Water Absorption of Biochar

One of the most important properties of biochar is its incredible ability to retain moisture.

It would be good to see how it compares in this respect with other garden additives which also help retain moisture, like the popular vermiculite and perlite. Vermiculite and Perlite have been popular for many years and are prized by gardeners who want to prepare seed beds and hanging baskets. Their ability to absorb water and also to make soil lighter is really good, however the tests here show that for water absorbtion alone, biochar comes out ahead.

First we measured out 300ml (30 cu cm) of each product and weighed it. Then we placed it in water overnight, before draining them for 4 hours. At the end of this period we reweighed them. The results are shown below:

Measure/ProductVermiculitePerliteCharboy Biochar
Dry Weight42g28g103g
Final Weight182g123g301g
Water Retained140ml95ml198ml
Water %ge47%32%66%

The saturated biochar is exactly two thirds water by volume. Significantly higher than either vermiculite or perlite. Perlite and vermiculite have other benefits of making soil more friable so you will still want to prefer it for some uses like seed raising mix or hanging baskets. But especially for hanging baskets, definitely add some biochar as well to juice up the water retention.

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