SUSTAINABLE SOILS

Exploring the characteristics of soils in your region can provide helpful insights into creating sustainably designed and maintained home gardens.

WHY IS SOIL HEALTH IMPORTANT?

Soil is critical to the success of sustainable gardens, and it provides important environmental benefits. Using sustainable gardening practices can help us restore the benefits our soils provide. Modern industrial society has left much of the Earth’s soil eroded, exhausted and polluted. Many unsustainable gardening practices, like applying too much fertilizer or compacting soil, have unwittingly contributed to the problem. The good news is that it’s not too late! The health of our soils can be restored, and even enhanced, through the implementation of sustainable gardening techniques. Nature can take more than 500 years to form just one inch of topsoil — even more reason to take care of this valuable resource.

Soil in hands

Damaged soil can be converted into healthy, fertile soil with good stewardship and sustainable practices. Image credit: Microsoft Images

Earthworm

Healthy soil provides habitat for worms and other important organisms. Image Credit: Bigstock, Earth worm 1662502

THE ROLE OF SOIL IN A SUSTAINABLE GARDEN

Soil is the foundation of a sustainable garden. It provides a variety of benefits, often without our knowing:

 

  • Absorbs rainfall and mitigates flooding
  • Removes pollutants and cleanses water
  • Stores water for plants, wildlife and people
  • Provides habitat for organisms such as microscopic bacteria and earthworms that transform wastes into nutrients for plants.
  • Stores atmospheric carbon
  • Sustains plants, which provides food, fiber for clothing, timber, medicines and other goods

MORE ON SOIL

Soil is a complex mixture of weathered rock and mineral particles, the living organisms of the soil food web, and the decaying remains of plants, animals and microorganisms. Good garden topsoil is typically about 45 percent mineral particles, 25 percent air, 25 percent water and 5 percent organic matter. Soil scientists have identified more than 70,000 kinds of soil in the U.S. based on the many different combinations of mineral particles — sand, silt and clay — and various amounts of organic matter and nutrients. Gardeners must determine the texture, structure and pH of a given soil to properly identify its makeup and type. In doing so, exploring the characteristics of soils in the region can provide helpful insights into creating sustainably designed and maintained home gardens.

International Decade of Soils – The International Union of Soil Scientists has proclaimed 2015 – 2024 the International Decade of Soils and is a continuation of the efforts made during the International Year of the Soils in 2015.

Clay pit soils

Layers of soil and roots are exposed in this clay pit. Image credit: Shutterstock/Ievgenii Meyer

Texas bluebonnets have roots that are only a few feet deep, but they do the important job of fixing nitrogen in soil. Image credit: Wikimedia Commons

Phosphorus supports a plant’s ability to flower and develop fruit. Image credit: Wikimedia Commons

Plants, including wildflowers, also need secondary nutrients to thrive, but these are typically found in sufficient quantities without soil amendments. Image credit: Wikimedia Commons

SOIL NUTRIENTS

The elements essential to plant health are classified as macronutrients, which are needed in the largest quantities, or micronutrients, required in minute amounts. Both are necessary. The primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K). The relative proportions of these nutrients are listed as N-P-K on fertilizer labels.

Nitrogen (N)
Stimulates plant root growth and the uptake of other nutrients. Plants deficient in nitrogen tend to be chlorotic —  meaning they aren’t producing sufficient amounts of chlorophyll, leaving them a pale yellowish green — and stunted with thin, spindly stems. Most nitrogen is derived from the decomposition of organic matter and nitrogen fixation by bacteria. To maintain nitrogen levels in fertile soils, mimic natural processes by mulching with compost or other organic matter. Alfalfa, blood meal or other natural fertilizers as well as nitrogen-fixing green manures can increase the nitrogen levels of infertile soils.

Phosphorous (P)
Phosphorus enhances photosynthesis, nitrogen fixation, flowering, fruiting and seed production. It also encourages root development. Symptoms of phosphorus deficiency include delayed flowering or fruiting and a purplish cast on leaves and stems. Bone meal, a slow-acting and long-lasting natural fertilizer, is high in phosphorous and also contains calcium. It is commonly used early in the season during planting, but it can attract animals; to deter this, mix with compost before adding it to the soil.

Potassium (K)
Potassium is known to activate 80 enzymes responsible for basic plant processes such as carbohydrate metabolism and photosynthesis. It is critical to reducing the loss of water from leaves and increases the ability of the roots to take up water. Adequate soil potassium is linked to improved drought tolerance, improved winter hardiness, better resistance to some fungal disease and greater tolerance of pests. When plants suffer from potassium deficiency, the tips and edges of the oldest leaves yellow and appear burned around the edges. Compost can help maintain good potassium levels in fertile soil, while kelp meal is a renewable source that can help raise potassium levels in deficient soils. Composted wood ash is another source of potassium, but should be used only on acidic soils.

Other Nutrients
Other nutrients are considered secondary because they are typically found in sufficient quantities in the soil and no amendments are required. Secondary nutrients include calcium, magnesium and sulfur. Micronutrients or trace elements include iron, boron, copper, manganese, zinc, chlorine and molybdenum. Except in highly acidic or alkaline soils, micronutrient deficiencies are uncommon, and a balanced supply can be maintained with regular applications of organic matter.

Unsustainable vs. Sustainable Gardens:
How They Compare

BECOME A LANDSCAPE FOR LIFE TEACHER!

Landscape For Life includes a complete kit of teaching resources which can be used to conduct classes in sustainable home gardening. Become a teacher using Landscape For Life's self-paced webinar series.

Landscape For Life™ is a collaboration between the Lady Bird Johnson Wildflower Center and the United States Botanic Garden based on the principles of the Sustainable Sites Initiative (SITES®).