For potting soil that dries out too fast, so Calatheas curl and crisp at the edges and seedlings wilt between waterings. Vermiculite holds water like a sponge and gives it back slowly, keeping a mix evenly damp without making it heavy. It's also one of the best things to start seeds and root cuttings in. Fine 0–5mm grain. 3L resealable bag.
Vermiculite is a natural mineral that, when heated, unfolds into soft, golden, accordion-like flakes. Those layers soak up water and nutrients and release them gradually to the roots. Mixed into soil, it keeps moisture steady and the texture light, and it doesn't break down. It does the opposite job to perlite: perlite lets water run through, vermiculite holds onto it. Many growers use a little of each.
Which plants it suits
Plants that like to stay evenly moist: Calathea, Maranta, Alocasia, ferns and other thirsty tropicals. It's also good for seed sowing and propagation. It isn't the right choice for cacti and succulents, which want a mix that dries out quickly.
How to use
- To hold more moisture: stir roughly one part vermiculite into four parts potting soil.
- For seeds: mix it with seed compost, or sprinkle a thin layer over newly sown seeds to keep them damp while they germinate.
- For cuttings: root them in damp vermiculite, alone or mixed with perlite.
- Water a little less often once it's in the mix. It keeps the soil wet for longer.
At a glance
| What it is | Horticultural vermiculite |
| Grain size | 0–5mm |
| Origin | South Africa |
| pH | 8–9 (alkaline, so use it as part of a mix rather than on its own for acid-loving plants) |
| Water holding | High, up to about 95% |
| Lasts | Years; it doesn't break down |
| Volume | 3 litres, resealable bag |
- Suitable for organic growing.
- Can be harmful if eaten. Keep it out of reach of pets and children.