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How To Build Healthy Soil With Compost

How To Improve Garden Soil

What makes soil different from dirt? In a word, life. Soil may look inert, but it's teeming with activity, both visible and invisible. It contains a dynamic ecosystem that's constantly changing. One of the keys to growing healthy, thriving plants is to understand and nurture that ecosystem. Read our simple guide to review what makes healthy soil, how to understand your soil type, and the best way to improve and maintain healthy soil in your garden.

What Is Healthy Soil?

A soil scientist would describe healthy soil as containing about 45% mineral particles (clay, sand, silt), 25% each of air and water, and about 5% organic matter. But that can be very difficult for a home gardener to measure! Let's take a practical look at what soil provides to plants:

  • Water: Plants contain up to 90% water, so it's vital that plant roots have a ready source of water in the soil.
  • Air: Plant roots also need air, and they absorb the oxygen they need through their roots.
  • Nutrients: Plants take up the minerals they need for healthy growth from the soil. These nutrients are dissolved in the moisture between soil particles.
  • A place to grow: Soil provides a place for roots to anchor themselves, to keep plants growing upright.

Healthy soil provides all these things to the plants growing in it.

What does good soil look like? It's dark,  moist, and crumbly, with air pockets throughout. Healthy soil is like a wrung-out sponge — it's moist, yet contains plenty of air, too. On the other hand, unhealthy soil may be too dry or too muddy, or compacted, with no room for air and water to move or roots to grow freely. 

What Type of Soil Do You Have?

It's handy to know what type of soil you have, because different plants prefer different soil types, and you'll be able to maximize your soil's potential.

The size of the mineral particles in the soil determines its texture:

  • Clay soils are made up predominantly of tiny, flat clay particles. These particles stick together when wet, forming a dense, slippery mud that drains slowly, leaving soil saturated after it's been soaked. When dry, the clay particles pack down into a hard surface (think clay pot). Clay soils contain plant nutrients, but it can be tough for plants to get those nutrients. Wet or dry, clay soils are tough on plants.
  • Sandy soils are made up of relatively large sand particles. They fit loosely together; water drains through quickly so sandy soils tend to dry out quickly. They also contain few nutrients.
  • Silty soils contain mostly silt particles that are larger than clay and smaller than sand particles. They drain better than clay soils and retain water better than sandy soil. They usually contain a good amount of nutrients. They can pack solid when dry, however, can be prone to blowing away in wind.


To determine what type of soil you have, follow these simple steps:

1. Pick up a handful of moist soil. Try to roll it into a cylinder about an inch in diameter. 

  • If it immediately falls apart, it's probably quite sandy. 
  • If it holds loosely together but crumbles when you poke it, it's likely silty.
  • If it sticks together like modeling clay, it contains mostly clay particles.

2. Rub a bit between your thumb and finger.

  • If it's gritty, it contains sand.

Learn More: Best Plants For Clay Soil  |  Learn More: Best Plants For Wet Soil  |  Learn More: Best Plants for Sandy Soil

Soil pH: Acidity or Alkalinity

Soil pH is a measure of its acidity or alkalinity; it's a measure of the amount of lime (or calcium) you have in your soil. Soil pH is measured on a scale of 0 to 14, with 7 being neutral. On the pH scale, soils with a pH higher than 7.0 are considered alkaline, and below that number are considered acid. Soil with a rating of 7.0 is considered "neutral."

Most plants prefer a slightly acidic soil with a pH of around 6.8, but some, like blueberries, need a more acidic soil to thrive.

Generally, moist climates have soils that tend toward acid, and dry climates tend toward are alkaline.

Often, the pH of any soil is created or at least enhanced by the history of the land. Land that has been evergreen forest for centuries is almost always heavily acid. Conversely, land that contains lots of limestone is usually alkaline.

Soil Testing

Testing your soil is extremely important for two reasons. First, it will tell you if your soil is perfectly healthy, preventing you from unnecessary tampering. Second, it will also let you know, if needed, how to amend your soil to make sure you are providing the best growing conditions for your plants. 

A pH test will determine the acidity of your soil.

  • A test result below 7 means that your soil is acidic. To raise the PH of your soil, try adding limestone – most packages will tell you how much to add to increase your PH to the correct levels. 
  • A test result above 7 means that your soil is alkaline. To lower the pH of your soil, you can add sulfur, compost, pine needles, or pine bark. This will help to add some acidity to your soil.

Nutrient Test

You can also test for the other three major elements of healthy soil: Nitrogen, Phosphorous, and Potassium.

  • Nitrogren is the element in the soil that is responsible for healthy, green growth.
  • Phosphorous is vital for healthy root development.
  • Potassium is essential for producing healthy, vibrant blooms.

The Best Way To Improve Garden Soil

The single best thing you can do for your soil is to add organic matter. and the best organic matter is compost. Compost is simply once-living matter (leaves, kitchen vegetable scraps, garden trimmings) that has decomposed into a dark, crumbly substance. Whether you make your own compost or purchase it in bags or bulk, compost is often called "garden gold" for the miracles it can work in your soil.

Organic matter nurtures life in the soil. Beneficial soil organisms, including microscopic bacteria and fungi, beetles, earthworms, and other insects, consume the organic matter, further breaking it down the material in nutrients that plants can use. In the process, they aerate the soil so plant roots can get the oxygen they need, and they keep pest organisms in check.

Plus, organic matter helps sandy soil retain water better, and helps clay soils drain more easily. Organic matter also helps soil particles form small clumps called soil aggregates, which help prevent it from compacting. Organic matter contains some plant nutrients, too.

Soil improvement isn't a one-time proposition; it's an ongoing task. Soil organisms break down organic matter, so to maintain healthy soil for a thriving garden, be sure to regularly add compost and organic matter to feed the soil, and the soil will feed the plants.


Learn More: Early Spring Soil Preparation

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