[Journal](https://thecomposta.com/journal) How to # Vermicompost in potting mix and seed starting: how much to use The shares that extension services recommend, why they are capped, and a few cautions on salts and acidity. 8 October 2026 · 5 min read _Illustration: A terracotta pot with a young plant on a sunny windowsill in front of an open-shuttered window, a scoop tipping a handful of castings into it and an earthworm waving beside it_ Key points - Extension services suggest 20 to 25 percent vermicompost by volume in a potting mix. The University of Maryland says no more than a quarter. - For seed trays and nursery bags, 10 to 20 percent: one part vermicompost to four to nine parts soil or cocopeat. - Pure castings can be high in soluble salts, so avoid using it alone and keep it away from seedling roots. - Research found the biggest yield gains at 30 to 50 percent of the soil volume, but those mixes need checking for salts and pH. Vermicompost is at its best in a mix with other things. It supplies food and microbes, while cocopeat, soil or sand supply the lightness and drainage. The question is how much. Shares of vermicompost in a mix, by volume | Source | Share | | ---------------------------------------- | ---------------------------------------------------------- | | NC State Extension | 20% (one part to four) | | Oregon State University Extension | Up to 25% | | University of Maryland Extension | No more than a quarter, used sparingly | | The Composta, seedlings and nursery bags | 10 to 20%: one part to four to nine parts soil or cocopeat | | Blouin and others (2019), yield gains | Best at 30 to 50% of soil volume | ## Why the share is capped The University of Maryland warns that pure castings can contain a lot of soluble salts, which can harm seedlings. In one trial with peat, the best growth came at 25 to 50 percent vermicompost, but that vermicompost had a pH of 8.8, and it needed the acidity of the peat to balance it. A mix that suits one vermicompost may not suit another. ## A mix for seed trays 1. Fill a bucket with cocopeat, or cocopeat and fine soil, that has been wetted and squeezed. 2. Mix in vermicompost at 10 to 20 percent of the volume, so that it is spread evenly and not in lumps. 3. Fill the trays, sow, and keep them evenly damp and out of harsh sun. 4. Try one tray first before you fill a whole batch, and compare it with a tray of plain mix. Cornell's extension team found that vermicompost can replace synthetic fertiliser in potting media for vegetable transplants, and that one facility's product protected cucumber seedlings from a Pythium disease. That was a property of that product and not of vermicompost in general. ## Common questions ### What percentage of vermicompost should I put in potting mix? Extension services suggest 20 to 25 percent by volume. For seed trays and nursery bags, 10 to 20 percent is the usual share. ### Can I start seeds in pure vermicompost? It is not advised. Pure castings can be high in soluble salts. Mix it with cocopeat or soil and keep the share modest. ### What is the ratio of cocopeat to vermicompost? For seedlings, one part vermicompost to four to nine parts cocopeat or soil. For larger pots, up to about one part in four. ### Does vermicompost need sieving for seed trays? Fine, even material mixes better and the Fertiliser (Control) Order expects 90 percent of a pack to pass a 4 mm sieve. A finer sieve helps for the smallest seeds. ### Can vermicompost burn seedlings? It is much milder than raw manure, but too much can raise the salt level around young roots. Keep to the shares above. ## Terms in this guide - [Cocopeat](https://thecomposta.com/glossary#cocopeat) - [pH](https://thecomposta.com/glossary#ph) - [Potting mix](https://thecomposta.com/glossary#potting-mix) - [Vermicompost](https://thecomposta.com/glossary#vermicompost) - [Vermicast](https://thecomposta.com/glossary#vermicast) ## Sources - [NC State Extension: vermicomposting in childcare center gardens](https://content.ces.ncsu.edu/childcare-center-production-gardens-8-vermicomposting-in-childcare-center-gardens) - [Oregon State University Extension: using compost](https://extension.oregonstate.edu/catalog/pub/em9308) - [University of Maryland Extension: worm composting](https://extension.umd.edu/resource/indoor-worm-composting-or-vermicomposting) - [Blouin and others (2019): vermicompost effects on plant yield, a meta-analysis](https://doi.org/10.1007/s13593-019-0579-x) - [Cornell Waste Management Institute: vermicompost](https://cals.cornell.edu/ny-center-organics-recycling-education/composting/vermicompost) - [Belda and others (2013): vermicompost in peat-based growing media](https://riunet.upv.es/handle/10251/67384) - [Fertiliser (Control) Order, 1985, Schedule IV (consolidated copy)](https://odishaagrilicense.nic.in/actsRules/Fertiliser%5FControl%5FOrder%5F1985.pdf) ## Keep reading [_Illustration: A terracotta pot with a plant on a potting bench, a can, a scoop and a trowel resting beside it; the scoop tips castings in, the trowel mixes them into the top and the can waters, one at a time, and a wall calendar marks the monthly feed_GuideHow much vermicompost to use: per pot, per square metre and per acreRates from ICAR, TNAU and Kerala Agricultural University, turned into amounts you can measure out.8 October 2026 · 6 min read](https://thecomposta.com/journal/how-much-vermicompost-to-use)[_Illustration: A balcony: a railing against the sky, a row of planters in front of it with a chilli plant, marigolds, a herb and a fern, and a hanging basket above_GuideThe best organic fertiliser for a terrace or balcony garden in IndiaA clear way to feed pots on a roof: the potting mix, how much vermicompost, how often, and what to check before you load a terrace.8 October 2026 · 6 min read](https://thecomposta.com/journal/best-organic-fertiliser-terrace-garden-india)[_Illustration: A cut through soil: cow dung and plant scraps on the surface, an earthworm below them, fine castings falling from its tail into a dark mound that a seedling's roots reach into_ComparedVermicompost vs compost vs cow dung manure: which is better?What each one is, what the published Indian nutrient figures say, and which to use for pots, vegetables and orchards.8 October 2026 · 6 min read](https://thecomposta.com/journal/vermicompost-vs-compost-vs-cow-dung-manure) ## Put it to work Fine, odourless castings, delivered to your door and quoted to order. [Get a quote](https://thecomposta.com/shop) _Illustration: A garden running the width of the page: a freshly packed pouch of castings sitting on a low wall beside a seedling in a pot, a trowel stuck in the soil at the foot of the wall and an earthworm pushing a barrow of castings toward it_ --- Source: https://thecomposta.com/journal/vermicompost-potting-mix-seed-starting The Composta is a brand of Nutrify Private Limited, 1st Floor, Plot No. B & B1, Vanijya Nikunj, Enkay Centre, Udyog Vihar Phase 5, Gurugram, Haryana 122016, India. Contact: contact@thecomposta.com, +91 90535 19734 (also WhatsApp). Quotes: sales@thecomposta.com. Importers and bulk buyers: export@thecomposta.com. More for agents: https://thecomposta.com/llms.txt