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How to Amend Clay Soil for Vegetable Gardening

How to Improve Clay Soil for a Vegetable Garden

Clay soil has proven to be a nightmare for most gardeners. Yet, many have been able to conquer the stubbornness of clay soil. So, there’s no reason to give up on your garden because you can actually amend clay soil to make it suitable for your vegetable garden.

How to amend clay soil for vegetable gardening

During the wet season, your clayey garden will probably have puddles. And it will be dry and cracked in the hot summer.

I call it the curse of clay soil.

And honestly, breaking this curse is not an easy task. It takes time, patience and a lot of hard work to reclaim clay soil in order to grow crops on it. It can take years as you try to rototill, add compost and manure to make clay soil farmable. 

(You may also want to read this article on the vegetables that grow well in clay soil).

Related Article: Can Potting Soil Go Bad?

Misleading Information about Clay Soil Amendment Debunked

In England, clay soil is improved by burning a portion of it and scattering it through the farm. Burning clay makes it more like sandy soil as it becomes less compact. This increases the air spaces between the individual particles so that plant roots can breathe.

However, I would not advise you to do it; burning clay soil kills some microorganisms. It would also alter soil pH. And is it really possible to burn all the clayey soil in your garden?

It does not sound plausible, does it?

Another popular suggestion is to mix clay soil with builder’s sand. From our research, though, adding sand to your clay soil does not have a similar effect compared to what clay soil would do when added to your sandy soil.

In fact, a report released by Oregon state university claims that no amount of sandy soil added to a clayey garden could improve it.

But why?

Because clay soil particles are highly structured like crystals and the only thing that sand soil would do is provide a sticking surface. “The result is that the soil you get could actually be more difficult to manage than the original clay,” quotes the report.

Christopher Enroth, a horticulture extension officer at Illinois University, adds that if you want to see sandy soil cancel out clay’s stickiness and water retention effect, you would have to add an equal amount of sandy soil to it. This way, you will have a ratio of 1:1 because failing to do it is like making concrete.

However, adding an equal amount of sand to your clayey garden is preposterous because it means bringing another garden of sandy soil to your clay garden? It would just be too expensive!

Linda Chalker Scott, an extension researcher at the University of Washington, adds her bile to the argument that adding sand to clay would improve it.

She says that it would just be impossible. “A soil needs to have at least 50% pore space to be considered good for farming,” she says.

This would mean that you have a more compact soil similar to concrete used in building every time you add sandy soil to clayey soil. “This results in heavier soil, denser than either clay or sandy soil. You do not want this,” she adds.

There are other suggestions to add gravel at the bottom of the planting hole. However, according to the University of Vermont, this will only create the perched water table. The soil structure is not improved at all.

Far from those myths and misinformation, let us look at pragmatic ways to amend clay soils. The methods you will find below have been tried, tested and proven to work.

10 Pragmatic Ways of Amending Clay Soil for Your Garden

#1. Use Gypsum and Later Treat Your Soil PH

Although you can amend clay soil by adding gypsum to it, this report by the University of Vermont claims that gypsum might end up increasing the pH levels of your soil. Gypsum can also cause leaching of most of the soil nutrients and elevate calcium levels. So, be sure to work on the soil pH afterwards as well the soil fertility.

#2. Add Organic Matter (The Best way to Beak Down Clay Soil Quickly)

Linda Brewer, a teaching assistant at the Department of Soil Science, Oregon University, says that the best way to amend clay soil is to add organic matter six to seven inches deep. Adding compost manure to clay soil reduces its stickiness and improves drainage.

As you add your organic matter, make sure that it is well decomposed to not cause further problems to your growing plants.

Fresh animal manure, for example, has been found to release too much ammonia. It also contains human pathogens such as E. coli which is dangerous if it gets into contact with your almost ready vegetables.

Dig your land deep, like 1 to 2 feet during the dry season. As it is turned, air pockets are created. Add decomposed organic manure to it and mix thoroughly.

#3. Aeration – The Best Way to Improve Clay Soil without Tilling

When air pockets are injected into the clay soil, they help improve drainage, break up compaction, and attract useful soil microorganisms.

You can use tools like a digging fork, plug coring aerator, and broad fork to aerate your garden soil at least twice a year- that is, as the season ends in the Fall and before planting; in the spring.

Aeration during the Fall is crucial because it deals with any acts of compaction that may have occurred during the season. The good thing with aeration is that you don’t even have to till the whole yard repeatedly.

Types of aeration

Below are some ways to utilize aeration in improving clay soils.

Liquid Aeration

There are several liquid aeration formulas sold out there, but they all have one thing in common. They contain Ammonium Laureth Sulphate.

This compound can facilitate water infiltration in clay soils, especially after compaction. It takes time to see the results, but it will do wonders for your soils.

Topdressing and Core Aeration

Topdressing involves laying organic matter on the soils. While this may work in other soils, it doesn’t always work on clay soil. This is because you’re hoping for the organic matter to infiltrate into the soils slowly on its own. And that can’t happen if the soil is compacted.

This is where core aeration comes in handy. It involves removing lumps of soil without tilling, creating air pockets, and facilitating organic matter releasing into the soils. It also makes the soil more favorable for soil microorganisms.

#4. Apply Mulch

Another good option when it comes to amending clay soil is to apply mulch underneath the plant. But you have to be mindful of the type of mulch you use.

Mulching with fresh sawdust, for example, has been found to cause a nitrogen deficiency in plants. The fresh sawdust needs to be broken down by microorganisms, and they use lots of nitrogen to do this.

This depletes the nitrogen reserve for plants. It is therefore advised that you first compost your wood product waste before mulching your garden with it.

#5. Use Cover Crops

Planting of cover crops has been shown to effectively increase organic matter in clay soils. You could plant buckwheat, oats, ryegrass and clovers. Cover crops also work to suppress weeds. It is advised that you do the cover crops a year before you think of growing your vegetables.

#6. Avoid Compaction

Clay soil is compact in nature. It is made of fine granules. Anytime you bring in a heavy machine on your clayey garden or walk around during the wet season, the granules tend to stick together.

While it would be impossible to cut all forms of work on the farm during the wet season, I suggest you avoid introducing heavy machinery to work on the land.

Heavy machinery would only further the caking of the clay together, deteriorating the already poor soil aeration.

Avoid heavy machinery working on your clayey garden. When walking around in your garden while it’s wet, you can utilize planks of wood. This will help distribute your weight and prevent compaction.

#7. Add Perlite and Vermiculite to Your Soil

Perlite and vermiculite are two commercial mediums found to improve clay soil’s aeration and water retention properties.

But because the ratio needed to produce the right mix of perlite or vermiculite to clay soil is high, it would be implausible to try to buy it for your entire garden. So gardeners who use it buy it for their potted plants.

#8. Use Planting Beds Filled with Loam Soil

If you are interested in planting only a few plants in your clayey garden, you can dig it up with a fork, erect a raised bed and fill it with loam topsoil. You can then proceed to plant the crops on these raised beds.

#9. Under-Drain the Soil Using Trenches Around the Garden

Under-draining clay soil to remove excess moisture improves the aeration and makes it warm faster. You can do this by digging out trenches around your garden to allow excess water to drain away. 

#10. Builders’ Sand

You can also use builders’ sand for clay soil amendment. You will need a considerable amount of soil for heavy clay soil. To improve the drainage of clay soil, it’s recommended that you get sand into the top nine inches of your soil. To achieve this, you’ll need to spread several inches of sand over your garden soil, and then dig to mix the sand and garden soil.

Factors to Consider When Choosing an Amendment for Your Clayey Soil

A soil amendment is a material that improves soil aeration, moisture content and drainage. The amendment needs to be mixed thoroughly with the soil and not buried deep as some farmers are wont to do.

While some amendments would improve your clayey garden by increasing the soil aeration and water drainage, you will find that they affect the soil’s property. For example, some will affect its pH or make it saline.

You, therefore, need to make the following considerations before choosing your amendment:

1. How long the amendment will last in the soil as well as what time it takes before its full effect is felt.

2. How the amendment affects the soil pH and salinity levels.

Final Thoughts on How to Amend Clay Soil for Vegetable Gardening

We have tried to debunk some of the falsehoods about clay soil amendments. Adding sandy soil will not improve your clayey soil; it might actually get you a worse soil structure. The best bet for improving clay soil is the use of decomposed organic matter to improve aeration and drainage.

Always remember that improving clay soil will not be easy. It takes time, patience and hard work. But, it’s doable.

How to improve clay soil for a vegetable garden


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