If you follow our Facebook page, you know we spend a lot of our time mulching landscape beds and tree circles. It’s a task that is both never-ending and strangely satisfying. It’s also critically important for the long-term health of the park’s plant collection.
Mulch is any loose material that covers the top of the soil. It can be organic, such as wood chips or bark dust, or inorganic, such as gravel or pebbles. Green mulch is term gardeners use when low matt-forming groundcover plants serve as a mulch, although it’s not loose.
Mulch provides several benefits. It conserves soil moisture, it reduces weed seed germination, and it buffers the soil’s temperature change, providing plants with some protection for unusually hot days and cold nights. It also reduce soil compaction from foot traffic and rain. Plants that are surrounded by mulch better resist climate change, need less supplemental water, and are more resistant to stress. Trees that are not under stress better resist disease and insect pressure.
Selecting the right type of mulch is important to get the full benefits. Surprisingly, there has been a lot of scientific research on mulch and one type stands out: arborist chips. Arborist chips are shredded tree trimmings, including bark, stem, and leaves. The mix of material feeds microorganisms in the soil, which helps free up nutrients for the plants. It also stimulates earthworms and other soil-dwelling critters, whose activities build soil structure. Arborist chips, unlike bark dust, is also course (i.e. chunky), which allows air exchange between the atmosphere and the soil.
The arborist chips we use in the park are free and come from tree work done by the City’s urban forestry program and park crews. If you would like to use arborist chips in your garden, check out Chip Drop, a national program that matches people looking for arborist chips with companies looking to dispose of chips. In general, experts recommend a 3-inch layer of munch.
Arborist chips are not the most attractive option, though. That’s why you will also see us use bark nuggets and pebbles in selected areas. These choices provide the same key ecological services as arborist chips except they don’t provide nutrition. And, unlike arborist chips, they are not free.