Compacted Soil

Clay soil is prone to compaction.

​Healthy soil is loose enough to allow roots and earthworms to move around freely, while still providing support and structure. Unlike sand (which has its own problems), compacted soil has too few macropores and micropores (larger and smaller spaces) between soil particles. These spaces are needed to hold air, water, and nutrients for plant roots.

Loose soil (left) has plenty of room for water (blue) and compacted soil (right) does not

Compacted soil can prevent water from moving into the soil (infiltration), through the soil (permeability), and out of the soil (drainage). Standing water can drown plants and create mosquito habitat. It can also make life difficult for tender new seedlings trying to get a healthy start by reducing nutrient uptake and poorly anchoring plants to the ground. Soil compaction hurts mature plants, as well, by reducing nitrogen levels in the soil, as well as other nutrients.

What causes soil compaction?

Every step you take presses down on the soil beneath your foot. Healthy soil can spring back. Soil that is walked on too frequently loses that ability and it becomes compacted. Other common causes of soil compaction include:

• Overwatering
• Digging wet or overly dry soil
• Insufficient organic material
• Digging repeatedly in the same area

Stepping stones protect against soil compaction

Plants that counteract compaction

Deep taproots can help break up compacted soil. Put these plants to work for you, rather than compounding the problem with further digging. Adding these plants to your landscape can help reduce compaction and improve soil structure:

• annual rye grass (Lolium multiflorum)
• Atlantic coreopsis (Coreopsis tripteriscilantro)
• Autumn onion (Allium stellatum)
• cowpeas (Vigna unguiculata)
• Culver’s root (Veronicastrum virginicum), ‘Adoration’, ‘Apollo’, ‘Erica’, ‘Fascination’
• false indigo (Baptisia australis)
• forage radish (Raphanus sativus var. longipinnatus, cv. ‘Daikon’)
• mustard
• prairie dock (Silphium terebinthaceum)
• purple milkweed (Asclepias purpurascens)
• rapeseed (Brassica napus, cv. ‘Essex’)
• rough blazingstar (Liatris aspera)
• sorrel (Rumex acetosa)
• southern blue flag iris (Iris virginica)

​Other tips to reduce soil compaction

• Aerate compacted soil
• Apply mulch
• Do not add sand or gravel (unless you want to create concrete)
• Encourage earthworms with compost and coffee grounds
• Install stepping stones in high traffic areas
• Plant ground covers to protect topsoil

Free arborist wood chips are a good treatment for compacted soil

The very best thing you can do for compacted soil is cover it with a thick layer of aged mulch or some wood chips and leave it alone for a while. ​​​