I’ve seen peat humus in some potting mix recipes. What is it, and where can I find it?
Answer: Peat humus is a common potting soil ingredient used for soil enrichment. Unlike Sphagnum peat, which comes from Sphagnum moss and is partially decomposed, peat humus is derived from Hypnum moss and is fully decomposed. Peat humus is also referred to as black peat or Michigan peat. It is dark brown to black in color and its water-holding capacity is low. Despite this characteristic, peat humus is quite heavier than most other peat mosses. Other characteristics of peat humus include a pH between 4 and 8 and it also contains a small amount of nitrogen, usually between 2.5 and 3 percent. I am unaware of any other peats containing nitrogen. There are two types of peat humus: amorphous and granular. Amorphous peat humus has very little structure and is highly acidic. Although it is found in the greenhouse/nursery, garden, and landscape industry, it does not make for a very practical soil component. Granular peat humus contains humates and has a structure that allows for good air and water movement. It tends to do better for potting mixes and in improving sandy soils. Peat humus is usually available through garden supply centers. If you are unable to locate it for your potting mix, you may want to consider adding perlite and/or vermiculite instead. For more information on making your own potting mixes, see the ATTRA publication Potting Mixes for Certified Organic Production, available at https://attra.ncat.org/attra-pub/viewhtml.php?id=47.