Mulch is a term that one hears a lot in gardening circles. But it is sometimes hard to determine exactly what all the talk is about. Generally speaking mulch is an organic or non-organic material that is placed on top of the soil in flower and vegetable beds. A layer of mulch helps to retain moisture, prevent weeds, reduce soil compaction and maintain an even ground temperature. Mulch can be applied in late fall after the ground freezes to give plants a little extra protection through the winter or in late spring after the soil has warmed to keep their beds weed free and moist through summer.
My mulch of choice is shredded hardwood. I like it because it is natural in appearance and it breaks down over time, adding organic matter to the soil and improving the soil structure. It also stays in place better than other wood barks like pine bark nuggets or ground bark. The pieces are stringy rather than chunky so it doesn't wash away.
But what's good for the goose isn't always good for the gander. Here is a list of popular mulching materials along with a few considerations that will help you make the best choice for your garden.
Tree Bark - Pine bark nuggets, ground pine bark and shredded hardwood are all types of bark mulch. Bark is a long lasting choice because it actually contains natural waxes and suberins that make it somewhat waterproof. Fresh bark sometimes contains toxins that are harmful to plants, but this shouldn't be a concern if you are buying commercial bagged mulch. When buying in bulk ask the vendor about the age of the bark. Apply a 2 to 3 inch layer, keeping the mulch about 1 inch away from plant stems or trunks.
Wood Chips - Fresh wood chips may pull nitrogen from the soil as they age. Allow the chips to mature or supplement the soil with a nitrogen fertilizer. Fungus problems and toxins also occur with fresh wood chips, but commercial products are sufficiently aged. Apply a 2 to 3 inch layer, keeping the mulch about 1 inch away from plant stems or trunks.
Pine Needles - Pine needles are an attractive, long lasting and readily available choice. Best used as a mulch around acid loving plants. Apply a layer 4 to 8 inches thick, keeping the mulch about 1 inch away from plant stems or trunks.
Sawdust - Sawdust should be aged for 6 months to one year to prevent nitrogen depletion. Use around acid loving plants. It may compact preventing water from soaking into the ground so one of its best uses is in a 3 to 6 inch layer for paths.
Shredded Rubber - I commend the use of recycled materials used to produce this product. It is a great choice for paths and playgrounds. For this purpose apply a 6 inch layer. In the garden apply a 1 to 2 inch thick layer, keeping the mulch about 1 inch away from plant stems or trunks.
Straw - This material is commonly used to cover newly seeded lawns. It breaks down quickly adding nutrients to the soil. Select seed free varieties such as wheat straw. Try to avoid hay because it contains seeds. I like to use wheat straw as a path material between my raised vegetable beds. Apply a 6 to 8 inches thick layer for winter protection.
Cocoa Hulls - This is a relatively new mulching material. It has a nice polished appearance and smells like, you guessed it, chocolate. Because of its fine texture it's a great choice for containers. The chemical that makes chocolate dangerous for pets, theobromine, may also be found in cocoa mulch. Be sure the mulch is theobromine free or select a different mulch if you have pets, especially dogs. Apply a 1 to 2 inch layer, keeping the mulch about 1 inch away from plant stems or trunks.
Crushed Stone/Gravel - The ultimate in long lasting mulch is crushed stone, gravel or rocks. This material will stay in place, keeping the area weed and disease free. It's also a good choice if fire proofing the area around your house is important. Down the road, its longevity can be a problem if you ever wish to remove it. The rocks tend to work themselves into the soil. This can be avoided by laying down a filter fabric before spreading the rocks. Avoid light or white gravels that will reflect light back up on the plants. Be aware that rock mulch can create a warmer microclimate in the area where it is applied. Limestone will increase the pH of soil, adding alkalinity. Depth depends on the size rock you use.
Newspaper - Layers of newspapers are an effective choice for killing existing vegetation to create new beds or for controlling weeds in the vegetable garden. Most modern papers use soy based inks, which are harmless. When in doubt about the type of ink call and ask the publisher. Avoid the slick pages often included in papers as these may be produced with metal based ink. Some cities offer bales of shredded paper as part of their recycling program. Apply 1/4 inch layer, moisten to keep in place and top dress with compost to make attractive.