As much as I love the practice of mulching there are both pros and cons the home gardener needs to be aware of. Wow, I feel almost like an “organic heretic” just thinking about saying anything negative about mulch, but here goes…
There are a few pros and cons with each type of mulch. Let’s look at some of the most common types of organic and inorganic mulches that are readily available to the home gardener.
- Shredded hardwood bark mulch is made from pure tree bark and not ground up wood.
- Pros: It contains a lot of nutrients that will improve the soil as it decomposes.
- Cons: Wood chips may wash away as the wood decomposes, and they pull some nitrogen from the soil.
- Grass clippings mulch should be used after they are dried and spread in thin layers to prevent them from rotting.
- Pros: Grass clippings are free from your lawn and supply compulsory nitrogen nutrients to the soil. If you do not use lawn chemicals, it is also organic.
- Cons: It is often difficult to separate the grass from the weeds, which can increase weed growth in the garden.
- Straw mulch has become increasingly more popular over the last several years.
- Pros: Straw is inexpensive, provides good insulation for a winter vegetable garden and suppresses weeds.
- Cons: Straw decomposes quickly, can be unattractive, may contain weed seeds and is flammable.
- Rock, gravel, stone and lava rock mulch materials do not break down. If this type of mulch is properly installed, it may never need to be replaced.
- Pros: It is available in a wide range of colors, sizes and shapes. It will not decay or blow away.
- Cons: These can be difficult to keep clean and difficult to remove. Rocks draw heat and should not be used with acid-loving plants, such as rhododendrons. Must use fabric under the rocks to prevent them from sinking in the soil.
- Shredded rubber mulch offers the benefit of using recycled rubber as a mulch so that you will be preventing the material from ending up in a landfill.
- Pros: Available in several different colors and it will not blow away or decompose.
- Cons: It is often difficult to remove, it is inorganic and is flammable.
- Plastic mulch is typically sold in sheets that are placed directly over the soil. In most situations, a layer of another type of landscaping mulch is placed over or mixed with the plastic.
- Pros: It is very effective at controlling weeds and absorbs heat, making it especially useful in gardens where warm soil is desired.
- Cons: Soil cannot breathe under the plastic. It’s also inorganic, unattractive and may tear easily.
In my own yard and garden, I go with organic mulches, mainly woodchips, grass clippings, leaves, and cardboard. I recommend mulching 100% and truly believe it is among the best ways to combat our hot summer months.
That having been clearly stated, and without wanting to be denounced as an “anti-mulchite,” I must point out a few more Cons. First, a too thick layers of mulch can absorb light rains (and water from sprinklers) and stop it from getting through to the soil. Secondly, mulch can keep soil too cool in spring, when you want it to warm up. Thirdly, with woody mulches there’s a phenomenon called nitrogen drawdown, caused by micro-organisms drawing nutrients out of the soil to break down mulch above. (A layer of compost or a sprinkling of blood and bone meal beneath the mulch can help counteract this). Finally, mulches can attract slugs, snails, mice and other unwelcome guests to the garden.
My hands down favorite mulch is cedar mulch. It offers an excellent option when it comes to perennial flower beds and other landscape gardens.
Cedar mulch, as well as other bark and wood mulches, are quite long lasting and break down over time to provide added nutrients to the soil. Cedar mulches also discourage insects from taking up residence in the garden, thus making the use of insecticides unnecessary. Cedar Mulch is also readily available in most nurseries and garden centers and presents an organic and cost-effective option for mulches.
Although cedar mulch breaks down and is organic, it takes longer to break down than alternative bark mulches or wood mulches. Because of this, cedar isn’t as effective in returning nutrients to the soil as some other forms of mulch. Cedar mulch does discourage insects from moving in, but it must be remembered that not all insects are harmful. Cedar mulch may discourage beneficial insects as well as traditional pests from entering the garden.
Whichever way you choose to mulch, just do it! The positive benefits absolutely outweigh the negative – so get out there and mulch away!
I want to talk a bit more about Organic Mulches.
Organic mulches such as shredded bark, wood chips, bark chips and others are commonly used on landscape plantings. As with anything, they have both pros and cons pointed out above. But again, I firmly believe the pluses outweigh the minuses.
On the plus side, organic mulches in gardens, on ornamental beds, and in borders help to conserve moisture which helps reduce the amount of irrigation needed. It also helps keep the plants growing at an even rate uninterrupted by periods of drought stress.
A two or three-inch layer of mulch makes it difficult for most weeds to emerge into the sunlight. This greatly reduces the amount of hand weeding or chemical herbicides needed for a bed.
Mulch also has an impact on soil temperatures. For some plants such as clematis, high soil temperatures are detrimental to maximum growth. A layer of mulch during the summer helps keep the soil cooler. Conversely, in the winter, mulch will help to keep the soil a warmer, more even temperature often extending your growing season. But also, once the soil does freeze, mulch helps it stay frozen – this may sound odd, but it is very helpful as keeping the soil frozen will help to prevent the damaging effects of the alternate freezing and thawing of soils which is called ‘heaving.’
Finally, organic mulches look good. The aesthetic properties of much should not be forgotten. A uniform layer of mulch on all beds in an area will bring a sense of unity to the layout. It will help tie the beds together and make them look as if they all emerged from the same plot.
There are some negatives to the use of organic mulches, but these are generally minor. Of course, there is usually some cost involved with using the mulches listed above. Whether purchased by the bag or by the cubic yard, it costs money to put down mulch. Also, it must be applied which takes time and effort. Organic mulch will need to be replaced over the years as it decays kind of like a “wash, rinse, and repeat” process.
In extremely rare instances, plant diseases may be spread by mulches. The most serious potential seems to be in the spreading of certain root rots by using the mulch made from trees that were infected. The best bet is to use materials that have been partially "composted" by setting in a pile for six months or more. This will help to minimize this problem.
As these mulches decay, they become excellent breeding grounds for slugs. When the mulch becomes water soaked and slimy, slugs love it. So, if this pest is a problem, instead of adding new mulch on top of the old, rake up the old and put it in the compost pile. Replace it with fresh, new mulch.