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Vermiculite or perlite?

13 January 2022

Vermiculite and Perlite are both light, gritty grains that barely weigh anything at all, but although they look similar, they have different characteristics. When and how should you use them? Read on to find out!

They are often found next to each other, those bags that the shop sells as soil improvers or accessories for starting seeds. Although they are similar in appearance and to some extent have similar characteristics, they perform different functions. If you choose the right product for the right purpose, you are more likely to get the desired result.

But what are they?

Vermiculite and Perlite are both minerals, which means that, unlike organic materials, they are not broken down by microorganisms in the soil. Both substances are also naturally sterile and therefore do not bring diseases or pests to your crop.

What is Vermiculite?

Vermiculite is a clay slate which is heated to give it a structure that both absorbs and releases moisture. The grains are soft and ‘spongy’ and have a slightly brownish colour.

What is Perlite?

Perlite is a volcanic material which turns white and porous after intense heating, almost like crumbled Styrofoam. The grains are completely white.

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Vermiculite is ideal for sowing tiny, photoblastic flower seeds.

What functions do Vermiculite and Perlite have?

Both substances retain water in the soil. Vermiculite absorbs water like a sponge while Perlite stores water in its porous structure.

Vermiculite absorbs water easily and retains moisture longer than Perlite and is a good choice for starting seeds. It can be mixed into the soil to make it retain moisture for longer. You can also add a layer over the soil’s surface to better preserve the soil’s moisture and prevent moss.

When sowing photoblastic seeds, you can fill the planting pot with soil, sow the seeds and cover them with Vermiculite. This gives the seeds access to light but means they won’t dry out as quickly.

Perlite has a neutral pH and makes the soil more aerated than Vermiculite, which is especially good when transplanting small plants, and it can also be mixed into seed compost. More aerated soil gives the plant roots more oxygen and helps seeds to germinate faster and young plants to root better.

Mix some Perlite into the flower compost if you have sensitive houseplants to help them to thrive.

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Perlite helps keep the soil around your plants’ roots aerated without allowing them to dry out.

How should I use them?

Choose Vermiculite for starting seeds and for plants that need a moisture-retaining soil.

Choose Perlite when repotting or for your plants that need a sandy and well-drained soil.

Use them together to improve soil structure and properties. Mix two parts soil with one part Perlite and one part Vermiculite.