Mulch is any material used to cover bare soil; it plays a vital role in the health of your garden or flowerbed. It inhibits weed growth and protects soil and roots from sun exposure, regulating soil temperature and moisture content. Some mulch also releases beneficial nutrients into the soil during decomposition and acts as a barrier between the plant and the soil, protecting the plant from soil-borne diseases and erosion.
There are several mulch options to choose from depending on your garden preferences, plants, and individual needs, each with their own benefits and drawbacks.
1. Shredded Wood Mulch
Shredded wood mulch is often made from pine shavings or from cypress or cedar. The key benefit of using shredded wood mulch is water retention, both in excessively wet or dry conditions. Wood absorb excess moisture in the soil during times of heavy rains, taking the burden off the soil. During dry times, wood mulch releases retained moisture into the soil, keeping it hydrated. Depending on how shredded it is, this type of mulch also decompose relatively quickly and releases beneficial nutrients into the soil. It’s important to apply at least 4-6 inches for optimal benefits. Note: Shredded wood mulch is not be confused with wood chips or bark chunks which do not absorb water as well (see #2 below)
It is important to keep in mind that wood mulch consumes nitrogen as it breaks down, and eventually will also become part of the soil. However, it also consumes nitrogen – an important element for plant growth – in that process. To help keep nitrogen from being depleted from your soil, sprinkle a slow release non-burning nitrogen fertilizer like Milorganite on your beds before adding mulch to help retain or supplement the nitrogen in the soil.
Tip from the pros: Colored mulch – usually red or black – is very popular in some regions and can often provide a more finished look. However, the wood that’s used in dyed bark varies by manufacturer and can even be from demolished buildings or construction projects, wood which can include chemical-laden pressure treated wood. If you’re determined to use colored mulch, consider spending the extra money to purchase it from a reliable source.
2. Wood Chips
Wood chips, like those generated from tree removal companies, are the roughest kind of mulch. These chips are generally free or inexpensive. They are okay to use in areas where you want to remove/reduce all vegetation but are not appropriate for ornamental or vegetable gardens as they not only use a huge amount of nitrogen as they’re breaking down. In addition, depending on the wood used for the chips, they might also raise the acidity level in the soil.
3. Rock Mulch
An advantage of rock mulch—medium to large stones—is temperature regulation. Rocks absorb heat during the day and then release it at night, maintaining consistent soil temperatures. This is especially beneficial in cooler climates. Rock mulch is also economical because it doesn’t decompose or require frequent replenishment or replacement. Additionally, rocks can retain moisture underneath which can nourish the underlying soil.
This lack of decomposition, however, can also be a drawback, as it doesn’t allow for the release nutrients into the soil as other organic mulches do. Larger rocks can also be difficult to move around when the need arises. Smaller stones, like pebbles and gravel, do help regulate temperature, but unlike their larger counterparts, pebbles can work themselves into the soil, requiring more maintenance. Pumice rock is a unique rock worth considering; it is light, porous, retains moisture, and is a perfect mulch for flowerbeds housing perennials.
4. Straw Mulch
If layered thickly, straw is a strong mulch option, providing adequate protection from the sun, blocking weeds, and regulating moisture. Its lightness prevents rot from building up at the base. Even more convenient, straw can be tilled into the soil at the end of a growing season, breaking down and releasing nitrogen into the soil in preparation for the following year.
You should ensure your straw is virtually weed-seed-free or the mulch will lose its ability to suppress new weed growth. It can also be difficult to spread a thick layer over a larger area without a diligent effort. Another disadvantage of straw is its attractiveness to all sorts of creatures, such as rabbits, voles, and mice. Critters won’t hesitate to nest in the straw and take advantage of the buffet provided in your garden while they’re at it.
5. Shredded Rubber
Although on the higher end of the cost spectrum, shredded rubber is quite long-lasting. It provides adequate insulation from both heat and cold. Rubber mulch is also non-porous and doesn’t absorb water, allowing moisture to drain directly into the soil. It’s excellent for preventing weed and fungus growth. Furthermore, it lasts much longer than wood-type mulches and recycles material that could otherwise harm the environment sitting in a landfill.
Even though rubber breaks down extremely slowly, it does break down, and may release toxic chemicals into the soil depending on its origin. It is also flammable and not recommended for areas where wildfires are common. This is a situation in which the gardener must decide for themselves if the benefits outweigh the potential risks. Some landscapers are vehemently against the use of rubber, but there might be certain scenarios where it remains a viable option.
6. Leaves and Grass Clippings
Mulching leaves and/or grass clippings is a very economical option. As many lawnmowers now come with a mulching feature, you can create your own mulch, making use of a resource you would otherwise remove, sometimes even paying to do so. Like straw, leaves and grass clippings can be tilled into the soil to add nutrients. Though this might not be the most aesthetically pleasing, leaves and grass clippings are incredibly rich in nutrients that will make your garden (and you) quite happy!
If you decide to choose this option, be sure to use clippings that are herbicide-, pesticide-, and fungicide-free (in other words, think twice if you have your lawn treated!). As freshly cut grass clippings can lead to rot, it is best to dry out or compost them first when using them as a top layer. Fresh cuttings can, however, be beneficial when tilled into the soil, as these begin to release nitrogen immediately after cutting.
7. Pine Needles or Pine Straw
Pine needles or pine straw offer the same nutrient benefits as other organic mulches, but they cannot be used with every type of planting. The acidity of pine needles necessitates using them for plants that thrive in acidic soil. This also means that pine needles should only be used as top layer unless thoroughly composted. Tilling into the soil can throw off the pH balance of the soil.
Pine straw must be applied in a thick layer to provide protection from the sun. Pine straw’s benefits increase as it ages, so it might be best to wait until the pine straw has thoroughly been composted or aged. Luckily, pine straw and needles can be quite affordable, especially when sourced from nature rather than purchased; they simply require a little more patience.
Either laid flat or shredded, newspaper is a viable mulch option at a very affordable price. They make a great barrier to weeds and act as an insulator, especially if layered at least 6-8 inches. Unfortunately, newspaper mulch is not very pleasing to the eye and usually require another more decorative form of mulch to accompany it. Another biodegradable, organic mulch layered on top of the newspaper helps to hold it in place and retain the moisture, allowing the newspaper to break down while still holding back weeds.
As the ink in newspaper can be hazardous, particularly colored ink, it is best to stick to black carbon-based inks. Glossy pages from inserts should also be avoided, as they may release heavy metals.
Regardless of which mulch you choose, make certain to use at least 4-6 inches for maximum benefits. Otherwise the weeds can grow right through it and water evaporates too quickly. There’s no one-size-fits-all mulch option. Weigh the benefits and drawbacks for each one as it applies to your garden and watch your beauties grow.
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Olivia Warfield is a contributing writer and media relations specialist for DIY Retractable Awnings. She writes for a variety of DIY blogs and strives to learn more each day to cultivate the green spaces in and around her home.