What is Lightweight Potting Soil?

Container gardening is gaining popularity since apartment dwellers and those with no access to a garden also want to enjoy growing their own plants. Filling large pots with regular soil would make them very heavy and hard to move, and this is one of the reasons why lightweight soil mix was invented.

Another reason lightweight soil is at the top of everyone’s minds is the popularity of green roofs, a beautiful and popular architectural feature that covers flat roofs with living grasses and greenery. This works very well as insulation, and also reduces the building’s carbon footprint and cleans the air. The soil used in a green roof is known as "lightweight roofing soil", and like the name suggests it must be light so that the roof can hold the weight of the soil, but it also must be rich, so the plants can thrive. 

Must Drain Well

Potted plants always run the risk of being waterlogged if the soil and the pot don’t drain well, and excess water around the roots may lead to disease and yellowing. Lightweight soil usually contains vermiculite and perlite to aid drainage of any excess water. 

Good drainage is especially important on green roofs, since any water that doesn’t drain will add to the weight of the roof, and may even start creating cracks or leaks on the structure underneath.  

Must Have Good Water Retention

Besides good drainage, lightweight soil must also have good water retention properties - you cannot really go up to the green roof to water it every day. Adding pumice stone to the mix usually helps a lot, since its porous texture helps absorb, retain and distribute water.

Must Have Ideal Air Management

Gardeners tend to forget the importance of keeping air in the soil. In containers or roofs, the soil does not get disturbed often, and this is why it is so important that it has built-in aeration, to prevent compaction and keep roots healthy and free from mold. Mixing in porous materials such as vermiculite and pumice stone helps keep the mixture light and aerated.

Compost

Compost is vital to healthy plant life for many reasons. First and foremost, it carries a rich mix of nutrients and microbial activity that keeps plants and soil healthy. Compost is also wonderful at managing the water content in the soil - you add it to dry soils to bring in moisture and add it to wet soils to help them drain. Finally, good compost is “fluffy”, and will improve the aeration of the soil.

Sand

Sand is part of any quality soil and especially of lightweight soil, since it balances out the organic matter and stabilizes the soil structure, for optimal water retention and drainage properties. 

How is Lightweight Soil Used?

Green Roofs

Creating a green roof calls for several soil products, lightweight soil being one of them. A green roof must have a waterproof and root-proof base, to protect the roof that supports it, followed by a layer of light aggregate to ensure good long term draining. A filter fabric and moisture blanket go on top of that, and finally the lightweight soil on which the plants will grow.

Container Plants

Container gardening is a source of great joy, and it fits all lifestyles and living arrangements since you can keep plants both indoor and outdoor. Fill your planters and other containers with high-quality lightweight soil and enjoy growing your own flowers, herbs, and even vegetables no matter where you live. 

How Do You Care for Lightweight Soil?

Any soil requires certain care, and while lightweight soil can go for long periods without any fussing, eventually you will have to look after it to keep your plants happy.

Fertilize regularly.

Whether you use compost tea, pellet fertilizer, or a compost-rich top dressing, be sure to add nutrients to your potted plants or green roof at least twice a year. Compost is usually added in late fall or early spring, and a spot of fertilizer is also recommended in the middle of summer if you’re growing fruit or veg. 

Replace the mixture every few years.

Remember that all the organic parts of the soil will eventually be used up, or break down as part of their natural cycle. This is why you should replace your lightweight soil every few years, so you don’t end up with just pumice and perlite sitting on top of your green roof, making it look like a job site instead of a garden. 

Where Can I Find Lightweight Soil?

Minick has been working with materials for over half a century, and we have all it takes to mix up beautiful lightweight soil for your project. Our customer service experts will be happy to help you get the optimal mix of sand, aggregate, compost, and other ingredients so you can have the container garden or green roof you have always dreamed of.