Bark mulch vs stone

Looking at the pictures of the conifers at the National Arboretum, many of which seem to be planted with stone mulch, got me to thinking about this issue. I love the look of stone, but tend to feel that the bark mulch is better for the trees. Anyone have insight on this topic?

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

HG - That's a very nice piece you wrote about the things you need to consider if using a rock mulch. I have it down in one place at my home. Its located in an 18" strip between between the side of the house and a sidewalk. After years of trying hostas and other small groundcovers I found rock to be the perfect solution. It provides perfect drainage and, being flat, allows the best use of the walking space. However its definitely not maintenance free. The over hanging oak trees supply endless twigs, leaves and acorns that have to be removed by hand each year. Also , even though the sidewalk is a perfect egding material, the rock always manages to migrate out over the sidewalk. I get good exercise bending over and picking up the pebbles and tossing them back where they belong. I've not had to replenish due to a substantial weed mat underneath. Rock mulch does have it uses. But, in my view they are limited.

Exactly. Points well made, Snapple45. I don't encourage the average gardener to do extensive rock mulching until the disadvantages are experienced. Once down, it's a real pain to tear out... and I've done plenty of jobs where we have to remove old rock and disintegrated plastic. Ex...pen...sive!!!

This topic makes me scree-m...

It definitely is a hard topic.

Downright gritty.

But actually, it's sedimentary, my dear Watson.

You can tell it's winter and we're all going crazy....Thank you, HoosierGreen for the thoughtful reply. I have a small Japanese style rock garden so I'm familiar with keeping the rocks clean! I'm thinking that is probably enough work for me, and much as I like the look of stone, I'm probably better off without it for the other beds.

Well in SC stone mulch pretty much requires you own one of these. http://www.sears.com/shc/s/p_10153_12605_00920690000P?vName=Tools&cName=WeldingEquipment&sName=Welding%20Accessories&psid=FROOGLE01&sid=IDx20070921x00003a

You may be able to pull it off better up North but down here even with landscape fabric underneath you will still have stuff growing out of the stones every where.

Amen to that! It's good for people to be aware.