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This question is just concerning the realm of landscaping for flowers around a house. We need to add mulch again this year, as the previous mulch has broken down enough that there are some thin spots and some spots not covered at all.

We noticed that every place now carries rubber mulch. Would this also be good to use in our various flower boxes around the house? What would be the benefits and drawbacks? If rubber mulch lasts indefinitely, how long does it keep its color?

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Rubber mulch is a better insulator which may be important in very hot or very cold climates. It also doesn't absorb or retain water which helps keep it weed free since weed seeds won't germinate in it like they can in some other types of mulches. It will last a long time. Different agencies and labs have tested the use of rubber mulch in playgrounds and found it to be safe to people and the environment. I have seen some sources state that rubber mulch used approved for playgrounds may be safer but I'm not sure.

It will eventually break down in 20, 30 maybe more years. When/as it breaks down the stuff the tires are made from I guess would wind up in the soil which I can't imagine is good. Also, some chemicals used by some tire manufacturers may leach into the soil.

I did find this one account of health issues from rubber mulch along with this linked report. This other well-referenced document discusses some issues with rubber mulch.

It's still fairly new and I wonder if people are pushing it because they don't know what to do with all these used tires.

Natural mulches feed the soil and increase biodiversity. That's one of the main reasons I use it. I didn't use mulch in the past and I notice a big difference in the soil now compared to years ago.

Some people have an issue with shotgun fungus (aka artillery fungus) with wood mulch. It appears to be more of a problem with wood instead of bark mulches and cedar, redwood and cypress do not appear to be affected because they decompose slower. I believe licorice root mulch is also less prone to shotgun fungus.

I like to use cedar mulch. It's a little more expensive but I like the look and smell plus it lasts longer Every spring I fluff it up and spread it out evenly. Every 2 or 3 years I may need to add a little more. After the first season it turns grey. I don't mind the color but I've been thinking about using mulch dyes.

I really want to switch to compost as mulch Looks like black dyed mulch (which I like) and is even better for the soil. I'm not quite making enough compost to use in the garden yet and have left over for mulch. I might have to buy the initial compost and then hopefully be able to replenish it with what I make.

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    Accepted for raising the health concern, with the report. I would like to know, however, how they can all be labeled "non-toxic" when there are obviously going to be some chemicals involved. How bad does something actually have to be to receive a toxic label? – Mike Guthrie Apr 29 '14 at 14:51
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    @MikeGuthrie "non-toxic" is apparently a meaningless marketting term. See more here greenerchoices.org/eco-labels/label.cfm?LabelID=131 I also added another link with some more info on rubber mulch that has a lot of references. – OrganicLawnDIY Apr 29 '14 at 16:03
  • Black is not beautiful in nature. It doesn't look natural. Go for a dark taupe. The most beautiful mulch I have ever seen and the only one I will use on my projects, my home is mulch made from human sludge mixed with sawdust and completely decomposed. It is no longer human sludge nor sawdust chemically and smells wonderful. No pesticide residue, no weed seeds...a little high in heavy metals but 3/4 of the world fertilizes their crops with human manure. We don't, we supposedly know better. Look up and see Chemtrails. 60 years we have been spraying heavy metals...plus! – stormy Jun 21 '14 at 23:27
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Mulch should FEED the soil! Un-decomposed organic matter, rock, plastic, rubber...do nothing for your soil. Your plants NEED a live, thriving, communal soil or they won't thrive. Healthy soils have micro and macro organisms (the more the better) that need to be fed. These critters eat decomposed organic material on the soil and digest it then poop it out in your soil profile. This activity mixes organic material into your beds and aerating at the same time. They also work with the plant roots to help plants uptake the nutrients they need to make their own food and be vigorous.

These important soil organisms go to sleep if all there is is non-decomposed bark, wood chips, straw on top of the soil. The decomposers get busy of course but they need a lot of nitrogen for their fuel to do the decomposing. Making less available for use by plants.

I remember researching this rubber mulch (for a play lot) and found this material was FLAMMABLE. Maybe that has changed...but not a good solution for plants.

If you need mulch for ornamental plant beds, not vegetables, the BEST mulch in my opinion is Gro-Co. Human poo mixed with sawdust and completely decomposed. It is tested by law, you can get test results, there are no WEED-SEEDS, no PESTICIDE RESIDUE. 2" smothers existing weeds and weed seed and looks gorgeous. A natural dark taupe, no rocks, no sticks, a very fine texture and...it smells NOTHING like what it came from...honest. You have to check in your own city for who makes this product. Gro-Co was just the name of this product in the Seattle, Washington area. This stuff looks great, your plants will actually look better in one week (no kidding), it is better at weed suppression than bark, plastic...yet it also feeds your soil which helps your plants function with vigor in making their own food. Kinda kills 3 birds with one stone? Grin. Hope this helps...

  • Adding a little non-decomposed whatever on the top of current mulch that is composted is not a problem. It I when a non-decomposed is added on top of poor soil that the problems comes. (Think what happens in woods every year...) – Ian Ringrose Apr 28 '14 at 11:02
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    Very good answer. When you mention the rubber mulch is flammable, do you mean more so than wood chips would be? – Mike Guthrie Apr 28 '14 at 20:13
  • Yes...they tried once to make a road out of recycled tires. It went up in flames quite soon after being constructed. – stormy Jun 21 '14 at 23:12
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Providing some links to some good material I found while doing my own basic research.

This document from Nature's Way Resources addresses each of the alleged benefits of rubber mulch, and provides all the references.

This post at Wall Street Journal points out that rubber mulch from steel-belted tires (common) may still have some steel wire inside (processing uses magnets for removal, but not 100% effective), which hadn't occurred to me, making a bit of an unexpected hazard until it rusts fully away.

I'm finding a lot of negativity toward rubber mulch (such as here), but not any (non-corporate) support for it. I'd like to get both sides covered, however. Will try to update here with more links, if I find anything helpful or decisive.

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