Build Your Garden Soil By Adding Nitrogen to Wood Chips

Learn about wood chip mulch pros and cons and why you should be adding nitrogen to wood chips for long-term benefits in the garden.

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by Adobe Stock/Elroi

Learn about wood chip mulch pros and cons and why you should be adding nitrogen to wood chips for long-term benefits in the garden.

Most organic gardeners find that following nature’s patterns serves them well. When it comes to building richer soil, nature’s plan relies heavily on trees — fallen limbs, leaves, cones, seeds and eventually, the massive trunks. Adapting this plan for building garden soil by using a wood mulch — such as wood chips, sawdust or other woody residues — is a strategy that promises huge, long-term returns.

Field studies dating back to the 1950s  suggest that a high-fiber diet of woody materials is exactly what many soils need. Rotted bits of wood persist as organic matter for a long time, enhancing the soil’s ability to retain nutrients and moisture, which results in bigger, better crops.

But wait: Woody materials are high in carbon and cellulose, so they need nitrogen and time in order to decompose. If you ignore these facts by mixing fresh sawdust or wood chips directly into your soil, the materials will bind up much of the soil’s nitrogen and render the spot useless for gardening for a season or two.

The outcome changes, however, if you add nitrogen or time. For example, when researchers planted a new organic apple orchard in northern Maine in 2005, fresh wood chips combined with blood meal (a very high-nitrogen organic material with a typical analysis of 12-0-0) and tilled into the top layer of the soil — plus a surface mulch of wood chips — proved better than three other treatments at promoting rapid tree growth. And, in less than two years, the organic matter content in the chip-amended plots went from near zero to 2 to 3 percent.

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