What is compacted soil?

About half of a healthy soil is made up of mineral particles like sand, silt and clay plus organic matter. The remaining half is called pore space. That is the room for air and water movement around the mineral particles. Pore space is required in order to have a healthy environment for plant roots and beneficial microorganisms and earthworms to break down plant residue into organic matter.

Compacted soil can make growing plants in a vegetable or flower garden problematic.

Many gardeners are not aware that the difficulties with their vegetable garden or flower garden could be caused by compacted soils. Lawns can also be affected. You may find soil is difficult to dig in or till up and plants do not grow well. They do not develop as large of a root system as they should. Water may collect after a heavy rain and will remain rather than soak in.

But what is causing this?

Compaction is most likely to occur with heavier soils like clay but when heavy equipment is used even sandy soils can become compacted. These are soil particles that are packed closely together. The problem may be compounded by events that have happened to the soil over the course of years. The pore spaces are reduced to the point that air and water cannot move freely and plant roots cannot grow easily into the surrounding soil. The soil could remain overly wet longer than is healthy for the plants growing there.

Factors contributing to compacted soil

  • Over-tilling soil

    Over-tilling breaks up the small soil aggregates into single particles. The soil should have little clumps of particles that are bound together in small, pea-sized lumps. When tilling an area multiple times, those little aggregates are broken down. When the soil later gets wet, it does not allow the water to pass through. A mini-pond is created and when the soil finally dries, it resembles an alligator’s skin. This linear pattern of cracked soil does not let air or water in.

  • Working up soil when it’s too wet

    Before tilling a garden or working up the soil, make sure the soil is not too wet. Before working in the garden in the spring, take a handful of soil and compress it into a ball. When gently poked, it should fall apart. If it does not, the soil is too wet. Wait until the soil crumbles.

  • Mixing sand in to loosen soil

    Adding sand creates the opposite of the desired effect; the soil can become like concrete! Add organic matter such as compost or leaf mould when loosening the soil.

  • Compressing soil with weight

    Vehicles parked or driven over an area, construction activities or places with a high volume of footfall can become compacted. It could even be due to a ride-on lawn mower’s tyres running over an area repeatedly.

What can you do to prevent this?

Resist the urge to routinely rototill or cultivate the garden. Instead, consider adding organic matter by using compost or mulch over the top of a flower bed or simply hand-spade it into the top 3 to 6 inches of soil. For ease of use we have pre-mixed a good quality compost into our Regal Topsoil creating the Regal Blend.

Using organic matter like compost, straw or chopped leaves in a vegetable garden that can be mowed and turned into the soil in the spring or autumn will add more organic matter.

For a large vegetable garden, another solution is to grow a cover crop at the end of the season then mow and turn in the following spring before planting. The roots penetrate the compacted soil and loosen it. By mowing and turning the mowed tops in, the soil is additionally loosened. Cover crops could include annual ryegrass, winter wheat, winter rye, buckwheat and oilseed radishes.