Moisture and PH levels?

The ideal moisture level will depend alot on the exact substrate mix and in particular it’s saturation point (the maximum level of water it can hold before becoming saturated).

Straw has a high saturation point of around 72-74%, whereas coffee with it’s much smaller particle size can only hold around 55% water before becoming saturated.

Going beyond the saturation point is not good as you tend to get water collecting in the bag causing poor air exchange and increased contamination.

One of the downsides of growing on coffee is the low saturation point meaning that it doesn’t have so much water left in the substrate after the 1st flush. So – you can either soak your bags a day or so after the first flush and/or you can add more straw to the mix to bump up the overall moisture content of your substrate.

Hi Gabriel,

The ideal substrate pH is between 5 – 6.5, though mycelium can survive between pH 4 and 7.5. The pH level in the substrate should ideally be around 6 – 6.5 at the start and then it will drop during the incubation and fruiting stage as the mycelium utilises nutrients in the substrate. After 2 crops it will likley be below or around pH 5, and this is a good time to compost your bags as the mycelium is no longer at it’s strongest.

I don’t know with regards to a difference in pH of espresso or filter/cafetiere coffee but there is certainly a big difference in moisture content which can have a huge impact on your growing. Filter and cafetiere grounds tend to be too wet which can cause problems with poor air exchange and contamination in your bags. Espresso grounds are much better, especially when mixed with 20% straw to break up their density.

It depends on the particle size mostly, but tends to be around 60-65%.

You can test by squeezing a handful – if more than a few drops of water come out, it is oversaturated.