Trees, Shrubs and Conifers: Bark mulch vs stone, 0 by HoosierGreen

HoosierGreen wrote:
If your soil is excellent to begin with, stone mulch is an option worth considering. Bark mulch, or any other organic mulch, has the benefit of enriching the soil over the years as it decomposes. In 99% of the landscaping installations I do, I push for bark mulch. It does have to be renewed every other year or so, but I consider that helping the soil and the plants. It's a common misperception that rock is a one-time-forget-about-it mulch, which is definitely not the case, which I will explain in a bit.
But, the first consideration is cost. Most any rock can be used for mulching, and locally native stone is the cheapest. However, many of the most popular rock mulches can be very, very expensive. A cubic yard of rock usually covers about 100 sq. feet of area. A cubic yard is usually a ton or a little more, depending on the rock of course. In my area of the country, we have a natural resource called "river gravel" which is like large pea gravel, deposited by the glaciers. It's cheap, about $10 per ton if you go to the gravel pits to pick it up yourself. Other rock mulches that are brought in from other parts of the country range in price up to around $200 a ton. And those prices are NOT figuring delivery charges. A normal front yard landscaping needs at least five tons of rock, which with delivery would cost from under $200 to over $1100... AND then there's the labor! Shoveling and spreading a ton of rock is a lot more work than a yard of bark mulch.
When you use rock as mulch, you will need to spread some type of underlay fabric to keep the rock from eventually disappearing into the soil. Many people make the mistake of using cheap plastic sheets (like painter tarps). Bad idea, as they will disintegrate in a few years and you end up with a real mess. You should use a weed fabric designed for landscaping, and they range in cost from a few pennies per sq. foot to about 50¢ per sq. foot. It can be a real chore to lay around existing plants, and you have to allow for growth.
Edging is a concern for some cases, to keep the rock from spilling or scattering into grass, etc. Another cost, but you can leave it out with a good spade-cut edge if you want.
The biggest thing to keep in mind though is that rock is NOT maintenance free, which is what most people aren't aware of to begin with, and actually think the opposite. Over the years, low spots will appear and need some replenishing. But, the biggest thing to remember is that to avoid weeds, you must keep the rock mulch as free as possible from any leaves, needles, blow-in dirt, etc. that will decompose in-between the rocks and provide a growing medium for weeds. They will get a start in the thinnest layer of organic matter. The gardener must blow out any accumulating leaves, etc. at regular intervals to avoid this. Once a layer of decomposed matter gets in the rock, you're back to weeds to content with every year.
So, when using rock for mulch you need to consider: 1.) Initial cost of the rock, weed fabric, and labor 2.) Health and condition of the plants and soil and 3.) Maintenance
(One more thing: If you like to add plants, move things around, plant bulbs, etc., working in a garden with rock mulch makes those tasks much more difficult.)

I obviously prefer using bark mulch. It's cheaper and great for the soil and plants. Yes, it has to be renewed, and that is a recurring cost down the road, but I look at it as a soil enhancer. (In the 30 years I've used it in my gardens, it has helped change my heavy clay soil into wonderful, deep loam.) The final decision is up to individual gardeners, but they should be fully aware of the pros and cons of their choice. Rock mulch definitely has its uses, and can be very attractive in rock and alpine gardens (duh!), with dwarf conifers, desert landscapes, dry river bed plantings, Japanese gardens, and others. However, for the average landscape of perennials and shrubs, the gardener should carefully weigh the advantages and disadvantages.


This message was edited Jan 3, 2010 10:53 AM