Tips to break up clay soil and improve the structure and drainage

  • If the clay is not causing water logging, but you want to improve the structure and break up hard soil to make digging and planting easier this article may help. 
  • If waterlogging is the problem go to my lawns and garden drainage page.
working with clay soil
working with clay soil

Frequently asked Questions about improving and breaking up clay soil Answered in this article

  • What is clay soil? 
  • What are the problems associated with having clay soil in a garden?   
  • What's good about clay soils? 
  • How can I improve and break up clay soil?   
  • When is the best time of the year to dig clay soil ?  
  • What tools and materials will I need.
  • What's The best way to improve and break up clay soil long term.  
  • How soon can I plant in the improved clay soil.
  • Use the correct sand (builders sand will clog up the soil) and use heavy duty spade and fork.

Firstly a few facts about clay

Clay soil can be a good thing many plants grow well in it.  

Clay soils are hard to dig, but retain moisture better than sandy soil. Drought is much less damaging on clay soils than other soil types. 

Clay is rich in the nutrients plants need to grow, holding calcium, potassium, and magnesium. 

Improving the soil to make it easier to dig is a better and cheapest option than replacing it.

I'll show you how lower down on this page. 

What is clay soil?

Clay soil is composed of mostly clay particles. Ordinary clay soil contains about 30 percent fine clay particles. Soil that consists of over 50% clay particles is referred to as heavy clay.

Clay soils take longer to warm up in spring and clay soils are easily damaged when dug or walked on. 

Carry out this simple test to find out if you have clay soil: if the soil sticks to your wellies, garden spade and fork like glue and forms big hard lumps of soil that are difficult to break up and the garden surface cracks up in dry weather, it's clay. Types of Soil 

What is bad about clay soil in my garden.

Clay soil can be a nuisance, even if it's not waterlogged. Hard clay soil is hard to dig and although many trees and shrubs grow well in clay.  The roots of some annuals, perennials, and vegetables, especially root crops like carrots and turnips can't grow through heavy clay.

Clay soil is slow draining, slow to warm up in spring and compacts easily into large hard lumps of soil making it difficult for plant roots to grow. 

In dry weather the surface cracks up. 

What's good about clay soils?

Clay soils retain moisture better than sandy soil, handy during long dry spells. It's also rich in the nutrients plants need to grow, holding calcium, potassium, and magnesium. See the note here to understand a little more about calcium, potassium, and magnesium in garden soil.

Can I improve and break up clay soil myself?

YES, it is possible, with some hard work, to make clay soil more workable and suitable for planting and growing most plants and at the same time keeping the good things about clay such as the nutrients essential for plant growth. Clay also has moisture retention properties which can be useful during long dry spells.

Improving your clay soil will take a lot of digging, but will improve the structure of your soil making it easier to work.

This is how I improved and broke up my clay soil.

The problem with improving a small area
  • Digging out and improving a small area or a planting hole doesn't work. The plant will be OK for a while, but as it starts sending out roots, the new roots will hit the hard clay, and start circling around the planting hole. Just like in a flowerpot and become pot- bound.
  • The other problem with just improving a small area, the surface water will drain over the unimproved clay area into the area you have improved and subsequently water log the area.
So it's best to improve an entire planting area, decide how much of the garden you want to improve and dig out any plants you want to keep. There are no short cuts.

The process to improve, breakup and make digging clay easier

There are 3 stages to improving clay soil to make digging easier and growing possible.

  1. Spread Grit sand over heavy clay soil. On heavy clay It's worth extra work spreading a one or two inch layer of grit sand across the clay soil before spreading the organic matter and digging the whole lot in at the same time. This will help break up even heavy clay soil. You will need to work at it over the years by repeating the process though. Baked clay is almost impossible to break up, rotivate or dig, it's easier to spread the organic matter and grit and wait until the worms have done some of the work for you.
  2. Spread the organic matter,  Cover the entire area of clay soil you have selected to be improved and broken-up, with about eight inches of organic matter. This could be anything that hasn't been treated with chemicals, including compost from your compost heap, rotted manure, leaf mold, fruit & veg waste from the kitchen. hay and straw bales or lawn cuttings (in fact anything that has ever rooted and lived, but not meat).
  3. Dig it in to the clay. Now the hard bit. This can be carried out over several days. Dig the organic matter into the top 10 inches of the clay soil, working backwards trying not to compact the dug soil. Digging with a sturdy spade is the best way, but using a rotavator works OK too. Be careful if you are using a rotavator, it's likely to bounce off the compacted clay until you get the hang of it. 

The garden bed will end up a couple of inches higher when you have finished digging in the organic matter, however as the clayey soil improves will gradually settle down over a season. 

Once you have started the process to improve and break-up clay soil without using chemicals, you will see the change, your spade and knees will feel it and your plants will thrive in it. Well worth the hard work!  So get your wellies on and get started. 

Now all you have got to do is maintain the improvement!

How to keep improving the usability of clay soil

 Each year as the clay soil improves, digging will become easier and the variety of plants you can plant will become greater. Read my article listing plants that will tolerate clay. Some root crops like Turnips, Radishes, Potatoes and Beets actually help break up heavy clay soils. But, what the clay soils will need to keep the improvement going to stay loose and workable is organic matter. As the clay soil improves, just after harvest time add more organic matter to the top of the garden bed each year. This can be left on the surface for the worms to take down into the clay for you. Or you can dig it in.

Let worms help break up the clay for you.

Think of worms as little gardeners digging and aerating the clay soil for you (and they don't need paying) As they toil away for free, taking the organic matter you have spread across the surface of the ground down into the earth to eat and feed their baby worms. Then, bringing nutrients containing nitrogen, phosphorus, potassium, and calcium back to the surface in the form of castings that provide the necessary nutrients and minerals plants need too thrive. 

All worms ask in return is to be left alone to get on with it. Ohhh and a continual supply of organic matter.


When is the best time of the year to dig clay soil?

The best time of year to start working to improve clay soil is late spring or early summer (providing the soil is relatively dry) right after the winter frosts have finished and helped break up the clay and the clay has warmed up a bit.

If you dig or walk on wet clay it loses its structure and can become puddled and compacted. 

How soon can I plant in the improved soil.
As soon as you have recovered from digging it all in. And remember - try not to compact the freshly dug soil. Use a roll out track if you are wheel-barrowing over it.
Here are 4 links to my articles that may help. 
  1. Wild meadow flowers that will grow and thrive in claysoil wildflowers grow in  
  2. Garden and other plants  plants to grow in clay
  3. Alternative to digging clay soil to make it workable, check out my article here  no dig gardening
  4. Essential Minerals for healthy soil  Magnesium, Potassium and Calcium.

The best tools to use digging clay.

Cheap spades and forks are not much use when digging clay soil, the handles bend and break and the fork prongs bend, I have broken more than i care to remember.

Grit sand for breaking up and improving heavy clay soil.

It's extra work but worth spreading a one or two inch layer of grit sand across the clay soil before spreading the organic matter and digging the whole lot in at the same time. This will help break up even heavy clay soil. You will need to work at it over the years by repeating the process though. Baked clay is almost impossible to break up, rotavate or dig, it's easier to spread the organic matter and grit and wait until the worms have done some of the work for you.
This is the Sharp Sand I use its composed of grains of rock,  with a high percentage of larger grain sizes making it ideal for improving clay soil. 
Bulk bags weigh a minimum of 800kg, cost about £80  inc delivery.
Do not use ordinary builders sand it will clog up the soil.

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