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Compost Biochar mix (80/20)

  • Product Code: COMPBCMIX
  • Availability: In Stock

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What does the 80/20 compost/biochar mix contain?

Made in the UK using PAS100 quality green waste compost (80%) mixed with biochar 0-8mm granules (20%).  The product is 100% Organic, 100% natural and made from sustainable ingredients.

What is the 80/20 compost/biochar mix used for?

This mix is ideal for use as tree planting backfill and for improving heavy clay soils which are often found in 'gardens' of new-build houses. 

How is the 80/20 compost/biochar mix used?

It is ready to use straight away - just dig it in

How does the compost/biochar mix work?

The biochar acts as ‘sponge’ for water and essential nutrients – storing them ready for use. The ‘sponge’ matrix supports increased levels of soil microbes. The microbes (notably mycorrhizal fungi) can access the stored nutrients in the biochar. They form symbiotic relationships with plant roots and supply nutrients to the roots. This mechanism leads to improved plant health and growth. (More detail via our SF60 FAQ blog post)

The compost will decompose slowly releasing nutrients, However, this is not the main benefit of adding the compost. A big barrier to plant growth is adequate porosity to provide oxygen for root respiration. But we also need the right balance between porosity to hold water and porosity that allows rapid drying out of the soil. Particles of compost help with aeration and drainage in heavy clayey soils. Biochar granules will also do this and do it better for a very long time. But compost is cost-effective in the short-term.

80/20 compost/biochar mix Features

  • Improves soil porosity
  • Biochar provides excellent water retention 
  • Contains slow-release macro-nutrients (NKP) supply
  • Contains plant micro-nutrients (Ca, Mg, etc)
  • Improves nutrient supply to plant roots (increased microbe/fungal roots associations that increase nutrient supply to roots (eg mycorrhizal fungi, AMF)
  • Improves soil aggregation leading to improved tilth and aeration (essential oxygen flow to roots and microbes)

Pack sizes

  • 10 Kg sack (approx. 20 litres)
  • 20 Kg sack (approx. 40 litres)
  • Contact us to discuss 1m3 bulk bags

How much 80/20 mix should I apply to the soil?

  Apply  Approx. Volume Ratio
Target 2-5 Kg/m2 5-10%
Minimum 0.5 Kg/m2 1%
Maximum 10 Kg/m2 20%

The % volume ratio varies with depth of soil mix. For more detail on application rate calculations by area, volume and weight and tips on how to make your budget go further, please visit the application ratio blog. We also have a free Excel calculator if you need to work out accurate application ratios.  

It is important to dig (or hoe) the compost/biochar into the root zone - preferably to a depth of 5-10 cm.

The 80/20 compost/biochar mix is used to improve your soil to the best it can be. This improvement in soil fertility water, nutrient management and tilth results in better plants, vegetables and crops - and all in a sustainable manner.

Why use the 80/20 mix over biochar granules or SF60?

We have lots of blogs/articles describing the different SoilFixer products and when to use each. If in doubt, we would much rather you contact us or read further before purchase. 

Improving your soil is a balance of cost, effort and the time span you are willing to wait. 

You can read about soil structure and improvement using different additives at this blog. If we think about this as steps from basic soil to better and onto the best soil than we can simplify the model:

Basic topsoil is likely to be clayey or in rarer cases sandy. A small proportion of gardeners will be blessed with super fertile and easy to till loam. The rest have to work hard to improve our soil over time into good quality loam topsoil.

Adding lots of top quality (PAS 100 certified) compost is a good starting point. It is relatively cheap, easy to spread and rake or dig in. But do not add too much (more than 20%) by volume in any one year. Remember compost is not humus and contrary to many blogs - you can add too much compost.

What happens if you add too much compost to topsoil?

In summer, your soil will dry out rapidly. There is a large risk it will become ultra-dry at which point the compost particles become 'hydrophobic' (ie they repel water). At this point, compost will no longer re-wet (absorb water) or have any glueing aggregation effects. Your plants will wilt and show signs of stress such as stunted growth. It is important to understand that compost is not humus and only a minuscule amount of compost added to soil turns into longterm humus. Hence it can take many years (think 10+) to convert a sandy or clayey soil into loam by adding 5-10% compost each year.

When to use Biochar versus the 80/20 mix?

Adding activated biochar is great - it helps in many ways (read our biochar article). But we cannot avoid the fact that it is an expensive additive. Some of the benefits such as enhanced microbial activity cannot be gained from any other additive, but other things like sand and compost can help at a lower cost.

If you have a big area of soil and cost is a concern, then the 80/20 mix is an option.  

When to use the 80/20 mix versus SF60?

The usual goal is to develop a super fertile loam with Amazonian Dark Earth (ADE,  or Terra Preta) like fertile quality.  This is not achieved by just by adding biochar. Soil fertility, tilth, and soil aggregation are functions of humus which in turn is a result of microbial and root hair activity. Humus is the sticky, nutrient holding, water holding compound that is key to fertility. Our biochar super compost goes through a special composting process with a humification agent to create a high colloidal humus-biochar-compost mix.  Adding SF60 to your soil is a rapid way to create highly fertile topsoil that works much like ADE/TP.

Incredible as humus is - the fact that it is sticky, holds lots of water and is is made from lots of small particles. This means it can block some of the essential air pores in soil. Lack of aeration is already a problem in heavy clay soils, so the 80/20 mix has a slight advantage over SF60 in very heavy clay soils. 


How to use / Specification
Pack size 10, 20 Kg sacks, 0.8m3 bulk bags
Particle size PAS100 compost screened to below 15mm. Biochar 0-8mm granules.

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