Landscape mulch has become very popular in recent years because of the neat and tidy look it gives to gardens and landscaping.  What some people may not know is that wood mulch not only looks nice it is also very beneficial for plants.  Mulch reduces evaporation keeping moisture in the soil where plants need it.  It also prevents the soil from getting hot during exposure to the mid-day sun, reducing heat stress on plants.  Organic mulch also builds organic matter in the soil, creating loose, loamy soil that is a pleasure to cultivate, and it increases the population of microscopic plants and animals living in the soil.

May is a good month to apply mulch around trees and shrubs, because by now the soil has warmed up and begun to dry.  Covering cold, wet soil slows plant growth and it can cause mold and fungus problems.  Once soil warms up, the microorganisms become active, breaking down organic matter and releasing nutrients needed by plants during their busy spring growth.  Mulching now will prevent sunlight from germinating weed seeds and save you a great deal of time weeding in June and July.

There are many types of mulch available in a wide range of colors, textures, and materials.  It can be confusing when trying to decide on the best mulch to buy.  If economics are an important factor, here is some information that will help you decide.

Bagged mulches cost about $2 per cubic foot (cu.ft.), which translates into $54 per cubic yard (or simply "per yard").  Bulk mulch ranges widely in price but the average is about $25 per yard, or half the price of bagged mulch.  Specialty mulch such as cypress or redwood, however, cost as much as $50 per yard.  If you've always bought mulch by the bag and you don't know how big a cubic yard is, the bed of a standard sized pick-up truck will hold about 2 yards of mulch.  If you don't have a truck but want to buy bulk, delivery costs will increase your price.  You can expect an additional cost of anywhere from $25 to $75 per truckload.  If you have a landscape service deliver and spread your mulch you can expect to pay $50 to $60 per yard for the service.

Many people will select mulch based on how it looks in the store bin.  A word of caution, if you've never used mulch before, the color of mulch in the bin is not the color it will be as it ages on the ground.  Once mulch is exposed to sunlight and rain its color will fade.

There are two main types of wood mulch, colored processed wood and natural wood.  Colored mulch is made by adding dye to ground up processed wood such as pallets or lumber.  It is a great way of recycling wood that would otherwise go to the landfill.  Natural wood mulch is made from grinding up branches and trees that have been recently cut down.  This is how yard waste is recycled in many communities with curbside collection.  Lumber mills also recycle bark and tree scrapes to make natural brown mulch.

Although it is much better for plants to be mulched than not, mulching can cause some problems and headaches.  Freshly dyed mulch can bleed color onto sidewalks and clothing.  Also, the color of dyed mulch will fade and it can become a very different color than what you expected.  Processed wood has been kiln dried so it is very dry and blond when ground, making it ideal for dying.  But this characteristic also makes it less than ideal in the soil.  It breaks down much more slowly than natural wood mulch and it reduces nutrients in the soil.  Homeowners that use dyed mulch find that they may be stuck using the same color year after year.  By spring, there is still too much of it on the ground to change to different color mulch, but they have to add more because the old mulch looks too drab.

Natural wood mulch contains more nutrients than processed wood, and it will break down to form soil faster.  It comes in many shades of brown and usually many different textures.  Ground up tree branches makes mulch that has more fines in it than ground up tree trunks, which can have many more larger hardwood pieces.  Although some people may prefer uniformly fine textured mulch, natural mulches that contains coarse as well as fine sized particles actually perform better than uniform mulch.  It will settle less than fluffy fine mulch, and the coarser pieces provide better weed control.

The main problem with natural wood mulch is that is can harbor pests (such as termites) or (more rarely) disease from trees that were cut down.  Although it is recommended that homeowners burn diseased wood, they may not recognize what killed their tree, and the diseased wood can end up being processed into mulch.  It is good advice if you have wood siding on your house not to put any wood mulch up against your house.  And be careful of the type of mulch you use around trees that are susceptible to diseases.  If you like natural mulch but these potential problems concern you, then the best mulch for you to buy is mulch that has been composted.  Composting organic matter destroys the pests and disease-causing organisms.

Composting mulch in windrows and turning it periodically allows plenty of oxygen to get into the pile.  Composted mulch has a pleasant earthy-smell not a sour smell.  It is a rich, dark brown color created naturally by the humus that forms during the composting process.  Composted mulch is already partially broken down so it will settle less after you spread it on the ground.  It will also enrich your soil more quickly than fresh mulch.

Not many people realize that fresh mulch can be toxic to plants when the manufacturer has stored it improperly.  Toxic (or "sour" mulch) occurs when manufacturers create mountains of ground up wood.  Large piles don't allow oxygen to get into the pile.  As the piles heat up, the mulch deep in the pile becomes sour and has a recognizable offensive odor.  When spread around plants sour mulch can damage or kill plants.  If your mulch smells sour let your pile sit for 48 hours to release the sour gases before spreading it.

No matter what type of mulch you choose, May is the month to get out and spread it around your landscaping plants.  If last year was the first time you mulched, start by tilling last year's mulch into the ground to speed up its decomposition and enrich the underlying soil.  Then apply a 3 to 4 inch cover of new mulch.  If this is the first year that you've mulched, consider adding compost to enrich the soil before applying mulch.  Once you begin mulching every year you will not need to add as much mulch the next year.  Your landscaping will look better, and your plants will be healthier and grow faster.  The key to growing beautiful healthy plants is to make healthy, fertile soil.


Jody K. Tishmack has a Master's Degree in Soil Science and a Ph.D. in Civil Engineering.  She developed a composting and soil manufacturing process at Purdue University in 1996, which has grown into a commercial business called Soilmaker.  Soilmaker is Lafayette's largest yard waste recycling operation, selling compost, organic soil, and composted mulch.


Jody Tishmack
3878 South River Road
West Lafayette, IN 47906