How Micronised Volcanic Rock Dust compares
Full guide and scienceMicronised volcanic rock powder (this product)
- Fine powder with the most surface area per gram, so it weathers first
- Suspends in water: the only format that works in compost tea or a drench
- The right choice for pots, potting mixes and one-season results
- Raises pH usefully at 200–400 g/m²
- Dusty. Apply on still days, or to moist soil
Dr Forest granulated volcanic rock dust
- Coarser grains that release over months to years
- Spreads cleanly across lawns and large beds without dust
- Builds a mineral reserve that stays in the soil for years
- Will not suspend in liquid, so no use in tea
- Most people end up using both: powder for the season in hand, granules for the years after
Customer highlight
I just love these products. It’s just rock dust right:) no lol not really.. and I can’t explain it tbh but it looks and feels quality! And my plants absolutely love it!! The silica and the minerals seem very balanced and easily broken down in the soil. But the vigorous look and thicker stems are noticeable visually. They have vast knowledge in their field and test for heavy metals and mineral content. All the things you want to hear if you have questions they have answers :)
Editorial highlight from marketplace and store reviews — separate from the full review list below.
Micronised volcanic rock dust: fine volcanic rock powder for beds, pots and compost tea
Micronised volcanic rock dust is finely ground volcanic silicate rock that weathers in moist soil to release silicon and trace minerals, and raises the pH of acid soil as it does so. Grinding the rock to a fine powder gives soil water far more surface to work on than a granule, so the same weight of rock reacts sooner. This is the fast format of the pair Dr Forest sells: a zeolite-bearing volcanic silicate, 48% silica, pH 11, milled fine enough to stay suspended in an aerated compost tea.
It is a soil conditioner, not a fertiliser. There is no useful nitrogen in it and it will not replace your feed. What it does is put back the slow-release minerals that decades of cropping and peat-free compost leave short, and it does it in a form that gets going within a single season. Use it in potting mixes, rake it into beds at planting, dust it through the compost heap, or add it to a tea brew. For lawns and large areas where dust is a nuisance, the granulated rock dust is the easier product to spread.
What micronised rock dust is used for in the garden
- Compost tea mineral enrichment — the powder stays in suspension in an aerated brew, so a trace-mineral drench goes on with the microbes
- Potting mixes — 5 g per litre at potting; fine particles weather within the season, which granules in a pot do not
- Remineralising beds — raked into the top 5 cm at 100 g/m², or worked deeper at 200–300 g/m² on new or tired ground
- A gentler lime alternative — at pH 11 it lifts acid soil gradually, and brings silica and trace minerals that lime does not
- Silicon supply — silicon deposited in stems and leaves gives structurally stronger plants that hold up better under drought and heavy fruit loads
- Compost heap activation — a dusting between layers, where heat and microbial acids weather the rock faster than open soil
- Carbon capture — silicate weathering ties up dissolved CO₂ as bicarbonate; a small contribution per garden, but a measured one
Micronised powder or granulated rock dust?
Micronised volcanic rock powder (this product)
- Fine powder with the most surface area per gram, so it weathers first
- Suspends in water: the only format that works in compost tea or a drench
- The right choice for pots, potting mixes and one-season results
- Raises pH usefully at 200–400 g/m²
- Dusty. Apply on still days, or to moist soil
Dr Forest granulated volcanic rock dust
- Coarser grains that release over months to years
- Spreads cleanly across lawns and large beds without dust
- Builds a mineral reserve that stays in the soil for years
- Will not suspend in liquid, so no use in tea
- Most people end up using both: powder for the season in hand, granules for the years after
A single mined ingredient, milled fine, weighed out and packed by hand in small batches in Stockport, Greater Manchester. Vegan and free of animal by-products by nature; nothing added. Safe to use around children, pets, bees and wildlife once it is in the soil. If you want the longer story on what rock dust can and cannot do, read How volcanic rock dust works. Made by Growers. Backed by Science.
Why this powder weathers faster
What is in this micronised powder
This rock is a volcanic silicate with zeolite minerals intact: 48% silica by analysis, pH 11 in water. Milled to a fine powder, it presents a large reactive surface to soil moisture. It does not dissolve like a soluble feed; it weathers. Water and the weak acids from roots and microbes free silicon, calcium, magnesium, potassium and trace elements slowly, along with bicarbonate that buffers acidity.
| Property | Value | What it means in the garden |
|---|---|---|
| Silica (SiO₂) | 48% | Weathers to silicic acid, the only form plants can take up |
| pH (dry powder) | 11 | Raises acid soil gradually; not a concern at compost-tea rates |
| Format | Micronised powder | Stays suspended in aerated liquid; weathers within a season |
| Mineral class | Zeolite-bearing volcanic silicate | Cation exchange and water holding alongside mineral release |
Finer grind means a response this season in pots, beds and compost tea — that is the SKU job. For the full evidence on silicon, yield trials, liming and carbon (Kelland, Skov, Beerling and the rest), read How volcanic rock dust works.
How to use micronised volcanic rock dust: compost tea, soil rates and pH correction
The micronised powder is very fine and will become airborne in dry, windy conditions. Apply on calm days or when soil is moist. Wear a dust mask when handling in enclosed spaces such as polytunnels or glasshouses. Outdoors in normal conditions no mask is required for typical garden quantities.
Rock dust supplies minerals; it does not replace nitrogen or fast-acting nutrition. Run it alongside a base feed such as Organic All Purpose Fertiliser 4-4-4 or a crop-specific blend, and give it a season. Even the fine powder works by weathering, not instant solubility.
Method 1: compost tea mineral enrichment
Adding the powder to an actively aerated compost tea brew introduces a broad trace-mineral spectrum alongside the microbial content of the tea. The fine particles suspend in the aerated liquid and the minerals are partially chelated by the fulvic and humic acids produced during brewing, which makes them more readily plant-available.
- Prepare your compost tea as normal. Fill your brew vessel with dechlorinated water, add compost or worm castings in a mesh bag, and start your air pump and airstone. Begin aeration before adding the rock dust.
- Add the powder at 1–2 g per litre of brew volume. For a 20-litre bucket, add 20–40 g. The agitation from the airstone keeps the fine particles in suspension throughout the brew.
- Brew for the normal period, 24–48 hours. Keep the air pump running throughout. The rock dust remains suspended during active aeration and minerals are progressively chelated by the organic acids produced during the brew.
- Apply immediately after brewing. Use within 4 hours of switching off the pump. Stir well before applying to redistribute any settled particles. Apply as a soil drench or foliar spray (filter through 200 micron mesh for fine spray nozzles).
Compost tea rate reference
For an enhanced mineral drench, add Fulvic Acid Powder at 1–2 g/L to the finished tea before application. The fulvic acid chelates the volcanic minerals into a more immediately plant-available form.
Method 2: soil broadcast and incorporation
Vegetable beds and borders: maintenance
Scatter over moist soil surface and rake into the top 5 cm immediately to prevent wind dispersal. Water in well. The fine particles begin weathering on contact with soil moisture.
New or depleted beds: first application
Incorporate into the top 15–20 cm thoroughly before planting. Use the higher rate for soils that have never received rock dust or that are known to be mineral-depleted. The fine particles begin producing silicic acid and releasing trace minerals within days of incorporation into moist soil.
Containers and potting media
Mix thoroughly into compost before planting. Far more effective than granulated rock dust in containers: the fine particles weather within a single growing season, releasing their mineral content while the plant is actively growing. Worth doing in peat-free media, which contain very little native mineral content.
Compost heap activation
Dust between green and brown layers as you build or turn the heap. The heat, moisture and microbial acidity within an active compost heap weather the fine particles far faster than open soil, and the finished compost carries the mineral content with it.
Acid soil pH correction: lime alternative
At pH 11, the powder raises soil pH progressively through the same weathering reaction that releases its minerals. Apply 200–400 g/m² annually and test soil pH each spring. The correction is gentler and longer-lasting than lime, with no overliming risk, and it supplies trace minerals and silica that lime does not. Expect pH to rise by approximately 0.3–0.5 units per growing season at the higher application rate, depending on starting pH and soil type. If you are not sure which way your soil needs to go, start with how to make soil more acidic, or raise the pH.
Rates at a glance
| Situation | Rate | Frequency |
|---|---|---|
| Compost tea | 1–2 g per litre of brew (20–40 g per 20 L) | Each brew; use within 4 hours of stopping aeration |
| Beds and borders, maintenance | 100 g per m² | Spring and/or autumn |
| New or depleted beds | 200–300 g per m² | Once, before first planting |
| Containers and potting media | 5 g per litre of compost | Once at potting |
| Compost heap | Light dusting between layers | Each time you add material |
| Acid soil pH correction | 200–400 g per m² | Annually until target pH is reached |
Even micronised powder works through mineral weathering rather than instant solubility; this is not a liquid fertiliser. The finer particle size means faster results than granulated material, but the full mineral benefit still builds over one or more growing seasons. Most growers notice silicon-driven improvements, stronger stems and firmer fruit, within the first season. The mineral reserve compounds over successive annual applications.
Combine with a base granular fertiliser, the Organic All Purpose Fertiliser 4-4-4 or a crop-specific blend. Adding Fulvic Acid Powder to compost tea applications improves mineral uptake, since the fulvic acid chelates the volcanic minerals for root absorption. For long-term soil building, combine with soluble Humic Acid Flakes as a monthly soil drench and Granulated Volcanic Rock Dust for the slow-release reservoir. Use Grow-Kashi to inoculate the biology that weathers rock particles fastest.
Keep the bag sealed, or decant into an airtight tub, somewhere cool and dry. The powder draws moisture from the air and clumps if left open; clumping does not affect it, but it makes measuring a nuisance. Stored dry it does not go off. Rock does not have a shelf life.
Frequently asked questions about this micronised powder
Here. This micronised volcanic rock dust is packed in Stockport in 500 g, 1.5 kg, 4 kg, 9 kg and 15 kg bags and posted to any UK address. It's the fine powder: a zeolite-bearing volcanic silicate, 48% silica, pH 11, ground fine enough to stay suspended in compost tea and to start weathering in the first season. If you want a slower, longer-lasting dressing for open ground, the same rock comes as granulated rock dust.
For established beds and borders, 100 g per m² in spring and/or autumn, scattered on moist soil and raked into the top 5 cm. For new or depleted beds, 200–300 g per m² once, worked into the top 15–20 cm before planting. In pots, 5 g per litre of compost (about a teaspoon) mixed in at potting. In compost tea, 1–2 g per litre of brew. If you're using it to raise the pH of acid soil, 200–400 g per m² a year, testing each spring. Rake it in straight away so it doesn't blow about.
