We are planning to put down a seasonal mulch this spring and fall, and wondered what your opinion is of colored bark. Would brown, black, red, or some other color be best in our ornamental beds?
May I answer none of the above? There are better options. I can’t think of any good reason to apply mulches which have added dyes and colorants to any landscape. Check the Material Safety Data Sheets for each product to verify the source of the dye to be sure that they are not going to cause harm (to the landscape and the people and animals in it, and to stormwater). Some packaged colored mulches also have herbicides added, and I would highly recommend not using them. The sources of the “bark” may be an even more important cause for concern. This information from University of Massachusetts Extension points out that dyed bark mulch made from recycled treated wood can introduce toxic substances you would not want in your garden.
Although this is an aesthetic judgment call, to my eye, colored mulch always looks unnatural in the landscape compared to materials such as compost, leaf mulch, and arborist wood chips. Washington State University Extension professor of horticulture Linda Chalker-Scott is a strong advocate for the use of wood chips as mulch. My own observation is that bark mulch (in general, not just the colored bark products) often introduces weeds into a landscape. Chalker-Scott supports this observation in her book, The Informed Gardener (University of Washington Press, 2008):
“I have seen a number of landscaped sites where applied bark mulch immediately gave birth to horsetail seedlings.”
She further states that bark mulch from trees which have been kept in salt water can increase salt levels in your soil. Tree bark has a waxy covering, so bark mulch is not the best choice for absorbing and releasing water.
To summarize, unless you have your heart set on the look of dyed bark mulch, your garden beds would benefit from the alternative mulch materials (compost, leaf mulch, free arborist wood chips) mentioned above, plus planting an appealing and naturally colorful selection of ground cover plants in areas where that is possible.