Your first encounter of perlite might have been when you first bought your commercial potting soil where you have seen white particles mixed with the dirt. You might have also encountered perlite when you saw these white, jagged pebbles in plants and succulent pots. Through the years, you have heard of perlite’s glory and now you want to try it in your own garden. But before you go down the perlite road, you have to know everything about what it is; the good, the bad and the practical. Thus, in this post, we will cover everything that you must know about what perlite is.
What is perlite?
So let us start with the basic question, what is perlite? When you buy a commercial potting soil, perlite is the white styro looking, rocky particle used and recommended in many horticultural endeavors. Perlite is not naturally white though because it is a by-product of volcanic activity. As a matter of fact, perlite is scientifically categorized as a volcanic glass. It comes in gray or deep black and is industrially processed to become white in color.
What does perlite look like?
As have been mentioned, raw perlite comes in gray/black color but when processed under high heat will change into color white. When mixed with commercial potting soil, they will look like crushed white shells. When bought for construction, perlite will look like small white pebbles. When bought for gardening and landscaping, perlites are amorphous which means that they do not have exact shapes. Of course, in hydroponics, perlite will be diluted in water.
What is perlite used for?
For this section, we will highlight why perlite is a mainstay in many gardens and hydroponics setup. To start, perlite is used for gardening and hydroponics because of its very distinct mineral properties and as such is beneficial in:
- Maintaining a neutral pH level for the soil.
- Aid better aeration thanks to its porous build (with its own water and air pockets).
- Maintaining the nutrient level in the soil as it is organic and its mineral properties are not toxic to the soil.
- Improve water drainage by allowing the right amount of water to be retained while the rest will be drained off.
- Being a soil substitute in soilless gardening called hydroponics.
What is perlite made of?
Perlite has been an existing and known mineral for the longest time because volcanic areas were everywhere and we all know that these areas became settlement areas due to its fertile soils. This gives light to why up to today, perlite is considered as an important ingredient in gardening and hydroponics. The reason is, perlite is made of 75% silicone dioxide and 25% aluminum oxide; a combination that we know now to be good in producing stronger roots and sturdier stems among plants. Alongside this combo, perlite is also infused with other beneficial minerals for the soil and plants like sodium, potassium, magnesium, calcium and 5% water.
How is perlite made?
In nature, perlite is made from hydrating an obsidian rock. But the perlite we know that is used in gardening and hydroponics is processed further. You see, the perlite we know undergoes a popcorn cooking like process. First, the gray/black obsidian are mined to be crushed in fragments. After this, the fragments will be heated until the temperature reaches 900 degrees Celsius. At that point, the obsidian fragments are already soft and the water trapped in each fragment has vaporized. Soon, each fragment will expand to more than ten times its original fragment size and its color will turn white. The outer surface of perlite will resist compaction and shall block moisture from entering it by absorbing water.
Pros and cons of perlite
With its nature as a volcanic glass, perlite sure has its own pros and cons. Of course, the pros and cons that we will mention here will still be related to gardening and hydroponics being used in many horticultural activities and as a go-to soil amendment for soilless gardening as in hydroponics. As have been mentioned in the previous sections, perlite is advantageous for gardening because it has a neutral pH level which is good for the soil. Furthermore, it has the ability for water retention which is good in draining excess water in the soil and avoiding overhydration. Above all, perlite is cheap and reusable. As perfect as it may seem, perlite also has its own set of drawbacks. One, it is too light and buoyant thus, incapable of anchoring the plants in place in certain hydroponic setups like ebb and flow and flood and drain systems. Due to its buoyancy, perlite will float away and will become an added errand since you have to take them off from the flow system for the water to drain. Second, perlite is dusty and when inhaled by people, the dust is unhealthy. Other than this, the dust could also induce clogging which will disturb the solution or mix where the perlite will be added.
Types of perlite
In case you noticed, we have been using the term perlite here loosely. To draw out the confusion, you need to know that there are three types of perlite and that we have been generally referring to horticultural perlite in the majority of the article. Let us get into the details of each type.
1. Expanded perlite
This type is used for construction and industrial activities. With only 6% water component and 15 times larger than its volcanic glass size, expanded perlite is sourced because it is fire resistant and self-regulating thermal properties which are good features in modern construction.
2. Horticultural perlite
This type is the one used in gardening and hydroponics. It comes in four grades depending on the level of size and water holding capacity (whc). The finer the size, the higher the water holding capacity. These grades are as follows: super coarse perlite used drainage and aeration (19% whc), coarse perlite which is best for succulents and orchids (34% whc), medium grade perlite for potted seedlings and as component for commercial soil potting mix (46% whc) and the fine grade perlite for starting seeds and rooting plant cuttings (52% whc).
Speaking of industrial grade perlite, we have the third type. Instead of crushing the perlite, it is coated with hydrophobic coating to create vapex. With its high liquid absorption feature, it is used to absorb crude oil, lubricants, petrol and other oily substances that are spilled in water which are oftentimes caused by ecological catastrophes and unwanted cargo ship collisions.
How to make lightweight concrete mix with perlite
Perlite concrete is a lightweight mix which can be used for many garden projects including perlite concrete boxes. Making one can be easy as long as you have the following components:
- Pour a 94 pound (or 1 cubic foot) dry cement in a concrete mixing machine.
- 13 gallons of water for 1 cubic foot of dry cement poured in the same mixing machine.
- After stirring, pour 6 cubic feet of perlite (the perfect ratio for 1 cubic of dry cement used) into the wet cement mixture.
- Make sure that the perlite is evenly distributed in the mix. Avoid overmixing to prevent perlite crushing.
How to use perlite in potting mix
Perlite is added in soil mixes or pre-added in some potting mixes because it helps a lot in aeration and water draining in potted plants and in garden plants. If you intend to have a DIY perlite mix in your potting mix, you must know how to do it.
Mix #1: Sterile seed starting mix with perlite
Seed starter mixes should be lightweight but firm with the ability to retain moisture for the seedlings to grow. Seed starters should not have compost or weed in it and that is why perlite is a good mix. To make this, you should mix the following: 3 parts perlite, 3 parts coconut coir, 3 parts peat moss, 1 part worm castings and filtered water.
Mix #2: Soil based potting mix with perlite
The first one can be used in hydroponics but this perlite potting mix is made exclusively for potted plants or generally in the garden bed. Now, the only trick here is the topsoil. Of course, not all plants thrive in a generic topsoil type. Thus, you have to identify first what type of topsoil will go with specific plants. After this, you can now mix the following: 1 part compost, 1 part topsoil, 1 part perlite, water (rainwater is highly commendable).
How to use perlite in hydroponics
Perlite is a go-to choice for soilless gardening especially during harsher seasons like winter. Banking on a nutrient-based solution increases the likelihood of plant survival but you have to know how perlite is used in hydroponics.
1. Bucket system
In here, you will line up perlite filled buckets with seedlings along a water line with a reservoir where the water will circulate.
2. Combine with other mediums
It was stated earlier that perlite will float and clog flow systems because they are too lightweight for hydroponic gardens. This will cease to be the case if you combine it with other growing mediums with higher densities. The most common medium combined with perlite in hydroponic gardens would be coconut coir and vermiculite.
Perlite for succulents
The best soil for succulents is one that drains fast and well. Since perlite is known for water retention enough for good moisture, draining capability and soil compaction feature, it is good for growing succulents. If you want to make your own perlite soil mix for succulents, just mix the following: 2 parts coarse sand, 2 parts black soil and 1 part perlite.
How to use perlite for cuttings
It has been found out by horticulture research that soilless potting mixes will result in sturdier cuttings and 80% chance of surviving with healthier roots. In the absence of sand topsoil, perlite is the best recourse for propagation through cuttings because of the good drainage it offers. To propagate cuttings using perlite, you have to use plant bags. All you have to do is fill 1/3 of the plant bag with perlite, pour enough water to add moisture and allow the water to settle at the bottom of the bag. After this, put the cuttings in the plant bag and wait for it to root.
Is perlite organic or toxic?
Because it comes from natural obsidian rocks from volcanic areas, perlite is organic. However, because of this nature too, perlite could become toxic for humans if it is ingested or when perlite dust is inhaled in excessive amounts.
Perlite vs vermiculite
Both are used in gardening and horticulture and they can be combined as growing mediums in hydroponics but independently, they can be used for different things. Perlite is used if you need to loosen the soil’s clay component, if you have plants that you need to drain of water before watering again or if you have to move your seedlings to different pots in the future. On the other hand, you need vermiculite if you need a growing additive to keep your plants moist or for stronger seedlings.
Perlite vs pumice
Perlite and pumice are both used as substitute soils or mixes when growing succulents. Both of them do not retain water which plants need to get excellent drainage. They are mostly mixed together in one potting mix or hydroponic solution especially in propagating cuttings and in making sterile and weed-free mixes.
Perlite vs sand
On its own, sand can be too fine to allow drainage although it allows the mix to become less soggy. When you use quartz infused sand or #12 and #14 sand mixes, you can grow plants perfectly. We all know how perlite works and unfortunately, you cannot mix sand and perlite together. If left with one choice alone, perlite is a better alternative to pure sand.
Perlite vs diatomaceous earth
Shortened as diatomite, diatomaceous earth comes from the remains of a single-celled algae called diatoms. It shares with perlite in terms of processing under high heat and being used in gardening and hydroponics. The upside to diatomite is that it does the work of perlite with less amount but the important downside to think of is that it is way more dangerous than perlite and has been regarded as a hazardous waste by international health agencies such as FDA. So given the chance, perlite is still the safest choice.
Does perlite break down?
In contrast with vermiculite, perlite does not break down or decompose with time. This is the reason why it is a bankable choice for plants that will not need frequent repotting and in growing seedlings through hydroponic setups.
Does perlite hold water?
Perlite does hold water through water pockets created after expanding it under high heat. Its capacity for water retention is not the only reason as to why it is a mainstay in gardening, horticulture and hydroponics. It is also capable of draining out excess water making it versatile for any plant and in whatever gardening setup.
Where to buy perlite
You can buy perlite in home depots, hardware and gardening shops available near you. You can also conveniently buy perlite online through Amazon and eBay.
To conclude, perlite is a volcanic by-product that is proven to serve many functions. While it does aid construction and other industrial activities, perlite is more mainstay in gardening, horticulture and hydroponics. It is versatile to use in many garden setups. It is loved because of its water retention and drainage capacity. It can also be mixed with other growing mediums to be used as seed starter, cuttings grower and in strengthening plant roots and stems. And since it can be bought anywhere, no wonder that it is here to stay.