Compost Screening Equipment: Trommel vs. Star vs. Vibrating and Screen Sizes

Compost screening equipment: trommel vs. star vs. vibrating, and what screen size to run

Screen choice comes down to two questions: how wet and sticky is your compost, and what product grade are you selling? For most compost yards a trommel is the safe default, a star screen is the answer to sticky, high-moisture material, and a vibrating screen is for dry, cured compost you want to run fast. Then your screen size — 3/8", 1/2", 5/8" and up — sets the grade and the price. Here's how to line all of that up.

The three screen types, and where each one wins

Trommel screens are a rotating drum wrapped in screen mesh. Material feeds in one end, tumbles as the drum turns, and the fines drop through the openings while the overs carry out the far end. Trommels are forgiving — they handle a wide range of moisture, they're simple to run, and they're the most common screen in compost yards for a reason. Throughput runs from a few dozen cubic yards an hour on small units up to a couple hundred on large ones. Their weakness is blinding: when compost gets wet and sticky it packs into the mesh openings and chokes throughput until you clean the drum.

Star (disc) screens solve exactly that problem. Instead of static mesh, they use rows of spinning rubber stars or discs. The constant motion is self-cleaning, so the screen doesn't blind on wet, sticky material the way a trommel does. Star screens also produce a fluffier finished texture. If you're screening high-moisture compost — or you're screening year-round in a wet climate — a star screen keeps running where a trommel bogs down. The spacing between the discs sets your particle size instead of a mesh opening.

Vibrating screens are a flat, angled deck that shakes material across one or more mesh layers. On dry, cured compost they're fast and clean — often the highest throughput of the three. But they're the most sensitive to moisture: push wet material (above roughly 40–45% moisture) onto a vibrating deck and it clogs. Vibrating screens earn their keep in dry operations or as a second, finishing stage after material has cured down.

Screen size drives grade, price, and contamination

Once you've picked the machine, the screen opening decides what product you're making. Smaller openings make a finer, higher-value product but move less material per hour and leave more overs to recirculate.

3/8" (ultra-fine). Bagged retail, potting mixes, topdressing. Highest price per yard, lowest throughput, and the least tolerance for contamination — every stick and shard shows.
1/2" (premium bulk). Garden amendment, raised beds, quality landscape supply. Strong demand and a good balance of throughput and value. For a lot of yards this is the money grade.
5/8" to 3/4" (standard bulk). General landscape and soil-blend supply. Faster throughput, a bit more visible wood, moderate premium.
1"–2" (coarse). Erosion control, bioswale media, mulch-adjacent products. High throughput, visible wood pieces, lowest price per yard.

Smaller openings don't just make finer product — they concentrate contamination. Plastic, glass, and rock that slip through a coarse screen get caught and highlighted in a fine one, which is why your cleanest feedstock should go to your finest grade.

Two-stage screening and moisture control

Two habits separate a clean compost product from a sloppy one:

Screen in two stages. Run a coarse scalp (2–3") first to pull sticks, rock, and trash, then screen the cleaned material to your finished grade. One-pass screening on dirty feedstock either blinds your screen or lets contamination through.
Manage moisture before you screen. Aim for roughly 35–45% moisture. Too wet and everything blinds; too dry and you make dust and lose fines to the wind. Moisture is the single biggest lever on screening throughput — bigger than the machine itself.

Match the screen type to your moisture, the screen size to your market, and stage the process, and you'll get a consistent, gradeable product you can actually price.

Where RPG fits

We move compost trommels, star screens, and vibrating screens across the US and Canada, so if you're trying to figure out which screen fits your material and your product mix, we can usually put realistic used options in front of you. See what's available on our listings page, or if you've got a screen sitting idle, consignment gets it to an operator who'll run it.

Have questions about compost screening equipment? Contact RPG Equipment — we work with buyers and sellers across the US and Canada.