Healthy soil is critical to good production, but no-one starts with perfect soil. Successful gardeners add amendments to their soil to adjust its pH, texture, nutrient levels, and other properties over time. Understanding soil amendments can help you choose the right ones to add to your garden.

Start with Soil Tests

To avoid wasting time and money, it’s a good idea to start with soil tests so that you will know exactly what you need. There are a couple of different soil tests you can do.

Soil Texture: The Jar Test

For this test, all you need is a jar, water, and a sample of your soil. It’s easy to complete at home and can give you information on the type of soil texture you have, like clay, loam, or sand.

Learn how to complete the jar test here.

Comprehensive Soil Testing

While there are some at-home soil tests that give information like pH, we recommend growers opt for a comprehensive soil test through their local extension agency or agricultural college. These soil tests are cheap and offer a wealth of information about the available nutrients and pH of your soil. Experts at the facility can also make recommendations on how to amend your soil based on your test results.

Learn more about having your soil tested here.

Soil Amendments to Add Organic Matter and Improve Soil Texture

Once you have your soil test results, you can start improving your soil. Few gardeners are blessed with loam right off the bat, so most will need to work on soil texture. Whether you have sand, clay, or silt soils, these amendments can help build up organic matter, improve drainage, reduce compaction, and improve water retention.

Compost

Finished compost is hands down one of the best soil amendments, no matter what your soil is like to start. Finished compost adds nutrients, adds organic matter, and improves soil texture. There’s no risk of overdoing it with finished compost; you can actually fill raised beds with nothing but compost.

Learn to make your own compost at home.

Aged Manure

Aged manure has similar properties to compost and is often available at garden supply centers in bags. If you don’t have enough compost, it can be an affordable way to add organic matter and nutrients to your soil while improving soil texture.

Generally, we don’t recommend adding fresh manure to a bed. Fresh manure has the potential to burn plants, and it can run off during the rain, adding nitrogen and other nutrients to local watersheds, which contribute to toxic algae blooms.

You should also be careful about sourcing manure that isn’t specifically for garden use. Unfortunately, the widespread use of herbicides in the United States means that animal hay and feed is often contaminated. When livestock like horses and cattle eat food containing herbicides, these chemicals pass into their manure and then into your garden, where they will kill vegetable crops.

A bioassay test can help you determine if manure is safe to use.

Peat Moss or Coconut Coir

Peat moss improves soil texture, increases acidity, and is a good option for loosening heavy clay soils. However, we now prefer not to use it because it’s a non-renewable resource that’s harvested from peat bogs.

Coconut coir is a sustainable alternative for potting mixes, but can be too pricey to amend a large area. Unlike peat moss, coconut coir doesn’t make the soil more acidic.

Vermiculite or Perlite

Vermiculite is a naturally occurring mineral that looks like little golden-brown or silvery-gray pebbles. In the soil, it improves aeration and drainage. It also acts like a sponge, holding and slowly releasing moisture, which is why is a popular ingredient in seed starting mixes.

Perlite is a natural volcanic glass that looks like little white rocks. In the soil, it improves aeration and drainage and reduces compaction. Like vermiculite, it’s popular for seed-starting mixes.

Other Options

Mulch and cover crops are great options to use with soil amendments to improve soil texture. As these break down, they will loosen the soil and add organic matter. Some of our favorite mulches for adding organic matter include old leaves, wood chips, grass clippings, and straw.

Buckwheat, wheat, rye, oats, and sunn hemp are good cover crops for adding organic matter and improving soil texture. Daikon radishes are another good cover crop option, especially for heavy clay soils, as their large roots can help break up hardpans and improve drainage and aeration as they break down.

Soil Amendments to Adjust Soil pH

Soil pH measures how alkaline (basic) or acidic your soil is on a scale from 0 to 14. On the pH scale, a value of 7.0 is neutral, while numbers below 7.0 are acidic and numbers above 7.0 are alkaline.

All crops have an ideal pH range, but for most vegetables this is slightly acidic to neutral, falling between 6.0 and 7.0. Soil that’s too alkaline or too acidic can prevent crops from easily absorbing nutrients. Soil amendments can help you adjust your soil pH to reach the ideal range for your crops.

The natural soil pH of soil ranges by region. In the eastern United States, most gardeners will find that they are starting with acidic soil.

Learn more about soil pH affects plants.

Lime

If you have soil that’s too acidic and need to raise the pH a bit, agricultural lime or dolomitic lime made from crushed limestone are great choices. When mixed into the soil, they release compounds like calcium carbonate or magnesium carbonate, which react with excess hydrogen ions in the soil and raise the pH.

While lime is the most common option for amending acidic soil, there are also a few other options like biochar or wood ash.

Sulfur

To lower your soil pH and make it more acidic, garden sulfur is the most common choice. Sulfur releases hydrogen ions into the soil, gradually reducing the soil pH. Some gardeners use garden sulfur or fertilizer with sulfur for acid-loving plants like blueberries, azaleas, or hydrangeas, some of which turn blue in acidic soil.

Other options for lowering soil pH include pine needles, peat moss, and fertilizer.

Soil Amendments to Add Nutrients

While having rich, fertile soil is a good thing, it’s important to remember that too much of any one nutrient can also lead to problems. For example, too much nitrogen will cause lush foliar growth with little fruit or root development in plants like tomatoes and sweet potatoes.

Agricultural experts divide nutrients into two categories. The first is macronutrients, which include primary nutrients nitrogen, phosphorus, and potassium, and secondary nutrients sulfur, magnesium, and calcium. The second category is micronutrients or trace minerals and includes boron, chlorine, copper, iron, manganese, molybdenum, and zinc. While these are still important to plant health, they’re needed in such small quantities that it’s less likely your plant is deficient in one of these micronutrients.

For this post, we’ll focus on macronutrients and the soil amendments that can help you add them into your garden.

Nitrogen Rich Soil Amendments

There are many ways to add nitrogen to your soil. Depending on your needs and product availability, you can increase nitrogen levels with bone meal, fish emulsion, liquid kelp, cottonseed meal, coffee grounds, soybean meal, compost, manure, or fertilizer. You can also grow nitrogen-fixing legume cover crops in your rotation to keep nitrogen levels up each season.

Phosphorus Rich Soil Amendments

You can add phosphorus to your soil using rock phosphate, greensand, compost, or bone meal.

Potassium Rich Soil Amendments

Good potassium sources include manure, compost, seaweed or kelp meal, potash, granite dust, greensand, and wood ashes.

Sulfur Rich Soil Amendments

Add sulfur with gypsum, compost, or sulfur.

Magnesium Rich Soil Amendments

To correct a magnesium deficiency, add limestone, manure, compost, or greensand.

Calcium Rich Soil Amendments

Use oyster shells, eggshells, limestone, gypsum, or fish meal to add calcium to your soil.

While a soil test will give you the best information, you can also learn to recognize signs of deficiencies in your plants. Check out our previous post, Common Signs of Nutrient Deficiencies in Plants.