Expanded vermiculite is available in two particle sizes: fine (1–3 mm) and medium (3–6 mm), both in 100 L bags. It is a heat-expanded mineral that provides water retention and cation exchange capacity (CEC) to the substrate — the opposite of perlite, which provides aeration. The difference in particle sizes does not change the chemical properties, only the particle size and, therefore, the crop or system where it is used.
🎯 Choose the variant in 10 seconds
- If your case is seedbeds, cuttings, or crops with high water demand: go to the fine particle size (1–3 mm)
- If your case is medium and large pots, gardening, or general substrates: go to the medium particle size (3–6 mm)
What to consider before choosing the variant
Both particle sizes are chemically identical (expanded vermiculite in 100 L bags) and provide the same functional properties: water retention, cation exchange capacity, lightness, and structural stability. The choice is based only on particle size:
- Crop type and root system: fine and young roots (germination, seedlings, cuttings) work best with fine vermiculite, which maintains contact with the seed or stem. Mature plants and larger crops benefit equally from fine, but can work well with medium in large pots.
- Crops with high water demand: leafy vegetables, tropical plants, and crops in hot climates benefit from fine vermiculite due to its higher capillarity. Medium drains somewhat faster and is suitable when the risk of waterlogging is high.
- Mixing with other substrates: fine vermiculite mixes very well with peat, vermicompost, or pith coco fiber in proportions of 20–30%. Medium is preferred for mixtures with coarse cocopeat or as an intermediate layer in deep planters.
- Combination with perlite: it is very common to combine vermiculite and perlite at 50%. Vermiculite provides water and nutrient retention; perlite provides aeration and drainage. Together they balance the mixture.
- Handling: vermiculite produces some dust when handled dry, although less than perlite. Moisten it slightly before mixing and use a mask when working with large volumes indoors.
Fine particle size (1–3 mm): for seedbeds and seedlings
- Maximum moisture retention near the seed
- Homogeneous distribution in trays and small pots
- Capillarity: distributes water evenly
- Provides CEC: retains nutrients for the crop
- Higher risk of saturation with excessive watering
- Possible compaction in large pots in the long term
Fine vermiculite is the standard nursery option for seedbeds and propagation: the small particle maintains moist contact with the seed, retains the nutrients provided by the base substrate, and helps develop a compact root ball. It is also used purely to cover seeds (3–5 mm layer) that need relative darkness but constant moisture. In crops with high water demand such as lettuce or basil, mixed at 20–30% with cocopeat, it significantly reduces irrigation frequency without saturating the roots.
Medium particle size (3–6 mm): the standard for pots and gardening
- Good balance between retention and drainage
- Long-term structural stability
- Lower risk of saturation in large pots
- Provides CEC without saturating the root bulb
- Leaves empty spaces in seed trays
- Not optimal for fine cuttings
Medium vermiculite is the standard option for medium and large pots, deep planters, and general substrate mixes for adult plants. The larger particle maintains the substrate structure in the long term, retains moisture and nutrients but allows excess water to drain, reducing the risk of root rot. It is the usual choice for balcony planters, nurseries with 5–20 L pots, and planting mixes for container shrubs.
Comparative table of variants
Both particle sizes are chemically and minerally identical. The difference is only in the particle size and, therefore, in how it behaves within the substrate.
| Characteristic | Fine | Medium |
|---|---|---|
| Ideal use | Seedbeds and seedlings | Pots and gardening |
| SKU | 564562 | 213432 |
| Particle size | 1–3 mm (0.04–0.12 in) | 3–6 mm (0.12–0.24 in) |
| Water retention | High | Medium-high |
| Capillarity | High | Medium |
| Drainage | Slow | Medium |
| Exchange capacity | High | High |
| Volume per bag | 100 L (26.4 gal) | 100 L (26.4 gal) |
Use case matrix → recommended variant
| If your case is… | Recommended variant |
|---|---|
| Germination tray or seed covering | → Fine |
| Rooting cuttings | → Fine |
| Leafy vegetables with spaced irrigation | → Fine |
| Pots for aromatics or ornamentals (5–20 L) | → Medium |
| Balcony planters with adult plants | → Medium |
| General mixes with cocopeat for shrubs | → Medium |
Vermiculite and perlite are complementary, not substitutes. Vermiculite provides water retention and CEC; perlite provides aeration and drainage. A classic seedbed mix is 50% peat or cocopeat + 25% fine perlite + 25% fine vermiculite. If your base substrate already retains a lot of moisture (dense cocopeat) and you notice plants suffocating, reduce vermiculite and increase perlite. If plants dry out too quickly between waterings, increase vermiculite.
Do not use vermiculite as a sole substrate for potted plants. Due to its high water retention capacity, pure vermiculite keeps the root ball permanently saturated and promotes rot. Always cut it with peat, cocopeat, or perlite in proportions of 25–50% vermiculite. The exception is seedbeds, where it can be used purely as a covering over the seed, or as a sole substrate during the 7–10 days of germination.
Fine or medium for your substrate?
Tell us what you will grow, container size, how much you can water, and the base mix you use. You will receive the exact particle size and recommended proportion for your case, and if it is convenient to combine it with perlite.
Frequently Asked Questions
Does vermiculite provide nutrients to the plant?
Vermiculite itself releases minimal amounts of potassium, calcium, and magnesium, but its direct nutritional contribution is low. Its real value lies in its cation exchange capacity (CEC): it retains nutrients provided by fertilizer or the base substrate and gradually releases them to the roots, preventing leaching by watering.
Vermiculite or perlite: which one should I choose?
Use vermiculite when your substrate needs to retain more moisture and nutrients (seedlings, vegetables with high water demand, sandy substrates). Use perlite when your substrate needs more air and better drainage (dense cocopeat, plants that suffer from waterlogging). In practice, it is most common to combine them 50:50 to achieve balanced aeration and retention.
Can vermiculite be reused?
Yes. After a growing cycle, remove the vermiculite from the substrate (you can sift it to separate it from peat or cocopeat), rinse it with water and disinfect it with a mild 1–2% hypochlorite solution or by steam pasteurizing for 30 minutes. Rinse well before incorporating it into a new mixture. Vermiculite is stable and can be reused for several cycles, although it loses some structural capacity over time.