How to prepare soil for a lawn before sowing

Q: How long should I leave the mix to settle?

As a guide, 2–6 weeks, sometimes around two for light soil. Sow only once levels have stabilised and uneven areas have been corrected.

First decide what to retain, where to break up an obstruction and when to replace unsuitable fill. Around 30 cm is the target for a continuous rooting space, rather than an instruction to replace the whole layer. First mix the soil, with sand if needed, through the full planned depth. Then incorporate amendments at progressively shallower depths according to the recipe; do not create separate layers. Before sowing, let the surface settle, check that levels have stabilised and finish the seedbed by correcting uneven areas.

30cm

model profile depth

2–6weeks

approximate settling time

300l

of soil beneath each m² at 30 cm

Chapter 01

Preparing and laying the mix in practice

A delivery of materials tipped onto a tarpaulin at the edge of a lawn: a pile of sand, a pile of dark soil and a stack of paper bags of amendments, with a wooden fence in the background. — **Fig. 01** A delivery on a tarpaulin: sand, soil and bags of amendments. Each material has a different place and depth in the mix.

Before bringing in material, check for compaction, building rubble and drainage problems; the three soil tests will help. Use the results to decide how much work is needed. Next come subsoil preparation, mixing, laying the mix and checking settlement. Choose component ratios and incorporation depths according to the recipe; the calculator linked below works out material quantities for your area.

Chapter 02

Thirty centimetres of freedom: why roots need space

Fig. 02 The same square metre, with a reservoir three times larger. At 30 cm, roots do not depend on the few centimetres that the sun can dry out in an afternoon.

Before we start bringing in material and mixing, we need to establish the main aim: a continuous, aerated and permeable rooting space reaching approximately 30 cm deep. Measure this depth from the final surface after it has settled.

Why do we need thirty centimetres when the seed lies at the surface and many grass roots are shallow? It is like drinking water at home: you may be drinking from a single glass right now, but it helps to have a supply in the pipes or a well.

The top few centimetres of soil depend heavily on the weather. Sun dries them quickly, watering wets them straight away, and soon they are dry again. If roots meet a barrier and cannot grow deeper, the grass depends entirely on this constantly changing surface layer.

An educational illustration without labels. At the top are two cutaway blocks of soil with lawn, each with the same square top surface of one square metre: on the left, a shallow block about 10 cm deep, with roots crowded near the surface; on the right, a block three times deeper, about 30 cm, where fine roots branch downwards — densest at the top, becoming sparser lower down, with only some reaching almost to the bottom. The soil is lighter and drier at the top, darker and moister below. Beneath are three smaller scenes: crumbly soil with a rake working only the surface; topsoil set aside and a digging fork breaking up the compacted layer beneath it; and fill containing brick fragments and rubble being removed with a shovel, with a pile of suitable soil alongside for replacement. — **Fig. 03** Continuous rooting space comes from removing the actual obstruction, rather than automatically replacing all the topsoil.

Imagine 1 square metre of your future lawn. If the soil is only 10 cm deep, the roots live in a volume of 100 litres. Give them 30 cm and they have 300 litres of soil available.

These are not litres of stored water, but a large usable reservoir of resources. Greater depth drastically reduces your lawn’s dependence on whether the sun is scorching the top layer at that moment. Water is used more effectively between periods of rain or watering.

Water and air must have a clear route, however. Spreading 5 centimetres of expensive growing medium over a compacted hard layer may create an excellent bed for seed germination, but it will not remove that layer. Water will collect above it and roots will remain shallow. Healthy soil works by holding water in small pores while air enters the large pores immediately after rain.

These 30 centimetres are a practical aim when establishing an ordinary lawn, rather than an instruction telling plants how far their roots must grow (that depends on the grass species, mowing and temperature). Above all, it does not mean you have to excavate thirty centimetres of soil and buy new soil!

You have just three options:

The soil works well down to 30 cm. Great: do not dig anything out. Simply level uneven areas, break up any local compacted patches and prepare the surface.
There is excellent soil on top, with a compacted hard layer beneath. Focus only on the obstruction. Put the topsoil to one side, loosen or break up the hardened layer underneath, then put the soil back.
The whole profile consists of building rubble or completely unsuitable fill. Here, the only option is to remove the unsuitable material and bring in a suitable mix. (If water collects here, deal with drainage first.)

Creating a functional growing environment does not automatically mean buying thirty centimetres of new soil. This realisation alone can save you thousands of Czech crowns and hours of hard work.

Chapter 03

From understanding the soil to preparing the mix

Checking the bed before sowing: a straight batten lies across the finely raked surface, a gloved hand tests the soil’s firmness, and a shallow footprint shows that the surface is no longer loose. — **Fig. 04** Before sowing, check the prepared surface, water drainage and areas where the soil may still settle.

Use the results of the three soil tests to decide what the garden needs. If infiltration is slow, deal with the cause first and repeat the test. Only then choose sand and amendment ratios for your soil type. Retain good topsoil; simply buying growing medium will not remove an obstruction beneath it.

Enter the area, planned depth and chosen proportions into the soil profile calculator. It shows the material quantities and the difference between keeping the level, incorporating amendments and creating a new layer. The ordering guide explains how to convert volume into kilograms and packs.

Check these five points before starting work:

Levels and topsoil. Decide how the surface will meet paths and patios and how water will drain. During renovation, separate usable topsoil from rubble and unsuitable fill.
Moisture and compaction. Work when the soil holds together after squeezing but can still be crumbled. Let sticky soil dry out. Break up the obstruction at its actual depth and protect the prepared area from vehicle traffic.
Lay pipes in time. Install any drainage with a working outlet, and irrigation pipework, while the ground is still open, before finishing the profile. Plan sprinkler positions and divide them into zones using the automatic irrigation design guide, while the area is still accessible for trenching.
Mix at progressively shallower depths. First mix the soil with any sand needed through the full planned depth, then incorporate amendments into their shallower zones. Do not create separate layers. Practical depths and tools are covered in the mix preparation procedure.
Give the soil time. Before sowing, water it, allow it to stabilise and correct any depressions. Details are given in settling and final surface preparation.

First understand and prepare the subsoil

A spade driven into soil being worked in low, warm sunlight; a pale compacted layer broken into clods lies in the foreground. — **Fig. 05** The pale clods are a dry, compacted layer. When dry enough, it breaks beneath the spade; when wet, it would simply smear.

The timing of the work matters. A moist clod that can be crumbled behaves differently from sticky clay that a tool smears into a smooth surface. Sometimes the most effective step is simply to wait until the soil has dried enough to be workable. The next stage will then do more than repair damage caused by the previous one.

Once the soil is exposed, remove building rubble and buried wood. Break up the compacted layer before laying the new mix, once the soil is dry enough to crumble as you work. A digging fork can be used on a small area; for a large area, it is worth arranging suitable machinery with the contractor. The aim is to loosen the continuous hard obstruction, rather than simply cover it with loosened soil.

If water remains in the exposed soil, arrange drainage with the contractor before bringing in more material. A more permeable mix on top will not solve this problem by itself.

Adapt deliveries and mixing to the size of the garden

A loosened garden area marked out with string on low stakes; three equal piles of pale sand stand at regular intervals along the strip. — **Fig. 06** One marked section with its share of sand in several piles. Neighbouring sections will receive their own.

Divide the area into manageable working sections and allocate each its share of the ordered materials. Mix the soil and sand first; the other amendments follow in order of incorporation depth. If there is not enough space for all the piles, deliveries can also arrive in stages.

The order is based on volume ratios and the supplier’s bulk densities; the weighbridge ticket confirms the weight. During the work, there is no need to measure bucket by bucket or chase a few kilograms in a mix weighing many tonnes. It matters more to spread the material across the whole area so that it does not remain in piles or strips. Smaller amendments, seed and other products must still be dosed according to their purpose and specified application rate.

Mix the mineral base first, then incorporate amendments more shallowly

Fig. 07 Each pass is shallower: mix the base through the full 30 cm, zeolite to 15 cm in the calculator’s default example, and biochar and Actino only into the upper 10 cm.

First follow the chosen mode: to keep the level, remove the calculated amount of existing soil; when incorporating amendments, retain it; and for a new layer, prepare the soil being brought in. If the recipe includes sand, spread it evenly over the working sections and mix it with the soil to the planned profile depth — approximately 30 cm in this model.

A rotavator can help, but a typical garden machine often cannot mix the full 30 cm in a single pass. Check the depth required against the machine and the soil condition; for greater depths, use suitable machinery or another mixing method. Loosening the subsoil alone does not mean that the sand has actually reached it.

Only after mixing the mineral base should you spread zeolite over the area. Incorporate it more shallowly, to the depth specified in the recipe: for example, approximately into the upper 20 cm, if that is what the calculation allows for. The calculator’s default clay example uses 15 cm; if you choose 20 cm, change the depth in the calculator before ordering.

For the shallower pass, set the rotavator’s working depth according to the machine. A faster forward speed can limit mixing, but does not by itself guarantee that zeolite will not end up throughout the full 30 cm.

Fig. 08 Soil cores at three points in the same area: amendments at their intended depth, a pile left in one place, and amendments spread right to the bottom by deep rotavating.

Finally, spread biochar prepared in advance evenly, along with Actino (formerly Biovin) if used, where the recipe places them in the upper 10 cm. Rake them into the surface; if they need to be mixed through the full 10 cm, shallow hand cultivation or a machine set to this depth will help.

Rakes alone will not reliably mix ten centimetres of soil. After this step, do not return to deep rotavating, which would spread the shallower amendments through the whole profile.

The same sequence applies to every chosen mix: mix the components of its mineral base most deeply, then add other amendments according to their own incorporation depths, working from deeper to shallower. Spread them progressively section by section, rather than in separate unmixed layers.

Use a spade or a small inspection pit at several points to make an approximate check that no piles remain in the mix and that amendments have not been unnecessarily spread right to the bottom. Millimetre precision is not needed. Rain will not mix solid grains to the required depth for us.

Time for settling is not wasted waiting

Levelled, freshly watered soil; a puddle stands in a shallow depression and reflects the warm evening light. — **Fig. 09** A puddle after watering reveals a spot where the surface is still sinking. More mix is added there once it has stabilised.

After levelling and watering, the freshly loosened mix begins to settle. Particles and pores rearrange themselves, so the surface level may also change. Settling itself is therefore not a fault; it is part of having first loosened, mixed and laid the material again.

As a guide, allow several weeks in the plan, approximately 2–⁠6, or sometimes around two weeks for light soil. The calendar, however, cannot tell you whether the surface has stopped sinking.

Watch the actual condition. Only once levels have stabilised should you correct uneven areas and prepare a finer seedbed — the surface layer into which the seed will go.

Waiting can also bring a practical benefit: weeds that emerge in the meantime can be removed shallowly before sowing the grass. Final preparation can then begin with a more stable surface and without these newly emerged plants.

Is the soil ready for sowing?

What to check	When you can continue
Subsoil and drainage	When you can continueRubble and unsuitable material have been removed, the compacted obstruction has been broken up, and water does not remain accumulated in the profile.
Mixing and depth	When you can continueSmall test pits at several points reveal no piles of amendments or separate unmixed layers; the mix matches the chosen recipe and its depths.
Settlement and levels	When you can continueAfter watering and settling, the surface no longer sinks significantly. Uneven areas have been corrected, and the level meets the paths and patio.
Moisture and firmness	When you can continueThe soil crumbles during work, does not smear, and walking on it leaves no deep footprints. The surface is reasonably firm, rather than compacted into a hard layer.
Seedbed	When you can continueThe top layer is finely crumbly and level; emerged weeds have been removed shallowly. Any planned pipework is already in the ground.

Only then choose a suitable time according to soil temperature and prepare the seed. The passage of 2–⁠6 weeks alone does not mean the area has stabilised.

A level, settled seedbed between a lawn and a wooden fence in low evening light; a paper bag of seed stands at its edge. — **Fig. 10** A level, settled bed before sowing, with a bag of seed at its edge.

Conclusion

Why does all this work pay off in the end?

Bare feet on a dense, healthy lawn in low evening sunlight. — **Fig. 11** Prepared soil is hidden from view, yet it underpins the lawn’s resilience and everyday care.

Before sowing, you can easily break up a compacted layer. Level the soil and sow.

But what happens if you encounter that same obstruction two years later, when your lawn starts dying? You will have to strip off the turf, take care around nearby plants, dig up hard ground in an established garden, sow again and painstakingly nurse the grass once more. The work multiplies. Repairing an established lawn is possible, but it severely disrupts how you use the garden.

Preparing the soil properly at the start reduces the risk of using water or fertiliser to address a problem hidden beneath the surface. Water, air and nutrients can reach the roots more easily. Looking after the soil will not remove the need to mow or rule out disease, but it will create better conditions for ongoing lawn care.

When you first walk barefoot across the new lawn, all that hard work below ground will be out of sight. You will only fully appreciate its purpose when torrential rain or a scorching hot week arrives. Then, instead of rescuing the garden, you will simply be enjoying it.

Questions and answers

Frequently asked questions about improving and preparing soil

Decide how much work is needed according to the actual condition. While working, check mixing, incorporation depth and surface stability.

Why 30 centimetres when grass has shallow roots?

A continuous, aerated space gives roots access to moisture reserves beneath the rapidly drying surface. Beneath 1 m², a depth of 30 cm means 300 litres of soil. It is a practical preparation target, rather than a guaranteed depth for all roots.

Do I have to excavate 30 cm of soil and buy new soil?

Usually not. Retain soil that works well and correct local shortcomings. Break up a compacted obstruction beneath good topsoil; remove unsuitable fill or building rubble. Decide how much work is needed from a test pit and infiltration, rather than the desired depth alone.

How do I calculate how much amendment, such as zeolite, to buy?

Work out the proportion from the volume of soil down to the chosen depth. Then convert the litres required into weight using the delivery’s bulk density. The soil profile calculator calculates both for your area and also offers a conversion into packs.

Do I have to build the soil profile in precise layers?

No. Mix the mineral base first, then incorporate amendments from deeper to shallower depths. Match the depth to the recipe and check it with a test pit; do not create precise layers.

Will rain finish mixing everything evenly?

No. It will not mix solid zeolite or biochar grains to the required depth. Check evenness with a test pit at several points.

How long should I leave the mix to settle?

As a guide, 2–⁠6 weeks, sometimes around two for light soil. Sow only once levels have stabilised and uneven areas have been corrected.

Key takeaways

Now you have a foundation to build on.

Deal with compaction, unsuitable material and drainage before bringing in material.
Mix the mineral base first, then incorporate amendments from deeper to shallower depths.
Finish the seedbed only after settlement and once levels have stabilised.

In the next article

The soil is ready. When and how should you sow?

Soil temperature, the amount of seed and a few millimetres of incorporation depth also shape the lawn’s start. Learn how to manage these details from sowing to the first watering.

Continue to sowing the lawn

The InteliDome system

When the soil controls irrigation, rather than the calendar

Wet soil does not mean roots have had a drink — and every extra watering of a waterlogged profile is wasteful. The InteliDome moisture sensor sits directly in the root zone you have just prepared and measures how much water is actually there.

With suitable sensor placement and settings, the system can adjust watering to the condition of the root zone and skip it after rain. This makes use of the reserve that the prepared soil can hold.

Sensor in the root zone

Measures moisture at the depth where roots actually take up water — rather than at the surface, which the sun can dry out in an afternoon.

Watering according to the soil

With suitable settings, the zone responds to measured moisture and can skip watering after heavy rain.

Rainwater storage tank

With a suitable setup, rainwater can be used first, with mains water as a backup once the tank is empty.