Rock Mulch is Wrong

deanikkiMay 4, 2008

I am a Landscape Architect, and have a degree in Horticulture.

I feel I am informed on the proper placement and amendments to make plants healthy. I do wonder how and where I can change the rest of the world. . .not on everything but regarding rock mulch. I lived in Las Vegas for years and have been fighting the "normal" process of placing rock down as a mulch for planting beds. I have seen far too few pros to understand this practice. Organic mulch will add nutrients to the soil, retain water, keep plants cool, and has a nice look. All direct opposites to rock. Yet people still want rock! I moved to ID a few weeks ago. Now people are talking about this new great thing called permi-bark or perminant bark. The area is a buzz with this great new thing, I had hoped to move away from it. How can we change peoples understanding? I even had some glimmer of hope that the new "green" savy consumer would welcome natural organic mulches but that has not happened yet.

Anyway just my little rant about people spreading rock everywhere and then wondering why their plants struggle and their water bill just goes up all the time!

If any one knows the best method and avenue to change this practice let me know.

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While they are not often my first choice, rock mulches do have their place. And aside from the missing organic content, they do function exactly the same as an organic mulch - they retard weed development, conserve soil moisture by preventing evaporation, can moderate soil temperatures the same as any organic mulch and in the right setting, can look extremely attractive and appropriate. Especially in the southwest where arid conditions lend themselves to xeric plantings, rock or gravel mulches are quite applicable. Having lived in Las Vegas, I'm a bit surprised you haven't come to that conclusion yourself. And if one is growing succulents or cacti, rock mulches are preferred, both to reflect heat and to prevent splashing of rain or irrigation water back onto the plants. Scree or alpine gardens is another situation where a gravel or rock mulch is very appropriate.

Rather than crusading on this rather personal rant, it might make more sense to rail aginst dyed colored mulches, rubber mulches or worse, not using any mulch at all.

BTW, a lot of us here on the Professional Gardening forum are degreed and credentialed. That does not necessarily mean we hold all the answers to every situation. Or that our opinions should be law. As is often remarked on in the LD forum, the answer to any given question is most often "it depends" and context is everything.

    Bookmark   May 4, 2008 at 8:42PM
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The problem is that people like the notion that they can set it and forget it. Obviously, this is not the case. If the masses can't figure that out, you are only going to be able to change one person at a time when you deal with them as clients.

I don't see how this is a problem for you as a landscape architect. Your training should have given you the skills to pursuade a client to do reasonable things and not to do unreasonable things. Your second degree in horticulture should give you the added advantage of more scientific reasons why it is not good which should make you that much more convincing. You are the designer. These decisions are made under your guidance rather than you getting stuck with them after the fact.

It seems that you should be in control. Why is there a problem?

PS. I was originally licensed in ID and know several LA's there. Are you working for one there, or doing your own thing?

    Bookmark   May 5, 2008 at 7:31AM
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So, Gardengal, if rock is not your first choice, what is? I mean that sincerelly. I am planning a small project for the yard involving a fountain (already have), 4' to 5' bordering, perhaps 3 strong flowers, and mulch. In my mind I saw white granite. It seems that bark mulch might attract a lot of insects. So enlighten me. What other choices do I have for mulch?

    Bookmark   May 5, 2008 at 2:35PM
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Sailor, since I do not live in an arid climate and don't have a collection of succulents/cacti in the ground or an alpine scree garden, I mulch with a high quality compost. In my situation, that's my mulch of choice, as it continues to improve soil conditions over time, is moisture retentive in our relatively dry summers and it provides a wide range of plant nutrients so that I do not need to supplement with fertilizers. And it does all the other things that mulch is usually intended to do - suppress weed development, reduce soil moisture evaporation, moderate soil temperatures and provides a clean, 'finished' appearance. But virtually anything organic can be used as a mulch - grass clippings, leaves, composted manures, pine straw, straw, cocoa bean hulls, hazel nut shells and any manner of bark, wood chips, sawdust or other wood products. And less organic materials as well, such as shredded paper, carpet remnants (natural fibre only), fibre matting intended for this purpose, shredded tires (which I DON'T recommend) and the stone or gravel the OP is on the bandwagon about.

Contrary to common belief, a bark or wood-based mulch doesn't attract insects - some mulches actually repel certain insects because of the oils and tanins they contain. If you live in areas where termites are an issue, the recommendation is to keep the mulch a sufficient distance away from the house or any other exposed wood surfaces. But wood-based mulches are slow to decompose (which many consider one of their primary advantages) and they do not contain similar levels or range of nutrients as does compost, so they have less of tendency to add to improved soil conditions. And if they are incorporated into the soil, either accidentally or intentionally, they do tie up nitrogen while they decompose, so adding a high N fertilizer is suggested.

ps. I do grow a collection of succulents in trough gardens and containers and these I DO mulch with a rock/gravel topdressing.

    Bookmark   May 5, 2008 at 9:45PM
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Situations and dynamics of what is unique to a project should affect what is used. It is just what Gardengal is talking about. If you undestand the variation in what these different materials do and don't do, if you understand the environment that you are working with, then you can apply your judgement as to what makes sense for what you are doing, you can use them effectively. If you put them in situations that are counter productive it would be a mistake.

It is also a mistake to use these things counter productively in the wrong situation and then announce to the world that they are always bad and no one should ever use them.

One thing that drives me nuts (if anyone wondered what got me there) is when people find that something works or does not work in one situation and then project that as a universal practice that is either always bad or always good. That is almost never true of anything.

The more you understand the materials and their affects, the more you can make wise decisions on if, when, and how you use them.

    Bookmark   May 6, 2008 at 7:26AM
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Embothrium(USDA 8 Sunset 5 WA)

Well, that depends! Some recommendations, like not whacking back tops of trees non-selectively at planting time or not amending backfill of small planting holes for large permanent plants like trees and shrubs are based on factors that make this advise pretty much universally applicable.

    Bookmark   May 7, 2008 at 6:53PM
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I said "in one situation" and then project that as a universal practice. That is not the same as saying that there is nothing that can be universally bad.

Is that an example of taking a phrase that applied to a specific and having it applied universally to drive me nuts even more? Very clever. I like it.

    Bookmark   May 7, 2008 at 8:44PM
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Embothrium(USDA 8 Sunset 5 WA)

Post was about what may be true, and not about you. You I know very little about, and certainly have no reason to try to give a bad time.

    Bookmark   May 8, 2008 at 2:48PM
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A PhD in horticulture doesn't even matter. It is all about attitude. If you can't get your customers excited about the best way to go, find the right employee to help. You lack confidence.

    Bookmark   May 10, 2008 at 1:58AM
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rhizo_1 (North AL) zone 7

deanikki, I've always found that being proactive really helps when trying to educate the public (or even professionals) about something. Find a venue where you can conduct classes on a variety of gardening subjects, for example. You can always slip in the topic of the benefits of organic-based (as in carbon based) mulch into ANY horticultural discussion. Write an article for the local paper, but make it positive and up-beat. Don't lecture against the rock mulch, rather focus only on what's good about bark, pine straw, woody chips, etc.

    Bookmark   May 10, 2008 at 12:45PM
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All Generalizations are false... including this one. I am happy that I don't need to deal with rock mulch in my area (lower mainland British Columbia) as there is little call for it here apart from an unfortunate fad involving red lava rock about fifteen years ago. I must however accept that for aesthetic and cultural reasons as much as botanical that it is and will be part of the palette that we work with. Laag hit on a big source of the problem when he/she talked about the impulse to set it and forget it. This seems to present an obstacle to creating living, growing, evolving garden spaces, but it is also an opprotunity that most of us owe our (modest) living to. Our clients look to us for guidance and are prepared to follow where we long as we deliver the results.

    Bookmark   May 20, 2008 at 9:08PM
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I once used lava rock mulch quite effectively, IMO. It was at an end-unit townhouse we owned, and we were trying to cope with the horrible grading job done by the builder. We installed double French drains and then put lava rock on top. It looked great with the super dark brick front of my townhouse as well as the shiny deep green dwarf holly bushes in front of the bay window. After we did that the water flowed great and stopped going under the house, instead flowing over the sidewalk and into the side yard. It seemed to me to be a near-perfect solution, and when it was time to sell a buyer snapped that townhouse up quickly, even though many others were on the market in the same neighborhood.

    Bookmark   May 24, 2008 at 6:38PM
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I am not a professional by any means, but merely a college student becoming ever-increasingly interested in landscape design and function. I do not see the good in using anything other than organic, natural compost for mulch. When i first started seeing ground rubber being used, and even for use around the garden, i was appauled. Do we even know the long term effects of degrading rubber on plants, and its run-off? Also why do we use salt to help the freezing roads? Does that not seriously build up in our rivers and streams? I just dont understand our screwed up way of building things, and our whole system.

    Bookmark   June 9, 2008 at 12:40AM
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Embothrium(USDA 8 Sunset 5 WA)

"The Bottom Line
 Rubber mulch is not as effective as other organic mulch choices in controlling weeds
 Rubber mulch is highly flammable and difficult to extinguish once it is burning
 Rubber mulch is not permanent; like other organic substances, it decomposes
 Rubber mulch is not non-toxic; it contains a number of metal and organic contaminants with
known environmental and/or human health effects"

Here is a link that might be useful: Rubber mulch.pdf (application/pdf Object)

    Bookmark   June 11, 2008 at 8:09PM
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Bogart(6 Ont.)

Interesting discussion.

The city planted a red maple in a front yard a few years back. I built up a compost saucer around the planting hole, and then mulched it all with red clay chips, to match some of the other areas in the tiny front yard.

The city came back and said the clay chips would do the tree harm - attracting heat and damaging/drying the roots.

    Bookmark   June 18, 2008 at 1:00PM
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