June 20, 2018
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Organic mulches sustain healthy garden soil

Reeser Manley | BDN
Reeser Manley | BDN
This is a photo of the onion transplants mulched with a thin layer of shredded leaves. Keeping the onion bed weed-free is essential and mulching helps.
By Reeser Manley

We planted peas and onions in Marjorie’s Garden last weekend while two crows watched from a nearby birch. I could feel the sun’s warmth on my back and the soil’s warmth in my fingers as I dug two inch-deep furrows down the length of a garden bed. Into each furrow I scattered pea seeds, plump with water just imbibed, then covered them with the warm soil, gently patting it down with the flat of my hand. All the while, the two crows were watching.

I pushed twiggy birch branches into the soil between the rows, forming a 4-foot scaffold for future pea tendrils and an immediate barrier to scheming pea scavengers. The crows flew off as I soaked the bed with a gentle shower.

Finally, I spread over the bed a thin blanket of shredded leaves, one handful at a time pulled from a bag stored in the basement since last fall. Dry leaf dust drifted downwind as I settled the mulch of leaves into place with a final watering.

We used shredded leaves to mulch the onion transplants, just enough to cover the soil, hold in the moisture, keep the root run cool, perhaps make it a little harder for weed seeds to get started. Later, after the plants are established and growing, we can lay down a deeper mulch.

As organic mulches work to suppress weeds and retain moisture in the soil, they also are slowly decomposed by soil organisms, releasing stored nutrients into the root zone. The autumn leaves of deciduous trees such as maple, beech, ash and oak contain about 0.5 percent nitrogen, 0.1 percent phosphorus, and 0.5 percent potassium, along with equally substantial amounts of calcium and magnesium, all essential nutrients for plant growth. Because decomposition of leaves is a slow process, these nutrients are released gradually — nature’s version of a slow-release fertilizer.

Decomposing leaves also improve both the structure and water-holding capacity of garden soil. While rich topsoil can hold 60 percent of its weight in water (compared to 20 percent for subsoil), leaf mold can retain 300 percent of its weight, or more.

We also do a lot of mulching with composted goat manure — “nannyberries,” applying it liberally around the high-bush blueberries, raspberries and grape vines as these small fruit crops begin growth in early spring. Nannyberries have replaced straw as the mulch of choice for these crops; we learned from a small fruits expert that mulching with straw can increase chances of root rot disease in raspberries. We threw the rest of our straw supply onto the compost pile.

Nannyberries are too coarse for use where vegetable seeds will be sown and often contain too much nitrogen to place in direct contact with tender transplants. We gently turn composted goat manure into the soil of most vegetable beds before planting, relying on shredded leaves as mulch for these beds.

A layer of composted goat manure does cover what will be this year’s potato bed. We will rake the compost aside to make furrows for the seed potatoes, then spread it back over the bed once the cut tubers are covered with soil. In two or three weeks, when the first potato leaves appear, the compost mulch will be well seasoned.

Finished garden compost is another excellent mulch. A mixture of vegetable scraps from the kitchen, spent plants from the garden, old potting soil, shredded leaves, seaweed (when we can get it), and nannyberries, our compost pile grows through the summer and, by October, yields a modest amount of rich, crumbly mulch. We screen it first, eliminating woody stems and other course materials that need more time to break down, then spread it where it is needed most, often on the strawberry beds.

And we mulch with worm castings. Over the course of a year, the worm bin occupants transform pounds of banana peels, coffee grounds and other kitchen vegetable waste into buckets of nutrient-rich castings. Blueberries and raspberries are the usual beneficiaries.

Organic mulches are the only fertilizer for our trees, shrubs and perennials. In the vegetable garden, organic mulches, along with compost turned into the soil, supply sufficient quantities of nitrogen and other essential nutrients for sustained vegetable and fruit production, year after year.

We do our part as well, minimizing disturbance of the soil organisms that slowly make nutrients available to plants; no synthetic fertilizers, no pesticides, no tillage other than the gentle forking of compost and cover crops into the soil.

Organic mulches nourish life in the soil, the source of a gardener’s success.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

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