Not many weeds get through mulch.

Mulch was not invented by humans. Most plants make some sort of mulch naturally. Even desert plants that live on bare ground shed foliage that decomposes to be recycled back into the soil, and provide nutrients for the roots below. Redwood, most pines and most eucalyptus are extreme mulchers that generate thick layers of foliar debris that benefit their own roots, but inhibit the growth of competing trees. Knotweed, Hottentot fig (freeway iceplant), ivy (both Algerian and English) and other dense groundcovers are their own mulch, and also work well for substantial plants that grow amongst them.

There are a few advantages to mulch. Although ground cover mulches consume some degree of moisture, mulches benefit plants by retaining moisture at the surface of the soil. Mulches also insulate the soil, so that it is more comfortable for roots that want to be near the surface. Most weed seeds that get covered by thick mulch can not germinate and emerge through it. Those that try to germinate on top probably can not get their roots through to the soil below. Besides, mulch simply looks better than bare soil.

Mulch is generally spread in early spring, before weed seeds are completely germinated, and while the soil is still damp. However, moisture retention is still a concern through the warm and dry weather of summer. A thin layer of finely textured mulch added over thinning groundcovers (without completely burying the foliage) can rejuvenate tired old stems by giving them something more to root into. This works well for knotweed, English ivy and even trailing gazanias.

Mulches should generally be well composted so that they do not take too many nutrients out of the soil for their own decomposition. However, uncomposted coarse wood chips, like those often recycled from tree services, are even more effective at controlling weeds while fresh, and they tend to decompose before they become a bother to larger plants.

Small volumes of mulch can be purchased in bales at nurseries and garden centers. Composted redwood soil conditioner is a popular soil amendment that can alternatively be a nice finely textured mulch to spread thinly over small areas or in planters. Larger volumes of more coarsely textured and less expensive mulching materials can be obtained by the yard from garden supply stores.

6 thoughts on “Much Ado About Mulch

  1. I wonder if this is a function of your drier climate? I weeded the mulch out in front of our office 2 weeks ago and it is already in need of more weeding. The area was weed-free before mulching–everything came up though or on top of our mulching. And it’s just our usual suspects: crab grass, oxalis, spurge and some very weedy alianthus. Oh well. Mulching is needed at commercial buildings..

    Karla

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    1. Was the mulch compost? We use compost at work, and because it does not compost thoroughly, weeds seeds survive, and grow abundantly in some situations. Not all of the composts contains an abundance of seed. We just do not know which portions are better than others.

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  2. I like to use pine straw for mulch. I noticed in our part of the state, the tall Lobolly Pine tree needles keep the weeds down and many of my shrubs like camellias and azaleas like the acid in the needles. Plus, it is really light, easy to carry and I can collect it for free.

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    1. Gads! I used to work for a so-called ‘landscape company’ that charged significantly to install mulch, and then charged for maintenance that involved blowing it all away with blowers.

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