The best mulch is one that fits your needs both functionally and aesthetically, so the answer is not the same for everyone. Every type of mulch has strengths and weaknesses, making it suitable for some situations and not others. Regardless of which type you choose, you should mulch. (Wondering how to mulch? here are some tips)
Mulching isn't just about making garden beds look pretty. Mulch is both an attractive “finishing touch” and an important part of landscape management for its ability to control weeds and retain soil moisture. No matter which material you choose, they are almost all equally effective. Let’s look at some of the benefits and drawbacks of the mulches commonly available to see which best fit your landscape.
Very popular here in the south, pine needles or pine “straw”is lightweight and natural looking. Pine needles are naturally acidic as they break down, making them excellent for mulching around plants that prefer acidic soils (azaleas, rhododendrons,camellias, etc.) During heavy rain events, pine needles tend to stay put and not wash away, making them an excellent choice on slopes. Harvested from the floor of pine forests and naturally shed by pine trees, needles are a very renewable product. Needles breakdown relatively slowly compared to other organic mulches. They can take some practice to put down so that they look tidy. As pine needles age they turn a silver-grey that some people find unattractive. Finally, bale sizes can be variable, and occasionally contain sticks, leaves and other forest trash (and sometimes real trash).
Ease of application is the strong suit of pine bark nugget mulches. Pine bark nuggets come in several different size grades, from “mini” to “jumbo” nuggets. (Soil conditioner is a ground pine bark product smaller than mini-nuggets that can also be used as mulch.) Pine bark is long lasting, and when it does break down it enriches the soil with organic material. Water pooling can cause bark nuggets to float and spread, and moving water can cause it to wash away, requiring it be raked back or replaced entirely. This makes bark nuggets less suitable for areas that tend to get flowing water in heavy rains.
Shredded hardwood has similar properties to bark nuggets but is less likely to wash away. Like pine bark nuggets, it is a byproduct of the lumber and paper industries. It spreads easily and is long lasting. When hardwood mulches break down they make soil more alkaline (raising pH), which should be taken into account when mulching around acid-loving plants. You may need to use an acid fertilizer or add sulfur to compensate. Hardwood mulch can compact over time and can block rain and nutrients from reaching the soil when that happens.
Colored wood mulch is often made from recycled wood that can contain objectionable additives—including arsenic from pressure-treated wood—and is not always 100% hardwood. Pressure-treated wood containing arsenic was phased out a decade ago by the EPA, but old crates and pallets may still be entering the recycling stream. If you’reconsidering colored mulch, be sure the manufacturer uses raw lumber rather than recycled wood. The dyes used for colored mulches are considered safe, however.
(Whenever using wood mulch products, never let it contact any wooden siding or other parts of your home. Termites can and do inhabit wood mulches, but it’s not necessarily a reason to avoid wood mulches altogether. Termites will take advantage of increased soil moisture provided by any mulch for shelter.)
Compost and manure used as mulch add large amounts of organic material to the soil quickly, improving soil structure and nutrient and water holding capacity. However,they do not inhibit weed growth nearly as well as wood or needle mulches. If you use your own compost to mulch, be sure you have not put any material that had herbicides in your mulch bin.
Rarely used alone, landscape fabric or weed barrier is usually covered with other mulches for aesthetic reasons. While the double-barrier is excellent for stopping weeds, using fabric barrier with mulch keeps desirable organic material from reaching the soil as the organic mulch on top breaks down. Eventually this creates a layer of “dirt” on top of the fabric which needs to be removed periodically. Weeds can and do develop in this dirt layer and can be difficult to remove if they root through the fabric into the soil below.
Still relatively uncommon due to its expense, shredded rubber mulch does not breakdown and can be considered nearly permanent. The color remains stable for many years and it stays put better than almost any other mulch. It is, however,very heavy and difficult to move, and adds no beneficial organic material tothe soil. Rubber mulch can also have a disagreeable odor that can persist for a while after installation. It is ideal for playground areas as it won’t cause splinters and absorbs impact from falls.
In the right setting, stone mulches (pebbles, gravel or rocks) can be a good choice. They stay put and don’t break down. Smaller sizes such as gravel and pebbles can eventually sink into the soil, requiring touch-up applications (this is where landscape fabric is best used-under stone mulches to prevent sinking) . Larger sized rock mulches can make it difficult to add plants and are difficult to move or remove if you change your mind. Stone mulches can be less effective in reducing water loss from soil when used in sunny areas-the rocks keep soil warmer, increasing evaporation.
There are several products that should never be used as mulch: sawdust, wood shavings and un-aged wood chips. As these materials begin to break down, they consume large amounts of nitrogen, depriving surrounding plants of this vital nutrient. Commercially produced wood products intended for mulch have been aged past this stage and are safe to apply around plants.