Organic mulch: the bedrock of sustainable gardening

Mulching bare ground and around plants is THE single most important thing gardeners can do to create not just healthy gardens but low maintenance ones, too. In fact, gardening guru Paul James calls it “the greatest labor saving gardening product ever invented.” It’s right up there with choosing the right plants and watering adequately.

Why?

Oh, where to start? What’s not to like about something that does all this?

• Suppress weeds
• Retain soil moisture
• Prevent erosion
• Reduce soil compaction
• Moderate soil temperature
• Prevent mud splatter on plants and hard surfaces, like your house
• Add nutrients to the soil and enable it to better use soil nutrients from any source
• Attract earthworms and beneficial soil microbes.
• Make your yard look well kept and amenable to planting—like a garden.

When?

• Every year, when soil has warmed in midspring..
• AND around the root zone of new plants, immediately after putting them in the ground.
• AND to cover bare ground at any time.

How much?

If you’re mulching on top of a layer of compost, apply 1-2 inches of mulch. More can be added as it breaks down over the season. To determine how many 2-cubic-foot bags you need to provide 2 inches of coverage, divide the square foot area of your garden by 12. For 3-cubic-foot bags, divide by 18.
If mulch is used alone (not on top of a layer of compost) apply 2-3 inches, but no more than 3. Too much mulch can harbor pests and keep water away from the plants. Sunny spots need more mulch than shady ones.

How?

• Remove weeds
• Loosen the top of the soil (a tool called a cultivator does this job very quickly), incorporating what’s left of the old mulch into the soil as you do it.
• Apply mulch and water well.
• Never mulch on top of plants, allow mulch to touch plant stems or, worst of all, pile it up against tree trunks. This practice of creating mulch “volcanoes” is common but deadly for trees.
• Avoid putting mulch against your house—it attracts termites.

Types

If your soil is already good, then you might choose pine needles, shredded wood chips or bark, which are all long lasting and look good. But if your soil could use some improvement, mulching is far and away the easiest way to accomplish that, as long as you use nutrient rich, fast decomposing mulches like leafmold, pine fines or compost.
Another factor to consider is that some mulches use up soil nitrogen in the process of decomposition, the worst offenders being wood chips, dry leaves, sawdust, and pine needles. For an attractive but still natural looking mulch, bark chips are probably the best choice, but they’re not cheap.
My favorite mulch and the one I use about 10 cubic yards of every year is leafmold from Takoma Park, which I use to cover all the bare soil on my property in April. Then for a fancier look in my seating area I use bark mini-nuggets. (**Asterisks indicate the best type of mulch.)

**Compost is plant or animal material that’s completely decomposed and now looks something like coffee grounds what a great source of nutrients it is, and a boon to soil structure. (It’s also the best soil amendment there is, meaning that it’s mixed into the soil itself, maybe half and half at the time of planting. I use either compost or leafmold for that purpose.) See resources below.
But here’s one problem about compost used as mulch: weeds just love it. While it doesn’t come with weed seeds in it, wind-blown seeds land on it and thrive, so compost isn’t as good at weed prevention as the other types of mulch. Some gardeners don’t like the way it looks on top of the soil because it already looks like soil and they prefer the look of organic mulches that are not fully decomposed.

**Leafmold is simply chopped and aged leaves. It’s rarely sold but lucky us, it’s free from Takoma Park’s Department of Public Works. It’s nutrient rich and excellent as mulch or soil amendment. See resources below.
Dead leaves are unattractive as mulch and will fly all over the garden unless they’re shredded first. The shredding also speeds their decomposition and prevents matting and subsequent smothering of your plants. This can be accomplished by mowing over them with a mower that has a grasscatcher. Dropping leaves into electric chopping machines is another option, but a lot of work.

Pine needles are often available cheaply and they’re slow to decompose, but they may deplete the soil nitrogen. Additionally, they make the soil more acidic, which is fine for some plants but not most.

Sawdust is the worst offender when it comes to drawing nitrogen from soil in the decomposition process.
Cypress mulch is to be avoided because cypress trees are needed where there are fragile wetlands.

Hay may be cheap but it’s not considered attractive, so it’s used mostly in vegetable gardens. It also contains weed seeds.

Straw is closer to being weed free but it’s still unattractive, unless chopped (and even then, not so much). It can also rob nitrogen from the soil. It’s used mostly in vegetable gardens.

**Bark is moderately expensive to expensive, slow to break down and good looking. Fresh bark can be toxic to young plants, so age first, or buy bark that shows some of the discoloration of age. And speaking of store bought, some brands are mixed with large amounts of shredded wood, which bleaches white, so look for an even dark color. It comes in nuggets and mini-nuggets, or shredded, with the shredded version preferred by many gardeners who’ve seen their nuggets wash away during hard rains. As to tree type, redwood is especially attractive but more expensive and not the best at retaining water, and cedar bark can crust, thus preventing water penetration, so pine or “hardwood” bark is best. Sometimes called pine fines, they’re actually fine-textured pieces of pine bark, aged and screened. Not only do they look great as a mulch; they’re excellent mixed into the soil as an amendment.

Wood chips or shavings are attractive, break down slowly, and are moderately priced and sometimes free from municipalities or tree companies. Still, because of their nitrogen depleting properties, I recommend them only on paths or play areas. (They won’t do much for your earthworm and soil microbe populations, either.)
Dyed mulches are usually made from waste wood like pallets and the dyes are reported to be nontoxic, but waste wood itself often contains arsenic and other toxins that leach into the soil. And they’re considered both unattractive and unnatural looking by many.

Rocks and gravel look good in rock gardens but they don’t improve the soil or prevent weeds very well. After they’re applied in planting beds it’s difficult for the gardener to get to the soil beneath. Plus, stones get dirty and need to have leaves and debris blown off and be “freshened” with new stones.

Other nonorganic mulches (rubber, anyone?) may work well under swing sets but I wouldn’t consider using them in gardens.

Sources

Takoma Park’s Department of Public Works has a pile of leafmold mulch there for the taking; any time, to anyone, no questions asked. Deliveries cost between $45 and $65 for residents and $65 to $105 for nonresidents. Call 301-891-7633.
The City of College Park sells three products:
1) Screened or “Smartleaf compost”(what I call real compost); fully decomposed black gold. It is an outstanding soil amendment but not the best for suppressing weeds as a mulch. It’s $11 per cubic yard.
2) Unscreened compost. It works well as a soil amendment and even better as a mulch because it suppresses weeds. It costs $7 a cubic yard.
3) Wood chips. They are great for paths or other nongrowing areas and cost $5 per cubic yard. Delivery fees start at $30. Call 301-474-4194. Supplies while they last; they’re taking orders now for their next batch of products available late this month.

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