Is It worth Sieving Your Homemade Compost - Update (Part II)

 It has taken a good deal longer than I planned but here, finally, is the promised review of the Mattis Soil/Compost Sieve. See here and here for earlier posts on the pros and cons of sieving homemade compost. Just a reminder of what this bit of kit looks like when in pristine condition.

Photo 1: Mattis Rotary Soil/Compost Sieve 

It is a bit awkward and unwieldy to manoeuvre so you might want to assemble the rotary sieve where you intend to use it.

I was keen to see how it handled my homemade compost but first had to relocate the assembled sieve to the outside patio area ...

Photo 2: Raw Homemade Compost (9th April 2024)

I added a trugful of raw compost (Photo 2) to the sieve ...

Photo 3: First Load of Raw Compost (9th April 2024)

... and turned the handle. The raw compost was smeared over the internals of the sieve (Photo 4) and very little, if any, sieved compost fell into the expectant yellow trug below.

Photo 4: Wet Compost Clogging Up the Sieve (9th April 2024)

A failure although the reason seemed fairly obvious. The raw compost was too wet and sticky (as any good compost should be!) and therefore prone to clumping. It also highlighted a potential flaw in the mechanism; the gap between the blades on the rotary arm and the mesh (Photo 3) was quite large which restricted the ability of the blades to force the compost through the mesh. I should point out that this rotary sieve was designed primarily for removing stones, etc from garden soil and I would expect it to perform that task efficiently. Wet homemade compost, however, is a different kettle of fish.

I covered the rotary sieve with a tarpaulin and let the compost dry out for a couple of weeks so I could scrape out the residual compost before re-siting the Mattis to its final position in June 2024.

Photo 5: Mattis Soil/Compost Sieve in its Final Position (June 2024)

I made a short video at the time showing the rotary sieve in action (Video 1). I added small amounts of drier (but still damp) homemade compost to the hopper while alternating the direction of the handle (clockwise then anti-clockwise).

Video 1: Mattis Soil/Compost Rotary Sieve in Action (June 2024)

I was happy with the quality of the sieved compost/soil conditioner though not so happy with the quantities achieved for the effort put in ...

Photo 6: Sieved Compost from the Mattis (June 2024) 

... due to the large amount of sievable material remaining in the hopper due to the clumping of the raw compost (Photo 7) ...

Photo 7: Clumped Raw Compost (Non-Sievable)

In the video below (Video 2) where the hopper is emptied, you can see this material still contains a high proportion of good compost along with the woody residue.

Video 2: Emptying the Mattis Hopper of Unsieved RawCompost (June 2024)

Unfortunately, further assessment of the Mattis Rotary Sieve had to wait until 2025 as a number of other projects took precedence.

We have had a prolonged dry spell in 2025 that provided the opportunity to dry out some of my homemade compost. I emptied one of my maturation bins (where the product from the hot composters is allowed to mature for 6-12 months) onto one of my vegetable plots (Photo 8) and left it for 3-4 days to dry out. The worms in the compost were enjoyed by the local bird population, especially the blackbird family who were nesting nearby.

Photo 8: Homemade compost Drying Out (June 2025)

The dry compost was easily processed through the Mattis Rotary Sieve (Video 3) ...

Video 3: The Final Experiment: Sieving Raw Compost with the Mattis Rotary Sieve

... leaving the twigs and any uncomposted material behind in the hopper ...

Video 4: Residual Uncomposted Material Left in the Hopper

... which can be recovered by unhooking the back flap on the hopper and turning the handle to push the material out (Video 5) ...

Video 5: Emptying the Hopper of Residual Unsieved Material

This twiggy wood residue (Photo 9) was free of soil conditioner and was bagged up so it could be added to future hot composting runs as a bulking agent instead of buying bark. Apart from woody sticks and twigs, this product also contained a few bits of wire, plastic labels, and the occasional plastic flower (from the church flowers?). Also present were supposedly compostable bags that appeared to have gone through the composting process completely untouched. The main culprit in this department was the fully biodegradable magazine wrappers used, for example, by the National Trust. Other compostable bags had disappeared without a trace! In any case, these extraneous materials are easily removed during the sieving process

Photo 9: Clean Twiggy Residue after Sieving Dry Raw Compost

The sieved soil conditioner still contains some woody material but is perfectly suitable for mulching and enriching your garden soil. Further sieving stages, using finer sieves, could be employed if necessary but this product (Photo 10) was fine for my purposes.

Photo 10: Sieved Soil Conditioner

Within 30 minutes, and without any great exertion, I produced 150 litres of sieved soil enhancer for one of my vegetable plots ...

Photo 11: Sieved Soil Enhancer Put to Immediate Use

It is worth noting that the raw compost contains lots of small tiger worms that successfully negotiate the sieving process and end up in the final sieved soil conditioner. I cannot, however, guarantee they all made it into the finished product; and some were eaten by the blackbirds during the drying out process.

Summary

• The Mattis Soil/Compost Rotary Sieve is a well-constructed piece of kit that takes about half an hour for one person to assemble. I managed to manhandle the finished product to its final resting place (50 metres to the bottom of the garden) but this would be much easier with two people.
• When the hopper is full of compost, there is some lateral movement and flexing when turning the handle but this is relatively minor. This is due, in part, to the supporting legs being quite long and it  can make the machine top-heavy when the hopper is loaded up with material. I recommend placing some weights (e.g. bricks) on the feet to stabilise the machine when in use.  A small amount of black paint has come off the inside of the hopper which will increase the chance of corrosion. I store the rotary sieve outside under a tarpaulin - it is too cumbersome and awkward to keep moving under cover when not in use.
• In operation, the machine works smoothly though the blades can jam up if there is too much material in the hopper or, in the case of compost, if it is too wet with a tendency to clog.
• With the proviso that the compost should be dry and friable, the sieving process is trouble-free. Do not overload the hopper and regularly clear the woody residue via the back hatch. The recovered woody residue can be added back into whichever composting system you use.
• The sieved compost still contains some woody material because this is a fairly coarse sieve. The sieved compost is perfectly fine as a mulch/soil conditioner but you might want to use a second, and finer, sieve if preparing your own sowing/potting composts.
• It is important to stress that this rotary sieve will not work efficiently if the compost is wet and sticky (as all good compost should be!!). But, if you have somewhere that you can leave the compost to dry out, you will be rewarded with a simple and easy method for producing top quality soil conditioner and mulch.