Opinions on combining shredded bark and compost as mulch

Question

I'm having a hard time finding anything through search and I'm hoping others here might have experience or opinions doing what I want to do.

I really like the look of black mulch (hardwood mulch dyed black commonly used in the USA) but dying my existing mulch is not practical and I'm not too keen on adding dye in the first place.

I have some garden beds that are currently mulched with cedar bark mulch. I'd like to start mulching with compost instead for a number of reasons, not just color.

I don't want to have to go through the hassle of removing the old mulch first and was hoping I could just start applying compost over top of the existing mulch (maybe 2-3" of existing mulch).

Has anyone done anything similar to this and has info on how it worked out?

I'm specifically looking for any information from people who have tried this such as will the compost help the cedar break down faster? Will the compost seep down between the bark after a few few rains and look nasty? Will the combination cause problems such as poor water infiltration?

It looks like I might be doing a little small scale test as a critter decided to dig up a shrub I recently planted and scattered the compost that was in the whole around the mulched area. :(

Answer 1

I'm not familiar with black mulch, but this year, I covered my existing cedar mulch with 2-3 inches of leaf mold. The plants in the beds with the added mulch did wonderfully. The cedar mulch is breaking down under the leaf mulch, but I'm not sure whether it is doing so any more quickly than it did before or not. I think I'd try adding it over the top, personally.

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Editing to add a picture. The leaf mold breaks down quickly, so at this point in the year, it is looking a little rough! It was much fluffier in spring and even in mid summer. If you look, you can see some of the cedar mulch poking through:

Answer 2

While adding compost on top of a bark mulch is possible, I find that the compost, since it consists of finer particles, fills in the gaps between the pieces of bark, with the result that I still see the bark after a few good rains. The compost will also degrade faster than the bark, so you are going to see the bark that is there now for the next several years. If the appearance of the bark is an issue, I would rake it away from the front of the beds and other areas where it is particularly visible, and replace it with compost only. You can redistribute the bark that you raked to areas that are not so visible.

With regard to water infiltration problems, I have not seen as obvious a problem with compost as with a peat moss mulch. With a peat moss mulch, the water beads on the surface. Compost is not as uniform in particle size as a peat moss mulch, which makes it more porous.

Answer 3

This article gives step by step instructions of how to create black mulch; it takes about 8 weeks.

Make Your Own Black Mulch

An overview involves:

• spreading manure over dampened cardboard layers
• adding a layer of vegetation (scraps and cuttings)
• adding a layer of peat moss (which I, personally, like)
• then repeating the layers (ensuring it is kept damp throughout the process)
• covering the pile with tarp, ensuring it remains moist
• after 9 weeks the pile is ready to be mixed and used as black mulch

There instructions are more detailed if you follow the link; it specifies the thickness of specific layers, and safety precautions.

Personally, I see no value in dying mulch. I have used cedar; as @Randy noted in the comments, it does turn grey. It takes a long time to break down. I would not use it again, as I suspect (and this is my own opinion, from experience) that, as it breaks down, the by products are not the best for creating a healthy garden). I wouldn't think it is such a bad thing if you are improving the soil by adding good quality mulch on top. It sounds like you already have a reasonably thick layer of mulch there. I would be reluctant to add another 2 inches straight over this; having said this it really depends on the types and stages of development of the plants that you are in the garden bed you are mulching.

Some plants can cope with a rising soil levels, some will die. I live in Australia and many of our natives are robust and cope with a variety of conditions so over-mulching would not be a problem for established natives. For any young plants, I think am excessive layer of mulch can be counterproductive. The best way to ensure plants are not damaged is to ensure that the base of the plants are cleared of a deep layer of mulch; so that they don't risk rotting. When I have used excessive mulch, I clear a "dish" around the plant of at least 4-5 inches, where the mulch is only an inch or so thick.

You can purchase prepared black mulch (at least in Australia); the problem is knowing whether or not is has been dyed, as not all vendors are honest in their dealings about this.