Rubber Mulch Vs. Lava Rock

Some rubber mulch is dyed to look just like wood chips.

Some rubber mulch is dyed to look just like wood chips.

Mulching is the gardener's weapon against weeds and soil moisture loss. Wood chips, compost and straw are common mulch materials, since they are organic matter, but they break down over time and require replacement. Some gardeners look to synthetic or inorganic mulches, like rubber mulch and lava rock, as alternatives to the common organic choices. Although both have their strong advantages in the garden, they each have distinct drawbacks as well.

Rubber Mulch Benefits

Often recycled from old tires, rubber mulch provides a long lasting soil cover. It is manufactured into different shapes, such as nuggets or strips, so that the garden appears to have a wood mulch covering, often with a red hue. Still relatively heavy in smaller chunks, rubber mulch will not fly away during windy days, making it a good alternative for blustery hillside gardens. Since rubber mulch has more density than organic mulch choices, you do not need to layer it as thickly compared to straw or wood chips for adequate weed control. As a result, you do not need to purchase as much mulch for the garden area.

Drawbacks to Rubber Mulch

Rubber's synthetic composition makes it useless to the soil as a nutrient contributor. Unlike wood chip mulches, necessary elements, like nitrogen, do not move into the soil, helping the ecosystem remain healthy. A non-profit organization consisting of accredited doctors and public health specialists, Environment and Human Health, Inc., reports that the zinc within rubber mulch leaches into the soil structure; zinc is known to cause stunted plant growth. In addition, rubber that catches on fire will burn at a higher temperature and its burning capability makes rubber a concern for fire-prone areas and nearby homes.

Lava Rock Advantages

Like decorative river rocks, lava rock provides a durable mulch alternative that does not need to be replaced constantly. Filled with air pockets, lava rock also acts as a warming mechanism for soil, so plants sensitive to cold weather will be insulated with the warming lava rock spread across the soil surface. In addition, lava rock provides a natural color tone in brown, black or red hues.

Disadvantages to Lava Rock

Like rubber mulch, lava rock provides no nutrient benefits to the soil. It keeps the soil warm, but the warmth factor can also be a drawback if the hot summer sun warms the rocks to high levels, harming plants with excessive heat. Additionally, as the rocks cool overnight, water evaporates from the surrounding soil creating a drier environment for the plants, compared to organic mulches. Garden functionality is also compromised since leaf and stem debris from nearby plants becomes stuck between the rocks, creating a messy appearance and creating the chore of moving the rocks to clean the debris.

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