Till or not to till!

Jun 29

Gavin from artisan horticulture elevating compaction with preping fork.

The antithesis of this article was my frustration with constantly coming into newly landscaped gardens with compacted soils, 50 - 100mm of topsoil put on top of hard pan clay subsurface, and the owners of the gardens asking why all the plants are struggling. Together, we will explore the pros and cons of tilling and when the proper context might be for using it.

You may have heard that tilling to elevate compaction is a terrible practice that should not be done because it kills the beneficial soil organisms when, in most cases, compacted soils will also not allow helpful soil organisms to thrive. Still, I ask you, is it as bad a thing as it is being made out to be, or is it like everything in gardening and Horticulture? It depends. It has fallen out of fashion in landscaping in recent years; hopefully, we can change that.

Most plants we use in residential horticulture and home gardening require loose, friable soil; the deeper, the better. Few numbers come to mind at first when thinking about when we may have compacted soil, that is at 300 PSI; root growth completely stops for the vast majority of plant species, and anything above 200 PSI is heavily restricted; most agronomists and experts like Grame Sate and John Kempf also state that in even slightly compacted soils, plants can use as much as 15-20% more energy to produce roots and that’s 15-20% less energy than the plant has to fight off the pest and disease and look healthy.

Why to Till the Effects of Soil Compaction on Plants

Bronzing of Buxus due to compacted soils

Root Growth: Compacted soils are denser and have reduced air spaces, making it difficult for plant roots to penetrate and expand. As a result, root growth is restricted, leading to shallow root systems. Plants with shallow roots are more susceptible to drought stress since they can't access water from deeper soil layers.

Nutrient Uptake: Compacted soils limit the movement of water and nutrients. Plant roots require oxygen to absorb nutrients effectively. In compacted soils, the lack of oxygen in the root zone can hinder nutrient uptake, leading to nutrient deficiencies. This limitation can affect various essential processes in plants, including photosynthesis and overall metabolism.

Water Infiltration and Drainage: Compacted soils have reduced porosity, so water infiltration is slowed down. Compacted soils can become waterlogged during heavy rains because the water cannot penetrate the ground efficiently. Conversely, during dry periods, water may not penetrate deep enough to reach the plant roots, causing drought stress.

Soil Aeration: Compacted soils lack proper aeration, preventing the exchange of gases between the soil and the atmosphere. Plant roots require oxygen for respiration, and when the soil is compacted, the oxygen supply to the roots is limited. In anaerobic (low-oxygen) conditions, harmful compounds can accumulate, negatively impacting root health.

Microbial Activity: Compacted soils can impede the activity of beneficial soil organisms such as earthworms and microorganisms. These organisms play a vital role in decomposing organic matter and cycling nutrients. Reduced microbial activity can result in poor soil structure and fertility.

Stunted Growth: Due to restricted root growth, limited nutrient availability, and inadequate water supply, plants in compacted soils often exhibit stunted growth. They may have smaller leaves and shorter stems, producing fewer flowers and fruits than plants grown in well-draining, aerated soil.

Increased Susceptibility to Pests and Diseases: Weakened plants are more susceptible to pest infestations and diseases. Stressed plants have reduced natural defences, making them attractive targets for insects and pathogens.

Why not till?

So we have considered all the reasons why we might want to till the soil, so why wouldn't we like to till all the time? Well, like everything in life, too much of a good thing can end up being detrimental, as you will see from the damaging effects of tillage.

Soil Erosion: Tilling can disrupt the soil structure, making it more susceptible to erosion by wind and water. Exposed soil particles are easily carried away by wind or water, leading to the loss of fertile topsoil. Soil erosion can degrade soil quality and reduce its productivity.

Loss of Soil Organic Matter: Tilling accelerates the decomposition of organic matter in the soil. Organic matter is crucial for soil fertility as it provides nutrients, improves soil structure, and enhances water retention. Tilling can lead to a rapid decline in organic matter content, especially in the topsoil layers.

Compaction: Paradoxically, tilling can lead to soil compaction in the long term. When the soil is exposed to the air and dries out after tillage, the soil particles can compact more quickly, reducing soil porosity and aeration. Compacted soil restricts root growth and limits the movement of water and nutrients.

Loss of Soil Biodiversity: Tilling disrupts soil habitats and can harm beneficial organisms such as earthworms, fungi, and other microorganisms. These organisms contribute to nutrient cycling, organic matter decomposition, and overall soil health. Disrupting their habitats can lead to a decrease in soil biodiversity.

Lactarius sp. growing dense organic mulch.

Greenhouse Gas Emissions: Tilling releases carbon dioxide (CO2) stored in the soil. When organic matter decomposes rapidly due to tillage, carbon is released as CO2.

Weed Growth: Tilling can disturb weed seeds buried in the soil, promoting weed growth. When seeds are exposed to light and air, weed seeds are more likely to germinate, leading to increased competition with crops for nutrients and water.

Water Quality Issues: Tilling can cause soil erosion, which can lead to sedimentation in nearby water bodies, impacting water quality. Sedimentation can smother aquatic habitats and transport agricultural chemicals, such as fertilisers and pesticides, into waterways, causing pollution.

Loss of Soil Structure: Tilling can destroy the natural soil structure, breaking down aggregates and disrupting the arrangement of soil particles. This loss of structure reduces the soil's ability to hold water and can lead to poor drainage.

What causes compaction? How can you keep your soil from compacting over time?

Rain compaction
- The soil will compact when rain hits bare soil or compost of a fine consistency.
  - Using large particle mulches (25mm or greater in size) to reduce rain compaction is probably one of the most underrated arguments for bark mulches. Keep your soils covered at all times with organic matter.
Foot Trafic
- Refrain from walking in your gardens.
  - Again mulch will greatly reduce this impact.
- Please don't walk on your soil and even lawns when it is very wet.
Equipment/Machinery
- Extensive equipment and cars can cause rutting and massive compaction in very specific area.

How do you test if you have compacted soil?

The home gardener can quickly undertake inspection for compaction by trying to use a shovel or trowel into the soil; if you are unable to do so with ease, your plants are unlikely to grow roots in the soil either.
In Horticulture, we measure this with a Penetrometer anything over 200 psi is at the point where the roots become restricted and unable to grow.

How to elevate compaction?

The Prepping fork was designed by Jodi Roebuck and made here in Australia by F.D.Ryan Traditional Australian Made Garden Tools.

One of our favourite implements is the above-prepping fork designed by Jodi Roebuck and made here in Australia by F.D.Ryan Traditional Australian Made Garden Tools. This tool cultivates a depth of 300mm, creating excellent tilth for your plants that, coupled with a small cultivator, makes for excellent soil conditioning when soil is compacted; check out our last Instagram reel for a demo of how we use it.

Are you starting a new garden?

Elevate compaction if present, ameliorate with a garden fork or broad fork and use a cultivator to break the larger clumps into delicate crumb-like structures. Alternatively, you can hire a tiller for the day if you have a large area and want to save your back.

When undertaking these practices, we want to cover the soil as quickly as possible with mulch to prevent it from washing away or becoming compacted again.

So, you have compacted soil in an established garden. What is it now?

This is tricky as most modern gardens have drip irrigation; I would only elevate compaction in a case-by-case situation. If a plant is struggling or has high pest pressure, test it using the same method above.
Pull back irrigation if present, and Elevate with a garden fork or broad fork to cultivate soil to break up clumps.

In summary

Tilling applied in the proper context effectively elevates soil compaction, but it does not need to be undertaken as an annual practice in most perennial gardens. Once the soil has a good structure and is well formed with a good pore structure, think of mud cake crumbles as a texture for reference; tillage will no longer need to be undertaken.

Keep growing,
Gavin.

Broad Fork Link:

https://www.fdryan.com/store/p83/Prepping_Fork.html

Till or not to till!

Why to Till the Effects of Soil Compaction on Plants

Why not till?

What causes compaction? How can you keep your soil from compacting over time?

Rain compaction

Foot Trafic

How do you test if you have compacted soil?

How to elevate compaction?

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