Growing Vegetables in clay soil made easy

In my current garden the soil consists of mostly clay. In fact going in with spade is almost impossible and because of neglect the years beforehand, comes more or less in brick form.

I still want to grow my own vegetables and fruits in this garden, so how do I make the soil more fertile? Is there any way to use such bad soil to grow anything? How does clay soil affect root vegetables?

Growing Vegetables in clay soil can be quite a challenge and requires a lot of work. Clay soil is the bane of every gardener but that doesn’t mean it’s completely useless. Adding organic matter into the soil to improve drainage and reduce compaction will help to make clay soil usable. Checking pH, nutrients and using growing holes (small holes filled with growing soil to help small plants to establish themselves) help to make use of clay soil.

How to identify clay soil

The first thing you need to do is figure out if you have clay soil in your garden and how “heavy” the soil is. The higher the concentration of clay particles in the soil the harder it will be to grow vegetables and other plants.

Clay can be easily be identified by the structure of the soil. Clay is very dense with a slight stickiness to it. It feels smooth and can be rolled up to a ball without any cracks when moist.

Very heavy clay will form a shiny top layer after being rolled, indicating a very high clay content. This soil will require a lot of work to be fruitful.

What is important to know about clay soil

  • Good water hold capacity: Clay soil consists of very small particles, which can hold a lot of water giving it a good water holding capacity. This helps to keep water longer during dry and hot months, but clay soil depends on having some amount of water, without it clay will dry out and form a cracked unusable surface.
  • Drains Slowly: Because of the small particles water takes a lot of time to go through clay soil. This causes puddles to form and can drown your plants if you don’t take care of it in time. Additionally working wet clay will compact the soil even more, only making the problems worse.
  • Warms up slowly: Sand soil in comparison is very fast to warm up with the rising sun but will cool down almost immediately after sunset. Clay soil and the water within the soil take much longer to collect enough heat, but once it’s warm it will provide your plants with some warmth even after sunset.
  • Hard to work: The high density and water in the soil make clay soil the bane of every gardener. It’s is very hard to work with this kind of soil, shoveling is nearly impossible, working in too wet conditions ruins the soil and there are a lot of steps you have to do prior to planting. Nonetheless putting in the work to make clay soil usable will yield great results afterwards.
  • Bad airflow: The high density of clay soil causes air to have a hard time going through the different layers of soil. This will further compact the soil over time if left unchecked, worst case the soil will no longer be useful for growing, but this can be prevented by simply adding some organic matter into the soil mixture.
  • Lack of organic matter: Clay soil is notorious for the lack of organic matter in its natural state. Unlike Humus, clay soil forms from minerals and other non-organic materials hence its very dense nature. Adding organic material like compost will help to loosen up the soil and improve drainage, airflow and attract useful critters like worms. I’ll go more in depth on this topic later.
  • Nutrient dense: Clay soil is also known for its high nutrient density, and can be very good to grow a lot of different vegetables and fruit once the soil is prepared for growing.
  • Compaction: Clay soil is prone to compact easily when worked too much or in wet conditions. The hardest part about working with clay soil is keeping it loose and light.
  • High pH: In general Clay soil also has a higher pH level and is, therefore, more alkaline. Soil pH is highly dependent on area and material in the soil and other external factors, so clay soil doesn’t always have to be alkaline but tends to be more often than not.

What to grow in Clay soil

Most plants will not tolerate very heavy clay soil, that is if you do not put in any work to improve the soil. In clay-ish soil, with medium to low clay concentration plants with shallow root will grow just fine.

  • Shallow root plants, like Lettuce, Leafy greens and Chard are capable of growing in unimproved clay soil. The soils ability to retain moisture and keep the plants watered, additionally, to the normally higher nutrient concentration enable these plants to grow quite well even in more dense clay soil. However, these plants will not survive in very compacted clay soil, it’s important to help your plants out a little bit and not work in too wet conditions or with heavy machinery.
  • Broccoli, cabbage and brussels sprouts are also some good vegetables to grow in clay soil. Heirloom verities generally tend to do better in clay soil, some options for cabbage are Brunswick or Danish Ballhead. Brussels sprouts specifically will require some careful pH work on your soil, as they need as close to 6.5 as you can get. Most clay soil will not fulfill this requirement, but this can easily be improved by adding fertilizer.
  • Pumpkins and summer squash, these plants generally prefer well-drained loamy soil, but that doesn’t mean they can’t also thrive in heavy clay soil. It’s very important to keep them from being constantly wet, this can easily be done by preparing a small planting hole in the clay soil, so the water can drain away from the plants.
  • Flowers like Daylily, Aster or Roses also grow in clay soil. Similarly, a host of different grass types can be grown easily some examples are Switch- and Fountaingrass.

Root vegetables in clay soil

Growing root vegetables like potatoes or carrots in clay soil can be quite challenging, this doesn’t mean it’s impossible, and besides a good harvest growing root vegetables will help to improve clay soil.

Naturally throwing in a couple potatoes in very compacted and unimproved clay soil will yield nothing but if you prepare your growing area properly before planting, then the root vegetables will help to loosen up the soil. Thus improving drainage, airflow and overall condition of your growing area.

That being said given enough effort even growing root vegetables in clay soil is doable. So are there any plants you can’t grow in clay soil at all?

What doesn’t grow in clay soil

Well, there is no definitive answer to this question. Plants depend on a host of different attributes, some of which are related to soil and some simply aren’t like sunlight or climate.

It mostly depends on the amount of work you want to put in the soil beforehand, to adjust pH, nutrients, drainage, and other soil-related attributes.

If your garden is like mine – a giant clay-block- you’ll have to put in a lot of work to improve soil, before pretty much anything can grow there. But that doesn’t mean you can’t grow anything in clay soil. On the other hand, if you expect to throw a couple seeds on the ground and watch it grow, clay soil will definitely ruin this dream.

As mentioned earlier, clay soil also tends to be alkaline, so growing plants which require an acidic environment, like blueberries, will not thrive in this soil without some serious modifications.

Nonetheless, I wouldn’t say there is any plant you simply can’t grow in clay soil, you just have to improve the soil beforehand, so how do we do that?

How to improve Clay soil

Adding organic material: The best way to improve clay soil is to add organic material like Compost, Manure, Peat moss, and straw. The mixture of Organic matter and Clay will be much easier to handle, clumping will be less common and drainage will improve drastically. The organic material will also slowly release nutrients, like nitrogen, into the soil further increasing its fertility. Organic matter will also help to cultivate a good soil microorganisms, attract critters like Earthworms and promote ventilation.

Digging up a whole growing bed and adding organic matter is a huge project and will take a lot of manual labor upfront. The good news, the more effort you put in, the easier it will get.

I prefer to prepare a whole growing bed at a time, as it will ensure the best conditions for the root of the plant in the whole bed. Alternatively, you can also only add composts in the small hole you transplant your crops, but sooner or later the roots will reach unprepared soil and impair plant growth.

So how much organic material do you need to add? I add about 3-5 inches of compost into the top 6-8 inches of the soil, and work the compost gently into the soil, to avoid unnecessary compaction -not that there is any way to do it in a rough manner, simply because of how hard it is to work with clay.

Your bed is now ready to be planted, but it’s beneficial to add some more compost once or twice a year to keep your soil in optimum conditions. The soil and organic matter will break down and settle over time, at this point, it’s about time to add some more, so there is always enough organic matter in the soil.

Adding Grit, Sand or Gravel: Diluting Clay soil by adding Sand or Gravel, on the other hand, doesn’t work in most cases. This is due to the high density of clay soil, compared to sand or grit. In most cases, it is easier to just use raised beds instead of applying huge amounts of sand (around 250kg(460lbs)/m²). Or improving soil composition slowly over time with organic material, which long term will be much more benefitial and cheaper.

Mulching: Clay is notorious for its slow water absorption rate, one way to prevent water from running off is by adding a layer of Mulch. This will not only help to keep water longer in place, but also reduce compaction, and as a bonus will also help to prevent your boots from an extra layer of clay each time it’s a bit wet outside.

It’s quite easy to get your hands on some cheap or in most cases free wood chips or other cover Mulch options. Here is a website, which offers free wood chips, which worked really well for a lot of gardeners already.

Adding Gypsum: Gypsum (calcium sulfate) can also help to loosen up clay soil. It’s important to know that Gypsum is not a substitute for organic material, but can be used in addition to it.

Before adding Gypsum on a large scale take the time to test if your kind of clay is working with it. Simply choose a small testing area, add it and see if any improvements are visible.

pH control: Taking the time to test the pH level of your soil can help you to adjust it according to the plants you want to grow. This is definitely not a must but sometimes can save a lot of worries and wasted time in plants not suited for your soil.

Alternative gardening methods

Sometimes a garden will require way too much work to be able to grow anything in there, so here are a couple of alternative gardening methods, which don’t require you to use the original clay soil. This is a bit of a workaround, as these methods just build a suitable planting environment on top of the unusable clay soil.

  • Raised Beds: By far my favorite and easiest way to grow vegetables in a completely unusable garden is through raised beds. Simply imagine growing in a giant pot, a raised bed is a frame mostly out of wood or stone filled with the optimal soil for the respective plants you want to grow in it. Choosing soil suited best for the plants you want to grow in your beds is one of the big advantages of this method. Raised Beds are, however, pretty expensive to install and require some maintenance.
  • Hugelkultur: Hugelkultur takes the idea of raised Beds and takes it a step further, by filling them with rotten wood and other organic materials. With time the internal wood core will break down leaving air pockets and giving of nutrients to the soil. Here is a link to a detailed description of Hugelkultur, how it works, and how to set it up.
  • Straw Bale farming: Another faster and easier method to grow without using the original clay soil in your garden is with Straw Bales. Using Straw and a core of planting soil plus fertilizer will give your plants a good place to grow without much soil at all. This method, unlike the others mentioned prior, will require you to buy Straw Bales every year but still will be a lot cheaper compared to raised beds in set up costs.

Related Questions

What fertilizer is best for clay soil? The best fertilizer for clay soil simply is organic compost or manure. Clay soil tends to lack organic materials, which help with drainage and loosen up the soil, I mostly use my own compost to improve the soil of my garden.

How to improve drainage of Clay soil? Introducing organic matter into the clay soil will help to increase drainage. Simply add 1-2 inches of compost and till it into the soil. Adding more organic material will help with very heavy clay soil.

What helps breaking up clay soil? Growing root vegetables, adding additional organic matter and avoiding to work wet clay to prevent compaction are all ways to help improving the state of your soil. Introduce and attracting critters like worms will also do a great job at loosening up the soil without much work.