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How To Garden In Clay Soil ?

Many gardeners consider clay soil unsuitable for gardening.

But heavy soils are often also rich.

And, if you know how to improve it, such soil will provide you with abundant crops.

I actually started gardening in very clayey soil.

So, of course, the work with the Grelinette was a bit more complicated than in a lighter soil.

But my crops were very nice!

We are talking about soil texture, i.e. particle size.

Soil contains different types of particles, which we classify by size:

the finest are the clays
then come the silts
then sand
Pebbles can also be present of course
Each soil will contain a variable proportion of these elements.

To put it simply (in reality, there is a more precise classification based on proportions), if clays predominate, we will speak of clay soil.

It is this type of soil that we will discuss today.

Note in passing that clay soils can be acidic, neutral or calcareous (marls for example)… but that’s another subject.

I would like to warn you: just because people (even farmers) around you say your soil is clayey does not mean it is!

I have indeed noticed this many times… at home for example: because they harden on the surface in summer (which is in fact due to the silts and the drought), most of my neighbors say that our soils are heavy… when in fact they are sandy-silty (therefore light)!

Laboratory soil tests have confirmed this.

But personally, I didn’t need any analysis for that… and neither do you: I present you in Mon Potager au Naturel, simple tests (in particular the one called successive manipulations), to determine, with a sufficient precision, the real texture of your garden’s soil.

A clay soil is… heavy, sticky and very difficult to work with when it is wet (we will see this below).

It will warm up slowly but will retain water and nutrients well (which often implies a certain richness… good news).

But it can become very hard in summer.

A clayey ground is thus heavy, often compact, even asphyxiated, and difficult to work.

In permaculture, our objective will be to lighten it and to make it more loose and aerated, while encouraging the development of life.

Let us see how…

Do not bring sand!

It is a piece of advice that we often see: “your soil is heavy… lighten it with sand!”


Not only will the sand not mix properly with the soil (and even more so with clay soil) – and as a result you will end up with a completely unstructured soil, unfit for rooting and, worse, for life – but bringing in sand is equivalent to impoverishing the soil since you are adding a particularly poor material…

Not to mention the fact that it would take huge amounts of sand to have a real effect on the soil texture.

So forget about the sand already.

In fact, we are not going to try to modify the texture of a given soil, but rather to improve its structure (i.e. the relationships between the different components and the characteristics that result from them: aeration, flexibility, biological activity, etc.).

Our objective is to loosen the soil.

To make a clay soil more flexible, grow green manure

A green manure has many advantages:

it protects the soil by providing a cover
it promotes life in the soil
it competes with weeds
the resulting organic matter will enrich the soil
some green manures will attract pollinators
But what interests us most here is its action on the soil structure.

Indeed, a green manure, thanks to its root system, will aerate the soil, naturally.

If you sow a mixture of different species, with specific root systems (plunging deep into the soil or on the contrary tracing, on the surface), a green manure crop will act at different depths of the soil.

Ideally, this mixture intended for heavy soils will be composed of 3 species (but one can of course put more), coming from 3 botanical families:

a cruciferous plant, the species commonly cultivated for this purpose being the white mustard (which has yellow flowers…). Its powerful pivoting system will plunge in depth
a grass, like rye or oats for example, which, with its dense root system spreading on the surface, will loosen the surface layer of the soil
a legume (vetch, clover, alfalfa, faba bean), which, because of its ability to capture atmospheric nitrogen, will enrich the soil (when its organic mass decomposes)
You can also add phacelia, especially for pollination.

Sow these green manures in late summer, early fall.

In order to sow a green manure (but it is also applicable if you want to sow a vegetable crop), you will probably need to work the soil… We will see how below.

In most cases, a green manure crop will be beneficial for a clay soil.

However, this is not necessarily a must… if your soil is not compacted, you may be able to go directly to the soil cover…

Cover your soil

choux, salades, pommes de terre paillées

cabbage, lettuce, mulched potatoes
A good mulching
Covering the soil of a garden is to encourage the development of life in the soil… an important objective in permaculture!

And, in particular (but not only), earthworms.

It is then these earthworms, and a multitude of other micro-organisms which will from then on take care to aerate the ground and to loosen it!

If your soil, although heavy, is not particularly compacted, you can try to mulch directly (without loosening it beforehand, and without growing green manures).

We won’t go into detail here, but here are some recommendations for mulching:

Try to diversify the materials as much as possible: green manure residues, hay or mowing, RCW, straw, comfrey leaves, nettle leaves, dead leaves…
Avoid green grass, grass clippings… or at least, put only a very thin layer (a few millimeters).
If you mulch in spring, do not mulch too early, but wait until the soil is well warmed up (see here)
Do not mulch on a too dry soil…

How to work a heavy soil?
If you start directly after a summer crop, on a covered soil, one pass with a tine cultivator may be enough to sow your green manure.

But if it is a new vegetable plot or a crop bed that has been left idle or overgrown, you will have to prepare the soil.

I’m not talking about plowing or turning over the soil… but simply loosening it up enough to accommodate a seedling.

When to operate ?

The best time to start a heavy soil is late summer or early fall.

Why is this?

Because at the end of winter, such a soil will generally be waterlogged… and we have seen above that it retains water well and is difficult to work when it is wet.

It will therefore take a long time to dry, and if you want to plant crops early enough in the spring, you will be stuck… or else, as many gardeners unfortunately do, you will work it anyway… in very bad conditions.

The consequence?

Big clods will form, impossible to loosen properly… and giving a structure not very favorable to the development of the soil life and roots…

Of course, some people will tell me that by going over and over again with their tiller (or hoe), they manage to loosen the soil… but it is of course even worse for the soil life!

If you have no other choice than to start in spring, don’t rush, but wait until your soil is dry enough (see below) to work it, with the Grelinette or the Campagnole.

This being the case, it is obvious that a clay soil is best worked in the fall, and even more so for the question that does not concern us here: the preparation for sowing a green manure.

The first condition is to work at the right time: the soil must be very slightly humid.

We will operate a few days after a good rain (or a good watering if necessary).

A simple test consists in planting the teeth of your Grelinette (or a spade with teeth) in the ground.

The soil must then hardly stick to the teeth of the tool to be able to be worked correctly.

If it still remains heavily stuck, try again 1 or 2 days later…

When it is good, you can go.

After having first mowed the weeds at ground level, work the soil gradually, without mixing the different layers of the soil. To do so, use a Grelinette (you can eventually use a spade with teeth… but it will be much more tedious):

Make a first pass by pushing only half the teeth of your Grelinette (the goal is to lift the root systems in place)
A few days later, make a second pass, but this time deeper.
A last pass (sometimes two) should allow you to refine the soil sufficiently this time.
This loosened soil is now ready for a green manure crop.

As we have seen, your objective in permaculture, in clay soil, will be to aerate it and to make it more alive.

And it is by combining the various practices seen above that you will achieve this.

In summary :

at the end of summer or beginning of autumn, loosen the soil with a Grelinette (at least the first year… this will not necessarily be necessary afterwards if your soil is permanently covered).
sow a mixture of green manures to follow
mow the green manures in the spring and let them decompose into a cover crop (or set them aside for later use)
when the soil is warmed up, mulch…
Repeat this process every year…

In a few years, you will have a rich and loose soil… and therefore beautiful crops, quite naturally!

And I am at your disposal to help you make the right decisions through the coaching service I offer.

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