Homesteading, Gardening, and Off-Grid Living

Mulch Vs Lava Rock for Landscaping: Pros and Cons

By: Zac Friedman

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When landscaping your yard, using some type of soil cover is a great idea. Two of the most popular options include organic mulch and lava rock. Both of these materials help to suppress weeds, maintain moisture, and reduce erosion. They can also improve the look of your garden. Organic mulches can release nutrients into the soil to help plants grow.

There are a wide range of mulches available. Mulch can be made from both organic and inorganic materials. This guide lists the pros and cons of using organic mulch vs lava rock for landscaping. We’ll cover moisture retention, weed suppression, cost, longevity, aesthetics, and more.

There are a wide range of organic mulches available including wood chips, bark nuggets, sawdust, leaves, pine straw, grass clippings, bark dust, compost, and more.

Lava rocks are a type of inorganic mulch. Lava rock is a type of igneous rock that forms when the lava cools. The molten rock undergoes a quick cooling process when it reaches the surface. Lava rocks are also known as scoria rocks or volcanic rock. 

Generally, organic mulch is better for plant and soil health because it breaks down over time and releases nutrients into the soil. This helps your plants grow. 

Inorganic mulch, such as lava rock, pea gravel, smooth river rocks, or landscaping gravel, helps to retain moisture and protect the soil from erosion. It also lasts longer because it doesn’t break down. 

A cactus with lava rock around the base

Pros of Mulch

  • Mulch enriches the soil with nutrients and organic material: Mulch contributes organic material to the soil as it decomposes. This improve soil fertility. Over time, microorganisms break the mulch down. This releases important nutrients such as phosphorus and nitrogen into the soil. These nutrients help your plants grow faster and stronger. Having organic material in the soil also improves soil structure. The organic material also helps the soil absorb more water. 
  • Moisture Retention: By covering the soil, mulch reduces evaporation. This helps the soil retain moisture for longer. It achieves this by shading the soil from the sun and blocking the wind. This moisture retention is particularly beneficial during hot or dry seasons. It helps with water conservation. You don’t have to water as frequently. This saves you time and reduces your water bill. It also makes your garden bed more drought-tolerant.  
  • Weed suppression: A layer of mulch can inhibit weed growth by blocking the sun from reaching the soil. This makes it harder for weed seeds to germinate. Weeds also have a hard time growing through the layer of mulch. Mulching is a great way to control weeds in sustainable gardening because it reduces the need for chemical herbicides. It can be even more effective if you install a fabric weed barrier underneath. 
  • Temperature regulation: Mulch acts as an insulator, keeping the soil cooler in the summer and warmer in the winter. It also helps to reduce temperature swings in the soil between the day and night. This can reduce stress on your plant’s roots. This is important if you live in an area with extreme weather. 
  • Erosion control: Mulch helps in preventing soil erosion by reducing the runoff of water. The mulch can absorb part of the water. It also slows the flow of water so the soil doesn’t get washed away.
  • Aesthetic appeal: Mulch can provide a neat, uniform look to garden beds. It is also a more natural look. It is available in a variety of colors and textures to enhance the visual appeal of the landscape design. Dyed mulch is also available. It can tie together walkways and flower beds. Wood mulch is beautiful.
  • Pest deterrent: Certain types of mulch can deter pests. For example, cedar mulch contains natural oils that insects, including mosquitoes, don’t like. It offers organic pest control. 
  • Cost-effective: Compared to other ground cover materials, mulch is relatively inexpensive and easy to apply, making it a cost-effective option for large areas in budget-friendly landscaping projects. You can apply it yourself. You don’t need to hire a professional. There are even free types of mulch. You can use grass clippings, dry leaves, pine needles, or compost for mulch. 
  • Soil pH Improvement: Some mulches, like pine bark mulch or pine needles, can help to slightly acidify the soil over time, benefiting acid-loving plants. Mulch can be useful for soil pH management. You have to be careful with this if you already have acidic soil. Woody mulches can lower the pH too much and make the soil too acidic. 
A pile of mulch and a wheelbarrow

Cons of Mulch

  • Frequent replacement is needed: Organic mulches break down over time and need to be replenished regularly. Most types of mulch need to be replaced once per year. Some can last 2-4 years. This adds to your garden maintenance costs. It also takes time.
  • Potential for mold, fungus, and disease: In wet climates, mulch can retain too much moisture, creating an ideal environment for mold and fungus. This can be detrimental to plant health. 
  • Attracts insects and rodents: Certain types of mulch can attract pests. For example, wood chips and bark mulch can attract termites. Mulch that is too thick can also provide habitats for rodents. These pests can damage your property.
  • Can wash away in rain: Heavy rains can displace lighter mulches. If you mulch on a slope, rain can wash the mulch downhill and cause it to pile up at the bottom. Some types of mulch, such as wood chips, float. If you apply these in an area that floods, they can easily wash away. This can be an issue in areas prone to heavy rainfall.
  • May contain weed seeds: If not properly composted or treated, some mulch can introduce weed seeds into the garden, creating more weed problems. This can be an issue if you mulch with compost.
  • Acidification of soil: Some mulches, like pine needles and pine wood chips, can acidify the soil as they break down. Most plants prefer soil with a neutral pH. If the soil becomes too acidic, some plants may not grow well. Before applying woody mulch, it’s a good idea to test the pH of the soil. If your soil is on the acidic side, consider a different type of mulch. 
  • Color fading: When wood and bark mulches are fresh, they have vibrant and beautiful colors. Depending on the species of tree they come from, they can have a beautiful brown or reddish color. Dyed mulches are also available in red, brown, and black. Mulch loses its color over time due to exposure to sunlight and weather. It can turn a dull gray, brown, or black color. This reduces the aesthetic appeal. If you want to keep the mulch looking fresh, you’ll have to replace it every year.
  • Not permanent: Unlike lava rock, mulch is not a permanent solution. Over time, it decomposes and needs to be replaced. 
A garden landscaped with lava rock

Pros of Lava Rock

  • Long lasting: Lava rock is durable. It doesn’t decompose, like organic mulches. It is a long-lasting landscaping solution. This is one of the main reasons it’s commonly used in commercial properties. 
  • Minimal maintenance: Unlike organic mulch, lava rock doesn’t need to be replaced yearly, making it a low-maintenance option ideal for those who don’t have a lot of time to work on their garden. A layer of lava rock will last forever. 
  • Weed suppression: Lava rock can act as a natural weed suppressant, reducing the need for herbicides. The rock blocks the sun to reduce the germination of weed seeds. It is also difficult for weeds to push through the rock to the surface if they do germinate. It’s a great choice for eco-friendly weed control. It can be particularly effective when you install landscape fabric underneath. 
  • Pest Resistant: Unlike organic mulches, lava rock does not attract insects or rodents. This makes it a good choice for areas near homes or other structures. 
  • Moisture retention: Lava rocks can help in retaining moisture in the soil thanks to their porous nature. Lava rocks contain air pockets. The rock soaks up water in the air pockets and releases it over the course of a few days. As a result, you won’t have to water as often. This is good for water conservation. The rock shades the soil and blocks the wind. This reduces evaporation. If you’re trying to build a drought-tolerant garden bed, lava rock is a good choice for maintaining moist soil.
  • Aesthetics: Lava rock is available in different colors. For example, you can red, brown, and black lava rocks. The unique red lava rock color comes from oxidized iron in the stone. The color won’t fade over time. It also comes in a variety of sizes. Lava rock can add a unique aesthetic touch to any garden. It can be used for decorative landscape features to enhance the curb appeal of your home. A lava rock garden can really improve the curb appeal of your house. It’s one of the most beautiful types of stone to use for mulch. 
  • Soil Insulation: These rocks can help regulate soil temperature, keeping roots cool in summer and warm in winter. During the day, lava rocks can shade the soil to keep it cooler and absorb heat from the sun. At night, it can pass this heat to the soil. This can reduce the temperature swings between the day and night, which reduces stress on your plant’s roots. Lava rock also helps your plants roots stay warmer in the winter by creating a barrier between the snow and ice and the soil. This is important if you live in an area with four seasons. 
  • Erosion control: Lava rock can be used on slopes to help stabilize the soil. It has good drainage. At the same time, it absorbs some water to reduce runoff. It also helps to prevent soil particles from washing away. 
  • Eco-friendly: Lava rock is a natural product. Landscaping rocks are a completely environmentally friendly choice.
  • They won’t blow away in the wind: Lava rock is heavy enough that it won’t move around during windy days. You can also use a leaf blower on it without blowing it around. This makes maintenance easier. It’s easy to blow away leaves and other debris.
  • Fire Resistance: Lava rock is fireproof, making it a safe landscaping material in fire-prone areas. This can be a major advantage if you live in an area that is prone to wildfires. Place the lava rock in your planting beds around your home or even your whole yard. It will help prevent a wildfire from spreading to your home. Lava rock can also be used in a fire pit or in outdoor kitchens.

Cons of Lava Rock

  • Higher initial cost: Lava rock can be more expensive upfront compared to organic mulch. Lava rock can cost anywhere from $100-$250 per cubic yard. The cost depends on the type of rock you buy and where you live. To compare, wood chips cost around $50-$100 per cubic yard, depending on the type of wood. This can be a significant factor for those on a tight budget. 
  • Difficult to remove or replace: Once laid down, lava rock is challenging to remove or modify. This can be an issue for those who like to change their garden design frequently or for those who want flexibility.
  • Heat absorption: Lava rocks can absorb and radiate heat. This can be hard on plants in very hot climates. It’s an important consideration for heat-sensitive plants. It can also make your yard and home feel hot.
  • Limited nutrient contribution: Unlike organic mulches, lava rock does not decompose and thus doesn’t enrich the soil with nutrients. Over time, lava rock can weather and release some minerals into the soil. Lava rock contains minerals such as magnesium, iron, and calcium. The amount released will be pretty negligible.
  • Uncomfortable to walk on: Its rough texture can make lava rock uncomfortable to walk on. You won’t want to walk on it barefoot. It can have sharp edges that can hurt your feet. Lava rock can also be noisy to walk on. It’s not a great choice for walkways. 
  • Incompatibility with some landscapes: The distinct look of lava rock may not suit all garden styles. The aesthetics of lava rock don’t match all homes and neighborhoods. Also, some people simply do not like the aesthetics of lava rock. It’s subjective. 
  • Not suitable for all plants: Some plants may not thrive with lava rocks due to their drainage and heat-retention properties. Before installing lava rock, you’ll want to check your specific plant needs. 
  • Wind displacement in lighter varieties: Some types of lava rock are less dense than others. A range of different sizes are also available. Lighter or smaller lava rocks can be blown away in strong winds. This could be an issue if you live in an area that regularly experiences strong storms or high winds. 
  • Lava rock can damage gardening equipment: If you run over lava rock with your lawn mower, the blade can get damaged. The rock can also be broken up and ejected out the side of the mower. This can be a safety issue. On one occasion, I had a piece of lava rock get jammed between my lawn mower’s wheel and the deck. This caused the self propulsion to stop working. It was very difficult to remove.
  • Lava rock is difficult to keep clean: Over time, debris such as soil and leaves will get caught in the lava rocks. This makes your lava rocks look messy and can be difficult to remove. Smaller lava rocks will blow around if you try to use a leaf blower. Lava rocks can also get lodged in the soil. They can be difficult to remove.
Bark mulch around a flower

Who Should Choose Lava Rock?

Lava rock is an ideal landscaping choice for those who are looking for a long-lasting, low-maintenance soil cover with a unique and beautiful aesthetic. 

Homeowners who value longevity and durability might also find lava rock particularly appealing. Its longevity makes it a cost-effective option in the long run, despite the higher initial investment compared to organic mulches. It doesn’t break down and need to be replaced, like organic mulch.

Those living in areas prone to wildfires may also prefer lava rock due to its fire-resistant properties. This natural stone offers an added layer of protection for your home.

Additionally, those who live in drier climates or regions with water usage concerns might find lava rock beneficial. Its ability to retain moisture can aid in water conservation.

Lava rock is also an excellent option for those who want a distinctive look for their garden. With its various colors and textures, lava rock can significantly enhance the curb appeal of your home. 

Who Should Choose Mulch?

Mulch is an excellent choice for gardeners who are looking to improve soil health and fertility. It’s great for individuals who are interested in organic gardening and wish to naturally enhance the quality of their soil. As mulch decomposes, it enriches the soil with essential nutrients.

Mulch is also a great choice for gardeners who are on a tight budget. Its relatively low cost and easy application make it the better option for those working with a tight budget or undertaking large-scale projects. You can even get mulch for free. 

Gardeners who are concerned about water conservation will also find mulch beneficial. Its moisture-retaining properties help in reducing water usage. In addition, those living in areas with fluctuating temperatures will appreciate mulch’s ability to insulate soil, protecting plant roots from extreme heat and cold. 

For more in-depth info on mulch and what it is, check out this helpful guide.

Final Thoughts

The choice between mulch and lava rock for landscaping comes down to personal preference, your specific garden needs, long-term maintenance considerations, and your budget. 

Mulch offers some major benefits like soil enrichment, moisture retention, and an organic approach to gardening, making it a preferred choice for eco-conscious gardeners and those looking to enhance soil health. 

On the other hand, lava rock stands out for its durability, low maintenance, and unique aesthetic appeal. It’s an excellent choice for those seeking a long-lasting and low-maintenance landscaping solution. 

Both options have their own advantages and drawbacks. Hopefully, this guide helps you choose the best ground cover for your garden.

Do you use lava rock? Share your experience in the comments below!

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