What is a soil conditioner?

Soil conditioners, also referred to as soil amendments, help improve soil structure by increasing aeration, water holding capacity, and nutrients. They help break up compacted clay soils, which lack sufficient space for air and water, both of which are important for microorganisms to thrive and for plant roots to grow. They also cycle nutrients otherwise bound up in the soil. Soil conditioners include a range of products made from many different materials, both organic and inorganic. Organic (carbon-based) soil conditioners like Bloom can be made of animal manure, compost from yard waste or food waste, cover crop residue, biosolids, sawdust, ground pine bark, peat moss or other materials. Common ingredients in inorganic soil conditioners on the other hand are often mineral based, such as expanded clay or shale and even sand.

Soil conditioners vary widely in texture and composition.

How does soil conditioner affect the soil?

Soil conditioners alter a soil’s structure, meaning how well the soil holds itself together, how well it holds or drains the water, and how easily oxygen is able to penetrate. It does not however change soil texture, which refers to the proportions of sand, silt, and clay in the soil. Organic soil amendments can also greatly increase the cation exchange capacity (CEC) of soils. This refers to the relative ability of soils to store nutrients in the form of positively charged particles called cations. The most common soil cations include calcium, magnesium, potassium, and ammonium. The total number of cations a soil can hold (otherwise put, its total negative charge) is the soil’s cation exchange capacity. The higher the CEC, the more cations that can be held and exchanged with plant roots, providing them with the nutrients they need. Soil conditioners may also be used to improve water holding capacity, particularly in droughty coarse soils such as sandy soils, which drain quickly.

Organic vs inorganic soil conditioners

Organic in the context of a soil conditioner refers to carbon-based material that was previously alive. Generally speaking, organic soil conditioners will improve any kind of soil in a number of ways.

Examples of organic soil conditioners include:

  • Animal manure (improves soil structure and adds plant nutrients)
  • Biosolids (improves all aspects of soil structure and plant nutrients)
  • Worm castings (adds nutrients)
  • Compost (improves all aspects of soil structure and plant nutrients)
  • Cover crops (prevents erosion and adds some organic matter and plant nutrients)
  • Peat moss (improves soil porosity and water holding capacity)

These organic materials are sometimes combined into a blend of one product, such as Bloom’s woody blend, which is a combination of biosolids and aged hardwood fines, made from tree bark.

Examples of inorganic soil conditioners:

  • Gypsum (adds calcium and sulfur)
  • Pulverized limestone, otherwise known as agricultural lime (increases pH and adds calcium)
  • Perlite (improves porosity and water holding capacity), used in potting mixes
  • Vermiculite (improves porosity and water holding capacity), used in potting mixes

How do I use a soil conditioner?

Application rates and best practices for soil conditioners vary. Soil testing is critical for understanding any soil deficiencies before amending soils, in order to select a product that will address any underlying issues. It is also important to follow the instructions provided for a particular soil amendment by its manufacturer, as its use will depend upon nutrient content and other elements.

When establishing new lawns and gardens, soil amendments should be mixed down into the soil. Ideally, it’s mixed well before planting time, so that there is better soil structure in the root zone and nutrients are available as the plants grow. For established lawns and gardens, soil amendments can be applied to the surface (known as topdressing) and watered in, so grasses and other plants aren’t disturbed.

What is the difference between a fertilizer and a soil conditioner?

Fertilizers supply nutrients to plants, whereas soil conditioners generally help improve the soil structure to enable plants to better utilize nutrients. Slow-release fertilizers made from organic materials, however can provide some of the same benefits as a soil conditioner (based on their application rate), and some soil conditioners can provide nutrients, too. Cured Bloom for example is a registered fertilizer, containing many of the micro and macro nutrients a plant needs, but also contains organic matter that will improve a soil’s structure. Synthetic chemical fertilizers, on the other hand, will typically not provide any additional benefit beyond nutrients, which is why they are often used in combination with soil conditioners that can render their usage more efficient.

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