Guide to Soil Amendments: What They Are and How to Use Them

Nadia Hassani is a a Penn State Master Gardener with nearly 20 years of experience in landscaping, garden design, and vegetable and fruit gardening.

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Amanda Rose Newton is a pest specialist and horticulture expert, reviewing pest control and gardening content for The Spruce's Cleaning and Gardening Review Board. Her passion for pest control and sustainable gardening allows her to review plant and pest content for best practices and accuracy. She is a board-certified entomologist and volunteers for USAIDs Farmer to Farmer program. She is a professor of Horticulture, an Education Specialist, and a pest specialist.

Unlike potted plants, your garden is subject to a lot of variables in nature and most will need soil amendments. Ideal soil—rich in nutrients and well-draining yet holding enough water so that the plants can absorb it—is rare. Luckily, soil is not static; there is a lot you can do as a gardener to improve it.

Before adding any amendment to soil, it is crucial to do a soil test. For accurate data on your soil and amendment recommendations, visit your local extension office for a specialized lab test.

Here's our guide to common soil amendments and their uses.

Coconut Coir

This fibrous material is extracted from the outer husk of coconuts. Coconut coir soaks up water, thereby improving the soil’s ability to retain water and nutrients. Best for: Sandy soil

Compost

By adding compost—which must be fully decomposed—to your soil, you accomplish two things at once. You add nutrients and improve the soil density. Not only does compost loosen up dense soil, it also does just the opposite and helps to clump together soil that is too loose, which helps root growth. Best for: Any type of soil that is short of organic matter; clay, sandy, and silty soil to improve soil structure

Vermiculite

Vermiculite, a finely crushed mineral that looks like shiny flakes, helps the soil retain water and nutrients. It also promotes root growth and facilitates the anchoring of young roots. Vermiculite is a key ingredient in soilless potting mixes and it is also available separately in bags. Best for: Sandy soil

Sawdust

If you want to use sawdust, make sure it is well-decayed and not fresh when you work it into the soil. Because just like wood chips and shredded bark, sawdust ties up nitrogen at the expense of plants as nitrogen is consumed by soil microbes when they break the sawdust down. Mix it into the soil very lightly, otherwise it might clump and become a barrier to water flow. Best for: Clay soil and other hard, compacted soil

Perlite

This crushed volcanic material is called perlite. It is mainly found in soilless potting mixes to help soil aeration and drainage, you can also use it for the same purpose in your yard. Best for: Clay soil

Straw

Inexpensive straw improves the soil structure of dense soils—it makes it more porous and the improved aeration helps roots to grow. You can directly work straw into the soil without detrimental effects on the nitrogen balance in the soil (unlike fresh wood chips or bark). You can chop up the straw before incorporating it into the soil by running over once or twice with rotary lawn mower. The straw provides micro-organisms like fungi and bacteria with carbohydrates as energy source. Best for: Clay soil

Wood Bark and Chips

Wood, either finely shredded bark or chips, do a good job in aerating dense, compacted soil and create spaces so that plant roots, water, and nutrients can move through the soil more easily. They also stabilize silty, slippery soil that is too loose, so it is less prone to erosion. However, if the wood is fresh, it ties up nitrogen in the soil, which leads to nitrogen deficiency in plants because the microorganisms in the soil use the nitrogen to break down the wood. That’s why it is important to only use composted wood chips and bark. Best for: Clay soil, silty soil

Blood Meal

Dried animal blood is a byproduct from slaughtering animals. It is high in nitrogen. Best for: Plants that require extra nitrogen such as green leafy vegetables, ferns, and any perennials with lush foliage