How Can I Improve Compacted Soil In My Garden?

Is your soil only moderately compacted?

Did you add organic matter to your soil?

Do you try growing deep-rooted cover crops in your garden?

If your soil is only moderately compacted, you can solve the problem mechanically by poking holes into the compacted layer of the soil. You will want to use a spading fork or a U-bar. Make deep holes at close intervals and go over the area in several directions. You can use this method even if your compaction problems are more severe, but you may want to go over the area several times, on consecutive days and/or weeks. Add organic matter after you have broken through the compacted layers.

Organic matter helps to solve compaction problems by adding microorganisms to the soil. As microbes break down organic matter, they create soil aggregates—that is, small, jagged lumps of soil particles. Rather than lying flat against each other, these aggregates pile up like bread¬crumbs, with spaces for air and water between them. Organic matter also feeds earthworms, which help to counter soil compaction by tunneling through the soil, leaving long channels for air and moisture to move between the surface and the lower depths.

Double-digging garden beds is an effective way to break soil compaction. Begin by digging a 1-ft wide and deep trench. Reserve the soil from the trench. Use a spading fork to aerate the subsoil at the bottom of the trench. Dig a second trench next to the first and put the soil from this one into the first trench. Aerate the subsoil in the second trench and continue in this fashion, finishing by using the soil from the first trench to fill the last trench. Once you have double-dug a bed, you don’t have to do it again if you treat it well. Don’t till it or break it down in any way, at any time. At the end of the season, simply pull the roots and plant a cover crop or apply a mulch.

Deep-rooted cover crops like alfalfa have roots that grow as deep as 25 feet into the soil and penetrates the most compacted soils. It also adds nitrogen to the soil while it is breaking up the compaction. Deep roots also recapture potassium as well as various trace elements and bring them up to the root zone of garden crops. Crops with tough roots, like daikon radish, breakthrough shallow but rigid hardpans. They do not add any nitrogen, but they do add organic matter. When you are using a crop to break up soil compaction, it's important to make as dense planting as possible. Plant the seed from spring to late summer, but leave perennials in place for at least a year.