Why do soil aeration with a broadfork?

Author: Linda Holliday

Broad fork aerating a long garden bed
  • Allows rain to soak deeply into the soil.
  • No damage to soil composition or organisms.
  • Easier and faster root growth for better crops.
  • Allows easier and safer harvest of root crops.

For gardeners needing a tool agile enough to maneuver inside a greenhouse, yet powerful enough to turn large areas of compacted sod, the broad fork is ideal. This ingenious device (also called U-bar, U-fork, grelinette or manual garden tiller) actually performs four valuable functions: soil aeration, cultivating, harvesting, and loosen compacted soil. This article focuses on the reasons to aerate with a broadfork.

A broadfork is basically a large two-handled fork with three to five sharp teeth or tines. In short, gardeners use leverage from their body weight instead of just their arm and back muscles to push the broadfork’s tines vertically into the ground, then pull the handles back to loosen the soil. See all our broadforks.

How to aerate soil with a broadfork

To aerate, the broad fork is pushed straight down into the soil using the gardener's weight as they step on the crossbar. The operator then steps back and pulls the handles towards them about 12 inches to loosen the soil and create air spaces deep in the ground. This improves the soil's water retention and allows deep root growth without mixing up the soil layers. Aerating in this manner can be also accomplished with a garden spade or potato fork, but more slowly, less effectively, and demanding more physical exertion. In contrast, a set of broadfork tines is about twice as long, and three to four times wider than the typical garden fork, greatly reducing time and effort.

Broadfork aeration retains soil structure

Gundaroo Tiller pulled back to loosen soil

Unlike a motorized garden tiller that churns and blends the soil, a broadfork loosens the ground without disturbing the soil layers or structure, an important consideration for two reasons. First, earthworms and other micro-organisms can keep working with little disruption to their habitat. Earthworms are especially crucial because they help maintain soil nutrition, structure and absorbability and allow air to enter the soil more freely. (Consider these creatures as mini aerators as they perform the same job as a broadfork.)

Also, without excessive tilling, the soil is less likely to become brick-like (hardpan or deadpan) after heavy rains. Soil compaction can impair water seepage into soil, seed sprouting, root penetration and crop nutrient and water uptake, all of which reduce crop yields.

According to this article about soil fertility:

"Soil depletion occurs when the components which contribute to fertility are removed and not replaced, and the conditions which support soil's fertility are not maintained. This leads to poor crop yields. In agriculture, depletion can be due to excessively intense cultivation and inadequate soil management."

A fundamental principle of organic gardening is to build up soil. Tilling too often, too deep, or under the wrong conditions (too wet or too dry), can actually damage soil rather than helping to enrich it. By comparison, a broadfork can be used for aeration in somewhat wetter soil than a tiller can.

Tiller versus Broadfork for aeration

Woman using the adjustable broadfork

As tiller blades slice through soil, they tear apart helpful fungi, slaughter worms, and crush other microorganisms, some of which may have taken years to get established. These bodies have a symbiotic relationship, so when some of these microbes die, other members will also disappear. Their departure affects soil nutrients and composition.

Malleability is lost, and watering and compaction start to become a problem. Eventually, diseases and pests find it easier to move in. The soil no longer functions as a nutrient workshop, instead needing chemical fertilizers to grow crops. Alas, fertilizers (as well as pesticides and herbicides) aggravate worms and other good bugs, preventing them from reestablishing. So, the chemical cycle continues.

This is not to say a tiller should never be used, but should be used sparingly, shallowly and for certain applications, such as breaking up prairie sod to create a new garden site or incorporating large amounts of organic matter (manure, compost, leaves, etc.).

Deep-tilling, or repeatedly rototilling an area, is never recommended and is unnecessary for aeration.

Soil Moisture and Nutrient Uptake

A June 1898 University of Illinois agricultural study of orchard growth in Urbana revealed that fruit trees cultivated between rows rather than interplanted with corn, grains or grasses resulted in measurably larger trees over the test period. Test plots left to grow over with sod yielded the poorest tree growth and fruit harvest. The study explains how cultivation and aeration works to benefit fruit trees:

"The root system is compact; and instead of lying near the surface of the ground where it is easily reached by drouth and meteorological disturbances, it strikes deep into the soil. This is the direct effect of the conservation of moisture in the subsoil by the protecting mulch formed at the surface by the cultivation and tillage. These have so fitted and prepared the soil that the plant is enabled to get its food at home; while the moisture that has been kept from evaporation by pulverizing the surface soil has enabled the roots to strike deep, thus giving the plant a firm and compact basis."

Based on the era, the 1898 study recommended horse cultivation for large orchards and hand tools (spades and forks) for home orchards. "Pulverizing" the soil has now been deemed too harsh, replaced instead with less disruptive measures.

For home gardens, according to the 1922 schoolbook, "Gardening - An Elementary School Text Treating of the Science and Art of Vegetable Growing,” the best tool was a four-tined fork.

Introduction of the Broadfork

Grelinette is French for broadfork

Small-scale family orchards and gardens were cultivated and aerated with garden forks, a backbreaking technique carried out for another 60 or so years until Frenchman inventor André Grelin (1906-1982) patented the grelinette in 1963.

Grelin's invention has been expanded upon to create the modern broad fork with more durable materials and heftier tines, making it even more attractive to home gardeners. See our broadfork history article for more information.

Broad fork vs. Double-Digging

Among the mostly widely referenced gardening books, The Vegetable Gardener’s Bible by Edward C. Smith in 2011, illustrates the benefits of aerating soil:

"You can provide for this additional growing depth by working the soil either by double-digging or deep-forking. I prefer deep-forking, because double-digging involves a lot more work for no more gain. Loosening the soil farther down usually involves getting into a different kind of soil – subsoil, as distinct from topsoil. Although subsoil contains very little organic material and therefor few of the nutrients plants need most, it often contains various other nutrients (micro-nutrients) that plants need in smaller amounts, which are often not present in the topsoil."

Smith goes on to explain that loosening the soil to allow roots and worms to penetrate deeper actually puts them to work for the gardener, further expanding the loosening and aerating process. "They will slowly improve the subsoil structure and build capillaries to connect it with the topsoil," Smith writes.

In Summary:

Aerating with a broadfork has four main benefits: Properly aerated soil allows rain to seep deeper into the ground without puddling or compacting soil. Broadfork aeration is less damaging to soil composition than mechanical means or double-digging. With roomier space for root growth, crops will absorb more nutrients for a bigger yield. Root crops are more easily harvested in aerated soil.

Click here for other broadfork articles.

Check out our Meadow Creature broadfork and also our Adjustable broadfork.