Soil improvement: better soil means a better garden
Soil improvement breathes new life into tired garden soil. Our guide will tell you how to improve the quality of your soil.
06.02.2025
Overview: Soil improvement
Soil improvement is good for plants and also better for water consumption, and reduces your workload when working in the garden.
There is more than one way of improving garden soil – you will need to use different methods depending on the soil.
There are various indicators that can be used as a guide when it comes to soil improvement (sludge test, indicator plants, finger test).
Spring is the ideal time to carry out soil improvement work.
There are various ways to improve soil depending on the soil quality: Hard soil needs to be loosened by sanding the lawn. On the other hand, if the soil is too loose you will need to improve its water and nutrient retention. This is best done using the clay mineral bentonite. In acidic soils, you need to neutralise the acidity by adding garden lime, and for nutrient-poor soil you should fertilise the garden.
Acidic soil can be neutralised by using garden lime. Simply scatter the lime on the soil and wait until the rain washes it into the subsoil, neutralising the acids.
Soil can be improved using plants that loosen the soil by means of strong root growth (in hard soil) and plants that hold it together (for sandy soils).
Why improve the soil in your garden?
Some soil is too sandy and some so clay-rich that the ground is as hard as concrete: not every garden has the perfect soil for the plants you want to grow in it. Soil improvement can make all the difference in these cases.
Soil improvement ensures healthy plant growth and makes subsequent garden work easier. After all, optimal soil allows you to work in a way that saves energy and resources, stores water more effectively (so you do not need to water as frequently) and, in the ideal case, is good for the environment (when the soil holds fertilisers effectively and they do not leach into the groundwater).
But where do you start when you want to find out whether improving the soil is something you need to do? Our article explains everything you need to consider – step by step.
As a starting point for any soil improvement plan, you first need to ascertain the quality of your soil.
Soil quality
The question of soil quality is more complex than you might think. Of course, good soil quality contributes to good plant growth. But how do you determine whether the soil quality is good or less good, so you know whether soil improvement is even necessary?
The ideal soil (i.e. a soil quality that does not require soil improvement) is loose, but also stable enough that the earth does not mush together to form a compact, clay-like substance.
The perfect soil stores water like a sponge and then later delivers it to plants. It also contains sufficient nutrients for the flora growing in it, and has a looseness which ensures sufficient oxygen and good growth for plant roots.
Soil quality is defined by the ratios of its components. Loam, clay and humus are the defining elements in this respect. The more evenly these components are distributed within the soil, the better the soil is for the plants growing in it.
The distribution of these individual components not only indicates the quality of the soil, but also determines whether and to what extent soil improvement is necessary.
How do you determine soil quality?
Before testing the soil quality, we first need to distinguish between the two extremes of soil types: sand and clay.
While pure sand is too loose to store water, clay holds water very well – but is poorly aerated. Sandy loam lies between these two extremes – and is the ideal type of soil you should strive for.
Loam stores nutrients well, and sand is loose enough to give roots the space they need. Adding humus provides nutrients, conserves water and lays the foundations for a long-term stable soil structure.
Now that you know the theoretical foundations of soil improvement, we can move on to the practical aspect. This begins with the first step of every soil improvement approach: determining the predominant soil type in your garden.
Step 1: observe the garden
To find out if improving the soil quality would help your garden, you should look around your garden and think about what your garden routine is like. As you do so, consider the following questions:
Is the water consumption very high?
Does the soil get very hard in the summer?
Does the soil get very muddy during rain or when watered?
Are there any plants that are failing?
If the answer to one or more of these questions is yes, and you are not aware of any other issues in your garden, it is probably advisable to carry out soil improvement. For the next step, you should determine the soil type. Then you can start working on improving the soil.
In the next step, you should determine the soil type. After that, you can tackle soil improvement.
Step 2: determine soil type
Before beginning soil improvement, you first need to find out what type of soil is predominant in your garden. This will be decisive in determining the soil improvement measures you later implement in your garden.
There are two methods you can use to determine the soil type and thereby test the soil quality: finger testing and sludge testing. For both methods you should take samples from multiple places within your garden, because there is a chance that the soil condition may differ from place to place within your garden.
finger testing
The simplest way to determine the soil quality for the purposes of soil improvement is known as finger testing.
To perform this test, take a handful of garden soil from a spade’s-depth below the surface and try to shape it into a sausage. The condition of the sausage provides information on the type of soil present in your garden.
| Clay soil | Loamy soil | Sandy soil |
|---|---|---|
| Can be shaped into a shiny, moist-looking sausage about as thick as a pencil. |
Good consistency, slightly crumbly but sticks together. With a higher sand content, the sausage breaks into multiple parts but each part sticks together well. | It is not possible to form a sausage because the soil constantly falls apart. |
sludge testing
Another test variant for determining soil type is the sludge test. This test enables you to tell both the soil type and the approximate humus content of the soil.
To perform the sludge test, take an empty jam jar and fill it a quarter full with soil from the garden. Fill the jar up to the top with water, screw the lid on and shake for 30 seconds. Then leave to settle for 15 to 30 minutes and check the result:
| Clay soil | Loamy soil | Sandy soil |
|---|---|---|
| The water is uniformly cloudy, with some sediment visible at the bottom. |
A relatively large amount of sand has settled at the bottom of the jar, the water is relatively cloudy and small pieces of humus are floating on the surface. |
The water is rather clear, with some sand lying at the bottom of the jar. |
For all of these states, the more humus floating on top, the better; and the darker the water, the more humus in the soil.
Identifying other soil problems for soil improvement
| Clay soil | Sandy soil | Acidic soil | Nutrient-poor soil |
|---|---|---|---|
| Dandelion | Common poppy |
Sorrel | Stonecrop |
| Field horsetail | Hare’s foot clover | Wild pansy | Thyme |
What you now know about soil improvement
Have you completed both steps? Congratulations! You have saved yourself the cost of a laboratory analysis and should now know where to start with potentially improving your soil quality. At the very least, you know the following:
Whether you need improve the soil quality at all (soil improvement step 1).
What type of soil is predominant in your garden (soil improvement step 2).
Whether there is a high or low quantity of humus in the places from which you have taken samples (soil improvement step 2).
Remember: the soil to aim for is a balanced mix of sand, clay and humus. Read on to find out how to proceed after your soil analysis in order to achieve this type of soil in your garden.
clay and loamy soil: Loosening and increasing permeability
Heavy soils that are mainly composed of very fine components such as clay need to be loosened. This is the only way to ensure they will store water better and allow plant roots sufficient space to grow.
The fundamental principle of improving the quality of heavy soils is to introduce additional materials to the soil. This will loosen any clay or loamy soil and make it more permeable. Silica sand or coarse, washed construction sand are particularly suitable for this, but you can also use lava granules or perlite.
In order to introduce these materials to the soil underneath your grass, simply distribute them across a wide area with a rake and work in with a yard brush.
When improving clay soil directly at a flower bed, spread the material on the surface and then work it in with a cultivator or metal rake.
You can find out more about sanding lawns in our handy guide.
Once everything has been well incorporated, you should add humus to the soil. You can do this in the same way as you added the material to loosen the soil.
Incidentally, humus does not remain in the soil forever, but is consumed over time by micro-organisms living in the soil. As such, it is advisable to improve your clay or loamy soil every year and to add more humus to it regularly.
Caution: We do not recommend using grit to loosen clay or loamy soil: sharp pieces of grit may injure unprotected hands, particularly in thawing soil.
Coarse construction sand is very suitable for improving loamy soil if it is washed and has a grain size of between 0.3 millimetres and 2 millimetres. However, we recommend silica sand, since this is available from specialist retailers already washed and in the right grain size.
sandy soil: Improving consistency
You will also need to add soil improvement material to sandy soils to optimise the structure of the soil and to increase its water and nutrient storage capacity.
The best material for improving sandy soil is the clay mineral bentonite: once it is added to the soil, the mixture produces a kind of instant clay soil, rapidly improving water and nutrient storage capacities.
For higher quality soil, add bentonite and humus to the soil simultaneously and work them into the soil with a cultivator or metal rake.
Improving acidic soil: neutralising the pH value
In addition to the soil type, you should also always measure the pH value of your soil. This is especially important if plants are weakening despite good soil condition and nutrient quantities. If this is the case, acidic soil may be the reason behind the poor growth of plants.
You can determine the pH value of the soil using a soil test that is available from any DIY store or garden centre.
Improving nutrient-poor soil: Fertilising and adding humus
Nutrient-poor soil? Indications of this problem include failing plants, very light green leaves and moss in lawns.
Nutrient-poor soil can be improved using a two-pronged approach: fertilise the garden soil (usually sandy soil) to increase the nutrient content and add a layer of humus to the soil at the same time. Humus retains nutrients and allows plants to help themselves as required. Find out more about how to fertilise your garden correctly in our handy guide.
By now, you should be well prepared for any soil improvement work you may undertake. Just one question remains: how often should you perform soil quality improvements? There are two parts to the answer: while the structural improvements to your soil will be long-lasting, the nutrients will be used up over time.
You should therefore add humus to the soil every year in spring, and then apply organic fertiliser when required. You will need to do this more often in a vegetable patch, for example, than for rockery plants. As a general rule of thumb, compost contains about 1/3 of the nutrients found in fertiliser and should only be used as a supplement.
How much you need to use of each to improve the soil quality to support fruit and vegetable growth will therefore be very different from the quantities needed to improve the soil of your lawn. Improving the soil quality for garden beds should always be performed in the spring before you plant out your plants.
Now all that remains is for us to wish you good luck with your soil improvement efforts in your garden!
