Mulch for perennial beds

newbiehavinfun(7a - Southern NJ)May 24, 2011

Hello all. I heard on a gardening radio show and read on a separate gardening blog that, while fine for around shrubs or trees, you should not use bark mulch or wood chips on perennial beds because it takes too long to break down. They recommended using a mulch that would decompose in a year, like cocoa hulls. Well, cocoa hulls are hard to come by around here, and I have a huge pile of ground up tree limbs (non-diseased) that I would like to use in my garden beds.

Is it really bad to use wood chips as mulch on perennial beds? If so, do you have recommendations for easily broken down, readily available mulches to use as an alternative? Thanks for your advice.

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kqcrna(z6 SW Oh)

I've been using wood mulch for almost 25 year. It disappears almost completely in a year.


    Bookmark   May 24, 2011 at 6:20PM
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newbiehavinfun(7a - Southern NJ)


Thanks for the response. If I could ask a few follow-ups Q's: How many inches thick do you pile on the mulch? Do you use cedar, hardwood, dyed or otherwise? I find that my neighbor's black dyed mulch disappears faster than the hardwood (maple) chips we have previously used.

I've also heard that wood mulch can tie up nitrogen while it decomposes. Does one add fertilizer to combat this? I suppose you could add mulch in the fall and it would break down sufficiently over the winter that this wouldn't be a problem....

    Bookmark   May 24, 2011 at 7:41PM
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Wood chip mulches are NOT ideal for perennial beds. How fast they breakdown depends a great deal on climate, the type of wood chips and the thickness applied. Wood chips are often used as a mulch as well as for pathways, playgrounds, etc. simply because they DO take longer to breakdown. They also tend to look kinda coarse :-) And while they only cause nitrogen tie-up/depletion at the soil surface or just below, for more shallowly rooted plants like most perennials and annuals, this can cause problems. A high N fertilizer will offset, however.

OTOH, mulching with compost is nearly ideal. Aesthetically, it looks much better and routine mulching with compost will virtually eliminate the need for any additional fertilizers. I mulched my old garden for nearly 25 years with nothing but compost and never needed to use any fertilizer except in containers

    Bookmark   May 24, 2011 at 8:56PM
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That's what I was going to say.

    Bookmark   May 24, 2011 at 10:56PM
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I'm not sure why anyone would believe that any mulch material that breaks down slowly would not be a good material to use in a perennial bed, but many people do have odd ideas. I have used wood chips as mulch on perennial beds with no problem, except on occassion having slime mold, Dog Vomit Fungus, show up. Since any mulch material, other than stone or rubber, will aid in moisture retention, weed suppression, soil temperature control, and add organic matter to the soil any mulch material is good to use.

    Bookmark   May 25, 2011 at 10:17AM
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Let's look at this a little objectively :-) Different types of mulches deliver different benefits to the garden. ANY kind of mulch can be used on a perennial bed.....even rock, gravel, recycled rubber, or old carpeting, if that is your desire. They will ALL help to insulate the soil, conserve moisture and suppress weeds.

But not all will add to soil fertility and tilth in the same manner. Inorganic mulches (gravel, rubber, etc.) not at all, wood based mulches to a modest degree but over an extended period of time and something like compost or composted manure, quite rapidly. If this is a primary intent for mulching, then it stands to reason that something that breaks down rapidly is going to provide more bang for your buck than something that holds up for an extended period before decomposition, like wood chips or bark.

The other aspect to consider is the root systems and nutrient demands of the plants in question. Trees and shrubs have wide spreading root systems that can access soil nutrients over an extended area. And they tend to have a more uniform growth habit, sustained over many years, so no need to absorb large quantities of nutrients to promote fast, rapid growth at a primary time in the growing season. Perennials have a more concentrated and shallow root system and need to find required nutrients close by. And, because the vast majority die to the ground each year and then return with a huge push of rapid growth in spring, their nutrient demands also tend to be concentrated to a similar time period. Especially N, which is what all that rapid new spring growth requires.

That is why I consider wood chips or other bark based mulches less than ideal for perennials. These mulches don't break down that rapidly - this is a primary reason why bark chips are recommended for long term container plantings.....they hold up for an extended period. And they tend not to be a huge source of available nutrients. In fact, the decomposition process for wood-based mulches tends to tie up nutrients rather than release them for the plants to absorb.

And since cultivation in a perennial planting bed tends to be far more frequent than with trees, shrubs or other woody plants with the need for routine division and often transplanting or adding new plants, it is inevitable that mulches will get mixed into the soil with this activity. When that happens with wood-based mulches, there is a big risk that nutrient tie-up will be increased. And the plants can suffer, unless this is addressed promptly.

Finally, there is an aesthetic issue to consider. Wood chips or chunky bark just don't look as good mulching perennials as does a finer textured, richer looking product. Like compost :-) This may not be perceived to be as important as other mulching considerations, but it is one of the reasons folks do apply a mulch. Combine this with the other issues outlined above, then it becomes very clear why a less long lasting, faster to release nutrients and OK to mix into soil mulch - like compost - makes perfect sense.

    Bookmark   May 25, 2011 at 12:00PM
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tishtoshnm Zone 6/NM

Newbie, There are ideal ways of doing things with reasons why but sometimes those ideal methods can run into reality. To me, the key words in your question was "I have." I would say always use what you have. If you have the chipped stuff, use it. One company out here sells a mix of compost and wood chips so you could mix what you have with compost and make it a feeding mulch. Or you can put compost down and then put what you have on top of it.

At my house, we are harvesting dead cholla cactus skeletons, tossing them into a wheelbarrow and pounding them with a sledge hammer for mulch. I have the cholla but my money has too many other demands on it for me to mulch with something I have to pay for (an added bonus is that it is wind stable to boot)!

Enjoy your gardening!

    Bookmark   May 25, 2011 at 12:44PM
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newbiehavinfun(7a - Southern NJ)

Thanks, everyone, for the advice.

tishtosh, I think you're on to something. The landscape supply place near me sells mulch, topsoil, and mushroom soil. I could ask them if they would mix mushroom soil with mulch for me next year, because that sounds like it would both feed and block weeds.

Since I'm just starting with compost, I won't have any this spring. For now I was thinking of getting the free compost from the municipal lot, but I'm a little leery of compost that I didn't make myself. I spoke to someone at the municipal waste/recycling dept. who said that it is wood chips, leaves, and grass clippings, but of course there are going to be weed seeds, especially if the pile wasn't hot enough to kill them, right?

The wood chips I have are from last year, so they have composted a bit and are about half the size they were when first chipped, so that is also a factor, and I did put a layer of mushroom compost (hot stuff) this spring. Well, it's all one big experiment, isn't it? :-)

    Bookmark   May 25, 2011 at 4:23PM
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Some people have the idea that "mulch" is either wood chips or shredded bark, instead of any material you place ON the soil. Mulches can be compost, shredded leaves, spent mushroom soil, as well as what gardengal outlined above. Some are good and some add nothing to your soil while some (rubber) will add contaminants.
If you have a landscape material supplier that will custom mix for your that is good.

    Bookmark   May 26, 2011 at 7:41AM
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ralleia(z5 Omaha, NE)

There's an excellent book on the soil food web called "Teaming with Microbes." It states that perennials, shrubs, and trees grow best in fungally-dominated soils (as opposed to the bacterial soils that annuals prefer). The preference has to do with the form on nitrogen most available in the two soil types.

The book recommends "brown" mulches for perennials, which includes wood chips, since brown matter supports fungal activity. The pinnacle of brown mulches is held to be shredded brown leaves.

They recommend first applying 1 to 2 inches of compost around all the perennials, and THEN brown mulch. Compost tea applied at the end of the growing season is supposed to speed decomposition of the organic matters and help support fungal activity in the soil.

    Bookmark   May 26, 2011 at 9:19AM
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newbiehavinfun(7a - Southern NJ)

I spoke to the landscape supply company near us, and they now offer compost! We're having 10 yards delivered this weekend. I would have gone with the free municipal compost, but they don't have a bulldozer handy to put the material in our truck. I just couldn't picture shoveling the compost into the truckbed and then shoveling it out again, and then repeating that process five times. Maybe for a smaller bed, or for lasagna gardening, but not my large front beds. No way.

    Bookmark   May 26, 2011 at 2:08PM
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According to Dr. Alex Shigo, late Chief of Research for the USFS, trees and shrubs grew best in, and made, soils that were fungal dominant and flowering plants and vegetables grew best in bacterial dominant soils. The fungal dominant soils were those where woody mulches were used, trees and shrubs dying, limbs falling aand being digested in place, etc. while bacterial dominant soils had mulches made from vegetative materials, such as shredded leaves, compost (not high in wood particles), and other similar types of waste.

    Bookmark   May 27, 2011 at 7:32AM
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