With the growing popularity of container gardening among apartment dwellers and those with no access to a garden or yard, lightweight soils have become a staple for many amateur and professional gardeners and landscapers.
As we explain all about the benefits of using lightweight soils, you’ll find out how to choose the right soil texture, moisture control, and long-term maintenance plan to grow healthy potted and green roof plants.
What Is Lightweight Potting Soil?
As most gardeners are likely well aware, there’s a huge variety of soils and sands you can use for planting or potting. While heavier clay soils have their advantages, filling large pots with regular soil would make them very difficult to move. This is one of the reasons why lightweight soil mixtures were 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 form of container gardening 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 as the name suggests, it must be light so that the roof can hold the weight of the soil. But light soils also must be rich and hold nutrients well, so the plants can thrive.
How Is Lightweight Soil Used?
Light potting soils can be made up of various combinations of sand, silt, and clay, which makes them suited to container gardening. Gardeners can choose the type of soil that works best for their plants based on the type of garden
Using Lightweight Soils on 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.
Using Lightweight Soils for 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. When selecting a soil composition for this style of garden, the top soil for containers is a lightweight soil.
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.
First and foremost, make sure to:
- 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.
Additional Guidelines for Using Lightweight Soils
Regularly adding fertilizer and replacing your soil mixture will go a long way towards keeping your green roof or potted plants healthy and strong. But there are other steps you can take to make sure that your plants are getting
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 adequate air spaces in the soil. In containers or roofs, the soil does not get disturbed or turned over often, and this is why it is so important that your soil 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.
What to Look for in Quality Lightweight Soils
A wide variety of plants can be potted or planted on green roofs, and each has its own unique needs depending on where and how it's planted. The location, temperature or climate, types of plant, or types of potting you are using will determine what type of lightweight soil and potting mixes are most suitable.
Soil Based in Compost
Compost is vital to healthy plant life for many reasons. Using compost soil 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 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.
Clay-based soils tend to be heavier, so most gardens that need lightweight soils should not primarily feature clay as part of the soil or sand mixture. However, clay in soil can increase its moisture control and retention, so consider where that’s an important factor when choosing the right lightweight soil for your potted plants or green roof.
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.