All You Need To Know About Clay Soil


Clay soil – has at least 30% fine clay particles – are often categorised as “heavy soil” and for good reason. Gardening in it is often met with drainage issues due to clay’s physical characteristics.

Moreover, clay-rich soil is susceptible to damage when worked or walked on, and it can take a while to restore its former structure.

But while it is hard to manage indeed, clay soil has its share of advantages: it’s self-cultivating – swelling and shrinking when wet and dry –and can be very fertile when cared for properly.

Soil – particularly its texture – is often defined according to the distribution of different mineral particles and these are clay, silt, and sand at the most basic level.Clay soil

Of the 3 basic particles, clay is the smallest with an average diameter of less than 0.002mm – viewable only through an electron microscope. This allows a large amount of clay particles to fit in small spaces minus the gaps common in larger soil particles. This explains why clay’s texture feels smooth to the touch: the particles are too fine to create a rough surface.

The extremely small clay particles also contain micro-pores, leading to a larger overall pore space and greater water retention compared to other particles.

To beginning gardeners, this feature of clay may sound positive (and it is) but it could lead to inadequate drainage and aeration when left unchecked. The air pockets in the ground are soon filled with water, greatly reducing the availability of oxygen which is essential for optimal root development and health of soil organisms.

Hampered drainage in clay soil also keeps it saturated long after the rainy season. Slow to warm, planting certain seeds and vegetables at the right time during the spring season becomes tricky – and it’s twice as troublesome for gardeners living in low temperature regions with already short growing seasons.

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Clay alone doesn’t offer much as far as plant nutrition is concerned. It has very little organic material and often found lacking in the nutrients plants need for growth and photosynthesis. Clay soils rich in minerals, on the other hand, are often alkaline in nature – which can be problematic for plants that thrive in soils with a neutral pH.

Don’t get us wrong though: successful gardening with clay soil is possible. It all boils down to preparation, which we’ll get to next.

But before we discuss clay soil preparation in-depth, you need to determine first if you indeed have clay soil. Here are some tell-tale signs to keep an eye for:

Clay soil looks solid at first glance and usually dons a distinct red or brown colour.
It often feels slick when rubbed using the fingers – sticking or leaving streaks on the skin while taking on a shiny, smooth appearance instead of the rough texture common in other soil particles.
Soils rich in clay don’t crumble easily. A sample of clay can be rolled into a ball and stretched slightly like a sausage without breaking.

One of the upsides with clay soil is that its compact, dense nature helps it retain nutrients well. But while that sounds nice, plant roots can have a hard time growing especially if your soil contains more than 35% clay. Fortunately, it’s possible to dilute the concentration of clay – making your soil easier to work on and more favourable for planting.

Large volumes of grit and other materials are often used to quell clay’s dominant physical properties. Soils with 40% clay particles, for example, would require 250kg of grit/square meter to reduce the concentration of clay in the top cultivated part of the soil.

But while a large amount of grit gets the job done, there’s some bad news:

First, it’s often impractical for most gardeners whose budgets are limited. And second, it’s not a be-all-end-all 100% guaranteed solution – one should remember that adding other materials to clay soil can lead to instability. So if you’re going down this route, be sure to start at a small scale to see if it’s worth your while.

The good news, however, is that there are budget-friendly ways to improve your gardening ground and reduce its concentration of clay.

Before we discuss specific methods for enhancing clay-rich soil, it’s important that you decide first how much area you need for your home garden. It’s almost mandatory to work on the whole area at once instead of starting slow with planting holes… working only on the area you intend to use as backfill. Doing so will accommodate your plants’ needs… but only for a while.

Eventually, your plants will grow (which is why we’re gardening in the first place) and so will their roots – creeping beyond the confines of your amended, backfilled soil. But since the planting hole is surrounded with dense and untended clay soil, the roots will start circling around the plant hole as it’s almost impossible to expand beyond it.

The end result: A root-bound plant that will not grow as large and as healthily as it should.

No doubt, working on your gardening area all at once will take a lot of time and effort. But know this – the hours and effort you put in will improve your garden soil’s structure instantly, making future projects easier to carry out as most of the upfront work is done. Hopefully, positive, long-term results are enough to convince you that it’s worth your while.

Here are the steps for preparing and gardening in your clay-rich garden soil:

If you are improving an existing garden, take the time to dig out the plants you want to keep.

Next step: apply 6 to 8 inches of organic matter on your gardening bed. Leaf mould, grass clippings, garden compost, and rotted manure are all good candidates. Apply the organic matter by digging in and mixing it using a shovel so it doesn’t pulverise the soil. The biodegradable matter will eventually decompose and release nutrients into the ground for your plants to feed on.

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Rinse and repeat the two steps above once or twice a year as you’d want to add more organic matter and offset any settling that occurs, keeping your gardening bed’s drainage and aeriation unobstructed.

Avoid putting any kind of pressure on your clay soil especially if it’s wet. Even the slightest foot traffic can cause hard-to-repair damage to clay-rich ground – giving it a more compact structure that stifles root growth and drainage. While it can be remedied, it’s a slow and tedious process so consider standing on a plank when working on clay soil.

Digging in your garden during autumn until early winter is highly recommended. The soil is not as damp and heavy during September, making it easier to work on. When digging in however, don’t break the lumps and let the winter frosts take care of it.

Annuals or bedding plants may not thrive in clay-rich ground as much as you’d like, but there are a lot of trees, shrubs (roses especially), bulbs, and main-crop vegetables that are easier to grow in clay soil.

                                                     PROS AND CONS
What’s Nice About Clay Soil:
When reading its properties, you may get the feeling that clay is a gardener’s curse. But this is far from the case – clay soil has its share of bright spots once you learn how to work with it.

For starters, it is easier to fertilise and water than other soil types. Its microscopic particles filled even smaller pores means clay has greater CEC than silt or sand – able to hold on to a lot of nutrients and water. This reduces the need for fertilising and watering – something that a busy gardener always welcomes with open arms.

The dense nature of clay also helps provide a sturdy foundation for plants and their roots. People that garden with sandy soil know sand’s notoriety for letting plants jump out of the ground and fall over – and many of these gardeners add clay to increase the ground’s density for better support.

Perennials and annuals – Lilium regale, Arthropodiumcirratum, Geummagellanicum, etc.– thrive better in clay soils than plants that require regular sowing, planting, dividing, etc.

The tiny particles help the roots get a firm grip in the ground – allowing the plants to weather extreme temperatures and high amounts of moisture that plants in other soils cannot.

So to sum things up, you get to water and fertilise less while giving your plants a better foundation with clay soil. But as you’ll now see, clay soil has its share of disadvantages that you should consider, too.

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What’s Not So Nice About Clay Soil:
When you decide to garden with clay soil, you better be ready for numerous challenges – most of which are hard to tackle (though not impossible) and one of them is waterlogging.

Unable to drain water freely, waterlogged clay soil prevents plants from getting enough air from the ground – leading to yellow leaves, root rot, or even death!

This is especially true during winter when clay ground is almost impossible to dig. And even if you can, you probably wouldn’t want to dig in your clay soil in winter as it almost inevitably leads to further compression of soil particles – leading to greater waterlogging. And let’s not forget how mucky and messy your tools, gloves, and clothes can get when working with wet clay.

The summer season doesn’t provide any relief as far as digging is concerned as clay particles shrink and turn rock-hard when dry.

READ MORE: Everything You Need To Know About The Different Soil Types

Clay soil is more than equipped to retain water and nutrients from fertilisers, but it also means it will retain unwanted guests like salt and other materials – leading to harmful build-up which is a pain to get rid of thanks to clay’s gripping properties.


Don’t let the name fool you. The false sunflower isn’t in any way inferior to real sunflowers. The perennial is one of the resilient plants you can have in your garden – shrugging off heat and drought with its amazing tolerance and bringing lovely blooms throughout summer.

This plant is a toughie – able to resist dry conditions and even deer! But make no mistake about it: it’s a tough plant but it’s beautiful too! It can grow silvery foliage along with a bouquet of golden blooms that never fail to attract butterflies.

These versatile flowers can have a variety of colours – white, purple, pink, lavender, and more. They grow anywhere from 2 to 5 feet tall and bloom during the Autumn.

The Russian Sage doesn’t mind growing in hot, dry, sunny clay. But be careful: Many consider it invasive and the plant is restricted in some areas so please double-check. Should you decide to grow a Russian Sage though, you’ll be rewarded with its lavender flower spikes and silver foliage – always a great addition to your garden!

Our garden-loving buddies in the USA dedicated an entire society – The American Fern Society – to this leafy plant, celebrating over 12,000 species of fern available today. What made the plant extremely popular is its unparalleled versatility – able to grow outdoors, indoors, and with or without shade, ferns can easily thrive in your clay-rich garden soil.

Want to adorn your garden with beautiful blue, star-shaped flowers in mid-spring and fall? Start planting bluegrass – a top performer in the garden that easily adapts to various growing conditions. Its supple foliage changes to a magnificent bright gold colour during the Autumn.

This flower thrives best with adequately drained soil. But no worries, it doesn’t mind growing in clay-rich ground. If your spot is sunny enough, there’s an added incentive for growing purple coneflowers as their beautiful blooms and colours (yes they are hybrids) are sure to turn your garden to a haven for butterflies and birds.

Gardeners – old-fashioned folks especially – love the bee balm for more reasons than one. Able to grow in heavy soil, rabbits and deer steer clear of it while hummingbirds flock to its red, lavender, and pink flowers.

The Japanese iris is like the peacock of the gardening world – it’s one of the showiest garden flowers around and people easily recognize it when they see one. As long as you keep your clay soil moist, this flower can adapt and thrive.