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What is Perlite?

Perlite is a lightweight, porous, and inert material made from expanding volcanic glass. It is a popular additive in potting mixes, as it helps improve drainage and aeration while retaining some moisture. Besides the gardening aspects, perlite is also used in a variety of other applications.

perlite in potting soil with seedling

What is Perlite Used For?

  • Construction: Perlite is a lightweight aggregate in concrete, grout, and other construction materials. It can also be used as a thermal insulation material.
    Thusly making the concrete material lighter and increasing the R-value.
  • Industry: Perlite is used in a var
    • Filter media: Perlite is used as a filter in water treatment plants and other industrial settings.
    • Grinding media: Perlite is used to produce ceramics, plastics, and other materials.
    • Extruded polystyrene (EPS) foam: Perlite is used as a blowing agent in producing EPS foam, which is used for insulation and packaging.

Garden Aspects of Perlite

Perlite is a safe and environmentally friendly material that is available in a variety of sizes and grades. It is a versatile material that can be used in various applications.

perlite in a potting mix

Here are some of the benefits of using perlite in potting mixes:

  • Improved drainage: Perlite helps to improve drainage in potting mixes, which can help to prevent root rot and other problems caused by overwatering.
  • Increased aeration: Perlite helps to increase aeration in potting mixes, which can help improve plant roots’ health.
  • Moisture retention: Perlite can help to retain moisture in potting mixes, which can help to prevent plants from drying out.
  • Nutrient retention: As perlite retains moisture in all of the small and microscopic pores, it also will hold water soluble nutrients that can be released to plants as they need them.
  • Lightweight: Perlite is lightweight, making it easier to repot plants and move potted plants around.
  • Inert: Perlite is inert, containing no nutrients or chemicals that can harm plants.

Perlite is an excellent option if you are looking for a safe, environmentally friendly, and versatile material to add to your potting mixes.

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Home Microgreens potting mix contains a small percentage of perlite.

Is Perlite Natural?

Yes, perlite is a naturally occurring mineral mined from the earth. It is a type of volcanic glass formed when recently formed and very hot obsidian, a type of volcanic rock, is exposed to water.

The water causes the obsidian to break down into tiny, glassy beads. These beads are then heated to a high temperature, which causes them to expand and become porous and lightweight, forming perlite.

Perlite Comes in Many Sizes

Perlite is sold under many size grades. From quite fine grained (small diameter) to larger than pebble-sized.

There are four grades of perlite, based on particle size:

  • Super coarse (also known as #4 perlite) has particles that range in size from ¼ to 3/32 inches. It has a water holding capacity of 19%.
  • Coarse (also known as #3 perlite) has particles that range in size from 1/2 to ¼ inch. It has a water holding capacity of 25%.
  • Medium (also known as #2 perlite) has particles that range in size from ⅛ to 1/32 inch. It has a water holding capacity of 46%.
  • Fine (also known as #1 perlite) has particles that range in size from 1/16 to 1/128 inch. It has a water holding capacity of 52%.

The different grades of perlite are used for different purposes. Super coarse perlite is often used as a drainage medium in potting mixes. Coarse perlite is used for a variety of purposes, including potting mixes, growing media, and insulation. Medium perlite is a good choice for rooting cuttings and starting seeds. Fine perlite is often used in hydroponics and aeroponics systems.

When choosing a grade of perlite, it is important to consider the needs of the plants you are growing. For example, if you are growing plants that need good drainage, you will want to use a coarser grade of perlite. If you are growing plants that need a lot of air space, you will want to use a finer grade of perlite.

Here is a table that summarizes the different grades of perlite:

Grade
Particle Size
Water Holding Capacity
Typical Uses
Super Coarse
1/4 to 3/32 inches
19%
Drainage medium, potting mixes
Coarse
1/2 to 1/4 inch
25%
Potting mixes, growing media, insulation
Medium
1/8 to 1/32 inch
46%
Rooting cuttings, starting seeds
Fine
1/16 to 1/128 inch
52%
Hydroponics, aeroponics, potting mixes

Perlite Mine

Have you ever heard of Apache Tears? They are a small oval to round shaped obsidian (black volcanic glass) clast that rockhounds often collect. Apache Tears are found in perlite deposits. Below is a video of some rockhounds looking for Apache Tears in an abandoned perlite mine in Arizona.

Where Is Perlite Found?

Perlite is found in a variety of locations around the world. Turkey, China, Greece, and the United States are the largest perlite producers. Other countries with significant perlite deposits include Armenia, Hungary, and Japan.

Perlite is a non-renewable resource. However, the world’s perlite reserves are estimated to be sufficient to meet demand for many years.

Here are some of the countries where perlite is found:

  • Turkey: Turkey is the world’s leading producer of perlite. The country has significant perlite deposits, which are located in the Aegean region.
  • China: China is the second-largest producer of perlite in the world. The country has significant perlite deposits, which are located in the provinces of Gansu, Qinghai, and Sichuan.
  • Greece: Greece is the third-largest producer of perlite in the world. The country has significant perlite deposits, which are located in the Peloponnese region.
  • United States: The United States is the fourth-largest producer of perlite in the world. The country has significant perlite deposits, which are located in the states of Arizona, California, Idaho, Nevada, New Mexico, and Oregon.

Dangers of Perlite – Handling & Dust

While perlite is inert, that doesn’t mean you should be nonchalant while handling it.

It is generally considered to be safe, but there are some potential dangers associated with exposure to perlite dust.

The most serious danger of perlite dust is its ability to irritate the lungs. Inhalation of perlite dust can cause coughing, shortness of breath, and other respiratory problems.

Perlite dust can also irritate the eyes and skin. Exposure to perlite dust can cause conjunctivitis (pink eye), dermatitis, and other skin problems.

In addition to the respiratory and skin irritation, perlite dust may also contain crystalline silica, which is a known carcinogen. The amount of crystalline silica in perlite dust varies, but it is generally considered to be low. However, even low levels of exposure to crystalline silica can increase the risk of lung cancer.

The safety precautions for perlite dust include:

  • Wearing a dust mask or respirator when working with perlite
  • Avoiding contact with perlite dust
  • Washing hands thoroughly after handling perlite
  • Keeping perlite in a well-ventilated area

If you are exposed to perlite dust, it is important to seek medical attention if you experience any respiratory or skin problems.

Here are some additional information about the dangers of perlite:

  • Perlite dust can be more harmful to people with pre-existing respiratory conditions, such as asthma or bronchitis.
  • Children and pregnant women are also more susceptible to the harmful effects of perlite dust.
  • The symptoms of perlite exposure may not appear immediately, but can develop over time.

Don’t Let that Scare You

Please use your head when handling large quantities of perlite. The small amount that is in potting mixes is not a problem. That said, breathing in any potting soil dust (any dust, really) is not a good idea. Use a mask or be in a well ventilated area and don’t work with your head down close to potting soil or any soil container.

Stock images by Depositphotos

Author

  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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