Organic vs. Inorganic Mulch

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spring hyacinth growing up through wood mulch

When it comes to protecting your soil, mulch is all the rage, but choosing between organic and inorganic mulch can be quite a tough call. If you’re looking to give your soil a natural nutrient infusion, organic is the way to go. If you want long-lasting weed prevention, inorganic mulch may be your best option. 

Whether you want to go earthy and organic or chic and synthetic, we’ll walk you through which mulch is made for you. 

What is mulch?

Mulch is any material you can spread on your soil — but don’t reach for the butter or jam just yet! The right mulch reduces soil erosion, prevents weeds, insulates soil from temperature extremes, and retains soil moisture for healthy roots. 

If you want to give your plants the full benefit of mulch, butter won’t cut it. You’ll want to choose something a bit more durable (and a lot less slippery!). Try organic and inorganic mulches.

The big difference between organic and inorganic mulch? Organic mulch breaks down (decomposes), while inorganic mulch doesn’t. Decomposition can be a blessing or a curse, depending on how much maintenance you want to devote to your mulched area. Organic mulch requires routine replacement while inorganic mulch can last for years. 

Organic mulch

Organic mulches are made of natural materials like leaves, tree bark, grass clippings, and pine needles. As organic mulch breaks down, it changes your soil’s structure and texture and gives it a long-lasting nutrient boost. A layer of organic mulch is like a picnic for your plants. 

Best types of organic mulch

From tree bark to compost, organic mulch is a nutrition gold mine. Plus, you can use your own natural yard waste as a completely free, nutrient-packed lawn amendment.

  • Leaves: Coarsely shredded leaves control weeds and decompose quickly, giving your lawn a strong nutrient boost. Leaf mulch is a strong choice for general yard use: It works well on turf, in vegetable gardens and flower beds, and around trees and bushes. 
    • Layer depth: 2-3 inches
  • Tree bark: Tree bark mulch can be sold shredded and in larger “nugget” form, in many varieties of hardwood and softwood. A healthy layer of bark mulch will resist soil compaction and wind erosion, so it’s an excellent choice for slopes and around trees. To protect young plants from potential toxins, choose aged bark over fresh bark. 
    • Layer depth: 2-3 inches

Pro Tip: For plants that thrive in acidic soil, pine bark is a great choice.

  • Grass clippings: Grass clippings prevent weed growth and decompose quickly, providing plenty of nutrients for your soil. Just make sure you’re using dry grass: Wet clippings can form a mat and prevent water from filtering into the soil. Avoid using grass clippings treated with herbicide, as harsh chemicals can harm your plants. 
    • Layer depth: 2-3 inches

Pro Tip: Want to use your own grass clippings as mulch? A mulching mower will recycle your clippings right back onto your lawn.

  • Pine needles: Pine needles, also known as pine straw, interlock to stay in place, so they’re perfect for slopes and ridges. They have a long lifespan (2-4 years) and release a pleasant aroma as they age. Pine needles are perfect in garden beds and around trees and shrubs that prefer acidic soil. 
    • Layer depth: 3-4 inches
  • Wood chips: Also known as arborist mulch, wood chips are an aesthetically pleasing, inexpensive choice for pathways, around trees, and in perennial gardens. You can often get them for free from local arborists and tree recycling centers. Unlike uniformly textured bark mulches, wood chips include a variety of bark, inner tree wood, and sometimes even leaves. They have a long lifespan, lasting 2-3 years. 
    • Layer depth: 1-3 inches

Pro Tip: When wood-based mulches decompose, they use nitrogen, so you’ll want to apply fertilizer to increase nitrogen availability for your plants. Avoid using fresh wood chips in vegetable and annual gardens. 

  • Aged sawdust: Aged sawdust is a favorite for acid-loving shrub crops like blueberries and rhododendrons. As it decomposes, it can rob soil of nitrogen, so apply fertilizer directly after you spread sawdust.
    • Layer depth: 2-3 inches
  • Straw: For vegetable gardens and newly seeded lawns, straw will save the day. It’s cheap and decomposes quickly, improving the soil as it goes. You can choose from a variety of straw types — from wheat and timothy to oats, rye, and barley. Just be mindful of weeds and unwanted plants: Straw often contains grain and weed seeds, which you won’t want in your garden. 
    • Layer depth: 3-4 inches
  • Cocoa hulls: Cocoa hulls are an attractive addition to annual gardens and weed-prone areas. They’re an aromatic, natural byproduct of chocolate. Lightweight and easy to apply, cocoa hulls decompose quickly to provide nutrients to soil. Don’t place them in a pet-accessible area, though: Chocolate byproducts can be toxic to animals. 
    • Layer depth: 1 inch
  • Compost: Compost is the star of the mulching world. It’s a nutrient-rich mixture of decomposing organic matter, from table scraps to fallen leaves. It fertilizes soil and gives plants an enormous growth boost. Compost is perfect for vegetable gardens, flower beds, trees, and shrubs. 
    • Layer depth: 2-3 inches

Pro Tip: You can buy compost at your local garden store or you can make it an easy, money-saving DIY project. 

Want the benefits of mulch in plant form? Ground covers like liriope, pachysandra, periwinkle, and clover prevent erosion and soil compaction, insulate soil, suppress weeds, and conserve soil moisture. They’re often referred to as living mulch or cover crops. 

Benefits of organic mulch

Increases soil nutrient levels for lasting plant health.

Organic mulches naturally add nutrients to your soil in the long term. If you opt for compost, you’ll give your lawn a gold mine of nitrogen, phosphorus, and potassium to keep it healthy and happy without the need for synthetic fertilizer. 

Improves soil texture and structure.

As organic mulch decomposes, it breaks up clay soils and increases sandy soil’s ability to retain water. It naturally amends your soil to be more hospitable to plant growth. 

Invites beneficial microorganisms and earthworms.

Nutrient-rich mulch (especially compost) attracts earthworms and beneficial microbes to your yard, and with earthworms comes healthier soil. Earthworms naturally aerate your soil and reduce compaction, and their castings (excrement) add even more nutrients to create a cycle of soil health. 

Less expensive than inorganic mulches.

While stones and landscape fabric can put a dent in your wallet, organic mulches don’t cost a penny. You use your own grass clippings or create your own compost to save money and help the planet. 

Stabilizes eroded areas.

Sturdy wood chips and interlocking pine needles prevent sediment from floating away during rainstorms, so they’re perfect for slopes and ridges. They prevent soil crusting and keep water filtering smoothly into the soil.

Won’t overheat your garden.

While rocks, gravel, and black plastic mulches can heat your plants (sometimes to lethal levels), organic mulches will keep your soil warm in winter and cool in summer. 

Disadvantages of organic mulch

Requires routine replacement.

Because organic mulch decomposes, you have to replace it yearly or every few years, depending on your mulching material. Pine needles and aged wood chips can last for a few years, while grass clipping and straw will need to be replaced annually. 

Some mulches contain weed seeds.

Organic mulches like straw and grass clippings may contain weed seeds, which is frustrating for homeowners who applied mulch to get rid of weeds. Hay is an especially weedy offender: Think twice before applying it to your lawn. 

Fresh wood mulches can temporarily deplete soil nitrogen levels.

Though organic mulches add nutrients to your lawn in the long term, fresh wood competes with your plants for nitrogen as it decomposes. You’ll want to add fertilizer at the time of application. Fresh wood chips work wonderfully around trees and shrubs, but they shouldn’t be applied in vegetable gardens or annual flower beds. 

Moist wood mulches can attract pests. 

Termites and roaches are attracted to moisture, and wood mulches are excellent at retaining water. So when wood mulches are placed around the foundation of your house, trouble is brewing. If you want to prevent pests, go with gravel.

Where to use organic mulch

  • In vegetable gardens
  • In annual flower and perennial gardens
  • Around trees and shrubs
  • In areas prone to erosion
  • On turf that needs a green boost
  • Around pathways

Organic mulch is a fantastic choice for vegetable and flower gardeners and homeowners who want to give their lawn a healthy jumpstart. It’s also a great idea to spread organic mulch around trees and shrubs to protect and strengthen roots. 

Inorganic mulch

Inorganic mulches can be artificial, like rubber and landscape fabric, or natural, like river rocks and gravel. Plastic and fabric mulches are usually used to prevent weed growth, while stone mulches give your lawn a stylish flair. 

If organic mulches are picnic foods for your soil, then inorganic mulches are the picnic blanket. Inorganic mulches won’t add nutrients to your soil, but they’ll protect it from weeds and last longer than organic mulches.

Best types of inorganic mulch

For rock gardens, rain gardens, pathways, and playgrounds, inorganic mulch is an attractive, weed-resistant lawn addition that requires minimal maintenance. 

  • Gravel, pebbles, and river rocks: A 1-inch layer of gravel or rocks is an effective form of weed control that resists soil compaction and wind erosion. Plus, colorful rocks are eye-catching decorations around driveways and footpaths. 

Pro Tip: If you have acid-loving plants, stay away from limestone gravel. Limestone will raise your soil’s pH level.

  • Black plastic landscape tarp: A layer of black polyethylene will prevent weeds in flower and vegetable gardens. However, black plastic doesn’t allow for the flow of air or moisture, so root rot can become an issue. Cut holes in the plastic sheeting to encourage the flow of moisture, and bury it underneath a more decorative, organic mulch (like wood chips or pine needles). 
  • Landscape fabric: Landscape fabrics, also known as geotextiles, suppress weeds while also encouraging a free flow of air and moisture. Anchor your landscape fabric to prevent slippage, and then apply a top layer of decorative mulch for visual appeal. If a weed pops up, pull it out immediately so it doesn’t get embedded in the fabric. 
  • Reflective metallic mulch: Reflective mulches look like they’re from outer space, but they’ll repel insect invaders like nobody’s business. These silver, shiny mulches signal to pests like aphids that they should “keep flying.” You’ll need to cut holes in the mulch for planting and install a drip irrigation system to ensure that roots get plenty of water. 
  • Rubber mulch: A 1- to 2-inch layer of recycled rubber from tires improves your soil’s moisture retention, controls erosion, and keeps soil warm in the winter. Plus, it’s sturdy and resists decomposition. However, zinc toxicity from tires can inhibit plant growth and some experts warn against the use of rubber as a mulch.

Benefits of inorganic mulch

Long-lasting.

Inorganic mulch does not decompose, or it decomposes very slowly, so routine replacement isn’t necessary. You won’t have to purchase fresh rocks or new landscape fabric every year. Depending on the type of inorganic mulch you choose, you may not have to replace it for five or more years. 

Doesn’t include weed seeds.

Inorganic mulch doesn’t contain organic waste, so unlike straw, hay, and grass clippings, there is no chance of weeds mixed in with your mulch. 

Doesn’t deplete nitrogen in soil.

While inorganic mulch won’t add nutrients to your soil, it also won’t temporarily deplete nitrogen levels like fresh wood mulch does. 

Eye-catching and versatile.

Multicolored stone mulches are gorgeous lawn additions around patios, footpaths, and other hardscape features. River stones are perfect for rock gardens and rain gardens

Prevents pests.

Moist, wood-based mulches will attract insects around the base of your house. If you’re worried about termites and roaches, a 6- to 12-inch layer of gravel around your home’s foundation will reduce moisture levels, making the area less attractive to pests. 

Disadvantages of inorganic mulch

Stone mulches settle deep in your soil.

Stone mulches can sink into your lawn, making future planting difficult. You’ll have to do a lot of digging and stone removal before you can get your plants into the ground. 

Rocks absorb and reflect heat.

During hot, dry summer months, the heat reflected by rocks can damage surrounding plants, burn roots, and hurt your feet (and your puppy’s paws). 

Plastic sheeting can prevent the flow of air and water.

Without air holes, plastic sheeting can trap moisture, leading to root rot. Black plastic isn’t a good choice around trees and shrubs. 

Landscape fabric can suffocate worms.

Though landscape fabric is more porous than plastic sheeting, it can get clogged with tiny particles of soil. This prevents water from filtering through and can suffocate beneficial insects like earthworms. 

Where to use inorganic mulch

  • Around footpaths, patios, and other hardscape features
  • In rock gardens and rain gardens
  • Around the foundation of your home
  • In areas that attract pests and weeds

9 general benefits of mulch

Different mulches offer different benefits, but mulch is one fantastic lawn amendment. Here’s why mulch — both organic and inorganic — is a yard superstar. 

 Mulch… 

  1. Keeps soil moist, reducing evaporation so you won’t have to water as frequently. 
  1. Prevents soil compaction, decreasing your aeration needs and keeping grass green and lush.
  1. Prevents weed growth, so desired trees and garden plants don’t have to compete for nutrients. 
  1. Encourages root growth, as roots can extend into the mulch instead of being confined to the soil.
  1. Protects trees and shrubs from mowing damage, so roots and bark stay healthy and intact.
  1. Reduces erosion from wind and rain, keeping the soil surface permeable and protecting your ecosystem from harmful runoff. 
  1. Prevents the spread of soil-borne diseases (which can damage or kill sensitive plants) by reducing soil splashing.
  1. Adds visual appeal: When it comes to designing an elegant lawn, mulch is a favorite among landscapers.
  1. Keeps soil temperatures stable, which prevents frost heaving. Frost heaving (the repeated freezing and thawing process that pushes plants out of the ground) damages roots and stunts future growth.

FAQ about mulch

1. When should I apply mulch? 

You can apply mulch at any time of the year, but it’s most beneficial to spread mulch around root zones in the middle of spring, as soil warms and the growing season begins. This will give plant roots protection and a nutrient boost as they’re entering their most active period. 

2. Can I layer fresh mulch over my old mulch? 

You can, but make sure you fluff the old mulch before adding the new to prevent compaction. 

Before adding new mulch, check your mulch depth: Your mulch layer should never be higher than 4 inches, so you may need to remove some old mulch before layering fresh mulch. 

3. Can I mulch around my trees? 

Absolutely! In fact, applying organic mulch (like wood chips) around a young tree is the single best practice you can do to give that tree a healthy start, according to the Kansas State Master Gardener extension. Just make sure you keep your tree roots safe.

1) Spread mulch 3-6 inches away from the tree trunk. Never mulch directly around the tree trunk. It’s unhealthy for the bark and can cause internal rotting, disease, and even plant death. Think of your mulch ring like a donut: You want a hole in the middle.
2) Extend your mulch ring 3-6 feet around your tree. To promote growth, you’ll want the widest ring possible. 
3) Spread your layer of mulch 2-4 inches deep. 
4) Add fresh mulch yearly. First, pull away the mulch that has settled at the tree trunk. Then, check your mulch depth and remove old mulch as needed: Your mulch layer should never be higher than 4 inches.
5) Expand the ring’s diameter as the tree grows to give roots the full benefit of mulch. 

Choosing the right mulch

Organic mulch both protects plant roots and infuses soil with nutrients, while inorganic mulch prevents weed growth and can give your home loads of curb appeal.

If you’re not sure which mulch to choose, or if you’d rather not haul a cubic yard of mulch onto your lawn, call a local lawn care pro to give your yard the royal mulch treatment.

Main Photo Credit: Coernl | Pixabay

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