This guide discusses the best landscaping rock to prevent weeds and shares some advice on keeping your garden in tip-top condition. Over the years, I’ve learned a great deal about landscaping and garden maintenance, and I can’t wait to share my knowledge with you.
In this article, I focus specifically on landscaping rocks which are extremely common but frequently misused. Many gardeners think they have to place sheets of plastic beneath rock beds to stop weeds from growing through.
This smothers unwanted plants before they can develop. However, it may also cause damage to the soil by impeding earth-moving organisms, reducing moisture absorption and increasing the risk of waterlogging.
I’ll explain why these plastic sheets are not needed if a gardener uses landscaping rock correctly.
Table of Contents
What Is The Best Landscaping Rock To Prevent Weeds
Lava rock (also called volcanic rock) is the best landscaping rock to prevent weeds. Lava rock has a low thermal mass which makes it a good insulator and an inefficient conductor compared with other types of rock. It helps the soil retain warmth but as it’s so porous, it loses heat quickly. If it does get hot, it doesn’t stay hot for long.
Lava rock isn’t a magic cure for unwanted weeds. Like all landscaping rocks, it’s not 100% infallible. Stubborn shoots may occasionally find their way through but, even without landscaping fabric underneath beds and walkways, it does a good job of putting up a natural barrier.
Crushed granite is another good option as the larger pieces of rock make it hard for weeds to take a direct path upwards.
I should stress that no type of landscaping rock can completely prevent weeds. Laying landscaping fabric underneath the rock does help but it adds unnecessary plastics to the garden.
I prefer to keep things natural. So, I’ll be giving you tips on keeping your garden weed-free without the use of plastics.
Top 3 Landscaping Rock To Prevent Weeds
It can be surprisingly tricky to find good landscaping rock online. When I shop for gardening rock, I often struggle to find it in suitable amounts. It can get very expensive very quickly because lots of retailers sell small volumes designed for indoor potting and decoration.
When browsing for new landscaping rock, make sure you know exactly what you’re getting. Always read product descriptions carefully so you know how much material to expect.
I’ve picked out three products I think are worthy of your time (and elbow grease).
Venetian Princess Lava Rocks (Red or Black)
Key Features and Specs:
- Available in 10lb or 40lb bag
- 1/2- inch and 1 1/2- inch rocks
- Black or red color
- Safe for use in gardens, fire pits and grills
These lava rocks from Venetian Princess on Amazon are a beautiful rich color whether you buy them in black or red. When spread over earth outdoors, they trap warmth beneath the surface but, above ground, they radiate and dissipate heat quickly.
This is different from a rock such as a basalt which absorbs heat and loses it slowly causing it to stay hot for a long time.
This landscaping lava rock is coarse and unshaped so it’s perfect for gardens with a rustic, natural aesthetic. If arranged correctly, with minimal gaps for weeds to push through, it provides a good degree of protection against common pests like charlock, groundsel and chickweed.
I recommend this particular product from Venetian Princess because it’s extremely versatile. You can use it to create walkways, borders and beds. You can add it to pots and vases as a decorative feature. It’s also safe to use in outdoor fireplaces and fire pits.
- Can be bought in large amounts
- Rocks are large enough to impede weed growth
- Available in red or black
- Coarse, unshaped for a natural aesthetic
- Very dusty straight out of the bag
- A percentage may be bigger or smaller than stated
Margo Garden Products Rainforest Snow White Pebbles
Key Features and Specs:
- 30lbs of landscape rock per bag
- All-natural river stones/pebbles
- Size – .39″ (1 cm.), .5-1.5″, 1-2″, 2-3″, 3-5″
- Tumbled to create a smooth surface
These Rainforest Snow White Pebbles from Mango Garden Products on Amazon are very different from Venetian Princess’ lava rocks. They have a much more refined aesthetic having been tumbled and partially polished.
Though they’re not as natural-looking, I still recommend these rocks because they’re great for moisture retention.
Their size makes them good at slowing down the growth of weeds. They can be arranged around a border or walkway in a manner that leaves minimal gaps.
This makes it tougher for pest plants to push upwards and out. When landscaping rocks overlap, weeds have to fight harder to find spaces and sunlight.
Whether these Rainforest Snow White Pebbles offer value for money depends on how you intend to use them. They’re only available in 30lb bags so, if you’re decorating a large outdoor space, it could be a pricey affair.
I like these white landscape stones because they provide a middle ground between coarse ultra-natural rock and very refined, decorative rock.
They’ve been polished but they retain a roughness that is evocative of their origins as river rocks. These landscaping rocks hold heat for longer than lava rocks but not as long as something like black gravel.
- Aids moisture retention and erosion
- Partially polished for a stylized look
- Uniform color and size
- All-natural river stones
- Can be very bright in sunny conditions
- A percentage may be jagged/have rough edges
Mother Earth Hydroton Expanded Clay Pebbles
Key Features and Specs:
- Available in 10, 25 and 50-liter bags
- All-natural (no artificial colors)
- Ideal for self-watering systems
- Retains water for prolonged irrigation
I suspect these Hydroton Expanded Clay Pebbles on Amazon won’t be to everyone’s tastes but they’re worth a look for several reasons. The first reason is that they’re all-natural.
The pellets are formed from mined clay that has been shaped into balls and kiln fired. They’re not polished or colored. Technically, clay is not landscaping rock. But I’m making an exception because it’s dense enough to slow the growth of weeds.
The first thing I noticed about these clay pebbles is their varying sizes and shapes. Not everybody will like this but, if you’re building an intentionally wild, unrefined garden, they’re a wonderful addition.
Plus, their non-uniformity means they’re easier to arrange in a way that shuts out weeds while still leaving holes for air and moisture.
This isn’t clay soil, so you don’t have to worry about the material getting sticky or misshapen in wet conditions as silt does.
These clay pellets are commonly used in hydroponics systems, and they have no trouble keeping their shape provided they have been kiln fired at a professional level.
Clay is semi-porous like lava rock but very tough with a balanced capillary action. It can even be relocated and reused in some circumstances.
- Great look/aesthetic for wild, natural spaces
- Semi-porous but density impedes weeds
- Highly versatile (suits many different systems)
- Available in large quantities
- Non-uniform colors and sizes
- Technically not rock
Do Landscape Rocks Prevent Weeds
No type of landscaping rock can prevent all weeds from growing. If there was, it would smother the soil of air and moisture leaving it dry, dusty and devoid of life. This is not ideal for a garden, so we’ve got to make some compromises.
Landscaping rock is a heavier, more secure alternative to mulch which is also used to reduce weed growth. The problem with mulch is it’s messy and can blow all over the garden in strong winds.
Rock cuts off unwanted plant growth in the same way – by covering up points of emergence – but a few stubborn weeds will always find their way through.
You can reduce the number of weeds that survive by laying landscaping fabrics underneath landscaping rocks. Paired together, rocks and fabrics are very effective, but gardeners are growing increasingly wary of artificial materials in outdoor spaces.
Many don’t want plastic sheeting underneath their flower beds. Another option is to lay newspaper underneath your landscaping rocks.
The truth is some weeds will always get to the surface. The trick is to use clever landscaping methods to minimize the number of pests that pop up.
- Apply a pre-emergence weed killer to the area BEFORE adding landscaping rock.
- If possible, build an edging border 3 to 4 inches high to stop weeds from sending their roots into your rock beds.
- Add layers of cardboard and/or newspaper (underneath the landscaping rock) to shut out the sunlight weeds need to grow.
- Spread your lava rock, granite, pea gravel, cobble clay or other landscaping rock over the top in overlapping layers.
How Do I Choose A Landscaping Rock
Here are some other landscaping rocks you might want to consider:
In this context, the term decomposed means rock that’s extremely fine and broken down. Decomposed granite is a very fine material that looks a lot like construction sand.
It’s easy to pour, spread and arrange but it needs to be applied in a thick, dense layer to stop the weeds from penetrating.
- Great value for money
- Available in large quantities
- Very soft and fine
- Comes dyed in different colors
- Lightweight so weeds can push through
- Can look a little unrefined
Crushed granite may be a misnomer because these landscaping rocks are commonly pebble sized. The pieces are small but distinct and rarely crushed up enough to form ultra-fine sand as with decomposed granite.
This makes crushed granite a slightly more effective choice for weed prevention. It’s denser so it smothers more of the weed roots.
Granite is also surprisingly efficient at draining water and won’t leave puddles in the garden.
- Good drainage qualities
- Great for dividing paths and plants
- Very long-lasting when stabilized
- Natural, earthy aesthetic
- More expensive than fine granite
- Non-uniform sizes and shapes
Pea gravel is just a fancy term for rocks and pebbles that have been polished by water over many, many years. They’re essentially the same as river stones, only much smaller.
Pea gravel is collected from rivers, streams and other bodies of water. It comes in a wide variety of colorful, all-natural shades.
Gardeners love pea gravel because it has an interesting look while providing all of the sturdiness and longevity of tougher rocks like flint. It’s normal to see hints of yellow, orange, blue and even red rocks.
- Great value for money
- Earthy colors are all-natural
- Creates a beach-like aesthetic
- Very fine pebbles leave room for weeds
- Light enough to wander in strong winds
River rocks are similar to pea gravel insofar as they originate from the same watery environments. River rocks are much larger though they can be bought in a variety of sizes and shapes.
Most have polished edges, so they are smooth with no sharp or jagged points. Gardeners say they’re one of the best alternatives to mulch with the added benefit of not decomposing over time.
- Smooth and polished aesthetic
- Great alternative to mulch
- Very long lasting
- Lots of naturally occurring colors
- More expensive than pea gravel
- Among the largest landscaping rocks
Lava rocks are some of my favorite rocks for landscaping. I love their rugged, natural exterior and think they’re great for cultivating wilder, less refined areas in outdoor spaces.
As temperatures increase around the world, volcanic rocks like this will only get more useful. They’re good at trapping heat underground while also radiating it away from plants on the surface.
Lava rocks are affordable, lightweight and they act as an effective deterrent against most weeds and many insects.
- Good barrier against weeds and bugs
- Great value for money
- Lightweight (easy to transport and spread)
- Aids with stable, steady irrigation
- Rugged, coarse texture won’t suit all gardens
- Non-uniform sizes and shapes
Brick chips are small sections of broken brick, specifically red brick. So they have a beautiful rich color that is irresistible to some gardeners. They are visually striking, and this is the main reason they get used for landscaping.
Brick chips aren’t as effective at preventing weeds as some other options. In very wet climates, they can subside and sink into the dirt if landscaping plastic isn’t placed underneath for support.
- One of the most visually striking rocks
- Lightweight and easy to use
- Not great for weed prevention
- Can subside/sink after heavy rain
Depth Of Gravel To Prevent Weeds
Let’s turn to the more technical aspects of using landscape rock. Whether you’re working on a pathway, a water feature or a rocky flowerbed, you need to get your calculator out before you start shopping for materials.
Sure, you can guess how much rock you’ll need but that comes with a risk of wasted time and resources. Or even worse, a landscaping job that has to be stopped halfway through because there’s not enough rock.
To determine how much landscaping rock you’ll need, get yourself a calculator (or a smartphone) and a measuring tape.
Step 1 – First, measure the width of the area you want to cover with landscaping rock. Then, measure the length. I recommend repeating these measurements two or even three times to make sure they’re as accurate as possible.
Step 2 – Next, figure out how deep you want your landscaping rock to be. A rule of thumb used by many gardeners is two inches deep for optimal weed prevention, aeration and moisture penetration. This should be more than enough depth for a low-traffic bed. If you’re building a driveway or path, consider going a little deeper perhaps up to four inches.
To calculate how much rock you need (in total), multiply the width of the space by the length, then multiply by the depth.
Width x length x depth = total cubic volume
Step 3 – Here’s a tip that will help you if you’re getting all tangled up in numbers. Start by measuring entirely in inches. For instance, say the area you intend to landscape measures 60 inches lengthways and 50 inches in width. You’re going to fill the space with two inches of landscaping rock.
To convert the calculation into feet – this is important when shopping for materials – divide all of the numbers in the calculation by twelve. For example, 5 feet x 4.1667 feet x 0.1667 feet. (This is why you need a calculator).
5 feet x 4.1667 feet x 0.1667 feet = 3.4729 feet of total volume
Each cubic yard contains 27 cubic feet. So now divide 3.4729 by 27 to get 0.1286 cubic yards. This is the amount of landscape rock you’ll need for your project.
If the calculations get confusing, you can always use an online tool and/or ask a landscaping professional to check your sums. It’s a really good idea to ask an expert to check the numbers no matter how confident you are.
One wrong digit and you could end up making a costly error.
Can You Use Rocks Instead Of Mulch
You can use landscaping rock in several different ways. A common application is mulch substitute. If spread and layered correctly, rock can suppress weed growth, retain water and maintain soil health just as effectively as conventional compost.
Though the best results are seen in drier, more arid spaces with low maintenance plants such as cacti.
The biggest downside of using landscaping rock is its cost. Compared with mulch, it’s fairly expensive but it does add more to a garden’s aesthetic and design.
Here are some conditions which suit the use of rock as mulch:
- Gardens with poor drainage that need efficient capillary action
- Open areas with no plants (low maintenance option)
- High-traffic areas to avoid trampled/messy grass
- Around water features and sculptures
- Gardens that require minimal upkeep
Some additional things to consider:
- Gardens with a lot of overhanging trees can pose a problem for landscaping rock because debris falls, gets mixed up in beds and is hard to remove.
- No variety of landscaping rock can wipe out weeds
- Areas with landscaping rock need to be contained with a raised border to prevent materials from blowing into the lawn and causing damage to gardening equipment.
- Flowers find it harder to grow in rock (in comparison with mulch) but many drought-tolerant varieties will thrive. The best plants to place in rock beds are varieties that crave warmth and don’t mind being thirsty.
Helpful Tips To Choose The Best Landscape Rock To Prevent Weeds
- Landscape rock is commonly referred to as ‘decorative rock’ by online sellers. Knowing this will help you browse for the right materials.
- Don’t rush your calculations. Remember, two inches of depth is recommended for rocky beds. Three to four inches is advised for high-traffic areas such as driveways and walkways.
- If your garden project is extensive and you have the option to buy landscaping rock in bulk, it’s probably the cheaper option. It won’t always be possible but shop around to make sure you’re getting the best deal. You may even want to contact a wholesaler directly to ask if they will offer you a reduction for a bulk purchase.
- Landscape rocks come in a variety of sizes. The most common sizes are 1/4 and 3/8 inch but gardeners can also buy 1/2, 3/4 inch, 1 inch and 1 1/4 inch rocks if they look in the right places. The right size for you will depend on the size of your garden, what type of aesthetic you’re trying to create and how much you’re willing to spend.
- Where possible, buy all of the rock you need in one single purchase. This is a natural material so there’s bound to be color and size variations if you buy in separate transactions.
This guide to finding the best landscaping rock to prevent weeds has explored all of the challenges associated with this gardening strategy. Swapping conventional mulch for landscaping rock can be a gamechanger for those living in drier climates because rocks are long-lasting, stable and great for improving drainage.
While it won’t stop all of the weeds from sneaking into your yard, it will significantly reduce their numbers.