Category Archives: Compost

Compost – Looks can be deceptive!

What comes out of your compost heap, compost bin and indeed your HOTBIN can vary an awful lot.

With many HOTBIN® composters coming up to their first autumn, there will be a lot of hot compost being taken out and used in the garden. We thought it would be good idea to let you know what to expect as ‘looks can be deceptive’!

To do this we will look at several batches of compost alongside some HOTBIN composts. Suggest how they might be graded based on common expert visual assessments. Then we will take you on a journey beyond the first look to give you some insight into compost stability and maturity tests (we’ve done them for you!), discuss what happens when you dry and sieve HOTBIN compost (don’t worry no-one is suggesting you need to do this) and finally do a bit of mud pie play to demonstrate a property called ‘colloidal behaviour’’. Finally we will tie these properties back to humeric substances and suggest that what you really need to look for in fabulous compost is high humeric substance content.

This blog is a little more scientific in nature than some of our others – so if you want the headline without the science it is this:

What a compost looks like can be deceptive. HOTBIN compost is often very sticky and very moist/wet and looks lumpy and perhaps even needing further composting. Tests show rather than it being ‘poorly’ composted, quite the reverse – it appears to have a very high humeric substance content and this is good news for your soil and plants – humeric substance is known as ‘black gold’ for a reason!

If your compost looks like (Fig 4&5), or even (Fig 6) below it is OK to dig in to your soil and does not need ‘more composting’. If you only want ‘fine’ particles of compost e.g. looking like (Fig 1) or (Fig 2) – the solution is fairly simple – dry your compost and then sieve it – you will surprised by how much fine material there is in HOTBIN Compost.

Our analysis tour includes;

1. Visual inspection

2. Carbon / nitrogen maturity test

3. Visual after drying and sieving

4. Pliability / colloidal behaviour

5. Humus test

6. Result to quality – is it fabulous?

1. Visual inspection – Below are 6 samples of compost 

(Fig1) Vermicompost

(Fig1) Vermicompost

(Fig2) Garden centre compost laid out dry

(Fig2) Garden centre compost laid out dry
(Fig 3) Typical cold compost

(Fig 3) Typical cold compost

(Fig4) HotBin compost at 3 Months

(Fig4) HotBin compost at 3 Months
(Fig5) HOTBIN compost that is it too wet

(Fig5) HOTBIN compost that is it too wet

(Fig6) HOTBIN compost that has gone anerobic

(Fig6) HOTBIN compost that has gone

anaerobicNow in our earlier blog (good, bad or fabulous compost) we outlined details on how different experts defined good compost. If we asked this group of experts to visually judge the samples above here is what we would expect:

(Fig1) Vermicompost – looks fine and rich, super

(Fig2) Garden centre compost laid out dry – looks very fine and free flowing, uniform and has probably been sieved

(Fig 3) Typical cold compost – looks mature, maybe 2 years old and as expected,

(Fig4) HotBin compost at 3 Months – looks ok, dark brown and a little lumpy

(Fig5) HOTBIN compost that is it too wet – looks water logged, lumpy, immature and soggy

(Fig6) HOTBIN compost that has gone anaerobic – definitely looks anaerobic, it’s black sludge not compost

2. Carbon / nitrogen maturity test

Industrial producers of compost (i.e. compost sold in garden centres) do a check to establish how active the bacteria are. Above a certain level and the compost is too active (i.e. not mature & stable) it needs to be left longer otherwise it can draw nitrogen from the soil as bacteria continue to use the carbon in the remaining compost. The maturity and stability test can be undertaken via the Solvita compost test method. You can do these at home, although it gets expensive!

Garden centre compost (Fig2) would not have gone on sale without passing the C/N maturity and stability tests. How did HOTBIN (Fig4&5) compare? Well they both fall in the stable and mature range. This will surprise a lot of experts as they look lumpy and lumpy normally means large pieces of non-composted material which is highly likely to result in an ‘active’ rather than stable result.

3. Visual after drying and sieving

We recently tested a range of compost sieves (see guide to compost sieves post). We know wet and sticky compost is a complete pain to sieve. When testing the Compostsifter it failed to sieve any of HOTBIN (Fig5). So we dried the compost and tried again. This reminded us of an old saying – ‘looks can be deceptive’. Below is the result of the sieving test.

HOTBIN compost sieved

HOTBIN compost sieved

The result was about 80% of all the compost went through the fine (8mm mesh) sieve. There is about 15% of wood chip pieces (0.8-1.5mm), and 5% oversize non-composted items (notably pampus grass roots – these are possibly going to take the record for the hardest most difficult material to compost – but that’s another blog!). I’d just like to say this sieve result is not a one off – we have seen it many times, same results.

If we visually compare the sieved HOTBIN compost with the sieved garden centre compost they now look very similar. So was the problem just that the HOTBIN sample has been stuck in the base and got wet? Is the difference just about one compost being very wet and another compost being dry? No!

4. Pliability / colloidal behaviour

When we sieve and handle HOTBIN compost we notice something else – it is very sticky. It rolls into balls in the sieves, when you grab a handful you can make a ball. It is ‘pliable’ just like a potter’s clay or children’s plasticine.

HOTBIN Vs Garden Centre on compost pliability

HOTBIN Vs Garden Centre on compost pliability

There are two common substances in soils and composts that create a pliable mix – clay and humeric compounds. Both these are ‘colloidal’ materials and it is this property and the resultant way they hold water that leads to the pliability.

We can take the pliability test a little further. If we make a ball of moist compost from Garden centre compost and HOTBIN compost (Fig5) and leave then to dry in the sun for 4 days. Now what happens when we try and squeeze each ball?

HOTBIN Vs Garden Centre - compost pliability after drying

HOTBIN Vs Garden Centre – compost pliability after drying

The garden centre compost sample behaves more like peat – it sticks when wet, dries fast (i.e. looses water 2-4 times faster) and then the organic material falls apart when the dry ball is pressed. Whilst the HOTBIN sample is still damp and pliable, it forms a very hard solid outer layer material with soft inner. Even after 100% drying and re-wetting the pliability returns.

At this stage we should mention that HOTBIN composting (and certainly the batch of HotBin compost above ) had no soil added – hence the pliability is not believed to be due to soil clay.

5 Humus test

We think (and we mean ‘think’ because we have no laboratory proof) that it is possible that HOTBIN compost has more humeric substances than many other composts.

HOTBIN compost - Pliable humus

HOTBIN compost – Pliable humus

Can we test for humeric substances? The answer is yes but not easily outside a fully operational soil testing lab. There is a relatively simple humus soil test – targeted at measuring the concentration of humeric substances in soils. The HOTBIN samples are off the scale – but a note of caution – the test aims to give a reliable field test for soils with 0.5-6% humeric substances. It cannot be relied on for concentrations well above this.

6 Result to quality – is it fabulous?

We believe there is a real difference between compost and compost that contains very high amounts of humeric substances. Partly decomposed material (compost) will continue to decompose when added to the soil and eventually the carbon cycle completes and it is returned to carbon dioxide and a small amount of recalcitrant humus in the soil. Humeric substances do not decompose in the soil (to any great extent) so adding a concentrated form will improve your soil faster.

HOTBIN compost - drying out

HOTBIN compost – drying out

As a company we are not into making claims about our products we can’t substantiate – to be clear – we believe we can explain the appearance and behaviour of HOTBIN compost. We believe we can trace (but not prove it yet!) this back to higher humeric substance content in HOTBIN compost. One day we will have the evidence – until then we believe our logic and science has merit, you can do your own testing, contribute to the debate or ignore our findings as just marketing waffle!



Filed under Compost, How to get the best out of your HOTBIN

Worms and HOTBIN composting

Worms and HOTBIN compostingA question we often get asked is; do I need to keep my Wormery now I have a HOTBIN?

The simple answer is no and the key benefit is that the HOTBIN can compost both food waste and garden waste. Therefore you can save space, reduce costs and still keep your food waste out of landfill.

So what is worm composting?

Worm composting is using worms to recycle food scraps and other organic material into a valuable soil amendment called vermicompost, or worm compost. Worms eat food scraps, which become compost as they pass through the worm’s body.

So what is HOTBIN composting?

The HotBin is a simple design that helps maximise what nature does by bringing together the right conditions to make hot composting easier. It does this by providing effective aeration between the bottom air inlet plate and the air outlet rotating valve, removing excess water through the valve as steam and allowing you to control the rate of heat loss. You can compost 100% of all domestic food waste in the HOTBIN without inherent problems with odour, vermin and flies. This includes left over meals, plate scrapings, meat, fish, small bones, bread, cakes, pasta and rice. Your food and garden waste will be turned into rich organic matter for the garden every 90 days.

Worms in the HOTBIN?

You do not need to add worms into the HotBin however you can – either directly by adding into the base layer (which is cooler) or inadvertently by adding worm eggs and worms into the bin via small bits of soil and old compost . Most of the worms and worm eggs will be killed by high temperatures (>45C) but a some will find there way down into the base layer and continue to work on the base layer compsot.

However, worms can be beneficial to composting and can be added if you want to. But a word of warning do not add them into the upper active layer (60°C will kill them) only add worms via the hatch panel where the compost will be cooler. Worms will help to decompose waste and leave mucus in the compost which is proving beneficial to soil fertility.

As the HOTBIN is no ordinary composting bin as you can use it to recycle than just vegetable kitchen waste in it. The hot temperatures achieved during hot composting make composting all food waste in the HOTBIN a safe home composting system that recycles a whole lot more than just potato peelings.

So if you were thinking about a Wormery as a form of recycling food waste why not consider a HOTBIN as it composts both your food and garden waste together.

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Filed under Compost, Compost Bins, Products

The Ultimate Guide To Compost Sieving and Sieves

Many people will just use compost ‘as it comes’ from the compost bin by digging it in to the soil around plants or into the vegetable patch.

Sometimes it is preferable to have fine compost for use in potting up seedlings or as I often do, use as a lawn top-dressing (it does wonders to reduce moss!) but large pieces of compost are hard to rake in and can cover the grass and act as ‘mulch’ – not the desired result.

Mature HOTBIN compost at 3 months

Mature HOTBIN compost at 3 months

I have tested a few compost sieves and I thought it was time to summarise how they perform and offer a view on the how worthwhile compost sieving is.

Sieving compost can be tricky and labour intensive – it does not take too many lumps of wet moist compost to clog up the sieves.

HotBin Compost - Good and ready after 3 months

HotBin Compost – Good and ready after 3 months

The Plastic Hand Sieve

A Plastic hand sieve will cost £4-10. These work OK if you just have a bucket of compost to sieve. When you only have small amounts of compost, the price/performance is hard to beat. However, once you start to get into bags or wheel barrow loads;  the hand sieves becomes far to time consuming and difficult. Most of us will just end up with aching arms and a stiff back! The plastic pan sieves struggle with moist compost – it will just roll into balls that won’t sieve. (There are a whole range of metal hand sieves that work the  same as the plastic but cost a lot more).

A 33cm plastic garden sieve

A 33cm plastic garden sieve

The Rotary Sieve

The Rotary sieve cost approximately between £30-40.  Now it is OK with dry compost and handles typical loads/sizes from the HOTBIN. However it tends to clog up when used with moist compost. Some large pieces can jam and you’ll need to stop and clear them before carrying on. (NB this review was based on third-party input not our own test).

The RS150 Rotary Soil Sieve

The RS150 Rotary Soil Sieve

The Watford Sifter

The Watford Sifter costs approx £120-150. It definitely works better with soil than compost. It did struggle with wet compost as it tends to clog and stick in centre of sieve and it did not tip ‘up and down’ far enough to move it from this position. Good for medium or large loads and certainly a good option if you have lots of soil and compost to sieve otherwise you might struggle to justify the cost.

The Watford sieving HOTBIN compost which is 3 months old and typically wet

The Watford sieving HOTBIN compost which is 3 months old and typically wet & sticky

Likes / dislikes:

  • You get two screens – fine and coarse.
  • Easy to push ‘up and down’
  • A bit of a ‘pain’ to get the retained coarse material out of the sieve tray. In the end, I was continually lifting the whole box and tipping it out. It’s a heavy lift when not much is sieved. This issue goes away if most of the soil/compost gets sieved through – but if it is all fine in the first place there is no need to sieve!

The Scheppach Sieve

The Scheppach  costs in the region of £350-400, this has to be a serious piece of kit. It is a trommel design (rotating cylinder) and uses and an electric motor to turn it so it also needs an electrical supply! It will handle significant volumes of soil and compost. We have not used this kit, but we know three large-scale gardeners/composters who do and they all rate it highly. If you are only using it 1-3 times a year, our opinion is it is questionable how much value you will actually get. Probably one for the professional and/or allotment/community schemes where you can share it. PS: It also takes a lot storage space.

The Scheppach RS400 rotart sifter

The Scheppach RS400 rotart sifter

The Compost Sifter

Compost Sifter costs £155 (excl £40 delivery to UK). This is very new and comes from Belgium. It uses a similar rotary tunnel (trommel) design as the Scheppach – but it is turned manually via a handle. By long way, it required the least effort and sieved more faster. The mesh (hole size) is smaller than the others (8mm) and this means it won’t sieve wet compost (based on our test of HOTBIN compost). However, after initial disappoint with wet compost, it absolutely cleaned up when it came to dry compost. Our current favourite – we may even resell it with a special HOTBIN specific tweaks!!

The Compost Sifter - Assembled with just wheels to go

The Compost Sifter – Assembled with just wheels to go

Likes / dislikes:

  • Ease of turning – real winning feature
  • Retains oversize and easy to get it out via panel that detaches
  • It is very heavy – fine once set up on wheels, but you may need 2-people to get it out of box and set up on the frame.
  • It still struggles with wet sticky compost – but so do all the rest!


Sieving compost can be tricky and labour intensive, especially if it is wet and sticky as it tends ball into large lumps and clog sieves.

After numerous tests on HOTBIN compost, we think we are on solid ground to say if you want to sieve the naturally sticky wet HOTBIN compost you will have to dry it first (see how below). All the sieves will perform significantly better with dried compost.

Our next question is: Is it worth sieving compost?

This is not just about the cost of the sieve and the time and effort that goes into sieving. The most beneficial part of compost is the group of humeric substances. These compounds impact soil fertility as they enhance root uptake of minerals and water. It therefore follows the biggest benefit comes from digging humeric substances into the root zone. If digging in, one has to question if the effort to sieve out any big bits.  Large over sized lumps will compost down in soil over 12-24 months. As long as the total volume of large pieces is low, the ongoing composting of these pieces is unlikely to affect nitrogen availability during the final composting period. With HOTBIN compost there is always about 10-15% of small 0.5-1.5cm wood chip (bulking agent) pieces that remain in the compost. Our tests show these pieces are covered in layers of humeric compounds. We believe these pieces of wood chip are slowly composted as they are coated and protected from rapid decay. Whilst in the soil, small pieces of wood chip also aid aeration and soil tiling.

There are applications where sieved compost is useful e.g. when used as a lawn top-dressing (i.e. raking in a thin layer of compost on to the grass), or when creating a potting mix for seedlings. Lawn care is a huge part of British gardening. I personally have seen good results from top-dressing moss ridden lawns (high clay, poor drainage) with sieved compost. For those of you that want to drop dress, the method is outlined below.

In summary, for most compost users and most types of compost application, we do not believe drying compost and then sieving is worthwhile.

Compost and lawn top dressing

  • In late Autumn take out your HOTBIN compost and dry it (we spread it out as a thin layer on patio / large sheet polyethylene)
  • Add dried compost to compost sifter or like to sieve
  • Sieve and bag up
  • Spread on grass and rake out to about 1cm layer.

This will take huge quantities of compost – but the rewards is you won’t be spending much on lawn fertiliser or moss killer!


Filed under Compost, How to get the best out of your HOTBIN, Products