Wanting to understand mulch


For a little background to my question, the power company right aways through my area just received their periodic tree service, and I had two large truck loads of wood chips dumped at my place. I also for the first time recently got a small pickup load of mulch from my county dump. (I assume that after another year that what I just had dumped here will look just like what I got from the county dump.)

What should I know about using mulch? What are the advantages/disadvantages of different types of mulch? What mistakes can I make or problems can I invite using mulch like I’ve got now? How does mulch like I have now affect nitrogen availability for trees? I don’t want to use herbicides, by the way. I’ve mostly just allowed a lot of grass competition with my trees so far. That doesn’t seem to have bothered my pears or chestnuts any, for example, but I suspect my apples languished a little for it, and I think my pawpaws really languished. What about voles and other rodents? What does mulch mean for them?

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You’re going to get a lot of different opinions, but I’ll share my experiences. I’m in the city and the city maintains a large dump comprised mainly of leaves and tree branches. They sift the material a number of times, in order to remove most of the debris that is picked up along with compostible material. When I started my 2 rose gardens, I purchased 30 pickup truck loads of this compost and tilled it into my garden. The roses thrive in it, and I would presume anything would do the same. But over time pieces of broken glass work their way to the surface, so you have to watch out for these. Your situation is a little different, but yet similar. You can use the compost in the same manner, once it has aged somewhat. If you apply the fresh wood chips as mulch, it’s going to deprive the trees of nitrogen during the decomposition process. So I would not add them, until they’ve decomposed, then you can use them as mulch. Yes those piles are going to attract bugs, rodents and snakes. I’m also a firm believer in maintaining grass/weed free zones around all of my trees. If you don’t, you’re forcing your trees to have to compete for water and nutrients with the grass/weeds. I use pine straw as mulch for all of my trees, and pine bark for my blueberries. But all of this stuff is free to you, complements of the power company, so I’d use it with these thoughts in mind.



You’re speaking my language here. I put 60 loads of wood chips on last year. I use herbicide, but don’t like to use it around younger trees, so mulch is a big help in that regard. It does a good job smothering grass and a lot of broad leaves, but know that some weeds will push right up through it.

Plantain, hogweed, sedge, morning glory, and particularly bindweed. I don’t know if you have bindweed in SC, but it can be a terrible pest here.

I haven’t noticed any nitrogen deficiency using wood chips as mulch. Strangely, I think I see the opposite. No doubt Rayrose is correct that bacteria first draw nitrogen from their environment to break down the wood (later releasing it) but my theory is that since the roots aren’t directly exposed to the wood chips, they don’t experience that effect. Further, I hypothesize the most broken down particles (richer in nitrogen) are most subject to leaching, and therefore leach down to the root zone during rain, sort of like a compost tea, which may actually add N. This is really conjecture on my part, based on simple observation of the trees.

As Alan has brought up, there is a risk prolonged use can cause excess vigor in trees. This is supported in the literature, but from what I’m seeing this problem may be quickly remedied.

I’ve had a hard time obtaining enough mulch, so some older trees have had to go without it here at the house. They are the most tolerant of weeds or herbicides, so some of those trees go without. Last season I noticed some of those trees actually didn’t put on enough growth, despite lots of mulch applied in previous years. This concerned me enough I thought I was going to have to apply chemical N to some of these trees, but I’ve since been able to get some mulch on them, so I’m going to hold off on the chemical N for now.

You asked about rodents. My experience is different from Rayrose in that regard as well. It seems to inhibit voles for me. Again, this is theory, but I think voles don’t like it as well because, with a good mulch pack, the entrances to the vole tunnels keep collapsing on them. Like us, I think they want to build a house where they can always find the door. At the farm, where I don’t have mulch, I have voles.

Like Rayrose, I do get trash in the chips, and this is a problem. I had to quit accepting truck loads of leaves for this reason. A lawn service was delivering leaves, but there was so much trash, I could fill the cab of my pickup with it some days. I also get logs in with the wood chips, but they aren’t too bad to sort out.

Wood chips can cause the soil to retain more water than is good for the trees (depending on how much rain and type of soil) but for me the benefits outweigh the costs.


My experience matches Olpea to some degree and the advantage of fresh mulch is that it is effective as weed control for that much longer than aged.

Olpea’s theory about mulch nourishing potential seems sound and if you can get woodchips from the electric co. it is usually mostly from smaller wood which has much higher nutrient content and higher nitrogen to carbohydrate ratio. Cuttings while trees are in leaf more so, but they transfer much (or at least some) of the N to the buds before they drop.

My east coast voles, however, are fond of mulch, maybe because I don’t pile it on as heavy as Olpea- usually only going about 4" deep.

Rayrose is sure dead on about municipal compost serving roses well- it is usually mostly made from grass and leaves and creates a superior compost. Roses completely thrive in dark, rich well drained soil (so do most plants but roses seem to require it). That compost goes a long ways to getting you there. Best deal in horticulture when the town gives it away or charges a reasonable fee for delivery only.

In some soils mulch can cause N deficiency as Rayrose warns, but that is usually in conditions of poor drainage or when applied to young annual plants. I have had an issue with very young peaches of N deficiency when using shredded wood (the fancy wood mulch you pay for) but it is an easy thing to adjust to with a handful of urea watered in.

If the shredded mulch is moist it breaks down quicker than chips and pulls more N out of the soil. If it is dry it can mat up and stop water from penetrating the soil, in which case it needs to be stirred. Its main advantage besides perhaps a more finished look, is it requires less to effectively block most weeds (not bindweed) so reduces application time.


Do any of you have any thoughts on thickness? I have heard conflicting reports (coming from different extensions) that talk about creating a “dead” layer if it is placed on too thick. The top roots need oxygen and should be closer to the soil surface it states and by going thicker than 3 inches creates this layer that can kill the tree. Other reports talk about needing to have a surface that is at least 4 inches thick to prevent weed growth and to help conserve water. I personally go 4+ inches and on my soil mixture I created for my peach trees planted last year I have not noticed anything wrong.

Also have any of you used Cedar mulch before? I seems to work well in preventing critters from setting up shop but I have also noticed that any fruit tree I have it around seems to have stunted growth. I’m wondering if its due to the cedar not breaking down and replenishing the soil. It seems as if it creates a nitrogen-sink environment and it just sucks it right out of the soil. My peaches with the cheap basic mulch from the home center have put on around 4-5 feet of growth (with one putting on well over 7 feet with a mid summer pruning) and other trees put in at the same time surrounded by cedar putting on maybe 1 foot with the same pruning.




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I’ve used mostly mechanical equipment to apply the mulch, so the thickness variance is not consistent for my trees. I rake it down by hand and it probably averages about 3".

I think it’s true in some cases mulch can inhibit oxygen. I also think this is related to retaining too much water in some soils. That’s one of the drawbacks of mulch. In a heavy soil, with lots of rain, too much mulch can suffocate the roots of young trees.

Another disadvantage is that in extremely dry years, too much mulch can block light rainfall to the roots, preventing the trees from getting a drink, when they otherwise would have gotten one. Generally speaking though, I think the advantages of soil water conservation, outweigh the disadvantage of blocking rainfall.

I can’t comment on cedar mulch since I’ve pretty much used what the tree trimming companies have given me. Sometimes it contains cedar, sometimes not. Once I received a lot of black walnut mulch, which contains the natural herbicide juglone. I never noticed it affected mulched trees, but did affect some tomato plants mulched heavily. Tomato plants are generally much more sensitive to herbicides than fruit trees.

I wonder if the difference b/t Alan’s vole experience and mine has to do w/ the two different kinds of voles. I think we deal with the more “above” ground meadow vole feeders. Since they have to go out there door to feed, a reliable front door may be a bigger deal to them.


Nope, meadow and pine voles both like mulch fine here.

I’m not always crazy about this persons interpretations but she’s certainly searched the literature for scientifically derived info about various mulches including cedar.


I know that no rose grower would ever use cedar chips as mulch. It has a toxic
effect. I don’t know about fruit trees, but personally I’ve never used wood chips
on my trees, only pine straw. It breaks down faster than wood chips, doesn’t retard rain absorption nor root aeration. I replenish mine every year. I use about 1 bale per 2 trees with a 5-6 foot diameter ring around every tree.


I have used cedar mulch or had clients use it, both the bark nuggets and shredded and observed no negative affects, although there was no real control because every fruit tree at these sites was mulched the same way.


It could also be the soil that I have here. I’m on what used to be farm land 30-40 years ago. Where my original trees are at its the area they disturbed to build the house. The back portion of the yard was undisturbed. You wouldn’t believe what I’ve found. Rocks larger than my head, small spools of barbed wire that’s been rusted solid, huge tree limbs rotting away buried 3-4 feet deep, etc.

But then again trees planted in this area too have all stunted that have been covered with cedar. The only trees that I didn’t cover with cedar have been my 12 new peaches. Those however only have native soil about 14-15 inches down… The top 14-15inches is my own soil mix that seems to do extremely well for me. These trees have nothing more covering them but the cheap dollar bag mulch from the big box store.


Cedar does have turpentine in the leaves and bark and could hinder the roots. It would probably be worse in areas that have less rainfall. I know that it has enough to cause problems in pets. I would not use cedar mulch on young trees but again, it is just an opinion.


I mulch very heavily with wood chips in my dry, cooler climate. No problems with rodents. They do recommend that you rake mulch away from the trunk for that reason. I don’t bother, but it certainly seems like a good practice. There is quite a lot of juniper in the chips. Does that count as cedar? If so, I don’t notice any ill effects. Maybe that explains the lack of rodents.

I’m fairly certain that chips spread on the surface don’t deprive the soil of nitrogen. Anyway, I scratch the fertilizer in under the mulch. Adding N is only the easiest thing in the world to do.

My suspicion is that the mulch keeps the soil a little too cool for optimum growth in Z5. I’ve tried half-heartedly raking the mulch away for a few days in early summer, but with no effect.


I believe any delay in active root growth because of cooler soil is more than compensated by the fact that feeder roots can function right at the surface and mychorizal strands might even extend into the mulch itself if it is moist. All research I’ve seen indicates substantially improved vigor as the result of mulch.

Each species functions best at certain soil temps. Peaches like the soil somewhat warmer than apples for best growth


Have any of you experience using flattened cardboard boxes under mulch? I spread about a dozen pick-up loads of free municipal arborist mulch about 4-6 inches deep over cardboard around raspberries, gooseberries, bush cherries, kiwis, and blackberries planted in a former pasture in order to kill the weeds, mostly goldenrod and grasses, but hesitate trying that with my many new fruit and nut trees. I know there are a lot of voles under the cardboard, so I have begun a trapping program. I keep the cardboard and mulch at least 10 inches from the plants. My main concern is if the trees would get enough rain and oxygen, plus the vole problem if using cardboard along with the mulch, although I do have hardware cloth around each tree. I have found from past experience that mulch alone doesn’t prevent the weeds from coming up, and I have several acres to tend without power machinery, except a rototiller and Swisher grass trimmer. The ground is too rough from groundhogs to use a lawn mower there. Things look wonderful after adding the cardboard and mulch, but I don’t want to cause problems down the road with the cardboard. I have also used newspapers under the mulch near many of the plants, but have an unending supply of cardboard, while newspapers are harder to come by.


Bindweed is a rotten SOB. I hate the stuff. Been battling it for years.


I’ve never had any problems laying down cardboard over my lawn when expanding/making new beds. Turns into worm castings pretty quickly for me, within a month or two. I just do a single layer or two where it overlaps and cover with 2-3" of wood mulch (whatever I can get cheap/free). The cardboard saturates pretty quick and don’t seem to stop water infiltration. Usually kills all the lawn (assorted grasses, clover, and creeping Charlie) except the tough buggers like violets and sedge.


Thanks for that info, Ampersand.


Like Apersand, I’ve not had any problems with cardboard. Once I needed to get rid of a ton of old books I didn’t have room for (I know this will make book lovers cringe - I love some books too) so I dumped piles of them next to the blackberries and dumped mulch on top. That was some good weed control. I never throw paper or cardboard boxes away, but lay them down before applying wood chips. The cardboard/paper disintegrates pretty fast, but every little bit helps.





Mulch encourages the right types of soil organisms such as earthworms and beneficial fungi. I recommend putting aged cow manure or humus down first before applying wood chips. Mulch helps maintain moisture. Anything else you want to apply to the soil prior to putting down wood chips will pay off later. I know some people say don’t baby your trees but it works for me.