Mycelium as a material: growing a plant pot in two weeks

Anyone who has had a grow kit knows the feeling: at the end, the block is firm, light and coherent, as if the substrate were held together by a white web. That web is the mycelium, and it is exactly that ability to bind loose material into a whole that designers and manufacturers have been working with in recent years. It is made into packaging, insulation panels, lampshades and even building blocks. The principle is simple enough to copy at home, with a pouch of spawn and an old flowerpot as a mould. A fun project for a rainy weekend, and a good excuse to learn what mycelium actually does.

How does it work?

Mycelium grows through a nutritious substrate and in doing so connects every particle to the next. Let that happen inside a mould and the mycelium takes on the mould's shape. Take it out afterwards and dry it, and the fungus dies, leaving a light, firm, insulating structure: compacted substrate held together by fungal threads. That is mycelium material. It is biodegradable, light and, oddly, fire retardant. The oyster mushroom is one of the best species for it, because it grows fast and accepts almost any substrate.

What do you need?

• An 80 gram pouch of oyster mushroom spawn.
• Substrate: chopped straw, hemp fibre or sawdust, about two litres. Fine material gives a smoother surface.
• Two flowerpots that nest, the large one as outer mould and the small one as inner mould. Or one pot and a plastic bag of sand as the inner mould.
• A large pan for pasteurising the substrate, cling film, and a clean workspace.

Step by step

1. Pasteurise. Substrate for an hour in water at 70 to 80 degrees, not boiling. Drain until moist but not dripping: squeeze it and a few drops come out.
2. Mix. Wash your hands, let the substrate cool to hand-warm, knead the spawn through it. Distribute well, every part of the mould must contain spawn.
3. Fill. Line the outer mould with film so you can release it later, substrate in, push the inner mould in firmly to create a wall two to three centimetres thick. Press down, top up the rim.
4. Let it grow. Whole mould in a large plastic bag with a few small holes, in a dark place around 20 degrees. After five to ten days the surface is white.
5. Demould and finish growing. Carefully remove from the mould, back in the bag, another three to five days so the surface also closes over into a smooth white skin.
6. Dry. In the oven at 60 degrees until hard and light, usually a few hours, or several days on a radiator. Drying kills the mycelium and makes the pot stable.

Why does it sometimes fail?

For the same reasons as a bucket of oyster mushrooms: substrate that is too wet rots and turns sour, substrate that is too dry does not colonise, and a dirty workspace gives green mould. The ratio of spawn to substrate can be more generous here than for growing, because you want speed, not a harvest. And do not take the pot out of the mould too early: if the substrate still falls apart, the mycelium was not done. Waiting one more day is then the whole solution.

Can you plant in it?

Yes, and that is the nice part. A dried mycelium pot lasts months if it does not get too wet, then slowly returns to the soil along with the plant in it. So put it in a decorative outer pot or on a saucer. Use it as a seedling pot and you can plant the seedling, pot and all, into the border and watch the pot disappear as the plant grows.

And why are we telling you this?

Because it is the same fungus, and the same insight. Once you have seen a handful of spawn bind a pot together in ten days, you understand better what happens inside a grow kit or an inoculated log: no magic, but an organism binding its food into a whole. For children who want more after a grow kit, this is the logical next step. And anyone who manages a lampshade is welcome to send us a photo.