How to till hard soil with a rotary tiller?

Improve its structure and prevent it from compacting again

Inspirations / How to


Estimated reading time 5 minutes

Hard or heavy soil, as the description implies, is hard to work. This type of soil mostly consists of clay, possibly with some silt or sand.

Everything depends on one intrinsic characteristic of the soil: its texture, also known as grain or particle size (soil). The texture indicates the composition of a soil, i.e. the relative percentages by weight of its different constituent particles. The fine solid part of the soil consists of elementary particles with different sizes and properties. These include, from largest to smallest, sand, silt and clay. The abundance of one over the other gives rise to soil types with different chemical and physical characteristics. There are sandy, silty and clayey soils and various intermediate classes in between (clayey-silty soils, sandy loam and so on).

Today we will delve into the characteristics of clayey soil, to understand why it is so hard and tiring to work, as well as finding out how to soften it and prevent it from compacting again.

Before tilling hard soil, identify it first

We were saying that every type of soil has peculiar chemical and physical characteristics, especially clay soil:

  • It contains and retains nutrients, so it is fertile.

  • It has very fine porosity (microporosity) which, on the one hand, makes the soil less permeable and prone to water stagnation but, on the other hand, holds any water that manages to infiltrate the surface.

  • It is poorly aerated.

  • When wet, it feels muddy and plastic; when dry it becomes hard, compact and cracked, with a surface crust.

  • It is difficult to work: in practice, it is generally described as heavy or hard soil, rather than clay soil.

If clay soil is fertile, conversely it tends to be less hospitable for plants, causing roots to suffer from rot and lack of oxygen, while beneficial microbial flora (aerobic) cannot survive in it.

Like humus, clay is a colloidal substance. This means that its particles can aggregate into flakes and lumps. This increases the size of the pores in the soil, favouring the circulation of water and air and therefore the life of plants. Consequently, it has a fundamental role in forming the structure of the soil, i.e. the way in which the elementary particles aggregate and organise in space. Thanks to more balanced porosity between macropores and micropores pores, a soil with a lumpy structure allows roots to develop and is easier to work.

The soil structure is less stable, but varies over time: although clayey particles form flakes, these flakes tend to return to single particles and compress into a solid mass. Therefore, if you have clay soil in your garden, vegetable patch or field, it is important to restore a good structure that allows plants to grow and produce. But what are the factors, natural and otherwise, that can degrade soil?

  • Mechanical action of driving rain, root growth, trampling by people and animals, compaction by tools and machinery traffic.

  • Working the soil: if done incorrectly, this can deconstruct soil instead of softening it. For example, working hard soil by hand or with a rotary tiller when it is wet compacts it, whereas in other conditions it can pulverize the soil.

  • Deficiency or excess of certain chemical elements, such as calcium (which has an aggregating effect) and sodium (disintegrating effect).

  • Lack of humus, i.e. the organic component of the soil, resulting from the decomposition of plants, animals and other organisms.

How to till or turn over hard soil

Generally speaking, working soil of all types, including hard or differently textured earth, helps to break and decompact the surface crust, introduce essential substances (nutrients, soil improvers and conditioners) and mix the different layers. It's better to do it between autumn and early winter, before the ground freezes. In subsequent months, the dormant period and the alternation between rain/snow and dry days, as well as the freeze-thaw cycle, will do the rest by further crumbling the soil. In the spring it will be ready, requiring only one pass with the rake or light surface tillage before sowing and transplanting.

To work clay soil you can use a spade or pitchfork. Alternatively you can till hard ground with a rotary tiller, which is especially useful for medium-large plots. Use a rotary tiller of suitable weight so that it is stable and the blades penetrate deep into the soil. The power rating must be adequate both for the weight of the machine itself and for the workload, otherwise you risk straining the engine. So, choose a rotary tiller of at least medium power, such as the Oleo-Mac MH 175RKS or MH 198RKS.

When you are dealing with a clay soil, to work it and keep it soft follow these steps:

  • Only work soil when it slightly damp. If it's dry, it will crumble and soon solidify again, whereas if it's too wet, it will deconstruct and become compacted (and also bog you down).

  • Incorporate sand to lighten its structure, as well as organic matter to improve it and replenish nutrients. In addition to manure and mature compost, you can add organic matter by sowing green manures. To make your own compost, start by building a do-it-yourself compost bin.

  • Don’t over-work the soil: by refining it too much, you risk it becoming hard again within a short time.

  • Raise the flower beds or sections of your vegetable patch (i.e. by mounding the soil into rows) to facilitate drainage of excess water and prevent roots from rotting.

  • Don’t tread on tilled soil: separate areas intended for crops from walkways (mounding also serves this purpose on vegetable patches).

  • Mulch using organic material such as dry grass, or the same compost you use for fertilising. You can find more information about mulching here.

  • As an alternative to mulching, carry out periodic weeding, which breaks up the surface crust while also eliminating undesirable vegetation.

The correct technique for tilling hard soil with a rotary tiller is to adjust the jackleg (also called “spur”) to till at depth while advancing slowly, or to limit tillage to surface layers if you only want to introduce fertilisers. Here you will find more information about tilling soil with a rotary tiller. If you have a garden tractor mower, it can help you to prepare soil.

Are you new to vegetable growing? Working or tilling soil is one of the main activities you will need to master — check out this summary on how to grow a vegetable garden and our video on how to use a rotary tiller properly.

As we already mentioned, clay-rich soil promotes water stagnation: to solve this kind of problem in the garden, you can build a drainage channel.

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