The soil is dry and cracked, does not work well or is particularly prone to weeds of any kind. These are not good conditions for flowers and plants to grow. But in recent years, lava mulch has been used more and more often in such cases. The following article explains the advantages of this type of mulching and when it is better to do without it.


As the name suggests, lava mulch is solidified lava rock. Lava gravel is therefore a natural product that is well suited for soil improvement. It is characterized above all by its low weight, the small stones therefore do not press into the earth but remain loose and are therefore above all permeable to water. In addition, lava gravel has the following properties:

  • ensures permeable structure in the soil
  • does not rot (unlike conventional mulch)
  • does not deprive the soil of any nutrients
  • Waterlogging doesn’t stand a chance
  • has a high mineral content
  • keeps the beds mostly weed-free
  • odorless
  • red-brown colored stones
Tip: If you don’t want a red-brown bed in your garden, you can also use many different other lava mulch products on the market, which are now also available in other colors.

Choose the right grain

Lava gravel is not only available in different colors but also in different grain sizes. These sizes are important for the individual functions that the mulch should provide on the garden soil. The rule of thumb when selecting the grain size is that the coarser the individual stones, the more difficult it is to remove weeds that have found their way here. Planting new plants can also be difficult if the lava is very coarse. Therefore, the following granulation is recommended in a garden bed as follows:

  • Grain from two to eight millimeters
  • or from eight to twelve millimeters
  • use different grits
  • this allows the pebbles to fit together more densely
  • use the same grain
  • Lava mulch stays loose
  • provides benefits when planting
Tip: A layer of lava mulch should always be between six and eight centimeters high on the garden bed so that the full effect can unfold.


There are many benefits to using lava mulch on garden beds. And that in all seasons. Since it does not rot, it does not have to be mulched every year, as is the case with bark mulch, for example. This is how the following advantages of using lava gravel can be named:

  • Beds become hardwearing
  • Compaction of the soil is prevented
  • no rot
  • very long lasting
  • Soil stays cool and moist in summer
  • Evaporation of water is reduced
  • Protected earth from cooling down in winter
  • Lava mulch warms up during the day
  • emits heat to the ground at night
  • Dampen the growth of weeds and wild growth
Note: If a weed fleece is laid over the ground below the lava stones, the effect against weeds and wild growth is increased.

effect on the garden soil

Applied to the garden bed, the mineral lava mulch should primarily ensure a constant temperature and even moisture in the soil. Since it warms up during the day via the sun and gives off this heat to the substrate at night, the warming of the earth can be accelerated in spring. Conversely, this also means that the gardening season can start earlier. Planted and sown crops grow faster and germinate sooner, resulting in earlier growth. In addition, lava gravel also has the following effects on the garden soil:

  • prevents soil erosion from heavy rains
  • same effect as a drainage laid in the ground
  • ensures rapid water passage
  • also for good ventilation
  • thus also prevents long-term waterlogging
  • yet soil remains moist for weeks
Tip: If the garden soil, on which quite robust plants grow, is mulched with lava, then the plants can easily survive longer absences of the garden owner without watering.

Lava mulch for visual garden design

Lava on a garden bed also offers a lot to the eye of the beholder and can turn a front yard or a patio border into a visual highlight. Because the lava gravel, which is available in different shades, can be used specifically for garden design. The following beds are ideal for mulching with lava:

  • rock or prairie garden
  • Garden paths and driveways
  • along a garden pond
  • around a fountain
  • near the lawn only with good edging
  • not under deciduous trees
  • cut grass and leaves cannot be removed

Anyone who spreads lava mulch on the right beds in their garden will notice over time that the maintenance effort is significantly reduced here.

Note: It is important that the small stones of the lava mulch do not end up on a lawn. Not only does it look unsightly when cut grass lies between the gravel. The small stones can also be dangerous when mowing the lawn if they get into the rotor blades and are then shot around like projectiles.


There are a few disadvantages that should be considered before applying lava mulch to the garden bed. Although it is a mineral rock, few nutrients are released into the soil when covered with a layer of lava gravel. Therefore, it must be considered here that the plants should be additionally fertilized. However, this fertilization can be done moderately, since the lava rock does not remove any nutrients from the substrate. In addition, the following disadvantages should be mentioned:

  • still grows weeds, difficult to remove
  • Gravel cover is then destroyed
  • must then be straightened again
  • New plantings in the existing layer difficult
  • do not use as an edging for a deciduous tree
  • falling leaves are difficult to collect
Tip: It is better to plan a bed in advance and plant the desired plants so that the mulch layer can be applied afterwards. Plants should only be used after mulching if there is no other option.

Use lava properly

The lava mulch layer can be applied all year round. There is no specific time for this. The light material is simply poured onto the bed and then evenly distributed with a garden rake. The following preliminary work should be considered here:

  • plant the plants first
  • grow
  • mulching takes place here in autumn
  • Keep the soil weed-free for some time beforehand
  • Do not injure or spill plants
  • apply only half the mulch in the fall
  • layer about four inches thick
  • then in December the second shift
  • another three inches
  • offers better frost protection for young plants
Note: If the lava mulch is applied in two steps, once in autumn and then again in December, this has the effect that any weed seeds that may be present on the first layer of lava can be prevented from growing.

The advantages of using lava mulch on a garden bed clearly outweigh the disadvantages. Because the mulch layer has either a warming or cooling and moisture-retaining effect. In addition, it offers the viewer a visual highlight in the garden. So if you plan correctly and lay the bed completely before applying the mulch layer, you have hardly any disadvantages. Only additional fertilization is required here, since the minerals contained in the lava stones are released very slowly and are not sufficient for the growth of most plants.

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