Perlite vs Vermiculite

You have planned your garden, whether in your yard or in planters, with intricate detail. Of course, you want your efforts to pay off and the last thing you want is for your plants to get off to the wrong start. Therefore, your plan must begin with the best start possible, which means the best soil, with the best amendments, is definitely putting your best foot forward. Some gardeners find that purchasing a prepackaged potting mix is right for them and others insist on mixing their own. There is no absolute equation for starter soil, primarily because the mix depends on the soil composition where you live, the type of application you will be using (i.e. planters, ornamental beds, fruit or vegetable gardening for harvest, etc.), and the actual plant you will be planting.

Perlite vs Vermiculite

However, it is true with all soil mixtures, that the happy gardener has ensured that their soil has included a lightweight material to allow for moisture retention, drainage and aeration, allowing the root system to grow and absorb nutrients properly. Two common, and widely used, non-organic materials are perlite and vermiculite. Let’s take a closer look at these two substances.

Perlite

An igneous volcanic glass, meaning it is created when magma is rapidly cooled, similar to obsidian; however, it is high is water content, and also contains large amounts of silica. White in color, perlite is porous and has sharp edges. The defining characteristic is that when heated to a specific softening range of temperature, it will expand due to the water expansion within the material, and it can increase in volume from anywhere between four and twenty-four times the volume with which it began. Additionally, it is organic, sterile, extremely lightweight, chemically neutral and inert. Therefore, it is an inexpensive addition to soil mixtures, making the mix light and fluffy. This improvement is excellent for heavy soils with a high percentage of silt or clay. One word of caution, purchased bags of bulk perlite should be opened with caution and it is advised that you cover your nose and mouth, stepping away for a moment to allow the cloudburst of dust to settle before proceeding. Perlite is not toxic but it’s not recommended that you breathe the dust into your lungs.

Vermiculite

Vermiculite is a part of a mineral group called mica minerals. Its formation is due to the weathering, or alteration due to natural forces, of biotite and phlogopite. In an original state, mica forms layers that break away in sheets. Brownish in color, softer in texture, and a little shiny due to the mica content, vermiculite has layers of water trapped between layers of silicate. To refine it for use in horticulture, the substance is heated, the water removed and the minerals expands. What remains is a lighter, expanded, form of vermiculite, which is well suited for use in gardening. It gains its name from the wormy shapes created when it is heated. Vermiculite is excellent for soil amendment, helping heavier soils to keep from compacting and causing water to runoff. Vermiculite tends to be a little more expensive at retail stores but is often preferred by some farmers in dry regions thanks to its exceptional water absorption rate. Additionally, vermiculite can add trace amounts of potassium and magnesium to soil, unlike its counterpart, which is chemically neutral.

Fantastic Alternatives or Flops

These two fabulous minerals are not the only materials that can be utilized in amending garden dirt, and to some degree, they should not be used alone, as they add little to no nutrient value to the soil. Some soils are not compact enough and require more dense material, such as clay, for proper amendment. However, peat moss, saw dust, wood chips, leaves, rice hulls, and other organic materials can be used in addition to or in place of perlite or vermiculite. All of these other resources add valuable nutrients as they decompose and several of them help to amend the pH balance of the soil as they compost as well. Sand is also an alternative for dense, compacted soils like clay. Sand helps to aerate the dense ground and allows for better absorption, holding water molecules between its particles but sand is heavier than perlite and vermiculite, so it is not preferred over them for the purpose of loosening the dirt composition.

Choosing Wisely

As mentioned before, choosing the right amendment for your gardening purposes is as individual as the gardens they improve. Local hardware and garden centers carry most everything you would need when it comes to amendments, including composed cow manure, premixed potting soil mixtures containing either perlite or vermiculite, and bags of perlite and vermiculite only. Perlite usually breaks down more slowly, but commercial growers in dry arid areas often favor vermiculite for unsubstantiated reasons. Regardless, there is no absolute right answer to choosing the right material for your application.  This fabulous duo is chosen over other organic resources for their amazing ability to retain and hold large volumes of water and slowly release it over time. They both have a neutral pH, whereas pine needles and peat are both acidic. Rice hulls and leaves add lightweight, airy, volume, as well as nutrient value, but they do not retain water the way perlite and vermiculite can. Vermiculite is rated as having a high water holding rate compared to perlite, which is rated as a medium. Perlite does not actually absorb water like its partner vermiculite, which behaves like an absorptive sponge, it holds onto water bubbles that trickle away from its holding spaces. Because vermiculite maintains a higher moisture content, it is preferred for tropical uses and with fungi, but discouraged in other applications, such as with cacti because it has too much water. In some cases, mixing half perlite and half vermiculite is the best course of action.

Conclusion

Selecting the proper amendments for your garden and planting amendments, should always be individual and intentional. There is no one size fits all. If you are a container or raised bed gardener, with the intent of bringing in all new soil, then choose a premixed soil. You may even be able to purchase a screen topsoil/compost blend from a local retailer that specializes in bulk/truckload quantities. But if your desire is to do it all yourself, first examine the natural dirt/soil composition you have (if necessary, you can contact your local agricultural extension service for help in analyzing your composition) and then determine how much water your project needs, for that if the primary difference between choosing perlite and vermiculite.

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