Worm Farm Castings Harvest Calculator
Enter your bin size, worm species, and feeding habits to estimate how much castings you'll get each month, when your first harvest is ready, and how often to check moisture. Nothing uploaded.
Bin & worms
Feeding
Feeding frequency
Food type
Understanding worm farm yields and composting cycles
How worm composting capacity and yield are calculated
Worm farm yield depends on bin dimensions, worm species, feeding frequency, and food type. Different species have different production rates: Red Wrigglers produce roughly 0.5 lbs of castings monthly per pound of worms, European Nightcrawlers produce 0.35 lbs/lb/month, and African Nightcrawlers produce 0.6 lbs/lb/month. Feeding more frequently increases castings production but also heat generation, which can stress the colony if the bin lacks adequate surface area. Food type matters too: cardboard-heavy feeds slow production but extend harvest time, allowing more stable colonies; manure-heavy feeds accelerate production but require more frequent moisture monitoring. This calculator multiplies your worm biomass (number of worms divided by species-specific weight per worm) by these factors to estimate monthly castings yield.
Stocking density and harvest timing
Optimal stocking density is roughly 1 lb of Red Wrigglers per square foot of bin surface (0.75-1.25 lbs/sq ft for other species). Overstocking leads to poor aeration and decomposition; understocking underutilizes your bin. First harvest typically occurs 8-14 weeks after bin setup, depending on species and feeding patterns. Staggered feeding (not daily) allows worms to fully process each batch before the next addition, improving castings quality. Moisture is critical: your bin should feel like a wrung-out sponge. Cardboard-heavy systems dry faster and need checking every 10 days, while manure-heavy systems stay wetter and need checks every 5 days.
FAQ
Why does my worm bin smell bad?
Bad smells (ammonia, rot) indicate anaerobic (oxygen-poor) conditions, usually from overfeeding, too much moisture, or poor aeration. Scale back feeding to once weekly, check that drainage holes are clear, and ensure the bin has ventilation. Add dry bedding (cardboard shreds or peat) to absorb excess moisture. A healthy worm bin should smell earthy, not foul.
Can I use outdoor worms or earthworms for composting?
Outdoor worms like Lumbricus terrestris (nightcrawlers) do not thrive in bins and typically escape or die. Composting requires species adapted to decaying organic matter in confined spaces: Red Wrigglers (Eisenia fetida), European Nightcrawlers, or African Nightcrawlers. Buy from a reputable vermicomposting supplier.
How do I harvest castings without harming the worms?
Gentle methods include the "light and separation" method (pile castings in a corner under a light; worms burrow away from it) or sieving (worms escape through the sieve's underside). Avoid fully stripping the bin at once - leave some bedding and worms, then top up with fresh food. Harvest roughly half the castings every 2-3 months, leaving the rest for worm habitat.