Best Compost for Clay Soil in New and Existing Gardens

by Alex Kountry
Updated on

For gardeners, clay soil can be difficult due to the small size of the soil particles that make up clay soils. They are dense and heavy. Because of this, clay soil retains water better than other kinds of soil. Unfortunately, this results in poor drainage and a propensity for waterlogging.

This type of soil is denser than others, so it retains nutrients better. However, clay soils might restrict the spread of healthy root growth in the summer since they become so dry. So how dense is clay the reason most gardeners cultivate and amend clay soil by applying compost?

However, not all of it is horrible because, with the best compost for clay soil and soil amendments, you can easily make it work for you. The best composts for clay soils will have mature compost, organic material, and a lot of bulk. This article will guide you on the best compost for clay soil and offer some times to improve your clay soil and get started on your garden bed.

Should I Add Compost to Clay Soil?

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You can add compost to clay soil for improvement, but you must know how much compost you should add. Clay soil won't be harmed by more than two inches of compost added to it. Over time, the compost penetrates the clay soil up to eight inches, enhancing drainage and lessening soil erosion.

Additionally, compost can be utilized as a soil conditioner to enhance clay soil structure and drainage. This is especially useful in garden beds with poor drainages, such as sandy or clay soils. Additionally, it can help increase the soil's capacity to retain water, reducing soil erosion likelihood.

1. Bonsai Soil Mix by Tinyroots - All Purpose Organic Mixed Bonsai Tree Blend

Bonsai Outlet Bonsai Soil Mix - Tinyroots All Purpose Organic Mixed Bonsai Tree Blend + Used for All...
  • ✔️ Created By Bonsai Experts: All-Purpose bonsai soil blend providing optimum growth for your bonsai trees.
  • ✔️ Remember: Bonsai Soil is NOT Plant Soil. Mixed and bagged at a real bonsai nursery and used by the Kaikou...
  • ✔️ Soil Consistency: Provides proper draining of water and the retaining of moisture.
  • ✔️ Bonsai Soil Mix: Ready to use & formulated with 100% double-sifted compost mulch, calcined clay, vermiculite...
  • ✔️ Tinyroots All-Purpose: Has been formulated for beginners or for those looking to repot a starter bonsai.

Last update on 2024-05-23 / Affiliate links / Images from Amazon Product Advertising API

If you are looking for the best compost for clay soil for Bonsai trees, then this is the best option for you. It is specially developed as the perfect all-purpose potting material for every bonsai tree.

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The proper blend should be used while purchasing bonsai soil. Because of this, we only sell soils that Tinyroots has specifically combined. The second most important factor in caring for your bonsai is the soil you use, which impacts rooting, feeding, watering, and transpiration because it is where half of your tree lives.


  • It is ready to use and formulated with 100% composted mulch, vermiculite, frit, and calcined clay
  • It provides the best draining of water and also helps retain moisture
  • It provides optimum plant growth for your trees
  • It is suitable for beginners who are looking to repot


  • It is quite expensive
  • Poor drainage

2. Blue Ribbon Organics Organic Compost

Ribbon Organics OMRI Certified Organic Compost Size: 7.9 Gallons, 32-35 Pound Bag
  • Improves soil structure & aeration
  • Promotes water retention
  • OMRI Certified for Organic Use
  • Safe for use at any concentration
  • Pairs wonderfully with worm castings & other soil builders

Last update on 2024-05-25 / Affiliate links / Images from Amazon Product Advertising API

This Blue Ribbon Organics compost is another excellent option to introduce compost to clay soil. It is an odorless, organic, premium-grade compost with small particles that promotes aeration and water retention. The store-bought compost also works well for promoting grass growth.

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We recommend using this compost if you want a natural organic product to add enough compost nutrients to your clay soil and increase its stability. In addition, this compost's diverse blend of nutrients might be considered the key to growing plants and high-yielding crops for your small garden.

This is crafted from organic materials that promote plant growth, including composted brush, herbs, garden shredded leaves, used firewood, horse bedding, grass clippings, and wood chips. This custom soil mix can also be made by mixing equal parts of manure, peat moss, and horticultural coarse-grade vermiculite.


  • It boosts aeration and the surface composition
  • Combines worm castings and other soil producers
  • Meets the OMRI standards to ensure organic growth
  • Made in a DNR-licensed facility


  • It comes with an expensive price tag

3. Black Kow Organic Brands Mushroom Growing Mix Compost

Black Kow Organic Brands Mushroom Growing Mix Compost Plant Fertilizer Soil Supplements for...
  • Black Gold 40 Pound Mushroom Media Compost
  • Three convenient sizes - 8 pounds, 15 pounds and 40 pounds
  • Note: eight pound and fifteen pound sizes do not come in factory bag. They are re-bagged into the appropriate size.

Last update on 2024-06-10 / Affiliate links / Images from Amazon Product Advertising API

This is the best compost I have found to work magic over time when working on a new garden or plant with clay soil. Not only is it good for clay soil, but it also works well for top dressing or planting, as it encourages the rapid growth of your plants. In addition, your existing soil will love this compost since it's easy to use, and you will not have to worry about the ratios and know too much chemistry.

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Black Kow Organic compost is made of composted mushroom soil, and although most people are skeptical of mushroom compost, there is a way to navigate. So, if you use mushroom compost for your clay soil, you should spread it early before the growing season to allow soluble salts to leach away and reduce impact.

We also recommend this compost since clay soils benefit from the additional gypsum making the clay particles clump together and avoiding nutrient deficiencies.


  • Organic and natural ingredients
  • Easy to use
  • One of the best options for blooming plants


  • It is quite expensive

4. Leaves and Soul Store Bonsai Soil Premium All-Purpose Blend

If you are shopping for a premium, fast-draining potting soil mix that is pre-mixed and ready to use, then this Bonsai Soil Premium All-Purpose blend will work the best for you. Your clay soil particles will love this compost, especially since it has been sifted before it was bagged.

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We noticed that this Bonsai plant mix was specifically made to give plant roots the perfect water retention, nutrient uptake, aeration, and ph balance. This will give your clay soils the perfect balance of moisture and air while it retains nutrients.

Bonsai Soil Premium All-Purpose blend will not only work for clay soil for only Bonsai plants, but it can also be used to plant types, including succulents, herbs, and many more. Also, it made it to our top list because of its 100% money-back satisfaction guarantee, so in case you do not love this soil mix.


  • Pre-mixed and ready-to-use
  • Optimum for the best results
  • A suitable mix of nature
  • Help with root aeration
  • 100% money-back satisfaction guarantee


  • It is not the best for starter seeds

5. Urban Garden Outfitters Premium Organic Compost

Urban Garden Outfitters Premium Organic Compost - Natural Soil Builder Garden Food - Resealable Bag...
  • Improves soil structure.
  • Balances soil pH.
  • Adds important nutrients to your soil.
  • High quality, premium compost. NO ROCKS.
  • Enhanced with compost tea.

Last update on 2024-05-23 / Affiliate links / Images from Amazon Product Advertising API

Another compost I have found to be the best to treat nutrient deficiencies, protect my plants against diseases, and improve your clay soil structure is this Urban Garden organic compost. Not only that but adding organic matter to your bare soil will also help to balance your soil pH level.

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I was impressed with how this organic compost is strengthened with volcanic rock dust and infused with a unique compost tea mixture. Also, since clay soils work best with mature compost, you can turn it about 18-23 times to guarantee it is mature. Apart from soil improvement, this compost will add beneficial microbes and nutrients to your clay soil to boost plant growth.


  • Improve clay soil structure
  • Balance your soil pH
  • It is enhanced with compost tea
  • It is a premium package and doesn't have rocks


  • It might need some work to get manure compost

How Much Compost Should You Add to Clay Soil?

Compost applied as a layer over the clay soil’s top layer aids in soil amendment. In general, clay soil should add 2 to 4 inches of compost for every 6 inches of topsoil. The amount of compost you use, between one-third and two-thirds, depends on the soil quality. Use your best judgment, but also keep the amount of compost you have at hand in mind.

When you add a layer of compost to clay soil, it will gradually work into your ground. However, adding compost or tiling the clay soil after aeration helps to speed up the entire process. Notably, depending on how much compost you add to your soil, it might take a while to see noticeable improvements.

Adding Compost To Garden Soil

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Nevertheless, be careful and avoid adding compost to very wet clay soil since clay soil is prone to becoming wet and compacting at the depth where roots grow and also becoming waterlogged.

If your garden bed has heavy clay soil, you might need to break up the soil at the surface before adding compost. Also, for dense clay, soil amendment is a wise choice. Clay soil may retain too much salt, hindering your plant’s ability to absorb nutrients or becoming too dry to work with.

Is Adding Too Much Compost Harmful to Your Clay Soil?

Although compost can be added in significant amounts to clay soil, compost can occasionally hurt plant growth. This especially happens when you are using immature compost.

The bacteria responsible for this type of compost’s ongoing decomposition require nitrogen to survive. As a result, applying uncured compost might result in a “nitrogen lockout,” a condition where plants cannot receive the nutrients necessary for growth.

adding compost

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Additionally, overusing compost made from manure might be harmful. Ammonium and salts are abundant in manure. Other nutrients may not be absorbed as a result of this. However, this shouldn’t discourage you, as compost will typically improve the health of clay soils when used in those ways.

Factors to Consider Before Buying the Best Compost for Clay Soil

1. Size

The compost’s size is another important consideration when shopping for the best compost for clay soil. Although a bag might be less expensive, you might realize that it only contains a small amount of compost.

Therefore, it would be better if you compared to ensure the best value for your money. Start by evaluating how much compost you will need to enhance clay soil in your vegetable garden.

2. Type of Sealer

This is crucial because compost left in an open bag is susceptible to quickly drying out when exposed to air, which reduces its usefulness. Since some compost bags feature airtight sealing, check the packaging before using it. 

Consider putting your excess compost in an airtight drum or a compost bin if you don’t place your compost in a container with an airtight closure. In addition, the garden soil surface can be covered with a layer of wood chips or stone mulch to help increase moisture. 

3. Loose Components or Pellets

When compost is made of compacted soil pellets rather than loose components, it can sometimes be poured out of the bag with less mess. The pellets, however, typically need more water to soak them before they dissolve and release their valuable nutrients into the clay soil. 

loosened clay soil

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4. Odor-Free

Some composts include potent, strongly smelling chemicals, especially when put on clay soil. This generally applies to products that contain worm castings or manure.

Although after some time, you’ll notice that the odor gradually fades with time. However, choose a compost mix that says it is odor-free if odors are a problem.

5. Materials

The best compost for clay soil is made with organic materials such as peat moss, pine tree bark, manure, humus, and sawdust. Other forms of compost include coffee grounds, grass clippings, and shredded newspaper.

Also, when choosing the best compost, ensure the compost materials you add to your heavy clay soil are free of heavy metals, toxins, or harmful agents. This is important because clay soil structure is known to absorb materials.

In addition, choosing organic compost with a high humus content will help to improve clay soil workability. Lastly, you can apply manure compost in any season since it has had time to cure. As a result, it will remain a stable leaf humus-rich substance. This will helps to improve water drainage and aeration in clay soil.

Conclusion on the Best Compost for Clay Soil

Organic material

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Choosing the best compost is one of the best ways to improve clay soil to help your garden achieve its full potential. Organic compost is nutrient-rich and aids in breaking heavy clay soil prone to compaction or inadequate air circulation. The best times to add compost are in the fall or spring, and you should give it time to increase the soil quality by a few months.

Compost is important since adding organic matter can be used as a soil amendment and cannot substitute compost. We have included all the information you need to improve soil structure and health in no time.

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About the author

Alex Kountry

Alex Kountry is the founder of HayFarmGuy and has been a backyard farmer for over 10 years. Since then he has decided to write helpful articles that will help you become a better backyard farmer and know what to do. He also loves to play tennis and read books


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