A good soil mixture is the foundation of every healthy plant. Aside from nutrient-rich soil, it is also important to provide a healthier environment for roots by adding soil amendments. One such amendment is perlite.
Perlite is a naturally occurring mineral that is added to soil to improve aeration and modify the substructure so it stays loose, well-draining, and doesn’t compact. Furthermore, its neutral pH promotes stronger roots and prevents root rot.
But, how much perlite should you use on your soil mix? Should you use perlite instead of vermiculate?
In this article, I will be answering all the questions you might have about using perlite for your garden and potted plants:
- Facts about perlite you should know
- Reasons for using perlite for plants
- How to choose the right perlite for your plant
- Different uses of perlite
- Substitutes for perlite
Let’s get started!
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What Is Perlite?
Perlite is the name for a volcanic rock often used as an ingredient in potting mixes. It can grow from four to twenty times its original volume when heated. Since perlite rapidly expands when wet or hot, it’s an ideal drainage material for gardening.
This material, also known as “volcanic popcorn,” is a versatile plant media additive that offers many benefits while having a few downsides. Perlite’s primary purpose for gardeners is to help with water retention and aeration and improve compost combinations.
A particle of perlite looks like a small white puff of foam, and its irregular size can help create air channels in dense dirt. It is also porous like a sponge, which can keep your potting soil from getting bogged down by the water.
Perlite is mined from many locations globally, and it’s always in high demand because of its uses in horticulture. The United States, China, Greece, Japan, Mexico, Hungary, Armenia, Italy, and Japan are among the countries that produce the most perlite.
Is Perlite Organic?
Finding a safe soil additive for growing edible plants such as veggies and fruits is challenging nowadays, with synthetic chemicals and pesticides rising. However, perlite is a classic, safe alternative to toxic plant potting media.
Perlite isn’t an organic material since it doesn’t contain carbon. However, it’s an all-natural substance that can be organically and humanely produced, so it’s safe to use when planting organic vegetables, fruits, and other edible plants.
By scientific standards, organic material is something that contains carbon. Since perlite doesn’t have carbon in its chemical makeup, it isn’t scientifically organic.
However, perlite can be organically produced with no synthetic additives. So, if your definition of organic is “all-natural,” it’s organic.
Perlite for plants is a natural substance, making it ideal for your garden. It’s not a chemical fertilizer, and it’s free of any potentially dangerous substances. Perlite is certified for use in organic agriculture by the National Organic Standards Board.
Additionally, perlite is a safe ingredient to put in your soil if you wish to develop an organic farm, allowing you to keep your organic status.
How Is Perlite Made?
Perlite is made from a volcanic stone called pearlstone, which is mined, crushed, and heated in perlite production. Since pearlstone contains water inside, it “pops” like popcorn in the microwave when it gets hot, forming foamy, white clusters of perlite.
Before perlite gets its foamy, puffy texture, it starts as a mineral called pearlstone. This mineral contains 3 to 4% water, which will help it take its final form of perlite.
Next, crude pearlstone is crushed and baked at 1650° F (898.9° C).
The heat weakens the crystalline structure, allowing the water trapped inside the perlite to expand by turning it into steam. As the moisture departs, the material expands, resulting in the perlite most commonly used in horticultural applications.
Perlite can swell up to 16 times its original size during heating. After cooling, the little white Styrofoam-like balls are permeable, sanitary, and stable.
How Much Water Does Perlite Hold?
Perlite can hold 20 to 50% water by volume, making this horticultural substance extremely absorbent and moisture-wicking. In general, smaller perlite particles will retain more moisture than coarser ones.
Perlite’s natural size and structure make it a suitable foundation for holding water. It stores water in three places:
- Between individual grains
- In channels leading to the grains’ centers
- On the uneven surfaces of each particle
These three water-storage surfaces allow each piece of perlite to absorb a significant amount of water.
Sometimes, perlite is used to retain water or other liquids to keep other things such as plants moist. However, you can also use it to wick away moisture.
Perlite can absorb and wick away a wide range of materials, although most practical uses include containing liquids such as water.
Why Use Perlite for Plants?
Perlite is a common additive to potting soils for all types of plants, and it has many benefits that can make caring for your garden or houseplant collection more accessible.
You should use perlite for plants because the coarse, absorbent particles can wick away moisture, keeping the soil from getting muddy if you overwater your plants. Perlite can also improve soil aeration and ensure that roots receive sufficient oxygen.
So let’s look at the pros and cons and talk about why you might or might not want to use more perlite in your horticultural practices.
Benefits of Using Perlite
There are many benefits of gardening with perlite, such as:
- It keeps the soil loose and airy.
- It’s better than vermiculite for aeration and drainage.
- It helps plants develop stronger roots.
- It keeps moisture in but doesn’t become mushy.
- It has a neutral pH level.
- It can ward off fungus, bacteria, weeds, and insects.
- It insulates and reduces temperature swings.
- It’s sterile, inorganic, and inert.
- There’s no known toxicity or fire risk.
Cons of Using Perlite
Here are the cons of using perlite:
- Adding too much perlite can drain away water too quickly, leaving the soil dry.
- It can be blown away and floats in extra water due to its light weight.
- It’s a nonrenewable resource.
- You have to moisten it before using it since the dust can be toxic.
- It may cause fluoride burns in sensitive plants.
Is Perlite Good for All Plants?
Perlite is an excellent material for plants that require well-draining soil since it promotes drainage more effectively than compost or other organic substances. However, it is not suitable for plants that prefer wet or marshy conditions to grow.
In addition, the sterile and pH neutral nature of perlite also makes it an ideal medium for the propagation of plants, as it accelerates the rooting process and plant growth.
Buying Perlite for Plants
How Much Perlite To Add to the Soil
Perlite is a versatile material that you can use in various soils to increase aeration and help drain moisture.
When mixed into another material or sprinkled on top, it’s excellent in propagation beds and seed starting containers.
Using Perlite for Seed Germination
If you want to use perlite to start some seeds, mix the perlite half and half with a soilless mix or sphagnum peat. You can use the same blend or as much as 100% perlite for cuttings.
Using Perlite for Garden Beds
To add aeration and insulation to garden beds, silty soils, or clay soils, rake 25% perlite into the first 2 inches (5 cm) of the dirt. This technical calculation is hard to follow, but remember that less is always better. Try to mix the perlite in so that your dirt looks like store-bought potting soil.
Perlite lasts quite a while after you apply it. Just one application will keep your soil light and loose for several years.
Using Perlite for Houseplants
You can also use up to ⅓ perlite per container for container gardens and potted plants. Perlite is a highly beneficial planting media for succulents and orchids, and potting soil made just for these plants can contain 50% or even more perlite depending on the type.
Using Perlite for Lawn
Perlite is beneficial to your lawn as well. If you distribute it evenly throughout the grass, it’ll gradually work its way into the soil. For the best results in rainy climates, spike or plug your lawn first to help the perlite get into the root zone faster.
Using Perlite for Preserving Bulbs
Additionally, perlite is excellent for preserving bulbs throughout the winter so that they’re ready to plant in the spring. Stack perlite and bulbs in alternating layers, cover with more perlite and keep them in a cool, dark, and dry location.
Signs You Are Using too Much Perlite
If there’s too much perlite in your potting soil, the water will flow out too quickly to keep your plants alive. So, if your plant begins to turn crispy brown and wilt or the soil remains dry despite regular watering, this could indicate too much perlite.
Grades or Sizes of Perlite
Perlite is available in four different grades and sizes, and each grade is best suited for specific uses.
| Perlite Size | Average Size of Particles | Water Retention | Best Uses |
|---|---|---|---|
| Super Coarse (grade 4) | 1 inch (2.5 cm) | 19% | Seed starting, propagation, aquaponics |
| Coarse (grade 3) | ½ inch (1.2 cm) | 34% | Potting medium for orchids or succulents |
| Medium (grade 2) | ¼ inch (0.6 cm) | 46% | Mixing into potting soils or raw earth |
| Fine (grade 1) | ⅛ inch (0.3 cm) | 53% | Mulch, sowing seeds, propagating plants that need lots of water |
Where To Buy
A big-box retailer like Home Depot is one of the most accessible places to get bulk perlite. Most supermarkets have a good assortment. However, it would be best if you double-checked the label to ensure that you purchase 100% perlite rather than a soil or fertilizer blend.
It’s also available from reputable hydroponics retailers.
However, getting it online might be best since you can quickly select the type of perlite that suits your needs. There are numerous options to choose from.
I always use this Gardenera Organic Perlite (available on Amazon.com), a mixed bag of medium and fine-grade perlite. It’s ideal for mixing into potting soil for succulents, flowers, veggies, fruits, and other garden or houseplants since it’s so versatile.
I highly recommend picking up a bag of this stuff over the others, which sometimes have chemical additives or sneaky pesticides.
Different Uses of Perlite
Use Perlite for Soil Mix To Aid Drainage
You can add perlite to mixes that lack soil to help with drainage and aeration, giving plant roots more oxygen. It’s also used as a soil addition in gardens with dense, clay-based soil to improve the soil structure and water drainage.
Perlite also aids in the decomposition of clay soils, making raw earth easier to grow plants in.
In addition, it’s commonly used as a stand-alone product in hydroponic gardening installations to germinate seeds, root cuttings, and anchor root systems.
Use Perlite for Rooting Cuttings
Perlite can help with water retention in compost, which can help your cuttings take root more easily. To root cuttings with perlite, follow the steps below:
- Fill some starter pots halfway with perlite and water thoroughly.
- Coat the cut end of the cutting with some rooting hormone to help it grow.
- Place your cutting directly into the perlite.
- Cover the starter pot with plastic wrap, a plastic bag, or any other clear plastic to trap moisture.
- Wait for your cutting to root, then you can repot it.
Use Perlite in Seed Sowing
Seeds of all types can also be rooted in perlite and potting soil. To do this, follow the steps below:
- Fill a small seed-starter pot with perlite.
- Place the seed on top.
- If your seed is large, put a pinch of the perlite on top to encourage germination.
- Place your seed-starter pot somewhere warm under a grow light, outside, or near a window.
- The sprout can be removed and potted in the compost once it has two adult leaves.
Use Perlite As Mulch
Another option to utilize perlite in container gardening is to use it as a light decorative mulch on top of beautiful container plants.
To use it, just lightly pack a layer of perlite around your plants to help encourage moisture retention. You can also choose to fill the top ¼ or ⅓ of your pot with perlite instead of soil for plants that like especially damp conditions.
Perlite mulch will also help your plants stay warm in the winter since the glass fibers are the perfect insulation.
Composting With Perlite
In potting compost mixes, perlite increases aeration, drainage, and insulation. You can add perlite to ready-mixed loam or peat-based composts to help them open up and let some air inside.
Use 3 or 4 parts sphagnum moss peat to 1 part perlite (80/20) for soilless compost blends.
You can also use equal parts loam, peat, and perlite (1:1:1), as well as limestone and nutrients, in loam-based compost combinations.
After adequately mixing your ingredients, water your mixture well and put some on top of your plants that need a nutrient boost.
Good Substitute for Perlite
There are several good perlite substitutes, such as vermiculite, pumice and LECA. However, each has some pros and cons, and they both retain and absorb moisture differently than perlite.
Perlite vs. Vermiculite
Vermiculite doesn’t look as bright or evident as perlite, so it may already be an ingredient in your favorite potting soil mix. It’s a deeper shade of brown that blends with the surrounding soil.
Vermiculite looks like small clusters with fine layers, similar to mica. Often, people describe these clumps of fiber as “accordion-shaped.” If you seek a substance that can retain water and aerate, vermiculite is a better option than perlite. Perlite is the best option for aeration alone.
The most crucial difference between perlite and vermiculite is that vermiculite is spongier and holds water better. While vermiculite is better for plants that love water, it’s not ideal for soils that need plenty of drainages.
So, vermiculite is ideal for growing veggies, fruits, and flowers that need consistently moist soil. On the other hand, perlite is perfect for plants like succulents and cacti that require plenty of air and very little water to thrive.
You can even use straight vermiculite as a seed starting medium since it holds water effectively. It also has a soft texture that’s perfect for new veggie plants.
Perlite vs. Pumice
A more environmentally friendly alternative to perlite is pumice. Compared with perlite, it requires less processing and is mined in an eco-friendly way.
This fine-grained volcanic rock is formed during eruption and cooled rapidly. As it solidified, it released the vapours dissolved in it and turned into a solid froth.
Generally, pumice is available in sizes and weight ranges between 1/8″ and 3/8″. Regardless of its size, pumice remains lightweight, but it is heavier than perlite.
Thus, pumice is a better choice when it comes to amending soil for taller plants, as its weight can help prevent pots from falling over.
Even though pumice has water-holding capacity, it is less effective than vermiculite at retaining water. Pumice is ideal for sandy soils because of this characteristic.
The only issue with using pumice is finding it in stores, especially crushed to mix with soil. In addition, they are more expensive than perlite.
Perlite vs Hydroton (LECA)
LECA (Lightweight Expanded Clay Aggregate) also known as hydroton or clay pebbles is very commonly used in hydroponic gardening.
The structure of LECA allows for lots of air pockets, which improves aeration. Thus, although LECA will soak up and retain water, the roots will not become suffocated by waterlogged soil.
The popularity of LECA has increased in recent years, as it can be used to replace soil completely.
However, due to its high price tag, LECA may not be suitable for larger hydroponic systems or commercial setups. In this case, perlite may be a more financially viable alternative.
Frequently Asked Questions
Does Perlite Cause Fluoride Burn in Plants?
Perlite can cause fluoride burn in plants since there’s fluoride in perlite. Some symptoms of fluoride burn include browning and discolored leaves. Still, there are ways to prevent this, such as using non-fluoridated water or lime to balance the pH.
Fluoride poisoning is an incredibly aggravating problem that discolors and damages your plants. Some plants are more likely to develop fluoride burns than others.
The Agavaceae family, which includes Dracaenas, Cordylines, and Yucca, is known for its fluoride sensitivity. In addition, some Marantas and Calatheas are sensitive to fluoride levels, as are Spathiphyllum, Aspidistra, and Chlorophytum.
Fluoride is a naturally occurring element that you can find in most rocks and soils. Some plants aren’t affected by fluoride at all. However, higher concentrations might induce browning and burning of leaf tissues in other plants.
Fluoride burns aren’t the end of the world for your plant, and they rarely affect healthy plant growth. However, they can cause leaf browning, which might be unsightly and concerning.
Air pollution, fluoridated water, fluoride in the potting media (such as sphagnum, peat, and perlite), and excessive fluoride in some fertilizer components can damage plants sensitive to this chemical.
Perlite doesn’t have enough fluoride in it to cause burns on its own, though. Excess fluoride damage and discoloration are frequently caused by or increased by multiple factors. Excessive soil wetness, root damage, a high salt level, and a low soil pH are all examples of this.
If you’re worried about fluoride burns, don’t fret! Here are some ways to keep the fluoride in your perlite from frying your plants’ tips:
Keep the pH Stable
To balance your soil pH, add lime, gypsum, or other calcium sources until the pH is between 6.0 and 7.0. Usually, about a tablespoon will do the trick, but use a soil tester to measure your soil before using it.
This method works because the calcium in the lime binds the fluoride molecules at this pH, preventing them from entering the plant tissues. So, with balanced soil, you can eliminate the threats of fluoride poisoning.
Set Fertilizer Restrictions
The majority of these fluoride-sensitive plants will thrive if fertilized once or twice a year. Keeping the fertilizer amounts a bit lower than recommended can ensure that your plant won’t suffer from other types of nutrient-based burns, which can keep it strong enough to be unaffected by fluoride.
Avoid Water With a High Fluoridation Level
Fluoride is everywhere, especially in the water that we drink. It’s almost always added to city tap water to help us stay healthy. However, this can be a disservice to our green-leafed friends.
To help keep fluoride from accumulating in your plant’s soil, try giving your plants rainwater, distilled water, or filtered water. You should avoid mineral waters and tap waters since these usually contain plenty of fluoride, which can build up in the dirt.
Although it’s not always possible to utilize water other than tap water, the first two measures can help you eliminate the need for water fluoridation control.
Use Low-Fluoride-Content Growing Mediums
If you’re worried about fluoride burns, try mixing your perlite with another soil ingredient that doesn’t contain fluoride. Usually, the best way to ensure that there are no unwanted chemicals in your soil is to read the label.
Usually, increasing drainage will help any fluoride escape, so using sand, loam, poultry grit, or any other bulky, water-wicking material will do.
Does Perlite Break Down/Decompose?
Perlite is a reliable material, not just for its ability to wick away moisture and increase aeration but for its longevity.
Perlite won’t break down or decompose over time since it’s a volcanic rock. Once you incorporate perlite into your potting soil mix, it’ll last forever. So, using perlite is a permanent and foolproof way to add more aeration and drainage to your soil without changing out the soil.
The only downside to perlite’s incredibly long life is that you can’t easily remove it once you mix it into the soil. So, be prepared for what you signed up for when you use perlite, and follow this guide to help you make the right decisions for your home and garden.