5 Types of Inorganic Mulch

rubber mulch on a playground

Inorganic mulch is often overshadowed by popular organic mulches, but it deserves its own spotlight. Inorganic mulches suppress weeds, insulate soil, and give your lawn curb appeal just as well as (or better than) organic mulch. So let’s pause the applause for organic mulch and give inorganic mulch its starring moment. 

This article is all about inorganic mulch: What it is, which types you can choose, how and where to apply it, and the benefits and disadvantages of it. Let’s mull over mulch!

What is mulch?

Mulch is a protective layer of material that you spread over your landscape to prevent erosion, control weeds, and keep soil temperatures stable for healthy plant growth. It’s an essential landscaping practice that promotes the health of your soil, garden plants, and trees.

What is inorganic mulch? 

There are two types of mulch: Organic and inorganic. Organic mulches decompose, while inorganic mulches either do not decompose or decompose very slowly. Here’s a quick rundown of what it means to have organic versus inorganic mulch. 

Organic mulch is made of plant-based materials like wood, tree bark, pine needles, and leaves. Because organic mulches were once alive, they decompose over time, adding nutrients and attracting earthworms to your soil.

Inorganic mulches can be natural (like river rocks and gravel) or synthetic (like landscape tarp and rubber), but they were never alive, so they don’t decompose. This means you don’t have to replace them as frequently as organic mulches, but it also means they don’t return nutrients to the soil.

The big takeaway? Organic mulches are best for homeowners who want to give their lawn long-lasting nutrients, while inorganic mulches are best for preventing weed growth and enhancing your yard’s appearance. 

If you’re ready to hop aboard the inorganic mulch train, read on! If you’d rather go with organic mulch, check out our article on the “10 Best Organic Mulches for Your Yard.”

5 types of inorganic mulch

Inorganic mulch ranges from beautiful rocks for your rain garden to metallic tarp that keeps insects away from your vegetables. Depending on the variety of inorganic mulch and how you install it, it can last years without you lifting a finger. 

1. Gravel, pebbles, and river rocks

garden featuring rock mulch and a variety of plants
James Steakley | Wikimedia | CC BY-SA 4.0

Rock mulches control weeds, stand strong against soil compaction, and won’t blow away in the wind. These yard superstars include:

  • Volcanic rock
  • Gravel
  • River rock
  • Pebbles
  • Marble chips

You can choose the perfect color and texture of rock to accentuate your landscape design and make your neighbors ooh and aah.

Rocks are an excellent addition around your home’s foundation. A 6- to 12-inch layer of gravel reduces moisture levels, making the area less attractive to pests like termites and roaches. 

Where to mulch: 

  • Gravel and stones look great around driveways, walkways, and hardscapes. 
  • They’re an eye-catching addition to rock gardens and rain gardens. 
  • Don’t spread rocks around trees and shrubs. They reflect solar rays and heat surrounding soil, which can stress plants and cause root burn.

Pro Tip: Use rocks with a diameter of half an inch or less to ensure you’re getting the benefits of mulch. If you have acid-loving plants, stay away from limestone gravel, which will raise your soil’s pH level.

Pros of rock mulchCons of rock mulch
✓ Visually appealing
✓ Excellent resistance to compaction
✓ Readily available
✓ Won’t blow away
✓ Controls pests
✗ Needs landscape fabric underneath to prevent sinking
✗ Won’t insulate soil in winter
✗ Can overheat plants and plant roots in summer
✗ Can be expensive

2. Black plastic landscape tarp

Fighting a weed army in your vegetable garden? Black plastic tarp can be your hero. A layer of black polyethylene will prevent weeds in flower and vegetable gardens and warm the soil in spring for a bumper tomato harvest.

Black plastic doesn’t allow for the flow of air or moisture, so it’s important to cut holes in the plastic sheeting to prevent root rot. Bury it underneath a more decorative, organic mulch (like wood chips or pine needles) to keep it in place and improve your soil’s resistance to compaction.

Where to mulch: 

  • Black plastic mulch works best in vegetable gardens. 
  • Don’t spread black plastic around your trees or shrubs, as this can lead to root rot. 
Pros of black plasticCons of black plastic
✓ Excellent weed control
✓ Inexpensive compared to reflective mulch
✓ Keeps soil warm and moist
✓ Readily available
✓ Increases vegetable yields
✗ Visually unappealing
✗ Degrades quickly when exposed to sunlight 
✗ Can lead to root rot and heat damage
✗ Poor resistance to compaction
✗ Removal of old tarp can be time-consuming
✗ Will fly away if not anchored down

3. Landscape fabric

Landscape fabrics, also known as geotextiles, suppress weeds while also encouraging a free flow of air and moisture. Unlike black plastic, fabrics resist soil compaction and won’t decompose easily. Landscapers tend to prefer landscape fabrics over black plastic. 

Firmly anchor your landscape fabric and then apply a top layer of mulch to keep your soil loose and uncompacted and give your lawn visual appeal. If a weed pops up, pull it out immediately so it doesn’t get embedded in the fabric. 

Where to mulch: 

three teenagers installing plants around stepping stones and pea gravel
Ryan Hagerty | Pixnio
  • Lay a landscape fabric around trees and bushes before layering an organic mulch. This gives your soil extra protection from weeds and compactions.
  • Geotextiles are a great option for slopes where soil erosion is an issue. 
  • Avoid using geotextiles in vegetable and annual garden beds where frequent digging is required.
Pros of landscape fabricCons of landscape fabric
✓ Excellent weed suppressor
✓ Keeps soil warm and moist
✓ Readily available
✓ Pairs well with organic mulch and can be spread beneath stone mulch
✗ Weeds can grow into the fabric
✗ Poor resistance to compaction
✗ Removal of old fabric can be difficult
✗ Will fly away if not anchored down

4. Rubber mulch

pieces of rubber mulch in a person's hand
Phasmatisnox at English Wikipedia | Wikimedia Commons | CC BY 3.0

Shredded rubber is sturdy, stable, and stands up to the elements. A 1- to 2-inch layer of recycled rubber from tires improves your soil’s moisture retention, prevents wind erosion, and keeps soil warm in the winter. If you want a natural look, you can choose rubber mulches that are dyed to imitate the tree bark look.

Before you go all-in on mulch, it’s important to note that zinc toxicity from tires can inhibit plant growth and some experts warn against the use of rubber as a garden mulch. But if you want to give your kids a springy landing place in your backyard playground, rubber is tough to beat.

Where to mulch: 

  • Shredded rubber mulch can be combined with organic mulch in perennial gardens.
  • It’s a fantastic foundation layer for your playground or underneath your treehouse. 
  • Rubber mulch is flammable, so don’t place it near your fire pit.
Pros of rubberCons of rubber
✓ Won’t blow away in the wind
✓ Retains soil moisture
✓ Excellent weed suppressor
✓ Resists fungus and disease
✗ Zinc toxicity can inhibit plant growth
✗ Flammable at high temperatures
Some parents have raised concerns about rubber’s safety
✗ Expensive

5. Reflective metallic mulch

These shiny silver sheets may look like they’re straight out of a sci-fi movie, but they’re highly effective at repelling invading insects. Reflective (aka metallic or silver) mulches signal to disease-carrying pests like aphids, thrips, and whiteflies that they should “keep flying.” 

Reflective mulches will give you a splendid crop of veggies: They increase yields by as much as 20% compared to vegetables grown on black plastic.

If you’re going the metallic route, cut holes (3-4 inches in diameter) in the material for planting and install a drip irrigation system to ensure roots get plenty of water. Once installed, your reflective mulch will last for at least three years.

Where to mulch: 

Pros of reflective mulchCons of reflective mulch
✓ Excellent weed suppressor
✓ Prevents insects without the use of pesticide
✓ Lasts longer than black plastic
✓ Great for growing vegetables and citruses
✗ A big eyesore
✗ Very expensive
✗ Poor resistance to compaction
✗ Will fly away if not anchored down
✗ Can overheat plants in summer

Why should I choose inorganic mulch?

Inorganic mulch isn’t just a forgotten sibling of organic mulch. Here’s how it can uniquely benefit your yard: 

Longer-lasting than organic mulch: Inorganic mulches don’t need to be replaced for several growing seasons.

Saves money: While inorganic mulches usually cost more than organic mulches, you save money on the cost of organic mulch replacement. 

Suppresses weeds better than many organic mulches (like grass clippings and straw).

Many are visually appealing: While black landscape tarp isn’t gorgeous, river rocks, gravel, and marble chips can perfectly accent your garden or footpath. 

Doesn’t deplete soil nitrogen: Fresh organic mulches can deplete nitrogen at the soil surface, which leads to nitrogen deficiencies in flowers and veggie plants. Inorganic mulches don’t decompose, so they don’t tie up nitrogen.

Prevents pests: Dry gravel or rocks around your home’s foundation keep termites and roaches away, while moist wood mulches attract them. 

Doesn’t include weed seeds: Unlike some organic mulches, inorganic mulches are safely weed-free.

✓  Won’t blow away in the wind: As long as inorganic mulch is properly anchored, it won’t take off in the next windstorm (as straw and leaves are prone to do). 

Disadvantages of inorganic mulch

Inorganic mulch …

Doesn’t add nutrients or organic matter to your soil like organic mulch does.

Doesn’t improve soil structure for lasting growth benefits like organic mulch does.

Dark-colored inorganic mulches absorb and reflect heat, which can damage plants during summer (and hurt your feet and your pet’s paws!). 

Landscape fabric and black plastic can suffocate earthworms and healthy microorganisms, which diminishes soil health. 

Stones may settle deep in your soil: Without a lower layer of landscape fabric, stone mulches can sink into your lawn and make future planting difficult.

Black plastic prevents the flow of air and water: Without air holes, plastic sheeting can trap moisture, leading to root rot.

FAQ about inorganic mulch

1. Where can I use inorganic mulch? 

Inorganic mulch can benefit any area of your lawn. It just depends on the type of inorganic mulch you use. Here are some quick inspirations for where to spread inorganic mulch. 

Use gravel or stones around footpaths, patios, and other hardscape features
Use gravel or stones around the foundation of your home
Use gravel or stones (with landscape fabric underneath) in rock gardens and rain gardensUse landscape fabric, black plastic, or reflective mulch in areas that attract pests and weeds
Use landscape fabric on slopes and hills
Use rubber mulch underneath your treehouse or swing set
Use black plastic or reflective mulch in vegetable and flower gardens

2. How much organic mulch can I spread over my landscape fabric or black plastic?

Spread 1 to 3 inches of organic material (like shredded bark mulch or buckwheat hulls) over your plastic or fabric sheet, depending on what type of organic mulch you use. Never add more than 4 inches of mulch, as this can damage plant roots and lead to disease and rot.

3. How much does mulch cost?

Different mulches come with different price ranges. You can find gravel for $1.50 per square foot, or you can pay as much as $400 for a sheet of reflective metallic mulch. Visit your local garden center or home improvement store to price out which types of mulch are right for your budget.

4. How do I install landscape fabric?

It’s a bit of a process, but once you’ve installed your fabric, it can last for years. Here’s what you need to do:

Remove existing weeds
Evenly rake the soil
Add soil amendment if needed
Roll out the landscape fabric
Anchor the fabric with staples
Plant your flowers and shrubs
Spread organic mulch

For step-by-step instructions, check out our “How to Install Landscape Fabric” article. 

Give your lawn a mulch makeover

If you’re looking for a fresh, stylish lawn aesthetic, or if you’re eager to protect your young veggies from ravenous weeds, inorganic mulch can be the perfect choice for your lawn or garden.

While inorganic mulches tend to be pricier than organic mulches, remember that you won’t have to replace them every growing season, which means you can save money in the long term. 

Ready to give inorganic mulch the attention it deserves? Make mulching a DIY project — just remember the wheelbarrow and bring along a couple of friends! 

Or if sweaty yard work is a bit too mulch for you, call a local lawn care team to give your lawn a magical mulchy makeover.

Main Photo Credit: Phasmatisnox at English Wikipedia | Wikimedia Commons | CC BY 3.0

Maille Smith

Maille-Rose Smith is a freelance writer and actor based in New York. She graduated from the University of Virginia. She enjoys watching theatre, reading mysteries, and listening to psychology podcasts. She is an orchid enthusiast and always has a basil plant growing in her kitchen.