What is mulch?
Mulch is any type of soil covering which is spread or laid on top of the soil. It is used primarily to help the health of the soil and the growth of plants, but it can also be used as a decorative feature.

One of the secrets to an amazing low maintenance yard is the proper use of mulch. It can help reduce weeding, watering, and even fertilization. In short, it makes life easier!

Why is mulch used in landscaping?
Mulch’s primary function is to cover the soil and fill in space. It is added in a relatively thick layer over any soil that would be exposed. The exact installation method varies depending on the type.

Nature hates a vacuum. If there is a blank space, something will grow to fill the space – and plants that colonize empty spaces are almost always weeds. Weeds grow well in disturbed soils i.e. freshly cleared and prepared planting beds.

There are two principle types of mulch—organic and inorganic—and they each have their pros and cons.

ORGANIC MULCH
What is organic mulch?
Organic mulch is any type of mulch that was once living. It includes things like wood chips, bark, and straw. All organic mulches break down and improve your soil. Organic mulches help condition the soil, even inviting earthworms to naturally aerate the soil, and help reduce with soil compaction. While decomposing, they add nutrients such as potassium, nitrogen, phosphorus and trace elements to the soil. But because they decompose, they will have to be replaced on a regular basis.

When should organic mulch be applied?
Most mulch should be applied twice each year, spring & fall. The application in spring should be after the landscape has had its spring cleaning and the turf has been edged. In the fall the best time is late summer to late fall, to help insulate your plants through the winter months.

BENEFITS OF ORGANIC MULCH
Mulch benefits your landscape in several ways. The primary benefit is that it protects the soil from the sun keeping the roots cooler and reduces moisture loss from evaporation with minimal watering and has an added benefit of reducing weed growth. It will also make your plant beds stand out more.
Your landscape will have a more stable soil temperature
Mulch helps with the prevention of soil compaction
Give your plant beds a finished look
Mulch retains moisture around plants
The weed growth will be reduced
Keep your plants clean
Reduce topsoil erosion
Protect plants from lawn mowers & string trimmers
Add organic matter to your soil

How does organic mulch stop weeds?
Mulch will stop weeds by taking advantage of some of the laws and rules of Mother Nature. The first is that mulch creates a barrier over the soil that is hostile to plant growth. Bare soil is the perfect medium for the growth and spread of weeds. Seeds, blown by the wind or distributed by critters, are looking for a patch of bare soil. If they cannot reach that soil, they are going to have a much harder time growing. A good mulch not only blocks the soil, but it also contributes to creating a hostile growing environment. Natural mulches, like native hardwood mulch, are partially decomposed. This means that microbes are working to decompose the mulch further. The microorganisms use the same nutrients that plants rely on to live, meaning they use up the available food, so it is not available for germinating weeds. This natural process only functions with a thick layer of mulch, with plenty of un-decomposed mulch at the surface.

Why is my organic mulch disappearing? Where is my organic mulch going?
Those microbes in the soil are doing much more than hoarding nutrients. Eventually, they eat up (decompose) the mulch, and then die. The result is incredibly rich healthy soil, but no mulch. This rich soil is amazing for plant growth – both intentional and invasive. If you are not careful, the weeds will explode, healthier than ever.

The beds are natural fertilizer factories, churning out the nutrients necessary for great plant growth. Eventually, the plants will use up every molecule of that rich humus, and nothing will be left. It all happens on a microscopic level so that sometimes it feels like your mulch is simply fading into thin air. The trick is to keep feeding that process. Keep those microbes working, keep those plants healthy, and keep those weeds out. The magic number is 3 inches of mulch. This keeps a layer hostile to plants on the top, and pumps out healthy nutrients at the bottom of the mulch, right were your lovely plants need them.

What else does organic mulch do?
We have already established that mulch helps keep weeds out, and it generates the nutrients that plants need to survive. It also helps regulate the moisture and temperature in the soil. Sunlight and wind can dry out the soil, removing water through evaporation. The layer of thick mulch helps keep the soil moist. This works best with drip irrigation systems, where the water is never exposed to sun or wind, but it will help hold moisture in the soil from rain and sprinklers as well. That same layer also acts like a blanket and insulates the soil from rapid shifts in temperature. This is most important in the winter when the temperature drops. Bare soil, exposed to falling air temperatures and wind, can quickly drop to temperatures that could damage delicate plant roots. Mulch can keep those delicate plants alive. Keeping the soil temperatures stable keeps plants alive. Additionally, the microbial activity that decomposes mulch generates a small amount of heat. Some horticulturalists have used large piles of decomposing mulch to keep tropical plants alive through blizzards far up north. Bananas growing in Idaho? Only with the power of our magic friend! (Though it’s easier to just grow potatoes.)

Why isn’t my organic mulch Magical like the mulch described here?
A healthy mulch layer does all the things mentioned here, but only if installed and maintained correctly. It is a natural balance, and it does have its limits and requirements. Not all weeds are stopped by this magic stuff. Weeds like Nutsedge will grow through anything – including solid asphalt and concrete. Other weeds are good at spreading into a well mulched bed from the edges, avoiding the hostile zone at the top, and making a beeline to the thick healthy soil at the bottom. Other solutions are needed for these problems, but it does not negate the value of healthy mulch eliminating all the other weeds that could be in the bed. It also needs to be refreshed regularly and maintained at a thick enough layer to get the natural decomposition engine fired up and running smoothly. A thin scraping of mulch that barely covers the soil will do nothing other than help the yard look good for a few weeks. If you put too much mulch down, the same process that stopped weeds will start killing the good plants too. The trick is a healthy 3-inch layer, maintained by adding mulch to keep the beds topped up once or twice a year.


Also, avoid using weed fabrics under natural mulch. The fabric stops the rich soil from reaching the plants, and eventually, weeds will take advantage and steal all those nutrients for themselves ON TOP of the fabric.
Also, make sure you are using good mulch.

COMMON TYPES OF ORGANIC MULCH
Compost
Compost is every gardener’s dream soil amendment. It’s a nutrient-rich mixture of decomposing organic matter — from table scraps to fallen leaves to grass clippings — and you can make it all by yourself. Compost protects roots, insulates soil, and amends soil texture and quality. The result? A garden filled with healthy soil and flourishing plants.

Pros of compost
✓ Excellent erosion resistance
✓ Easy to DIY
✓ Gives plants a strong nutrient boost
✓ Great for organic gardening
✓ Reduces the need to aerate
✓ Breaks down rapidly to increase soil nutrients
✓ Prevents plant diseases

Cons of compost
✗ Not as good at suppressing weeds as wood mulch and pine needles
✗ Takes time: Requires a waiting period as mulch material decomposes
✗ May release an unpleasant odor (during the decomposition process)
✗ Can attract pests (raccoons, rats, ants, and earwigs)

Tree bark
Tree bark mulch is the cream of the crop when it comes to preventing wind erosion, resisting soil compaction, and suppressing weeds and diseases.

A natural by-product of the lumber and paper industries, tree bark comes in many varieties of hardwood and softwood, with sizes ranging from finely shredded to larger nuggets. Bark mulches of all colors (both natural and dyed) are easy to find at local garden centers and home improvement stores.

Want a long-lasting mulch that releases nutrients slowly? Go with large softwood bark chips (like cedar, fir, or pine). Shredded hardwood bark (made of oak or a mixture of hardwoods) needs to be replaced more frequently. 

If you have acid-loving plants like blueberries, rhododendrons, hydrangeas, or azaleas, pine bark is an excellent choice.

Use aged or cured wood, when possible. Fresh tree bark is less expensive, but as it decomposes, it takes up nitrogen near the top of the soil, which can lead to a nitrogen deficiency in small plants. If you choose fresh bark, apply fertilizer to increase the nitrogen available to your plants. 

Pros of tree bark
✓ Excellent resistance to compaction
✓ High resistance to wind erosion
✓ Strong weed control and disease resistance
✓ Available in many attractive colors
✓ Long lifespan

Cons of tree bark
✗ Large bark chunks can impede the spread of plants
✗ Can form a crust and prevent water from reaching soil
✗ Aged bark chunks can be expensive
✗ Can attract termites or roaches around house foundation 

Wood chips
Wood chips are excellent at suppressing weeds and preventing erosion, and they look gorgeous doing it. Wood chip mulch looks lovely around trees, pathways, and perennial gardens. 

Wood chips contain tree bark, inner wood, and sometimes even leaves. This variety of textures and sizes reduces compaction and increases biological diversity to improve soil and plant health in the long term. Larger wood chips have a long lifespan (two to three years), while small wood chips decay quickly.

Wood chips are rarely tested and may contain pesticides and herbicides that can harm your garden plants and ecosystem. Fresh wood also tends to tie up nitrogen in soil, which can lead to a nitrogen deficiency at the soil surface. Wood chips steal nitrogen from vegetables and annual flowers.

Pros of wood chips
✓ Inexpensive or free
✓ Readily available and easy to find
✓ Excellent resistance to compaction
✓ High resistance to wind erosion
✓ Long-lasting

Cons of wood chips
✗ May contain harmful pesticides 
✗ Can form a crust that prevents water from filtering into the soil
✗ Textures and colors vary: Pieces are not uniform 
✗ Can attract termites or roaches around house foundation

Pine Straw
Pine needles, also known as pine straw, are airy and light, but they’re also tough: They interlock to stay in place, so they’re perfect for slopes and ridges. They’re springy and resist soil compaction so you can cut back on aerating your lawn. 

Pine needles are excellent for acid-loving garden veggies like tomatoes, celery, cauliflowers, and carrots. They have a long lifespan (two to four years), release a pleasant aroma as they age, and won’t form a water-resistant crust like wood mulches tend to do.

Don’t worry about pine needles permanently acidifying your soil. As they decompose, they neutralize. 

Pros of pine straw
✓ Excellent resistance to compaction
✓ Reduces the need to aerate
✓ Long lifespan
✓ Visually appealing

Cons of pine straw
✗ Can be a fire hazard
✗ Can prevent water infiltration if layer is too thick

Ground Covers
Want instant greenery without the hassle of spreading mulch? Ground covers smother weeds and keep soil pores open to stop compaction. Their dense root structures prevent erosion, insulate soil, and reduce evaporation. In other words, ground covers are the perfect living mulches.

Many ground covers attract pollinators and create a beautiful habitat for native animals and insects, so you can enjoy a lovely butterfly show while enriching your soil. 

Some popular ground covers for our area include:
Mountain Spurge
Algerian Ivy
Asiatic Jasmine
Autumn Fern
Bishop’s Hat
Blue Lyme Grass
Bugleweed
Cast Iron Plant
Carolina Yellow Jessamine
Christmas Fern
Comfrey
Common Rock Rose
Creeping Barberry
Creeping Raspberry
Creeping Thyme
Daylily
Dianthus
Dwarf Japanese Garden Juniper
Dwarf Japanese Plum Yew
Evergreen Candytuft
Foamflower
Hardy Ice Plant
Horizontal Junipers (Blue Rug, Blue Chip, Bar Harbour, etc.)
Japanese Rooftop Iris
Lamb’s Ear
Lenten Rose
Liriope (Clumping, Spreading)
Mazus
Mondo Grass
New York Fern
Orange Coneflower
Plantain Lily, Hosta
Plantain Pussytoes
Prostrate Germander
Prostrate Rosemary
Shore Juniper
Silver Brochade
Southern Lady Fern
Southern Maindenhair Fern
St. Johnswort
Strawberry Geranium
Stonecrop
Sweet Woodruff
Thrift, Moss Phlox
Variegated Ribbon Grass
Virgina Chain Fern

Pros of ground covers
✓ Excellent erosion resistance
✓ Roots resist compaction
✓ Perennials don’t require frequent replacement
✓ Reduce the need to aerate
✓ Low maintenance compared to other plants
✓ Attract pollinators

Cons of ground covers
✗ Require more maintenance than non-living mulch
✗ Individual plants can be expensive
✗ Can compete with desired plants for nutrients
✗ Take time to establish
✗ Can be invasive

Some other organic mulch types that Corona Lawn Care doesn’t currently offer installation of include: Partially Decomposed Leaves, Grass Clippings, Straw (not pine straw), Aged Sawdust & Cocoa Hulls.

INORGANIC MULCH
What is inorganic mulch?
Inorganic mulches do not decompose, or they slowly break down only after a long period of time. These can be either manmade products, such as rubber, or natural products like slate chippings. They do not improve soil conditions as they won’t release nutrients into the ground, and their permanence means they can be difficult to remove if you change your mind. However, they do have many benefits, and in some situations might be more suitable than organic mulches.

The benefit of inorganic mulch is that they may initially cost more, but they are more cost efficient because they do not need to be reapplied or topped off as frequently as organic mulches.

The disadvantages of inorganic mulches that do not decompose is that they do not add any nutrients to the soil, and, in fact, some can prevent nutrients from reaching the soil altogether.

Using inorganic mulches in gardens can definitely add aesthetic value and they work well to suppress weeds. However, they do not help much in retaining soil moisture, protecting plants through winter, or adding nutrients to the soil from decomposition as organic mulches do.

Common Types of Inorganic Mulch
Rock or Gravel
Decorative rock mulches can make flower or landscape beds look very clean and appealing. When applied thick enough or used with plastic or fabric, they successfully suppress weeds. While they can cost a lot at first, they rarely ever need to be reapplied or topped off. However, rocks do not add any nutrients to the soil or help retain moisture. In fact, rocks can absorb and reflect heat from the sun, causing the area to become too hot and dry for many plants. Rock mulch is best used for areas with no plants or drought resistant plants. It is also very heavy to apply and hard to work with and plant in once it has been laid. Gravel and river stone work well for plants that like additional heat and require good drainage. Gravel and river stone are also good choices for purely aesthetic purposes where plantings are few or non-existent.

Plastic Sheeting
In my personal opinion, plastic sheeting is the bane of the garden’s existence and should never be used. Everyone has their own opinions and preferences, though. Plastic sheeting does work effectively at suppressing weeds and is oftentimes covered with organic or inorganic mulches to make it look nicer. It also lasts for a long time, saving you money by not needing to be replaced often. Why I truly despise the use of plastic sheeting in gardens is because it does not allow water, air, or nutrients to get down to the soil. It is because of this, it is not recommended for use around plants, especially trees and shrubs with large root spreads. Additionally, it does not allow the soil to breathe, and it kills many beneficial insects, such as worms and valuable microorganisms that live beneath the soil. Ultimately, it kills the soil itself.

Landscape Fabric
Good quality landscape fabric effectively suppresses weeds while also allowing air, water, and nutrients to penetrate the soil. It is usually covered with organic or inorganic mulches to make it look more appealing. So, what’s the downside? Cheap landscape fabric can rip easily or breakdown quickly; therefore, it may cost you extra money in replacement or by combining other weed control methods.

Rubber Mulch
Rubber mulch is usually made from ground, recycled tires. Using recycled materials is always a plus. Rubber mulch can effectively suppress weeds and does help retain soil moisture, in some cases. It is also available in different colors for an interesting look. Rubber mulch is thought to be good for playgrounds because it is soft and rubbery. All that aside, the toxicity of rubber mulches is still being studied.
All that aside, the toxicity of rubber mulches is still being studied. Also, in a study by OSU, rubber mulch was found to be the most flammable of all types of mulch. It does not break down and can remain in the soil for a very long time.

Mulch is often partnered with planting or perhaps sod.