WARNING: Though mulches can dress up your yard and garden space, prevent weeds and hold moisture in the soil, some mulches on the market can actually cause harm to your plants and animals. Use caution when choosing your mulches.
Rubber Mulches: I was appalled to see chopped up rubber tires sold as mulch at stores. Here is a product that is being sold as a recycled product that will never break down. And it is true. It is recycled from tires, and it does not break down because it is RUBBER! Instead it will sink into your ground and contaminate any plant around it with petroleum that leaches out of the rubber and into your soil. Vegetable roots can suck up these toxins, sometimes extraordinarily well. Vegetables like garlic and onions have the ability to infuse their cells with higher amounts of toxins than other plants can. Not only can rubber mulch contaminate your soil, but it can be harmful to pets who could swallow pieces of these fun little chew toys. Just because it’s sold as mulch does not mean it is good for mulch!
Dyed Mulches: Bags of dyed mulches are becoming more popular, and are starting to pop up at nurseries as well as the big box stores. This is another case of you get what you pay for when it comes to quality. A quality dyed bark is dyed red with copper oxide or the color black with iron oxide. Adding dyed bark to your garden may look nice, but these metals can unbalance the nutrients in your soil and mess up the microbial fauna. The leached metals can be absorbed into vegetables too.
Still, these are not as bad as some very cheap bags of dyed mulches. Inexpensive bags of dyed mulch are dyed with more dangerous chemicals, though this is rare. You should be more wary of the wood used in these cheap bags of mulch than anything else. Instead of bark from lumber mills, the wood is instead pulled and chipped up from recycled old pallets, decks, and crates. Much of this recycled wood contains a preservative made with chromated copper arsenate (CCA). Even though using CCA to treat wood was banned in 2003, many times this wood is still pulled from demolition sites and recycled into products like dyed mulches. Spreading these mulches can be very hazardous to your health and your pets. CCA kills the microbes needed to compost wood naturally.
Natural Mulches: Mulching is still highly recommended for successful gardening, but stick with natural mulches! Leaves, straw, lawnmower trimmings (herbicide free), sawdust, shredded paper, wood chippings, and bark all are excellent and inexpensive sources of natural mulches. These will break down and add important nutrients to your soil, as well as hold in precious moisture through the summer months and squelch out those weeds!