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Why do plants need perlite?

Plants grow best when their roots have access to water, air, nutrients, and the soil is lightweight and resists compaction. Perlite does all these things by retaining just the right amount of moisture while allowing the soil to fully drain. This recharges oxygen levels in the rootzone each time you water, and by nature of being extremely lightweight, perlite keeps the soil from compacting, even when fully saturated.

What is perlite?

Perlite is a versatile, natural material produced by expanding naturally occurring volcanic glass to form lightweight granules with uses in horticulture, agriculture and other industries.

Up close, perlite has highly-textured surface that retains water and nutrients used by plant roots and the surrounding biology to enhance their growth and maintain health.

Perlite is lightweight, sterile, and pH neutral making it useful for all settings where growing plants is concerned. Originally developed for use by professional growers wanting a weed-free alternative to dense soil and sand-based mixes, perlite is now available to the individual gardener and hobby grower looking for clean, consistent product to mix with other ingredients, or use for hydroponics to enhance their home gardening experience.

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How is perlite used?

Because of its many useful properties and the variety of sizes available, perlite is adaptable to different growing settings. The way you use perlite will depend on your focus. Maybe you are interested in a seed starting mix to experience the wonder and joy of starting plants from seed. Alternatively, maybe your interest lies more in propagating larger plants from cuttings for your personal indoor plant collection or as a business. Or maybe you are pursuing the ultimate in controlled agriculture and need a sterilized media with the perfect balance between water-holding capacity and air-filled porosity ratio. Whichever the case, there is a grade of perlite that fits your growing style. Read on for more details of how to use perlite with your preferred growing method.

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As a soil
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Starting seeds &
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Hydroponics & Indoor
Agriculture
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Outdoor & Backyard
Gardening
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As a soil amendment

  • Perlite gives plants access to air, water and nutrients, while preventing oversaturated conditions from developing which can lead to root rot.
  • Perlite provides pore spaces which allow for the exchange of air in the root zone where the oxygen is used fuel new growth and in an organic system and used by the microbial community to unlock nutrients and make them available to the plant.
  • Perlite increases the size and number of pore spaces (or pockets) available for the storage of air, moisture, and nutrients and turns dense, compacted soil or growing media into a light, airy substrate with the characteristics of a sponge – able to absorb many times its weight in moisture and nutrients in solution.
  • The same pores act as pathways for channeling water throughout the entire rootzone rather than watching precious irrigation water hit the surface of the soil and run off to the sides. As the water descends into the soil, it draws fresh air behind it and allows excess water to drain out. Any excess buildup of salts exits the root zone, leaving it primed for renewed growth.
  • Finally, perlite provides structure to roots and keeps the soil from compacting as organic matter is consumed and begins to break down.
Process
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Starting seeds & propagating from cuttings

Seeds, starts or baby plants need more moisture to germinate and grow roots. At the same time, they need sterile growing conditions, and a balance between air and water to combat the growth of bad bacteria, fungi, and other pathogens.

Seeds also need more humidity to germinate; therefore, finer gradations of perlite are useful since they hold onto a greater percentage of water by weight.

Fine seed starting mixes benefit from finer gradations of perlite because it retains more moisture and blends more evenly into mixtures of fine gradations of peat or coir seed. If you’re growing commercially, these finer seedling mixes will fill the openings in small seedling trays and containers more evenly when using automated filling equipment.

Propagating from cuttings again calls for more humid conditions to set new roots. Cuttings can be started directly in perlite, however, remember to keep them watered and allow excess moisture to drain. Perlite will naturally maintain the right balance of air and water in the rootzone when drainage holes are added to the container, but will eventually dry out if the water level is not replenished. Use a soil moisture monitor to keep track of changes in soil humidity and indicate when it’s time to water again.

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Hydroponics & Indoor Agriculture

Hydroponics and indoor agriculture has given gardening enthusiasts a whole new outlet for growing indoors, and year-round. Those without access to physical garden space outside can still learn about the joys of gardening while at the same time growing with improved quality and yield, reduced pressure from diseases and pests, and optimizing the productivity space and water usage of the available space.

Perlite is ideally suited to indoor and hydroponic growing because it is clean, sterile, and will not rot or introduce pathogens. Plus, it is completely inert meaning it does not react with other minerals, nutrients, and pH adjusters in your system. This means you can spend less time fussing with your media, and more time focusing on optimizing the growth and productivity of your plants!

There are many systems out there from beginner to professional that use perlite as a pure substrate or in combination with coir or other ingredients. Search for “perlite” and “hydroponic gardening” on Youtube, Facebook, and TikTok for helpful tips, hints and tricks.

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Outdoor & Backyard Gardening

Rejuvenate backyard planters, raised beds, and compacted garden soil by mixing perlite in to your existing soil. For existing beds, start by tilling 2” of a mixture of perlite, peat moss and or compost into the top 2-6 inches of your soil or garden beds to reintroduce organic matter, and improve the texture of the soil that enables it to hold onto more air, water and nutrients and give plant roots room to grow.

Perlite can be used to break up dense compacted clay soil, improve drainage, and lowering overall density, or add water-holding capacity to sandy soils.

Growing flowers, herbs and veggies in a peat, perlite, compost blend either in containers – either store-bought or prepared from scratch – is another surefire way of adding satisfaction to your gardening experience, while beautifying even small spaces such as a sunny portion or patio, with a touch of color and greenery.

FAQs

How much perlite should my soil or potting mix have, or how much should I add when making my own potting mix?

As a general rule, potting mixes should have between 1/4 and 1/3 perlite by volume ensure adequate moisture-holding, drainage and aeration. Combine perlite with peat moss, coco coir, compost, forest products and or other organic media to make a well-draining, nutrient-rich and pH balanced growing media.

High porosity (HP) mixes used in hydroponic gardening typically call for as higher concentrations of perlite (as high as 50%). By increasing the percentage of perlite in your mix, you can increase the frequency with which you water and fertilize, which can boost the rate of growth in a controlled environment. In such a system, be sure to monitor moisture levels in the root zone to prevent the soil from drying out.

Certain plant types also call for a higher percentage of perlite. Cactus and desert plants require a mineral rich soil with lower organic content reflective of their native soil. Use a mix of equal parts soil or peat, perlite, and coarse sand to achieve a well-draining mix.

Orchid mixes are specialized blends of bark, perlite, sphagnum peat moss and other ingredients. See this list of 5 Recipes for Growing Different Types of Orchids or do your own search online.

What size or grade of perlite should I use?

All of our grades can be used to store moisture, lighten and aerate, and improve the overall structure of your soil, however, some grades are designed with a specific purpose in mind. Finer sizes hold onto more moisture and drain more slowly. They will also fit into void spaces between larger particles in a mixture, leaving fewer pore spaces for storing air. Use finer sizes of perlite with smaller containers and for starting plants from seed.

Larger particle sizes of perlite create more room for air and water to circulate and cause the soil to drain faster and retain less moisture. Use the following guide for help deciding which particle size to use for your growing environment.

GradeFine or MediumCoarseSuper Coarse
SizeFine (1-2 mm), Medium (2 – 3 mm)3 – 12 mm5 – 12 mm
BenefitsHolds more moisture. Fills small containers more evenly.Balanced between moisture-holding capacity and drainage.Maximum aeration and drainage.
ApplicationFine textured seedling mixes.All-purpose propagation, container growing, and gardening.Hydroponics, orchid mixes, large container growing, etc.
Suggested Container SizeSmall plug trays and liners. Pints and quarts.Pint size containers and up.Large gallon containers and up.
Can perlite be used as a fertilizer? Does it contain any plant nutrients?

No, perlite should not be used in lieu of a plant fertilizer regimen. Perlite may provide trace amounts of silica (an important plant micronutrient) but it does not contain the big three macronutrients (Nitrogen, Phosphorus or Potassium, or NPK for short) which are essential to a plant’s growth and development.

Is perlite a synthetic or natural?

Perlite is a fully natural, safe and non-toxic product. It is basically obsidian (volcanic glass) that contains a percentage of moisture allowing it to expand when heated rapidly in a specially-designed furnace. No other chemicals or additives are used in its manufacture.

Can I use perlite for organic gardening?

Yes, Supreme Perlite’s horticultural grade products are OMRI Listed® for use in organic agriculture.

How long will perlite last in my garden or container?

Perlite is durable and stable and should last up to 5-7 years in the soil. But eventually it will break down and need to be replenished. We recommend replacing your soil every year or every other year depending on what plants you are growing and the condition of the soil.

Can perlite be reused or recycled?

Yes, perlite in potting mixes can be recycled into more useful potting soil along with other organic matter that goes into your compost. Be sure you are using appropriate methods to get the compost temperature up high enough to kill off any diseases or pathogens.

If you intend to reuse your perlite in a hydroponic application, such as growing greenhouse tomatoes, some studies available on the internet show this to be an economical alternative to buying all new media. That said, the perlite must be separated from any soil and roots and sterilized accordingly, which can be a lengthy process. Be sure and read up on the pros and cons before trying these methods to ensure success with the lowest amount of down-time.

Is perlite safe to use around the home?

Yes, perlite is safe, non-toxic, and non-hazardous, however, be sure to keep it stored away from pets and children, and avoid creating excess dust when using or dispensing it. Perlite dust can be an irritant to the eyes, nose, throat and skin. To minimize these irritations, wear a dust mask and eye protection when working with perlite and allow for plenty of ventilation.

A proven method for controlling dust is to pour water over the surface or submerge it in a tub of water and use just the strained-out portion that floats. This will minimize the amount of dust and give plants an immediate source of water as soon as you’re done planting.

Is perlite sustainable?

Perlite is a mineral, therefore not a renewable resource in our lifetime. That said, perlite is a relatively low-impact material compared to many other substances and synthetic products on the market today. Supreme Perlite is committed to lowering the carbon footprint of our products. We use 100% green source renewable wind and solar power to power the electric parts of our plant. And very little water is consumed in the mining and manufacturing of perlite products.

As far as mining is concerned, only about 1% of the world’s proven reserves and less than 5 square miles of the Earth’s surface are actively mined in any given year, so the direct impacts from mining perlite are very minimal.

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Perlite contributes to the sustainability of other industries in a variety of ways. Perlite is used in greenhouse and nursery production, which in turn provides plant material for gardening, landscaping and agriculture which reduces greenhouse gases and beautifies the built environment and provides the fresh, healthy food we eat. Construction products use perlite as an insulator to protect from fire and improve energy performance. Perlite filtration applications improve water quality, keep pollution from entering the environment, and protect sensitive waterways from contamination.

Perlite, pumice, and vermiculite… How are they similar? How are they different?

Perlite, pumice, and vermiculite are sometimes confused with one another because they are all naturally occurring minerals, have similar-sounding names (in the case of perlite and vermiculite), and are occasionally used to replace one another in some situations. But each has specific properties and it’s important to know where and when to use each one.

PropertyPerlitePumiceVermiculite
ColorBright whiteGrey, buff or tanGolden brown
CEC (Cation Exchange Capacity)Little to noneLowHigh
pHNeutralNeutralSlightly alkaline
Loose bulk density4 – 8 lb./cu. ft.40 – 50 lb./cu. ft.4 – 10 lb./cu. ft.
Strength (durability)MediumHighLow, soft
Water-holding capacity (depends on grade)GoodLess than perliteMore than perlite
SterilizedYesNoYes
Primary benefitMaintaining balanced aeration, drainage, and water-holding capacity in soil; reducing compactionAdding porosity to soil for increased drainageAdding water-holding capacity, especially for seedling mixes

Perlite and Vermiculite:

Although perlite and vermiculite sound similar, they are different minerals. Perlite has a cellular structure and contains a percentage of glass bubbles that are sealed and do not hold water. Vermiculite, on the other hand, has an open, accordion-like structure, which accepts moisture more readily into the core of each particle. This is seen as a benefit in seed starting mixes but can lead to excess water-holding capacity under other circumstances. Vermiculite is also softer and more prone to compaction. Perlite is both more durable and offers a balance between water-holding and drainage, therefore, it is more widely used in container-growing mixes and potting media. See this Green Packs article for when and how to use perlite as a substitute for vermiculite.

Perlite and Pumice:

Perlite and pumice are also often mistaken for each other because they are both light in color, relatively lightweight, and used in potting soil to improve the drainage and aeration characteristics of the soil. But pumice is not sterilized, like perlite, and while it is more durable, pumice is also much denser, which can lead to issues with compaction. Plus, perlite has a more textured surface which offers more areas to store moisture and nutrients.

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Resources, Links & Inspiration

Here are some helpful links for using perlite in your garden or planters and to help you on your gardening journey.
Be sure to check out the many Facebook groups and Instagram posts for gardening tips sharing ideas online.
Or search the American Horticultural Society for gardening clubs, organizations, and societies in your area.

The external resources listed here are provided “as-is” and the views and opinions expressed in them are solely those of the authors and do not necessarily reflect the views or position of Supreme Perlite.

Helpful Tips & Tricks

#1 Pro Tip
When mixing perlite into potting soil along with dry fertilizers or other organic ingredients, use the perlite as an indicator of how well your ingredients are mixed as it stands out more against the background of the mix than the darker components.
#2 Pro Tip
Adjust the drainage profile and water-holding capacity of your soil or growing media by starting with the right grade of perlite. Use fine grades for seedlings and more moisture-holding capacity. Use larger grain sizes for more porosity, higher drainage, and more aeration.
#3 Pro Tip
To minimize dust pour water over the surface of the perlite before dispensing, or submerge it in a tub of water and use just the strained-out portion.
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