Though there are as many different gardeners as there are gardens in the world, there is a common thread binding them all. Every gardener hopes to raise the perfect specimen – countless hours have been spent inventing new tools and gadgets, and experimenting with new methods of cultivation.
Some methods are extremely successful, and some are not. Some chemical or organic additives are highly effective and others are not.
Whether used as an additive to potting soil or as the growing medium in a hydroponic garden, perlite has been proven to be of value to both the amateur and the professional horticulturalist.
The purpose of this article is to show you how to use perlite in hydroponics.
Perlite, those small white particles so recognizable from potting soil, is inexpensive and easy to use, and was one of the first reliable hydroponic growing mediums available.
What is Perlite?
Perlite is an ore derived from volcanic glass created when lava encounters water, and which contains a small amount of moisture inside.
When the glass is crushed and then superheated, the water vaporizes and causes the small granules to puff out like popcorn, creating a very porous surface. See what is perlite made of.
For decades, perlite has been used in cement, insulation and other building materials. Recently, it’s been used as a filtering agent and growing substrate.
Many hydroponic growers use perlite as their primary growing medium. There are advantages and disadvantages to using perlite, and growers should consider all aspects before choosing their medium.
Benefits of perlite
Like many hydroponic growing mediums, perlite can be reused. As it doesn’t hold on to nutrients, perlite can be easily cleaned in just a few moments; it can be gently shaken away from the root balls and rinsed until the runoff contains less than 150 ppm of particles.
If the perlite has been infected by diseased plans, it is also relatively easy to sterilize. It can be rinsed with a hydrogen peroxide solution or a bleach solution; remember to rinse extremely well with water if you’ve used bleach.
Sterile & pH neutral
Because perlite is inorganic, and given the extreme heat used to create it, there is very little chance for bacterial, fungal, or insect infestations. Therefore, unlike some other soilless media, it requires no sterilization before its initial use.
Perlite is also pH neutral, which is more convenient as it doesn’t require chemical adjusting of the pH levels in the growing system, leading to better long-term system health.
Perlite is very inexpensive – at approximately $1.00 per pound, it costs half as much as other sterile and pH-neutral mediums such as hydroton.
The coarse, porous texture of perlite allows it to hold air very well. The large size of the particles also provides natural air pockets while preventing compaction. This helps to reduce anaerobic conditions in the growing system – a lack of oxygen in the growing medium, whether it be water or soil, that can allow the growth of anaerobic bacteria and cause the plant to rot.
The disadvantages of using perlite
Perlite dust is fine enough to cause damage to pumps and tubing, so it should be rinsed thoroughly before being used in a hydroponic system to prevent dust from damaging it.
Perlite dust can also cause respiratory problems or irritation of the eyes, mouth, throat and lungs. It’s best to wear goggles and a dust mask when working with dry perlite – some growers prefer to fill their new bags of perlite with water before opening them in an effort to reduce or eliminate airborne particles.
Though perlite is not considered carcinogenic, its main component is alumina silicate, which can cause cancer. Research has shown that though exposure to perlite dust may aggravate pre-existing conditions such as asthma, and that long-term exposure to high levels of it may cause silicosis, perlite does not directly cause lung cancer.
Vulnerable to solids loading
In systems using an organic hydroponic solution, or in particularly dirty systems, the air pores in perlite are more susceptible to capturing solids such as biofilm, algae or other debris.
Subject to blockages
As perlite is composed of smaller particles than other growing mediums such as hydroton, plants with an aggressive root system can cause the pore spaces between the particles to block up with root formations, which can lead to clogging, debris build-up or pooling water.
Perlite is a non-renewable resource. And though we’ve used less than 1% of the estimated perlite ore on the planet in the past 60 years, perlite ore is not renewable in human time. It’s therefore not necessarily a sustainable resource.
Using perlite in hydroponics
Dutch bucket or Bato bucket systems
A series of buckets can be filled with perlite and assembled along an irrigation line so that nutrient solution can be circulated by pump from a reservoir placed below the level of the buckets and added to the bucket with a drip emitter. Each bucket is also attached to the return line, allowing the solution to return to the reservoir after use.
Propagating plants by cuttings
A well-draining medium such as perlite provokes cutting to root rapidly as they search out the small pockets of nutrients and moisture within the medium; it also prevents root rot.
Though perlite can be a stand-alone growing medium, in high-water settings such as deep water culture or ebb-and-flow hydroponic systems, the small size and low density of perlite means that it tends to float.
It does, however, combine well with many other hydroponic substrates which are larger, heavier, or denser. It is typically mixed with vermiculite or coco coir to prevent it from shifting or even washing away.
Perlite culture was primarily developed by a team of Scottish horticulturalists, and as it is easily managed, increases the overall plant yield, and has the fastest growth rate of any hydroponic technique in the U.K, it is now the most widely used method for producing greenhouse plants in Scotland. In fact, tomatoes grown in perlite have produced yields that are 7% higher than crops grown in rockwool.