Cocopeat Blocks Explained: Sizes & Expansion

Cocopeat is sold in blocks because shipping air is expensive. The material is dried, compressed under high pressure and cut into bricks. You add water, it expands, and you have growing medium.

Simple enough. But the numbers on a block — weight, dimensions, expansion volume, compression ratio — are not interchangeable, and confusing them is how growers end up short of medium halfway through filling trays.

What is actually in the block

Cocopeat is the fine pith left after coconut husk fibre is extracted. Good growing-grade coir is:

• Washed to reduce salinity
• Graded to remove long fibre, sand and debris
• Dried to a controlled moisture level before compression
• Compressed at a known ratio

The block should be uniform in colour and texture. If you break one open and find clumps of sand, strips of plastic or a strong sour smell, the grading was poor.

Weight vs volume: the number that matters

A 5 kg block is sold by weight. What you actually use is volume. The relationship between the two is the expansion volume, and it is the figure worth comparing.

In practice:

| Block | Weight | Water needed | Expansion | | --- | --- | --- | --- | | Standard | 5 kg | 18–20 L | 70–75 L | | Small | 650 g | 2.5–3 L | 9–10 L |

Two suppliers can both sell "5 kg blocks" where one expands to 65 litres and the other to 78. That is a 20% difference in usable medium for the same price per block. Always ask for expansion volume, and verify it once with a bucket and a measuring tape.

Why compression ratio matters

Compression ratio describes how much the loose material was squeezed. A ratio of roughly 7:1 means seven litres of loose coir became one litre of block. Treat the ratio as a transport figure, not a buying spec — expansion volume is what you actually use.

Higher compression means cheaper transport and storage, but it also makes hydration slower. A tightly compressed block needs water added in stages, or the centre stays dry while the outside looks fully expanded. This is the single most common mistake home gardeners make.

EC and pH: read these before price

EC (electrical conductivity) measures dissolved salts. For standard washed coir, aim for under 1.0 mS/cm. For hydroponic use, ask for the batch figure and aim lower, under 0.5 mS/cm.

pH for cocopeat typically sits between 5.5 and 6.8. Most crops are comfortable in that range. If a batch arrives far outside it, ask why before using it on sensitive seedlings.

These numbers vary by batch. A supplier who cannot tell you the EC of the stock you are receiving is asking you to take a risk you cannot audit.

Grading: why "cocopeat" is not one product

Coir is graded by particle size and fibre content:

• Fine pith — good for trays and small pots, holds water well
• Medium — the general-purpose grade for potting mixes
• Coarse with fibre — more air, better drainage, useful in long crops

A block sold as "cocopeat" could be any of these. For seedling trays you want consistent fine-to-medium pith. For a polyhouse crop you want structure and drainage, which usually means a coarser grade.

How to check a block in five minutes

You do not need a lab to catch a bad batch. Do this once per consignment:

1. Weigh one block on a kitchen scale. It should match the stated weight within a small tolerance.
2. Hydrate it in a measured bucket. Note how much water it absorbs and how many litres it fills.
3. Squeeze a handful. It should hold together without dripping. If water runs out freely, it is over-wet; if it crumbles, it is under-hydrated.
4. Smell it. Earthy is fine. Sour or chemical is not.
5. Check the run-off EC if you have a meter. This is what your roots will experience.

Five minutes per consignment is cheap insurance against a spoiled tray of seedlings.

Storing blocks

Unopened blocks keep for a long time if they stay dry. Stack them off the floor, under cover, away from direct sun. Once a block is opened and hydrated, use it within the crop cycle. Wet coir left in a heap for months is an invitation to algae, fungus gnats and mould.

Common claims worth questioning

"Expands to 100 litres." Possibly, for a very large block. Check the weight and how loosely it was measured. A standard dry 5 kg block should give 70–75 litres.

"Fully washed, EC near zero." Almost nothing is zero. Ask for the actual figure.

"Organic certified." Certification applies to a production system, not a material. Ask which certifier and which scope.

The short version

Buy on expansion volume and EC, not weight alone. Verify once with a bucket. Store dry. Hydrate slowly.

That is most of what you need to know about the block itself. For the practical steps of expanding and mixing it, read how to use a cocopeat block. To see sizes, current rates and batch notes, visit our cocopeat blocks product page.