The Keys to Building Healthy Soil

By Joe Lamp’l - Gardening Expert and Host of Growing a Greener World®
March 29, 2025

Feed the soil, and let the soil feed the plants. If there’s one thing I’ve learned after decades of gardening, it’s that healthy soil is the foundation of everything we grow. But what exactly makes soil healthy? It’s not just dirt—it’s a living, breathing ecosystem teeming with life.

Beneath our feet, an entire world exists—one that we rarely think about but that has an enormous impact on our gardens. In a healthy soil environment, it’s where plants find their nutrients, where microbes work their magic, and where the balance of life plays out in ways we’re only beginning to discover.

To gain a greater understanding of why good soil quality matters so much to us as gardeners, let’s take a closer look at what’s really going on down there, starting with what soil is made of.

If the main ingredients in soil were shown as a pie chart, there would be four slices, ideally proportioned as follows:

• Minerals – Sand, silt, and clay make up the physical structure of soil. They are the solid components, making up about 45% of the pie.
• Water & Air – These fill the spaces between soil particles and are essential to supporting plant roots and microbial life. The space between the solids makes up 50% of the pie, evenly divided between air and water.
• Organic Matter – Decomposed plants and animals that provide nutrients and improve soil structure. As important as this component of the pie is, native soils rich in organic matter often contain only about five percent of the entire soil volume - a very small slice of the pie.

Soil that is well-balanced with the proper proportions of these main ingredients supports a diverse array of living organisms: bacteria, fungi, insects, nematodes, protozoa, and other creatures that drive the soil’s natural processes. It’s these living organisms that collectively make up what we call the soil food web.

A well-balanced soil has just the right combination of these elements to support plant life. Too much clay and the soil holds too much water. Too much sand and it drains too fast. But when everything is in harmony, the soil becomes the perfect environment for plants to thrive.

Essential Nutrients Plants Need to Thrive

Plants, like people, need a variety of nutrients to grow strong and healthy. The three primary nutrients are:

• Nitrogen (N) – Essential for leafy green growth and photosynthesis.
• Phosphorus (P) – Supports root development and flowering.
• Potassium (K) – Helps with overall plant health and disease resistance.

Beyond the primary nutrients, healthy soil is full of secondary and micronutrients, including:

• Calcium (Ca) – Strengthens plant cell walls.
• Magnesium (Mg) – A key component of chlorophyll, which helps plants use sunlight.
• Sulfur (S) – Important for enzyme function and protein production.
• Iron (Fe), Zinc (Zn), Manganese (Mn), Copper (Cu), and others – These trace minerals are needed in small amounts yet play a critical role in overall plant health.

Getting the primary nutrients into the soil can be added through purchased manmade options, often referred to as synthetic fertilizer. Or, you can buy organically derived sources of those same nutrients. Blood meal and Milorganite are well-known options that provide nitrogen. Bone meal and rock phosphate are good sources of phosphorus. Greensand and potash are common natural sources of potassium.

Adding compost to soil

One of the best and simplest ways to ensure your soil has these nutrients is by adding compost. In addition to adding a low dose of N, P, and K, the organic matter in compost also provides secondary and micronutrients and improves soil structure, helping it retain water and nutrients more effectively.

Beyond the nutrients

Nutrients alone are not what makes the soil fertile. It’s the life in the soil food web where fertility is made available to the plants. This hidden world of microbes works 24/7 to break down organic matter, convert it into soluble nutrients the plants can take up, and create healthy conditions for growth.

Some of the most important soil microbes include:

• Bacteria – These tiny organisms help decompose organic material, fix nitrogen from the air, and make nutrients available to plants.
• Fungi – These microbes also play an important role in decomposing organic matter. Many fungi form beneficial relationships with plant roots, increasing their ability to absorb water and nutrients. Mycorrhizal fungi, for example, act like an extended root system for plants.
• Protozoa & Nematodes – These microscopic creatures consume bacteria and release nutrients in plant-available forms. While some nematodes are detrimental to certain plants, many others play important roles in nutrient cycling.

When soil is rich in microbial life, it’s healthy. Plants can access nutrients more efficiently, build stronger root systems, and resist diseases more effectively. But when soil is overworked, depleted, or treated with harsh chemicals, it becomes lifeless. This microbial balance breaks down, resulting in poor plant growth and increased pest and disease issues.

How to Build Healthy Soil

As gardeners, there are some simple things that we can do to improve any soil and nurture a thriving ecosystem. Here are a few significant examples:

Add organic matter – Compost, aged manure, leaf mulch, and more, all of which help feed soil microbes and improve soil structure.

• Minimize Tilling – Tilling disrupts soil life and can break down its natural structure over time. It can also deplete nutrients there. Try no-till or low-till gardening methods instead.
• Grow Cover Crops – Plants like clover and vetch fix nitrogen in the soil and protect it from erosion. Other cover crops, such as daikon radish, can loosen soil and draw up nutrients from deeper into the soil.
• Avoid Synthetic Chemicals – Overuse of synthetic fertilizers and pesticides can harm beneficial microbes. Choose organic or natural alternatives whenever possible.
• Mulch – A layer of organic mulch helps retain moisture, suppress weeds, and slowly enrich the soil as it breaks down.

When cover crops have reached the end of their season or served their purpose, it’s time to work them into the soil.

If there’s one thing I want you to take away from this, it is that healthy soil has everything to do with the success of everything growing in your garden—and it needs care just like the plants growing in it. By understanding what’s in soil, how nutrients work, and why microbes matter, we can make better decisions to support a thriving garden.

So the next time you scoop up a handful of rich, beautiful, healthy soil, remember: it’s an entire ecosystem, full of life, working undercover to help your garden flourish. Feed the soil, and let the soil feed the plants.