Compost soil vs woodchips

Do trees and other plants prefer compost soil or woodchips mulch? Science tells the "dirty truth".

It has long been said that decaying wood in the soil will deplete the nitrogen. You may have wondered if that is really true. Some of the science behind how different plant matter behaves in the soil tells a rather different story from what the old gardening books once told us.

Is it better to use compost soil or wood chips?Then where did all the lore about nitrogen depletion come from? It is true that buried wood fibers tie up some of the available nitrogen...for awhile. The organisms that work to turn the woody material into compost temporarily hold on to some of the nitrogen, but don’t worry they will return it later and invite their friends and family to do the same.

Benefit of woodchips mulch

Think of a good layer of woodchips as a slow release fertilizer. These woody mulches (especially mixed chip) greatly benefit woody plants. That giant cedar tree in the corner of your yard gets a huge amount of its nutrients from this type of action, a good deal of which just accumulates under the tree naturally.

Benefit of compost soil

In contrast, compost soil includes compost that has already "broken down" and is then mixed with dirt and usually some sand to help with drainage. Some compost is in the form of animal waste, while other contains a variety of organic materials, such as food scraps.

In our gardens, herbaceous plants (those with flexible stems like your tomatoes) need quicker nitrogen than slowly-breaking-down wood can provide. A lifespan of a tomato plant, for example, is a brief moment compared to that of the trees, they exist for a very short season; therefore, they need quickly available nutrients like those provided by the waste of chickens or bats. If we were to compost the wood fibers first, then herbaceous plants could make use of the nitrogen.

That is not to say that the tree couldn't use a quick dose nitrogen as well, but trees are patient. It is not nearly as crucial for a large cedar to receive quick nutrients and nobody cares if its cones take 180 days to ripen.

More cool science...

Wood fibers breaking down in the soil also bring along mycorrhizal fungi, which in turn help the uptake of sugars and other important micronutrients. One of my favorite products to “cure” sick plants is a B vitamin concoction that has been around since the 1940’s. It replaces some of the micronutrients lost when plants are in a tidy environment.

The conclusion is: material breaking down greatly benefits woody plants, but soft plants need something that will feed them a little quicker.

The real magic of wood is it does a great job at retaining moisture. You might decide to spread compost soil for the quick nutritious benefit and wood chips mulch to keep the roots from drying out in summer or getting too cold in winter. Oh...and let's not forget they also help as a weed barrier, but that's a topic for another blog.

To learn more about the amazingly wonderful interaction between compost soil, decaying wood chips and the plants they help, contact us at Environmental Construction Inc. We have several experts on our staff who know a thing or two about the plants in your landscape.

Category: Tips for Planting

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