How to mix soil for a lawn: ratios for clay, loam and sand

Choose a lawn soil mix to suit the starting soil: in heavy soil, focus on air and drainage; in poor sandy soil, on retaining water and nutrients. Calculate amendment proportions from the volume of soil down to their incorporation depth. The ratios given are models for the gardens described, rather than universal rates.

3recipes

clay, loamy and sandy gardens

0–10cm

where the most expensive amendments belong

5m³

how much space a tonne of biochar takes up

65/35

sand-to-soil volume ratio for clay

Chapter 01

Why we mix by volume rather than by tonnes

Fig. 01 The length of each bar is the volume of one tonne; dashed lines mark whole cubic metres. For zeolite and Actino, the drawing uses the model densities of 0.80 and 0.60 t/m³ from the soil profile calculator.

The three recipes in this article are model designs by InteliDome. The ratios 65/35 and 30/70, and the amendment ranges, explain the design and calculation; they are neither a generally applicable standard nor the result of measurements from one specific project. Check their suitability for your own garden by examining the soil and making a trial mix.

The roles, selection and preparation of the materials are explained in Sand, biochar, zeolite and Actino: what your soil needs. Here we use them to put together a mix by volume before moving on to the order.

Volume determines the component ratios; mass is used to plan the order and transport. A recipe by volume therefore cannot be converted into the same ratios in tonnes. Bulk density tells us how much a given volume of loose material weighs, including the spaces between particles.

Sand and biochar illustrate the difference well. At a model sand density of 1.5 t/m³, one tonne takes up about 0.67 m³. A tonne of biochar with a density of 0.20 t/m³ takes up 5 m³. The same mass therefore gives very different volumes; mixing equal tonnes of the two would produce approximately 88 % biochar.

Actual density depends on the material and the moisture content of the delivery. Converting cubic metres to tonnes, litres and packs therefore uses the supplier's figures.

When working with delivered soil, we do not need precision down to individual kilograms. We need to keep reasonably close to the chosen volume proportions and mix evenly. Rounding must not turn a few per cent into a proportion several times larger; for seed and concentrated products, the product's application rate still applies. The practical mixing method shows how to turn an estimate of quantities into work carried out in sections of the garden.

Quick overview: three soils, three conditional models

Starting soil	Mineral base by volume	Model amendments and depths	When to use the model and when to leave it out
Heavy clay	Mineral base by volume65 % sand + 35 % suitable existing soil	Model amendments and depthsZeolite 2–⁠5 % down to 15 cm; biochar 2–⁠5 % and Actino 2.5–⁠5 % down to 10 cm.	When to use the model and when to leave it outFor substantial restructuring of heavy soil lacking organic matter. Deal with compaction and drainage first; check the appropriate sand proportion with a trial mix.
Heavier loam	Mineral base by volume30 % sand + 70 % suitable existing soil	Model amendments and depthsZeolite 3–⁠7 % down to 15 cm; biochar 3–⁠7 % down to 10 cm; Actino 0 % in the model with maintained topsoil.	When to use the model and when to leave it outFor renovating heavier loam. If water drains, the soil crumbles and retains moisture, the amount of new sand and amendments may be zero. Where organic matter is lacking, 2.5–⁠5 % Actino down to 10 cm can be chosen.
Poor sandy soil	Mineral base by volumeExisting sandy soil; additional sand 0 %	Model amendments and depthsZeolite 8–⁠10 % down to 15 cm; biochar and Actino each 5–⁠10 % down to 10 cm.	When to use the model and when to leave it outFor soil that dries quickly and is poor in organic matter and nutrients. Do not automatically apply these rates to sandy soil regularly replenished with compost.

Sand-to-soil ratios apply only to the mineral base left after subtracting the amendments. Amendment percentages are calculated from the volume down to their own depth, rather than from the entire 30cm profile. Components in each zone must add up to 100 %. The biochar is pre-charged with nutrients; the mycorrhizal product is applied separately at the product-specific rate.

Chapter 02

Thirty centimetres of soil as space for life

A square test pit dug in the prepared bare area for a new lawn: vertical sides of crumbly brown soil, with darker, firmer subsoil at the bottom. In the background are a lawn and a wooden plank fence in the low evening sun. — **Fig. 02** The side of the test pit shows the prepared layer from the surface downwards; darker, firmer subsoil begins at the bottom.

For our examples, we choose a 30 cm deep profile for a newly established or completely renovated lawn. The profile means the layer of soil being prepared from the surface down to this depth. Thirty centimetres is a model, rather than a rule for every garden or an instruction to automatically remove thirty centimetres of soil everywhere.

Why a continuous space for roots matters, and why the depth of newly delivered material alone is not enough, are explained in the chapter on root zone depth. Here we use depth to distribute the individual components.

The upper part helps roots get started; the deeper part lets them continue

Fig. 03 Dashed lines at 10 and 15 cm divide the cross-section into zones: black biochar fragments only down to 10 cm, pale zeolite grains down to 15 cm, and only the base below. Longer roots cross both boundaries and continue down through it.

The upper ten centimetres have the most varied composition: biochar, zeolite and, where needed, Actino. Zeolite also continues between 10 and 15 cm. The 15–⁠30 cm zone consists solely of the mineral base, through which roots can continue to reach water and air.

We concentrate the more expensive amendments near the top because much of the root activity in lawns tends to be close to the surface. This does not mean that roots stop at ten centimetres. Amendments can also be incorporated deeper, but keeping the same proportion in a larger volume increases consumption and cost, while their benefit there tends to be smaller.

The zones in the drawing describe the final distribution of amendments, rather than a construction method using separate layers. In practice, we first mix soil and sand throughout the planned depth, then incorporate the other amendments at progressively shallower depths. The depths are approximate; the aim is to avoid spreading expensive material unnecessarily deep. Details are shown in the method from the mineral base to shallower amendments.

Chapter 03

Three gardens: which ratios to choose

Three small piles of different soils side by side on a prepared bare area beside a lawn: on the left, dense grey-brown clay clods with smooth faces; in the middle, dark crumbly loam; on the right, pale loose sandy soil. Behind them are a lawn in the low evening sun and a wooden plank fence. — **Fig. 04** From the left: dense, sticky clay; crumbly loam in the middle; and loose sandy soil on the right. These are the three starting soils for the model recipes.

Heavy soil needs better access to water and air; in loamy soil, we want to preserve a balanced base; in sandy soil, we want to help retain moisture. The following recipes are models for establishing or substantially renovating a lawn, rather than universal prescriptions.

Choose the appropriate example, check its conditions and select specific proportions within the ranges given. Only then calculate the quantities. If you do not know the soil type, start with the sample test in the palm of your hand; where there is waterlogging, also check infiltration and the route water takes into the subsoil.

Fig. 05 The left pan carries water and nutrients; the right carries air and drainage. The heavier pan shows the soil strength we preserve; the lighter one shows the weakness we improve. Well-functioning loam is balanced.

Choose a recipe according to the problem it needs to solve. Soil that works well does not need changing simply because there is a row for it in a table. With long-term waterlogging and poor rooting in heavy, impermeable soil, however, a more thorough improvement may make sense.

Even then, we do not have to remove all the clay soil and replace it with pure sand. We would also lose its ability to retain water and nutrients and would have to replenish them more often. Even golf courses are not established on pure sand in every area.

The loamy example in the table concerns heavier loamy soil being renovated, to which we add sand. Biochar and zeolite are intended to help the modified mix retain water and nutrients. The conditions for leaving amendments out, or instead adding organic matter, are given directly in the loamy variant.

Amendment rates for three model gardens

Amendment and incorporation depth	Clay garden restructured with sand	Heavier loamy garden with maintained topsoil	Poor sandy garden that dries quickly
Zeolite, 0–⁠15 cm	Clay garden restructured with sand2–⁠5 % by volume	Heavier loamy garden with maintained topsoil3–⁠7 % by volume	Poor sandy garden that dries quickly8–⁠10 % by volume
Biochar, 0–⁠10 cm	Clay garden restructured with sand2–⁠5 % by volume	Heavier loamy garden with maintained topsoil3–⁠7 % by volume	Poor sandy garden that dries quickly5–⁠10 % by volume
Actino, 0–⁠10 cm	Clay garden restructured with sand2.5–⁠5 % by volume	Heavier loamy garden with maintained topsoil0 %	Poor sandy garden that dries quickly5–⁠10 % by volume
Separate mycorrhizal product	Clay garden restructured with sandConsider after restructuring; use the specific product rate	Heavier loamy garden with maintained topsoilStarting variant without an addition	Poor sandy garden that dries quicklyConsider if a new mix is being created with little biologically active soil

Heavy clay soil: roots need air as well as water

Fig. 06 Clay surrounds the new mix underneath and at the sides like a bathtub. Blue shows water that has passed through the mix and is standing on the clay bottom; roots reaching into it have little air.

After rain it sticks to your boots; when dry it can become so hard that you need your full body weight to push the spade in. Fine roots have to grow between these two states. Yet clay is not a worthless material to be removed at all costs. It can retain both water and nutrients. The problem arises when particle arrangement and compaction restrict air and the movement of excess water.

For this model, we use a mineral base consisting, by volume, of 65 % sand and 35 % existing clay soil. The high sand proportion reflects the substantial change to the mineral mix considered here. The retained soil still provides finer particles and the ability to bind some nutrients.

This variant assumes heavy soil to which organic matter has not been added for a long time. First loosen compacted areas and deal with drainage of excess water; only then prepare the mix.

Choose both zeolite and biochar within 2–⁠5 %, and Actino within 2.5–⁠5 %, always in the defined upper zones. Clay particles already help retain nutrients, so we use less zeolite than in a sandy garden. Actino supplies the organic component.

Fig. 07 The position of the sample on the scale illustrates the sand proportion. The 65/35 ratio belongs to our model; check the appropriate composition for a specific clay soil with a trial before placing a large order.

After adding a large amount of sand, we are no longer working with the original clay. Even a low zeolite rate must therefore suit the behaviour of the new mix, rather than just the name of the starting soil.

The 65/35 ratio describes only the mineral base. Amendments take their own share of the total volume, so added sand does not make up 65 % of the entire upper mix. The calculation for a 100 m² clay garden shows this difference.

With heavy clay, it makes sense to carry out a test before placing a large order. A few shovelfuls of sand generally will not change the properties of the whole layer. The proportion needed varies with the existing soil and the chosen sand; a higher proportion may be necessary, but we check it with a trial mix.

Penn State describes the need for large amounts of sand to make a substantial change to clay soil. This general recommendation supports the explanation of the principle; the 65/35 ratio and the amendment rates given here are our model designs, rather than a recipe taken from Penn State or a universal rate.

A working route for water must remain beneath the new mix. Mycorrhiza, if used, cannot replace dealing with compaction and drainage either; decide whether to use it according to the separate rules for a mycorrhizal product.

Medium loamy soil: preserve a balanced base

A close-up of freshly turned loamy soil in a bed beside a lawn: dark brown crumbs and small clods, moist but not wet, with fine pale grass roots, in warm side lighting from the evening sun. — **Fig. 08** Well-functioning loam crumbles: it breaks into crumbs with pores remaining between them, and fine roots grow through it.

Well-functioning loamy soil often has an understated advantage: water infiltrates, the soil crumbles and it still retains some moisture in dry weather. Our model, however, deals with renovating heavier loamy soil with retained, maintained topsoil, which we want to make easier to work and more permeable.

The mineral base consists of 30 % added sand and 70 % existing loam by volume. Leave out Actino; choose both biochar and zeolite within 3–⁠7 % in their designated zones.

Sand modifies the mineral base, while porous amendments are intended to support retention of water and some nutrients. The ranges belong to this restructuring and do not prove that every loam needs more amendments than every clay soil.

Fig. 09 Loosening breaks the dark striped layer into blocks separated by cracks. Nothing is added, only moved: the stone out of its bed, and the hump into a hollow of the same size. Dashed lines show the stone bed and the target level.

If loam lets water through well, crumbles and does not dry too quickly, the amount of new sand, biochar and zeolite may be zero. Levelling, removing stones and loosening areas compacted by machinery may be more useful than a delivery of material. In the starting variant with retained biologically active soil, we do not buy a separate mycorrhizal product either.

The situation is different for loam neglected for a long time without replenishing organic matter. For this, a variant with 2.5–⁠5 % Actino in the upper 10 cm can be prepared, replacing part of the mineral base. But if the spade reveals a hardened layer left by an excavator, break it up first. Examining a soil test pit helps distinguish these two problems.

Light sandy soil: extend the time roots have a supply to draw on

Fig. 10 The pale dashed line marks the reach of the roots. Nutrient dots above it are a supply the roots can reach; those below it are carried by water along the blue route beyond their reach.

A spade slips pleasantly into light sandy soil. In July, however, its properties may be less pleasant for the lawn. Water passes through it easily, air is usually plentiful, but the supply available to roots is quickly used up. Some dissolved nutrients also travel with the water deeper than the roots currently reach.

We do not add more sand here. The mineral framework is sandy from the outset. Instead, we want to improve the soil's ability to manage water and nutrients: biochar and zeolite are intended to strengthen the upper part's storage properties, while Actino adds an organic component and nutrition.

Zero sand in the table does not mean soil without sand. It means buying no additional sand; the existing sand remains part of the original soil.

Here we assume soil poor in organic matter, with a small nutrient reserve and rapid drying. We therefore choose 8–⁠10 % zeolite in the upper 15 cm, and 5–⁠10 % each of biochar and Actino in the upper 10 cm. Choose the specific rate within each range according to the properties of the soil and supplied materials. This design is intended for poor sandy soil without regular additions of compost.

Always assess an amendment in the final mix: in clay, watch air and drainage; in sand, the length of time water remains available to roots.

How the ratios relate at different depths

Fig. 11 Each column is the mineral base of one garden down to 30 cm: added sand on the left, soil on the right. Dashed lines mark the zone boundaries at 10 and 15 cm; the dividing line passes through them unchanged.

Amendments replace part of the mineral base. In every zone, the proportions still add up to 100 %. Choose a specific proportion for each amendment and fill the remainder with the base. The lowest base proportion corresponds to the highest rates of all amendments, and vice versa; the extreme values cannot be added together arbitrarily.

In the clay variant, the remaining base is divided by volume 65/35 between sand and soil; in the loamy variant, 30/70. In the sandy variant, it consists of the existing sandy soil. The ratio of components within the base does not change with depth, but its share of the whole mix does. The calculator works out the volume of each amendment according to its depth.

Component ratios in the 0–⁠10, 10–⁠15 and 15–⁠30 cm zones

Zone	Clay example	Loamy example	Sandy example
0–⁠10 cm	Clay example85–⁠93.5 % base + 2–⁠5 % biochar + 2.5–⁠5 % Actino + 2–⁠5 % zeolite	Loamy example86–⁠94 % base + 3–⁠7 % biochar + 3–⁠7 % zeolite	Sandy example70–⁠82 % base + 5–⁠10 % biochar + 5–⁠10 % Actino + 8–⁠10 % zeolite
10–⁠15 cm	Clay example95–⁠98 % base + 2–⁠5 % zeolite	Loamy example93–⁠97 % base + 3–⁠7 % zeolite	Sandy example90–⁠92 % base + 8–⁠10 % zeolite
15–⁠30 cm	Clay example100 % base	Loamy example100 % base	Sandy example100 % base

When to adjust a rate and when to leave an amendment out

Fig. 12 Area A on the left contains the starting mix; B on the right contains the same mix with just one difference: fragments in dashed circles are extra biochar that has taken the place of mineral base.

For the initial preparation, choose proportions from the table for the relevant garden. If you want to reduce costs or compare mixes on a small area, you can start at the lower end of the range. Testing the upper end may make sense, for example, on very coarse soil that dries quickly; it is not automatically better.

When comparing, change only one rate at a time. Balance any added or removed volume with an opposite change in the mineral base; keep the other amendments the same. Half the rate does not necessarily mean half the effect, and more material does not guarantee a proportionately greater benefit.

In heavy soil, first remove compaction and obstacles to drainage. In light soil, compare whether it dries more slowly between watering. This assesses the specific property we wanted to improve, rather than the quantity of added material.

Questions and answers

Frequently asked questions

Calculate the mix by volume. The depths describe the final distribution of components; when working, do not create separate layers.

Why is the mix measured by volume rather than by kilograms?

Because different materials take up different amounts of space at the same mass. Volume determines the component ratio; we calculate the mass for the order from the density of the specific delivery.

How deep should each amendment go?

In the model 30 cm profile, biochar and any Actino go down to 10 cm, and zeolite down to 15 cm. The mineral base continues throughout the depth. This describes the final distribution: when working, first mix the base, then incorporate the amendments more shallowly. We do not build the zones as separate layers.

Are amendments added on top of a hundred per cent of base?

No. Amendments replace part of the mineral base, and the total in every depth zone remains 100 %. After changing one rate, adjust the base volume in the opposite direction; keep the other amendments the same.

Key takeaways

Now you have a foundation to build on.

Determine the mix ratios by volume, rather than by an equal number of kilograms.
The amendment proportion is related to the depth to which it is incorporated.
In each zone, the components add up to 100 %; adjust the model to suit your soil.

In the next article

How many cubic metres and tonnes will the recipe need?

A few per cent of amendment can mean hundreds of litres across a whole garden. Calculate what to bring in, what to retain and how much soil will need to be removed.

Calculate materials for the garden

How to mix soil for a lawn