Pozzolana in mulch or drainage, in the garden or in your pots


Pozzolana is a natural draining material that we use a lot in the garden but also for plants grown in pots or containers. Let’s see what exactly pozzolana is, what are its main strengths and how to use it.

What is pozzolana?

It’s about a rock from volcanic slag. It is also called the lava rock. It is a material 100% natural with an alveolar structure, the density of which is of the order of 800 to 900 kg / m3.

Pozzolan is used in many fields such as cheese making because it is used for refining, aquarium keeping, construction, sanitation, septic tanks, protection of spreading networks, lagooning, underground filling for road construction for example, aboveground agriculture where it is part of the composition of the substrate or gardening whether for plants in the ground or in pots.

If pozzolana is also used, it is because it is an interesting material on different levels: it is natural, light, porous, friable and sandy.

What are the main advantages of pozzolana?

Lava rock is a material that can hardly be done without due to its particular characteristics.

  • Sustainable,
  • Resists all types of bad weather,
  • Does not break down over time,
  • Does not acidify the soil,
  • Has good water retention capacity,
  • Draining due to its porosity,
  • Easy to carry,
  • Easy to handle …

Pozzolana is widely used in the garden and in pots. It is a real ally of plant lovers who appreciate multiple advantages of this amazing rock, namely:

  • Limits the phenomenon of beat, that is to say the compaction of the soil by water which disrupts the penetration of water and air into the earth.
  • Facilitates the work of the soil since it settles less if it is protected by a mulch of pozzolana,
  • Stabilizes the environment of the underground fauna which benefits the garden by transforming organic matter into humus,
  • Stores heat,
  • Limits watering,
  • Reduces the time spent on weeding since it reduces the growth of weeds,
  • Protects plant roots against frost,
  • Limits the risks of fungal diseases because a pozzolan mulch prevents splashing on the foliage and therefore the dissemination of spores,
  • Keeps slugs and snails away due to the sharp edges.

The pozzolana is also capable of highlight the plants at the foot of which it is used as mulch. Depending on the degree of oxidation, its red, brown or black color seems to change depending on the brightness. On an overcast day, its color is dark and on sunny days it is much more colorful.

What are the main uses of pozzolana?

This light and porous but also decorative material is very versatile since it can be used:

  • As mulch in the vegetable garden, in the orchard, in the pleasure garden, in the pots and patio planters,
  • As draining integrated into the soil for potted and container plants that are cultivated indoors such as orchids, bonsai, exotic plants, succulents,
  • In a draining layer which we cover the bottom of pots before placing the soil or to put at the bottom of planting holes if the soil in the garden is clay,
  • As ground cover for an effect that is both protective and decorative, whether in massive, rockery, at the edge of the aisle,
  • As protection of fruits and vegetables such as strawberries, tomatoes, squash for example since thanks to a layer of pozzolana spread at the foot of the plants, the good products of the garden are no longer in direct contact with the soil. They are therefore cleaner and are less exposed to the risk of being damaged.

We can use it alone or in combination with other materials in order to create a beautiful harmony during the development of a landscaped garden for example.

However, it should be noted that the pozzolana does not provide nutrients to the soil. It is a mineral element that we use in addition to organic mulching. Placed on compost, for example, lava rock brings an aesthetic touch.

Where to find pozzolana?

Anyone can buy pozzolana in garden center where it is sold in bulk or in bags in the section reserved for mulch. We find her in blocks, it is then rather intended for the creation of rockeries, fine crushed or even in different grain sizes, 7-15 mm, 12-20 mm and 20-40 mm. A small particle size is used above all to constitute a substrate while a large particle size is perfectly suited for mulching.

As an indication, there are approximately 70 to 75 kg pozzolan with a particle size of 6-12 mm per m². We buy it in bulk if we want to cover a large area of ​​the garden with this volcanic rock. It is necessary to count between 12 and 15 € for a 20 liter bag or about 16 kg.