Vermiculite Vs Perlite: When To Use Which And How
With millions of plants growing in the soil, sometimes you may wonder what is in your soil and if there is anything you need to add to your soil for optimal plant growth. Soil additives are materials like vermiculite, perlite, sand, mulch or others that modify the soil for the plant’s preferred environmental conditions (well-drained, dry, moist).
Among soil additives, vermiculite and perlite are the two that give gardeners the most questions, and we must remember that vermiculite and perlite are not the same substance! They are also both commonly used as a soilless medium.
Mixing and confusing these two substances will have a big impact on the growth of your plants due to their extreme differences.
Whether it’s origin, appearance or use, these two soil amendments have many differences.
History of vermiculite
At the end of the 19th century, the state of Montana was transformed for many decades after the discovery of shipments of vermiculite in the country.
If you look at the periodic table, vermiculite is mainly made up of aluminum, iron, and magnesium and contains vital water molecules and does not contain asbestos.
The scorching temperatures force the water to convert to steam, and that’s the product you see when you open that bag of cool vermiculite for your plants. In general, I use vermiculite for seedlings because it is known for its water-holding abilities; a main process of seed germination is imbibition, that is, when the seed absorbs water to germinate.
Micro and macronutrients that plants need such as potassium, magnesium, calcium and phosphorus are also contained and absorbed in the media thanks to the properties of vermiculite.
The water-retaining properties of vermiculite allow for ideal seed germination, as illustrated above.
Vermiculite is used in most potting mixes because the ideal soil contains 25% water. When you first see this substance, it may appear that it belongs to the bottom of your aquarium. Normally this mineral has a color range from gray to brown and is a tiny particle that looks like small scale gravel. Vermiculite is smaller than perlite.
When to use vermiculite
Common reasons for using vermiculite include germination, propagation, or non-drought tolerant plants. If you have issues with your soil drying out to the point that your plant is continually to blame, adding vermiculite may help.
It also helps with aeration, but that’s more of the job of perlite if you’re looking to achieve that ideal 25% air in the soil.
If you are looking to achieve the required 25% water in the soil, this hydrated phyllosilicate may be what you are looking for. You may want to be careful with this mineral if you tend to overwater your plants.
This mineral is generally gray to brown in color and has a small particle size.
Excessive water retention can lead to irreversible damage caused by organisms such as oomycete, Pythium (root rot).
This mineral can be useful when added to a soil mix that you use to propagate cuttings, especially those from stems and leaves. The composition of vermiculite facilitates the growth of young roots and facilitates the formation of the plant.
Since the plant needs to form weed tissue when propagated asexually, it is crucial to ensure a sufficient amount of water until the tissues are formed.
How to use vermiculite
As with perlite, the amount of vermiculite you will need to benefit from its properties depends on your plant, the texture of the soil, and the environment. The more you add, the longer the water will stay in the soil micropores.
Also, depending on your goal, you can buy vermiculite in different sizes (fine, medium, coarse).
Sprinkling some of this mineral on the soon-to-germinate seeds also provides them with a thin layer that can be penetrated with enough water. Along with this, the mineral also provides a significant aid in the conservation of nutrients for the plants, so that they are not washed away as quickly.
The above lemon balm loves water, and in summer the soil dries out quickly.
What plants do you have that could benefit from vermiculite?
- Ferns (Polypodiaceae family)
- Spider plants (Chlorophytum comosum, Asparagaceae family)
- Aloe plants (Asphodelaceae family)
- Pothos (Epipremnum aureum, Araceae)
- Lemon balm (Melissa officinalis, Lamiaceae Family)
- Tomato plants (Solanum lycopersicum, Solanaceae)
All about perlite
Has your cactus become mushy or has your spider plant developed fragile, brown tips lately? This can be due to excessive moisture buildup in your soil.
In my garden shed, there is never a time when a bag of this mineral does not lie in a corner of the room, accompanied by plastic plant pots. The versatility and characteristics of perlite are useful to any gardener or houseplant connoisseur.
When you look at secondary minerals like perlite and vermiculite, you’ll notice that both are successful because of their built-in water capacity. When you hear ‘volcanic glass’ it may sound like it has nothing to do with your potting medium. Although that is what perlite is, and this mineral also expands when exposed to extremely hot temperatures.
This mineral has a swollen appearance and looks like styrofoam. The white specs pictured above in soil are perlite and are common in soil mixes.
As for secondary minerals, it is originally formed from the primary mineral, black obsidian (volcanic glass). It is considered secondary because it has undergone a weathering process and formed a new substance.
When to add perlite
Imagine you’ve finally arrived home after a long day of shopping for plants and you’re ready to repot your favorite cactus. Many stores sell cactus-succulent potting mixes, which contain extra perlite, but you went ahead and bought pure perlite.
The swollen material is used for soil aeration and for manipulating the soil structure to make it less compact. When you open the bag of the white material which inflated more than 20 times its original size, be sure to keep your face away! The bag may produce white dust when you open it and is poisonous if inhaled.
While sharing similar appearances, be careful not to confuse perlite with styrofoam, as styrofoam is toxic to plants and soil.
This soil amendment is added to the soil when plants are suffering from saturation due to a mixture of poor soil textures (such as excessive clay content). In addition, plants generally like alkaline soils, so the pH of this additive of 6.6-7.5 can also provide soil benefits.
When you water your houseplants, do you feel like your fern plant never dries up? Long-term saturated soils can lead to plant rot and death, but perlite additions can often solve this problem.
Perlite serves a purpose similar to that of macropores in soil or soil aggregates; it allows air to enter the medium and has the ability to effectively percolate water to the micropores.
In the photo above, a few soil aggregates facilitate soil aeration.
This is also why you might notice that perlite is a bit bigger than vermiculite; this characteristic requires ideal ventilation.
Often, potted plants form a layer of crust above the ground and perlite can wash it off. Soil temperature is more important to plants than air temperature, and perlite can also provide stability to this factor.
How to apply perlite
You might be wondering how it is applied considering that every soil is different. Each branded potting mix contains varying amounts of nutrients, aeration, and water-retaining materials. Also, it depends on the type of plant you are growing to determine how much perlite to apply.
You may find it helpful to ask, does my plant need a lot of water or Is my soil compact and not well drained? Add more if your plant likes it to dry out and your soil isn’t draining well. If you want a specific ratio for a particular goal (rather than looking at it), information like this can be easily searchable.
Most cacti don’t like saturated soils, but this secondary mineral provides aeration and well-drained soil.
What plants do you have that could benefit from perlite?
- Cactus (cactaceae family)
- Succulents (Aizoaceae, Crassulaceae family)
- Lavender (Lavandula, Lamiaceae Family)
- Snake plants (Dracaena trifasciata, Asparagaceae family)
- ZZ factory (Zamioculcas, Araceae family)
- Geraniums (Pelargonium, Geraniaceae family)
Ground media and perch effect
When we are discussing soil amendments (like perlite and vermiculite) and adding minerals to achieve ideal soil characteristics for our plants, we need to consider soil science.
The potting soil is mass produced and each company sells different combinations of soil for plants.
You may have heard your friends tell you when you have a new cactus, to add a layer of pebbles to the bottom and top of your pot. Contrary to popular belief, this has a high potential to create problems for your plants.
Depending on what you can add to your soil, a change in environment is a disturbance. If the medium has been mixed well, there is more potential to absorb the remaining water due to the evenly dispersed materials; if you use a layer of rocks, it ends up forming a pool of water at the bottom, which calls for disease.
The photo above is a common misconception about placing a layer of rocks on top or below the ground. It does not actually benefit the plant.
The water goes to the bottom because not all the water is sucked up by the media due to the barrier of one layer.
Knowing when to use different minerals for soil amendments is important in the horticultural world. So keep in mind how much of your soil textures are mixed in your media, especially vermiculite and perlite!