Burl Sheldon prepares to add boron to the soil in his orchard on Sunday, April 7, 2024, in Haines, Alaska.
Burl Sheldon prepares to add boron to the soil in his orchard on April 7, in Haines.

Soil enrichment always involves banking carbon and nutrients: well-aged, non-pathogenic “humanure” from a composting outhouse is A-OK for an orchard, raspberries, or perennials; seaweed and grassy beach wrack are super for mulch, but can include unwanted weed-seed; spoiled hay from poultry or livestock is great, as is the aged manure. Another local resource for soil enrichment is small-diameter deciduous branches and stems run through a wood chipper. 

Soluble Lignin, Brown Rot, and White Rot

Lignin-containing compounds give strength to vascular plants and are abundant in small-diameter wood. These organic molecules provide about one-third of all carbon found in terrestrial soils. Most of the nutritional goodies found in a tree are in the small diameter wood—stems, leaves, small branches, cambium, and buds. Mycorrhizal fungi (mycorrhizae defined: “root fungi) feed on lignin-rich woody material and are integral to plant (and planet) health. 

Forests and terrestrial ecosystems are hooked-up through vast mycorrhizal networks. Some produce brown rot, others white rot. The brown-rot crew does their dance best with softwoods (spruce and hemlock); look for their cubical, dark-hued remnants. The white-rot gang courts our lignin-rich hardwood species—alder, birch, willow and cottonwood. 

Mycorrhizal fungi are symbiotic champs for trees, perennials and most vegetables. They do not form mushrooms and aren’t visible on the surface, but thrive in the top soil, where they mine, store and share nutrients. Their plant-partners are literally sugar-daddies—providing them with carbohydrate food energy they can’t produce themselves. The sticky, clumpy, binding nature of good soil—humus—results largely from the seasonal growth and die-back of mycorrhizal fungi (search: glomalin).

Mulching with Small-Stem Chipped Wood 

Lignin-rich wood chips rapidly boost fungal activity and accelerate soil building. A few hours behind a noisy chipper goes a long way. 

Only chip clean material so the cutter-head stays sharp longer. Learn to remove and sharpen the blades, so the machine operates cool, cuts smoothly, and lasts longer. Gloves and safety gear are essential. 

By “small-stem,” I’m referring to branches and stems under about 2.5 inches in diameter. Loaded with goodies, these have an admirable ratio of carbon-to-nitrogen ranging from 25:1 to 40:1. Again, target alder, cottonwood, birch orwillow, not spruce or hemlock (but some is fine).

Compost it for a year, or top-mulch directly each spring and/or fall. Both approaches work. Pile it directly on the ground and a white-rot fungal cafeteria will soon form under the surface. Mixing in some native forest soil primes the fungal-fire.

Mulch under the dripline of fruit trees and around perennials and berries. Do not pile organic material against the trunks of woody fruit trees. To jump-start a broad “fungal duff:” a) block out the sod and buttercup with corrugated cardboard, then b) sheet-mulch right on top (see photo). Enrich your soil’s fungal life and stand back!