Every gardener hopes for the best possible result from their crops – and will seek out the best techniques and tricks to improve the yield of their garden. Recently, several soil additives and alternatives have become popular. But how to tell which is right for your plants?
Should you add perlite or vermiculite to your vegetable soil? Which will help achieve the best result and why?
Similar yet Different
There are quite a few similarities between the two products – both soil additives are relatively sterile, inorganic materials. Both are designed to help regulate the levels of moisture and aeration of the soil.
There are, however, some rather important differences between the two materials. One allows for better drainage than the other, and their pH levels are not the same. Though their complementary properties mean they can combine well in potting soils, some vegetable yields will be higher if using either perlite or vermiculite.
Whichever you choose, the ratio should be approximately 75% potting soil to 25% additive – either perlite, vermiculite, or a combination of both.
What is perlite
Perlite is a porous material made by superheating crushed pieces of volcanic glass until they expand. This creates air pockets within the perlite that can also absorb and hold moisture. These small white granules are often mistaken for foam balls in potting soil mixtures.
What is perlite used for
This lightweight material can be used as a substitute for sand, as it can temporarily hold 3-4 times its own weight in water but yet still allow for excellent soil drainage. Perlite is odourless and non-toxic, though perlite dust can be an irritant – so it’s best to wear a dust mask and gloves when handling dry perlite, or to add water to the perlite bag, covering the particles, before pouring out the material.
Perlite is an excellent choice for rooting plant cuttings for propagation, or when moving seedlings into separate pots. It is recommended for plants that require highly aerated soil that drains quickly and doesn’t retain much moisture. As such, it’s ideal for succulents, and other plants that prefer a dry soil between watering.
Perlite has a rough, irregular structure and can be used alone in hydroponic gardens or as a component of the plant substrate. In large-scale greenhouse vegetable production, perlite is often used in large slabs that are 100 cm long, 20 cm wide and 15 cm high; each of these slabs can support 2 cucumber plants or 3 tomato plants. Perlite substrate is also used a lot in Bato buckets – each 3 gallon bucket can support two tomato plants.
One of perlites greatest advantages is that it can be reused for up to 5 years without losing any of its chemical or physical characteristics – however, it’s best to sanitize the particles with either steam or a chemical agent before transplanting a new crop into perlite.
Also keep in mind that perlite has a slightly higher than neutral pH level, so it will make the soil more alkaline – which can be a problem for some plants such as potatoes or sweet potatoes that prefer acidic soil. Asparagus, leeks, squash, and many leafy salad greens thrive in slightly alkaline soils.
What is vermiculite
This aluminum-iron-magnesium silicate physically resembles mica. For horticultural applications, vermiculite is also superheated until the particles expand creating a flaky, spongy, soft material that is usually golden brown to dark brown in colour. It contains trace amounts of minerals and can interact with and pass on ammonium potassium, calcium, and magnesium found in the soil to the plants. The natural pH of vermiculite is neutral (7.0) but it can make the soil slightly alkaline because of its associated chemical compounds.
What is vermiculite used for
When added to the soil, vermiculite acts like a sponge, trapping moisture close to the roots of the plants. It can absorb 3-4 times its volume of water, which can make potted plants rather heavy. For plants that love water, vermiculite is the better soil additive, but if it’s used with plants that don’t require a moist soil, it can contribute to the development of root rot.
Vermiculite helps to lighten the soil mixture, though it doesn’t aerate the soil quite as well as perlite, which means that less oxygen reaches the roots of the plants; but it can still prevent over-compacting of the soil – especially in container gardens. It can be used to increase the water retention of sandy soils but should be avoided for clay soils and it can cause them to be too soggy. Where the soil is very heavy or sticky, mixing in vermiculite can create air channels and help to maintain vigorous plant growth.
Vermiculite is often found in seed starting systems; it’s designed to retain water in the small pods in which the seeds are started while protecting the seedlings from fungus. When combined with peat or composted bark, it promotes faster root growth; the mixture helps to retain air, moisture and nutrients, releasing them as the plant requires them.
When the seedlings are ready to transplant, it’s easy to remove them from a vermiculate-based substrate without risking breaking off the hair roots. Vermiculite can also be beneficial when transplanting; if it’s mixed with the topsoil from the planting hole, then used to pack around the seedling, vermiculite will allow the roots to branch out quickly and penetrate deep into the soil. It also protects the roots from shock due to the drying effects of wind and sun on the plant as it provides excellent moisture control.
In addition to improving growth conditions, vermiculite can also help with the storage of bulbs or root vegetables. The particles will absorb any moisture around the tubers and help to prevent storage rot; it doesn’t however, draw any moisture from within the root vegetable. Tubers stored in vermiculite are protected from even the most extreme temperatures.
Perlite or vermiculite for vegetables
There is no definitive answer – some gardeners swear by perlite while others are adamant that vermiculite is the way to go. Whether to use one additive or the other – or both together – depends on the native soil composition and condition; also remember to consider the type of plant you’ll be growing and its particular needs.