by Tom Zink, Horticulturalist

During the early years of gardening, a new plot will face many challenges, ranging from pests to environmental pressure to soil fertility and soil texture.  Soil fertility is the ability to provide essential nutrients, water, and favorable chemical, biological, and physical conditions to sustain plant growth.

Fertility is the foundation of both agricultural productivity and ecosystem resilience, ensuring sustained crop yields while preventing soil degradation.  Maintaining and enhancing fertile soil requires a balance of proper chemical management, organic matter integration, and physical care.

This article will discuss key components of fertility, as well as offering instruction on building a robust, productive soil, and, most importantly, how to maintain it.

The first question to ask is, what is soil actually made of?  The answer is simple: minerals, water, air, and organic matter. Minerals are the base of the soil and determine composition. They are the inorganic, solid particles created by the weathering and breakdown of rocks.

The minerals determine the soil’s texture and are categorized by size – sand (largest), silt (medium), and clay (smallest). Soil composition and texture determine water retention, drain rates and how far plant roots will spread.

Water is another key element in soil. Acting as the nutrient highway, water carries broken down, dissolved nutrients to microorganisms that feed plants and keep the soil alive and working. However, too much water can be destructive, which is why overall soil composition is vital.

Space or pores not taken up by water is called soil air. Air determines soil structure and plant root space. Additionally, air provides microorganisms with a constant flow of oxygen to continue to fuel soil activity. Air prevents plants from drowning and helps maintain a robust rhizosphere (the space surrounding the plant’s roots).

This zone is where plants feed the soil and soil feeds the plant. It is packed with beneficial bacteria, fungi, and microorganisms. The rhizosphere acts as a hub for nutrient cycling, plant growth, and disease defense.

Finally, the last piece of good, healthy soil is organic matter. Living organisms like earthworms and bacteria, as well as the decaying remains of plants, are classified as organic matter. Decomposed organic matter forms humus, a dark, nutrient-rich material that improves soil structure and helps the soil retain water and nutrients.

Now that we’ve identified what soil is, let’s talk about how to build it.

Step one is to identify the composition of the soil. Identification can be done through a formal soil test, but there are also ways to do it yourself.

A soil jar test is easy to do:
1. Dig down six to eight inches in the area to be tested, removing any rocks or debris from the sample and breaking up clumps.
2. Fill a jar one-third full of the soil sample.
3. Add water, and a teaspoon of dish detergent to separate particles, and shake the jar for two to three minutes.
4. Let the jar settle for a couple days. Because sand, silt and clay have different weights, they settle at different rates, which will make it possible to measure each individual layer.
5. Calculate your exact percentages by measuring the height of each individual layer and dividing by the total height of all three soil layers combined. You can use the soil calculator from the USDA found here.

Another test method, the ribbon test, is simple and fast, but is the least accurate of all the methods. For this test, moisten a small sample of the soil, form it into a ball, and press it into a ribbon. If the pressed soil makes a ribbon shorter than one inch, soil is a sandy loam. If the ribbon is one to three inches, the soil is a silt or clay loam soil. A ribbon of three inches or longer indicates heavy clay soil.

Soil tests are very important in the sense that they provide a baseline in determining adjustments to make overall soil more workable.

Addition of organic matter to soil, whether sandy loam or heavy clay, can remediate soil texture and composition. Organic matter consists of compost, earthworm castings, plant debris like leaf litter (depending on species, be aware of acidic leaf litter), and growing green manures.

Green manures are a cover cropping system that can add biomass to a plot as well as add nitrogen and regulate phosphorus. (We’ll be talking more about cover cropping and green manures in a future article). Hardwood compost or composted chicken litter is another great wat to build fertility and correct soil structure.

Remember! Not all animal manures are equal, and it’s important to know where your manure comes from. For example, cow manure from a cow grazing on land sprayed with a picloram product (herbicide) can potentially kill your garden.
Work amendments into the soil, but avoid overtilling, as too much tillage will break particles down and create hard packed layers over time, especially in heavy clay soils.

Good soil structure builds a garden, but productive, fertile soil maintains it. Fertility is broken up into four components: macronutrients, micronutrients, soil pH, and organic matter. Macronutrients like nitrogen (N), phosphorus (P), and potassium (K) drive leaf growth, root development, and overall plant immunity. Micronutrients or trace mineral elements, like calcium, magnesium, iron, zinc, and boron, support plant cellular development and drive photosynthesis.

Soil pH is the measurement of soil acidity/alkalinity, scaled from 0-14, where most plants are comfortable in the 6-7 range. Organic matter, as mentioned above, consists of plant and animal products in various stages of breakdown.

Requesting a formal soil test, where analysis is performed in a laboratory, gives the most accurate data on all components and helps to properly assess a particular soil’s needs.

Addition of synthetic, salt-based fertilizers that are fast acting will provide nutrient balance, but since these contain no carbon, they will not add to the biomass/organic matter of a soil. Synthetic fertilizer is a quick fix, but be aware that overuse causes salt buildup, leading to “physiological drought,” where salt pulls moisture from plant roots, causing brown leaf tips, stunted growth, and white crust on the soil surface.

Organic products like compost or different meals (alfalfa, blood, bone, feather) build the soil at a slightly slower pace and feed the rhizosphere that feeds plants. With organics, it is less likely that plants will experience nutrient burns or toxicity, and as an added benefit, the soil is being enriched with supplementary organic matter.

Both forms of fertilization can lead to leaching and runoff, so use only what is necessary for the season. Over time, the soil condition will change for the better, as long as focus is on building and not overtilling.

Soil health is the key factor to a successful growing season. The goal should always be improving the soil and making it better, as well as thinking long-term and sustainably. A garden can give back for many years to come and will reward stewards of the land.