Soil cultivation: how to loosen compacted soil

Gardening in compacted soil is no fun! Plants cannot grow properly as they are not able to take care of themselves and may die quickly. Fortunately, there are several methods for loosening compacted soil.

Loosening your garden soil involves a lot of work. As a result, the questions of how useful loosening the soil is and why it is done arise quickly. Basically, plants thrive in loose soil because air and water can circulate better, and soil life remains healthy. Read on to find out which soil types need to be loosened, what tools can be used to loosen soil and what other methods there are for cultivating soil.

Soil cultivation: why should you loosen the soil?

Basically, soil is made up of soil particles, such as clay minerals and humus, with voids between them. These voids are filled with water or air, depending on factors such as pore size and precipitation. In compacted soils, the number of voids is very low, and the existing pores are very small. As a result, there is not enough space for water nor for air, reducing soil permeability greatly. Both water and air are essential for plant roots and the majority of soil organisms. Plants grow best in loose garden soil for four primary reasons:

1. Better air circulation: Thanks to more and larger pores, soil organisms and plant roots are able to get enough oxygen. If this is not the case, the roots may begin to rot. In addition, many vital soil animals and microorganisms will die.
2. Prevents waterlogging: In compacted soils, water can only drain slowly and poorly into deeper soil layers. If the water does reach these deeper layers, there will be more than enough available, but no air is able to reach the roots.
3. More space for roots: Plant roots primarily grow in coarse pores. As a result, the more coarse pores there are, the better the plant can establish roots. In unloosened, dense soils, the number of pores is very small. This means that plants will not be able to develop a large, well-branched root system that will supply them with nutrients and water.
4. Improved water availability: In terms of plant-available water, the soil should be neither too loose nor too dense. Water will simply flow through very loose soils, causing the soil to dry out quickly. In dense soils, many pores are filled with water. However, since there are practically only very fine pores, the capillary action is so powerful that plant roots cannot access water. These are known as dead zones as the bodies of water do not have sufficient oxygen.

As a result, good soils have a balanced ratio of coarse, medium, and fine pores, leaving ample room for roots, water, and air.

What kind of soils should be loosened?

Soil particles are classified into three types based on their size:

• Sand: the largest particles up to 2 mm
• Silt
• Clay: the smallest particles

Loamy soils with a generally balanced ratio of all three particle sizes are ideal for growing many plants.

There are two reasons why your garden soil is compacted:

• It contains too many clay particles, causing it to stick together.
• It has been compacted so much by frequently being walked or driven over that the percentage of coarse and medium pores is too low. As a result, vegetable beds need to be loosened once a year.

Depending on why the soil is compacted, different techniques are used to loosen the soil. These are discussed in greater detail in the next section.

Tip: By holding a soil sample in your hands, you can get an idea of the particle size composition and soil type. Roll and rub a slightly moist soil sample between your fingers and palms. The properties of the different particle sizes differ:

• Clay: well-formable; greasy, smooth, shiny oily surface
• Silt: non-cohesive; floury; not very malleable; sticks to finger ridges; rough lubricating surfaces; breaks when squeezed
• Sand: granular; not mouldable; not cohesive; does not stain the hands; too “big” for finger-ridges

Soil cultivation: how can you loosen the soil?

There are basically three methods for loosening the soil. Firstly, you can use equipment to break up and loosen the soil structure. Secondly, you can mix sand into the soil to change the particle sizes. And thirdly, nature has its own ways of loosening the soil, chiefly through soil organisms and plant roots.

Loosening the soil with tools

It makes sense to use tools when the soil has been compacted by driving or walking over it frequently. There is a wide range of garden tools for loosening soil, so there is a suitable tool for almost every situation.

Tip: Of course, it is preferable to avoid compaction in the first place. For example, in winter or after rain, it is best to walk as little as possible on wet soil.

Loosening soil with a spade

It was once common practice to dig up your garden with a spade in autumn. This was done to loosen the soil in the bed, bury weed seeds and encourage freeze-thaw cycles, which breaks up heavy soil into loose crumbs. However, in the meantime, this practice has been abandoned because digging up the soil essentially turns the entire soil life upside down and speeds up the decomposition of humus. As a result, the spade is typically only used when planting new vegetable beds. It is used to loosen lawn soil by turning over and burying the original vegetation. This way new plants can be planted in the exposed soil.

It makes sense to use a spade to loosen heavy, wet clayey soils. Using a spade can improve aeration and break up clods of soil that have stuck together. In addition, clay soils that would otherwise remain cold for a long time warm up more quickly thanks to digging it over.

Tip: Thanks to the no-dig method, it is even possible to create vegetable beds without digging.

Digging forks, sow’s tooth hoes, tillers, hoes and prong cultivators

All of these garden tools, unlike a spade, loosen the soil without turning it upside down. As a result, they are suitable for loosening soil without digging it up. In this way, the original layering of the subsoil, which only builds up slowly over years, is preserved. Soil organisms remain in the zone that is suitable for them, and the humus is better protected.

When choosing a tool to loosen the soil in your garden, it mostly comes down to your preferences. With a digging fork, you can loosen large areas deeply relatively quickly and with little effort. A sow’s tooth hoe is also relatively easy to pull through the soil and loosens it relatively deeply. These two tools are usually only used once a year, for example in the springtime before planting the beds.

Prong cultivators, tillers and hoes typically only loosen the topsoil and do not penetrate as deeply. These tools are great to use when working well-maintained, humus-rich soils as deep tillage is unnecessary. Plus, they can also be used throughout the gardening season, for example when replanting a bed.

Tip: For larger areas, you can rent motorised machinery such as rotavators or rotary tillers for a day. However, only use such equipment on dry soil. Otherwise, their weight can compact the soil. In addition, do not use them too often because the prongs can easily kill larger soil organisms.

Loosen the soil with sand

If you have done a finger test and discovered that your soil is very clayey, using tools and machines to loosen the soil will not help you to improve the soil’s structure. Instead, mix sand into your clayey-loamy soil to loosen it.

But which type of sand is suitable for loosening soil? The best sand is washed pure quartz sand with a grain size of 0.6 to 2 mm. Play sand, for example, is not suitable for loosening soil because it often contains clay to keep children’s sandcastles together.

Tip: Using machinery to loosen the soil beneath lawns is not recommended because doing so would completely destroy the grass. However, there are a number of techniques for aerating lawn soil and enhancing oxygen and water retention. These include scarifying and sanding the lawn. Here, sand is spread over the lawn. Through watering and rainfall, it is then integrated into the upper layers of soil without digging and gradually loosens the soil beneath the lawn.

Loosening the soil with soil activator

A soil activator does not directly loosen the soil, but it encourages the presence of soil organisms that build up a loose soil structure, such as earthworms. They dig tunnels, which improves soil aeration and water availability while also producing humus in the process. Earthworms and other soil organisms are essential for healthy, fertile and loose soil. However, these soil organisms need food, which they obtain from plant remnants and rotting roots, among other things.

However, in conventionally cultivated fields and many garden beds, the organic content in the soil is steadily decreasing. This is mainly due to the fact that a considerable portion of the soil is not vegetated, the use of primarily mineral fertilisers, and the removal of the majority of plant remnants after harvesting. In addition to various gardening methods that promote the build-up of humus in the garden, a soil activator also provides crucial nutrients and organic structural material for many soil organisms.

When selecting a soil activator, there are a few factors to consider. Many soil activators contain animal waste, such as blood or horn meal. If you wish to avoid this, we recommend using a soil improver that is animal-free and contains living mycorrhiza fungi, which are crucial soil companions for many plants.

Loosening the soil with plants

Many plants can develop a substantial root mass in a short period of time, and their roots can penetrate deep layers of soil. A plant cover, such as green manure, not only loosens the garden soil, but it also keeps nutrients from washing away and brings them up from deeper soil layers. This also prevents soil erosion.

What plants you choose to plant is also important. On the one hand, the plant families should fit into your garden’s crop rotation. You should also decide whether to grow hardy plants or ones that freeze in the winter like legumes. Seed mixes can be a good option because different plants take root in certain soil layers and mobilise different nutrients.

Plants that grow deep roots, such as lupins (Lupinus), oilseed radish (Raphanus sativus var. oleiformis), white mustard (Sinapis alba) and red clover (Trifolium pratense), are all good at breaking up and loosening compacted soils. Grasses like common rye (Secale cereale), which grow deep roots, also ensure a fine-crumbed, loosened topsoil in spring.

Find out our 7 tips on how to improve your garden soil.