All about Mulch
Mulching bare ground and around plants is THE single most important thing that sustainable gardeners do to create low-maintenance, healthy gardens. (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. Yep, I’d say those are the big three.
Oh, where to start? What’s not to like about something that does all this?
- Suppress weeds
- Prevent drying out of soil
- Prevent erosion
- Reduce compaction of soil
- Moderate soil temperature
- Prevent mud splatter on plant and hard surfaces, like your house
- Add nutrients to soil AND enable the soil to better use soil nutrients from any source
- Increase the populations of earthworm and beneficial soil microbes
- Make gardens look well kept and amenable to planting — like gardens
- Every year, when the soil has warmed up – midspring in most of North America, earlier in hotter places. Gardeners in cold climates often do their mulching in the fall, however, to prevent soil heaving through the winter months of freezing and thawing. More mulch can be added in the spring, as needed.
- AND immediately after disturbing the soil, especially for planting something.
- AND to cover bare ground at any time.
- Remove weeds.
- Loosen top of soil (a tool called the cultivator does this job very quickly), incorporating what’s left of the old mulch into the soil as you do it.
- Apply 2 inches of mulch.
- Never mulch on top of plants or have mulch touching their stems and most important of all, don’t pile it up against tree trunks. (The result is called a mulch volcano and it’s horrible for tree health!)
- And avoid putting mulch against your house, unless you’re trying to attract termites.
Types of Mulch (Asterisked are Best)
If your soil is already good, then you might choose pine needles, shredded wood chips and bark, which are all long-lasting and look fancy. But if your soil isn’t great, mulching is far and away the easiest way to improve it, as long as you use nutrient-rich, fast-decomposing mulches like compost and leafmold.
Another factor to consider is that some mulches use up soil nitrogen in the process of decomposition, the worst offender being wood chips, which should only be used on paths or play areas, never around plants. There’s disagreement about whether dry leaves, sawdust, and pine needles rob soil of nitrogen, however. One horticulturist I consulted recently opined that if used in layers of 2 inches or less, there’s no problem. 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, 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.
**Compost is plant or animal waste that’s completely decomposed and now looks something like coffee grounds — black gold. It’s expensive but wow, what a great source of nutrients it is, and a boon to soil structure. (It’s also better than anything else as a soil amendment — meaning something that’s mixed into the soil itself, maybe half and half, often at planting time, though I use free leafmold for this purpose.)
Here’s the other negative about compost: weeds just love it. So while it doesn’t come with weed seeds in it, wind-blown seeds land on it and thrive. So compost used as a mulch isn’t as good at weed prevention as the other types.
Oh, and some gardeners, including myself, don’t like the look of it on top of the soil because it looks like, well, soil. To me a garden that’s “mulched” with compost doesn’t look mulched unless it has some other mulch on top of it, an organic one that hasn’t fully decomposed.
**Leafmold is simply chopped and aged leaves. Though it’s rarely sold, it’s pretty easy to make and many local governments provide it for free or very cheaply, so check into it. (Or inquire about starting a leafmold mulch program in your area. Even better are the governments that provide leafmold AND compost AND chopped wood.)
But back to leafmold, it’s superb all-around — nutrient-rich and excellent as mulch or a soil amendment.
Leaves are not attractive unless shredded first, which is highly recommended to speed their decomposition and prevent matting and subsequent smothering of your plants. This can be accomplished simply enough using a rotary mower with a grasscatcher can be used.
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 they 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. Redwood is especially attractive but more expensive and not great at retaining water. Cedar bark can crust, preventing water penetration. So pine or “hardwood” bark is best (see next bullet point). 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.
**Pine Fines are fine-textured pieces of pine bark, aged and screened. Looks great as a mulch but is also outstanding mixed into the soil as an amendment.
Wood chips or shavings are attractive, break down very slowly, and are moderately priced and sometimes free from municipalities or tree companies. Still, because of their nitrogen-depleting properties, many experts recommend them only for 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 woods often contain arsenic and other toxins that leach into the soil. But then they’re so unattractive you wouldn’t want them anyway.
Rocks and gravel look good in rock gardens but don’t improve the soil or prevent weeds very well. And after they’re applied in planting beds it’s difficult for the gardener to get to the soil beneath. Plus, stone gets dirty and needs 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.
But I should add here that some horticulturists assert that any and all of these mulches work just fine, as long as they’re not used in layers thicker than 2 inches.