What is Perlite and How is it Used in Gardening?

What is Perlite?

Perlite is a popular soil additive utilized for plant growth. It is widely used by gardeners to improve their soil conditions or to use in hydroponic setups.

It is not a naturally occurring mineral, but it is a rock that does not contain any toxic chemicals and is safe to use in a garden or potting mix.

Perlite is a type of amorphous volcanic glass rock widely mined in many parts of the world. It is formed due to the hydration of obsidian, which is neither a true rock nor a mineral.

Due to its formation from hydrated obsidian, perlite has a higher water retention capacity than other rocks and minerals. 

Like vermiculite, this rock has an expanding characteristic as it expands when heated. It is obtained by opening pits methods like blasting or ripping.

Its original use was in construction for cement and gypsum plasters and masonry construction.

Related post: Various Types of Hydroponic Growing Mediums to Use

Different Grades of Perlite

Perlite rock can be found in three grades:

Large (coarse) perlite

These particles are used for garden beds or raised beds in clay soils with high water retention capacity.

Using it can create air pockets in heavy soils, improving the aeration.

Medium Grade Perlite

Medium-grade perlite pieces are mostly used in potting mediums.

Overall, this size can be used for all purposes related to gardening, like potted plants, hydroponics, or window boxes.

Fine perlite

Fine particles of perlite are great for seed germination because they can hold moisture for a longer period.

However, it’s difficult to find separately; you should, therefore, search for fine pumice as it is used for succulent or bonsai planting. 

Related post: Pumice vs. Perlite: When Do You Use Them?

How is Horticultural Perlite Made?

how-is-horticultural-perlite-made

Horticultural perlite is generally made by exposing it to heat.

When it’s heated to 1400–2000-degrees Fahrenheit, it causes the trace water to expand to 7-16 times its initial size [1].

During this process, the rocks begin popping like popcorn, and eventually, the rock becomes an extremely lightweight material.

If you continue heating, the rock will consist of tiny air compartments.

Remember that the dust particles generated in this process can cause eye irritation.

If you use a microscope to observe perlite, you will notice many tiny cells, and they can retain excess water on the particle’s surface.

Thus, plant roots can have access to more readily available moisture. 

This incredibly lightweight material is sterile, and you can use this perlite for organic gardening.

The expanded material can give the gardeners the same benefit provided by vermiculite.

They can also use it as a growing medium for root cuttings or directly as rooting mediums.

Learn more about the differences between perlite and vermiculite.

Various Uses of perlite in the garden

  1. Perlite in the potting soil is like a non-organic additive. It is used to aerate the medium as it is more porous than vermiculite.

    Remember that these two cannot be used interchangeably, though their functions are similar.
  2. Perlite can be an excellent rooting medium, but it can also be used for constructional purposes, like in gypsum and cement plasters or loose-fill insulation.
  3. A horticultural perlite is a pure form of naturally occurring rock that you can safely use for soilless media, like hydroponics.

    However, beware of fluoride burn while growing plants in perlite alone.
  4. Perlite’s neutral pH level does not affect soil pH. Hence, gardeners do not need to think about adjusting the acidity level.
  5. Perlite and vermiculite aid in facilitating moisture availability to the plants.

    The tiny air compartments of perlite can absorb moisture effectively and release it based on the plant’s requirements.
  6. Using it in soil mixes and potting soil can reduce the compaction risk, which is common in clay soils.
  7. It can improve the soil structure as it keeps the medium oxygenated. 
  8. You can plant your cactus or succulents or any plants that do not need very moist media for growing in perlite mixed soil.
  9. For seed germination, always begin with moistened perlite because it emulates the coffee filter system for starting seeds.
  10. It can also reduce soil temperature fluctuations and salt concentrations [2].

FAQs

Is perlite organic?

There is no such thing as organic perlite. Perlite is not organic because it does not contain carbon.

Can I use Perlite for organic gardening?

Yes, you can use it with other organic compounds in your garden effectively. Adding perlite to the garden is safe.

What are the disadvantages of perlite?

Water can escape the perlite media quickly. Also, because of being lightweight, perlite is blown away easily.

Can I use perlite in a hydroponics system?

Yes, you can use perlite in hydroponics.

Perlite helps stimulate root growth and protects plants from drowning by reducing excess water from the plant cuttings.

This results in the plants’ roots receiving the correct amount of water and oxygen.

Conclusion

To get the best result from perlite, you should mix it with vermiculite, coco coir, peat moss, or even rice hulls with soil in equal parts.

Both vermiculite and perlite enhance the moisture retention capacity of the soil.

However, comparatively, perlite is more porous than vermiculite, ensuring better and proper drainage.

Due to this characteristic, gardeners should use it for the plants that do not require more water and prefer growing in well-draining soil. 

References

[1] Markoska, V.; Spalevic, V. and Gulaboski,, R. 2018. Research on the influence of porosity on perlite substrate and its interaction on porosity of two types of soil and peat substrate. Agriculture and Forestry, 64(3): 15-29.

[2] Raviv, M., and Lieth, J, H. 2008. Inorganic and Synthetic Organic Components of Soilless Culture and Potting Mixes. Pp: 505-544. In: Soilless Culture. Academic Press.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.