Soil Amendment Guide: Improve Your Soil and Transform Your Garden With These Simple Steps
Your garden is only as good as your soil. Learn how to amend any type of soil so you can get the best results year after year.
Bonnie L. Grant
Soil amendments are materials added to your soil to improve its structure, nutrient content, and other physical properties it may be lacking. Poor soil grows poor plants. Unless you drew the lucky card and have a garden full of black gold, you'll need to know how to improve the soil.
Soil amendments for gardens can be organic matter, inorganic matter, fertilizer and additions that change the soil’s pH for better growing. It is an ongoing process as plants leach nutrients, leaving the soil inadequate for their needs. The first place to start is to determine what your soil is made of and begin building from there.
Whether your soil is nutrient deficient, compacted, heavy clay, or has any other issue, this soil amendment primer will get you started.
Article continues belowDo You Need Soil Amendments for Your Garden?
Amended soil, or conditioned soil, will help your garden grow healthier and stronger year after year. You can even add soil amendments to your lawn to improve its health.
Soil amendment can be as simple as mixing in leaf litter or it can be as complicated as running drainage pipes. The condition of your soil needs to be adequate for sustaining plant needs. A good place to start is by determining the current condition of your soil. Testing soil will tell you what structure your soil has (clay, sand, silt, loam), what nutrient deficiencies the soil may have, and what the pH level of your soil is.
A simple, DIY mason jar soil test will reveal a lot about the structure of your soil – the different components of your soil will separate so you can determine the composition. You should also check to see if your soil is well-draining. This means that water doesn’t sit for too long or run through the soil too quickly.
Make sure your soil drains well with a percolation test. Dig a hole roughly 12 inches (30 cm) deep and wide. Fill it with water, let it empty completely, then fill again and time how fast it drops. Good well-drained soil lets water fall 1-6 inches (2.5-15 cm) per hour. Faster and it's probably sandy—drains way too quick. Slower, or still sitting the next day, usually means heavy clay. Loam—that nice blend of sand, silt, and clay—tends to hit the ideal range pretty reliably.
There are home soil test kits, available on Amazon, that reveal your soil’s levels of nitrogen, phosphorus, and potassium, as well as soil pH. You can also send soil samples to a lab to professionally analyze the composition and nutrient deficiencies of your soil. A mail-in soil test, available from Amazon, will give you lab results in a couple weeks and make recommendations for soil amendments.
Once you know what type of soil you have and what it lacks, you can begin to mix in amendments to create a conditioned soil that is ready to grow flowers, vegetables, shrubs, trees, or the lushest lawn of your life.
How to Amend Soil
In most cases, the need for amending soil arises from having poor, compacted soil or nutrient-deficient soil. Once you have tested your soil, you can determine the proper amendments.
Amendments for Clay Soil
Clay soil is dense and doesn’t allow water to flow through easily. This means that plant roots will be sitting in near constant moisture. Some plants love clay soil, but many annual flowers and vegetables do not and will not thrive in clay.
To amend clay soil, mix in organic materials to open up the soil structure. Compost, leaf mold, dried grass clippings, leaf litter, perlite, and other materials will improve the clay soil’s texture, drainage, and nutrient levels. If using compost, mix 2-4 inches (5-10 cm) of compost into the top 6-8 inches (15-20 cm) of soil. You can use homemade compost or purchase organic compost from Lowe’s or your local garden center.
Amendments for Sandy Soil
Sandy soil has the opposite problem of clay soil. Water runs through the soil quickly and dries out before your plants can soak up the moisture and nutrients. The best way to amend sandy soil is by adding compost or other soil conditioners like humus and manure soil conditioner, which is available from the Home Depot.
Work 3-4 inches (8-10 cm) of compost into your sandy soil every year and be sure to top off with mulch. Mulch will help to hold moisture and will break down through the year and continue to add organic matter to the soil.
Amendments for Compacted Soil
Hard, compacted soil may be the result of construction or simply little ones running across it constantly in play. The depth of compaction is important to know how to deal with it. If you have very deep, hard areas, you may have to rent equipment to dig it up and loosen it.
Loosen the compacted soil to a depth of at least 12 inches (30.5 cm.) for most plants and up to 2 feet (0.5 m.) for trees and larger specimens. Manually shoveling garden soil is usually sufficient in most cases, but you can also rent a mechanical rototiller from your local home improvement store. Once the soil is loose, you may need to add several inches (7.5-13 cm.) of compost or fine bark to keep it loose and workable. Prevent soil compaction in the future by reducing foot traffic, avoiding working with soil when it’s wet, and use mulch to let water filter through the ground more evenly.
Amendments for Nutrient-Deficient Soil
Soil needs a good balance of macro-nutrients and micro-nutrients and a good balance of nitrogen and carbon. Adding compost to all soil types is beneficial and adding specific nutrients via fertilizers will boost what your soil is lacking.
Acidic soils can be amended with lime to sweeten the soil and alkaline soils with sulfur to increase the acidity. Wood ash and oyster shells also naturally make acidic soil more neutral.
Garden soil preparation with these items works best if they are dug into the soil to a depth of 6 to 12 inches (15-30 cm.). You can even save your kitchen scraps to work into the soil but avoid meat, bones, and fat. Cover crops provide “green manure” to work into soil in spring for an extra shot of nitrogen and increased soil percolation.
Shop Soil Amendment Essentials
Send your soil sample away for lab results that are available through an app. They provide recommendations to improve your soil health, too.
This organic compost from a small business will add nutrients and better structure to your garden soil.
This heavy duty garden cart makes it easy to haul around soil amendments. Lift the end to easily tip out its contents right where you want them.
Amending your soil might seem daunting at first, but start with a good test kit and work from there. And when in doubt, just add compost. A good quality compost goes a long way and fixes myriad soil problems!
