bring in tremendous amounts of potassium and other salts, not to mention chemical residues from persistent herbicides, antibiotics, and other industrial farming inputs.

Having way too much potassium creates “antagonisms”, preventing the plant from uptaking other nutrients such as calcium and magnesium. Potassium really isn’t toxic to plants, even at very high levels, but if there is loads of potassium in your soil you cannot grow nutrient dense food. The plants grow and look lush and large, but they are much more susceptible to pests and will show a low brix reading with a refractometer (a tool that very roughly correlates with nutrient density).

Every industrially produced compost in Colorado tends to be both inconsistent from batch to batch, and high in “salts”. Salinity of soil is simply a number that shows the total number of soluble salts in soil—from sodium to chloride to potassium salts. When certain salts get too high, plants suffer. With too much compost, you’re creating a very salty environment that hurts plant health.

So if the goal is to break up clay, and loads of compost isn’t the best option to get carbon in the soil, what is? This is the million-dollar question. In Colorado, we simply don’t have good sources of usable organic matter.

Urban Farm Company Soil Mix

It took me two full years to truly figure out everything written above. It sounds simple, but there is a tremendous amount of misinformation about what a “good” soil is. A black color, or a friable feel, or the existence of worms are all good signs, but they really aren’t sufficient in determining if a soil is going to produce truly nutrient-dense vegetables—remember, that’s the goal of food!

There are no silver bullet ingredient you can add to soil. Compost, rock dust, biochar, worm castings—they all have their place and are great tools in a gardener’s toolbox, but adding them indiscriminately is not going to improve nutrient density (unless you get lucky). It’s like running out of gas in your car and grabbing the first liquid you can find to fill your tank. Maybe it will be gasoline or jet fuel! Or maybe it will be milk…

Over the last year, we’ve been narrowing in on a true ideal soil mix. To us, an ideal soil mix is one that is easy to garden in, has a full spectrum of micronutrients, and most importantly has the proper proportion of nutrients seen on a base-cation saturation test (a fancy term for a common professional soil test).

Good soil has three things: good structure, strong biology, and balanced chemistry. All of these things affect one another in very real ways. As an aside, strong biology is the trump card in gardening and farming, and is essential to healthy plant growth. But you cannot have a truly functioning plant-soil system with strong biology if the chemistry is out of balance. Balance the chemistry, don’t compact your soil, and the biology will thrive naturally. “If you build it they will come”.

Because of this, we are focusing our efforts on developing a chemically balanced soil, and inoculating the seeds and plants upon planting to give the biology a jump-start.

After mixing dozens of batches of soil, we are honing in on a very balanced mix. We’re utilizing diverse and creative sources of “inert” organic matter while maintaining a topsoil base. We test each batch and amend the gardens based on the slight variations in test results. The soil is loose and fluffy but still has enough clay to hold water and nutrients, maintain good structure, and most importantly has low potassium and low salts! Every ingredient in our soil is also a waste product. So that’s cool…

You can look at the latest test results here.

This specific batch will be amended on site with gypsum, a slow-release nitrogen-heavy fertilizer, rock dust, and humates.

Once our gardens are filled with an ideal soil mix, we teach good gardening practices—proper soil hydration, keeping the soil covered, not compacting the soil, foliar feeding and soil drenching at the proper time—are the last pieces of the puzzle to grow nutrient dense food.

It sounds like a lot to think about, but it’s really not that difficult once you have good soil. Soil is 80-90% of the battle.

 

Existing Gardens that Don’t Have an Ideal Soil

The “ideal soil mix” conversation begs the question for anyone already gardening in Colorado. If you already have a garden, there is a simple protocol for creating soil for high nutrient density.

1. Get a soil test
2. Send the results to info@urbanfarmcolorado.com
3. We’ll tell you what to do for free. (And you can pay to have us do it for you if you want.)

 

What’s Next?

Everything discussed above is theoretical. I always ask myself, where’s the proof? We spend so much time and money working on soil, and our goal is to now quantify the nutrient-density differences so we aren’t doing it all for naught!

1) Experiments

This season The Urban Farm Company’s new Chief Operations Officer Kylie Manson will be developing and implementing extensive soil, irrigation, and fertilizer experiments at our “headquarters”.

We will be building about 15 raised beds with different soil mixes in them, and we’ll be taking numerous measurements through the season to compare them. We’ll be taking refractometer readings through the season to track dissolved solids in the vegetables, which are correlated with nutrient-density. We’ll also be tracking yield, germination, pest and disease pressure, and a few other things. Read more about our experiments here!

Kylie is brilliant farmer in her own right, and will also be plowing about ¼ acre for in-ground beds. We’ll be to growing food to feed our own souls, and any extra food will be sold to Duo restaurant in Denver.

We will also be exploring the differences between in-ground gardening and raised bed gardening. All of our information and knowledge comes from a long history of farming and in-ground gardening research and literature. Raised beds are a totally different monster with higher drainage/leaching and faster warming/cooling. We will be exploring these differences and changing our soil mixes accordingly.

2) The hunt for better organic matter.

Any idea of how to get carbon into the soil without using compost or other ingredients that bring in excess nutrients and salts? We have some ideas and we’ll be testing those too. Hint: We have a lot of leaves and wood chips in Colorado.

3) Continued learning.

I am personally going to continue learning about the connection between soil and nutrient density. I feel like I’ve personally only scratched the surface of how plants and soil work together (with biology) to create amazing vegetables. My goal is to better understand the biochemical pathways that lead to nutrient-density.

And of course, I’ll be trying not to spend too much time on soil for raised garden beds so I can grow The Urban Farm Company to reach more people around Colorado.