What in the world is perlite soil anyway? Is it organic? I do a lot of container gardening, especially with my herb plants. Since I try to keep things all natural and as organic as possible, I looked into what makes perlite soil. The answer surprised me because I thought it was little bits of Styrofoam! Ick! But it is not. Perlite particles are actually totally natural volcanic glass particles that undergo a heat process to change form.

In addition to good mineral nutrient content, air is an important part of the soil mixture for any garden. Container gardens need air to keep the roots from being compacted by the soil. Perlite soil to the rescue! Volcanic glass is the basis for perlite soil. It is formed when heat is applied to the perlite component of ash and acts like popcorn. The perlite particles expand and pop, trapping moisture inside and adding air in the space between particles. It does have a similar appearance to the man-made Styrofoam but is an inert and sterile mineral.

What is the Difference Between Perlite Soil and Vermiculite Soil?

Vermiculite is mined from silicate. It is commonly found in seed starting mixes and also plays a role in keeping moisture in the garden soil. It used to be more common to use vermiculite until asbestos was found in the mine in Montana. The industry changed its methods and vermiculite is still available. It has a strong moisture-retention ability without leading to fungus because of its spongy consistency. It is possible to use both vermiculite and perlite in your container gardening soil. Many gardeners prefer vermiculite for growing seedlings indoors and perlite soil for container gardening.

What Should be in Container Garden Soil?

Gardening discussions often center around the plants, but the soil is important too. Without good, nutrient-rich soil, your plants will not produce well, or at all. Nutrient-poor soil also contributes to weaker plants that are less disease and insect resistant. You do not need to use chemical or purchased fertilizer to add nutrients to the soil if you plan ahead. Although container gardens are a smaller scale production than a large garden bed, giving the plants the best soil will increase the production. If you are growing lettuce in containers or when growing flowers, starting with the right soil will help your results.

Compost for Container Garden Planting Mix

Compost is a great start when building soil and can be added to the container garden. In addition to the compost and garden soil, consider adding perlite for air. Many expert gardeners insist that air is one of the main components of healthy garden soil. The air provides oxygen, drainage and a lighter soil for deep root growth.

Using Peat Moss and Sphagnum Moss in Container Garden Potting Mix

Peat moss or sphagnum moss will help with moisture retention in the container garden. Garden soil lacks enough moisture, air and plant nutrition for successful growth and production. Adding peat or sphagnum mosses to the potting mixture helps change the composition enough to create the right soil for a container garden.

Should you Add Mulch or Wood Chips to Container Gardens?

Learning how to lay mulch in the garden helps with moisture retention and weed control. Mulching can also add to the nutrients in the soil over time. Susan Vinskofski, author of The Art of Gardening, Building Your Soil, states that using wood chips for mulch does not necessarily acidify the soil. Vinskofski regularly uses both hay and wood chips for mulch in her gardens. I think I will take her advice and start using mulch where I am growing vegetables in pots. I learned from Vinskofski’s blog posts that you need to make sure you push the mulch aside when planting and to not plant in the mulch layer itself but below in the soil. In addition, use no more than a couple of inches of mulch so that you can plant in the soil without having to dig through many inches of mulch.

Water Needs of Container Gardens

It has been my experience that my container gardens need to be watered far more frequently than my garden beds. The container garden itself is subject to heat and drying not only on the surface but also through the sides of the pot. During extremely hot weather, I need to water at least once a day. Sometimes I will carry some of the smaller containers to a shady spot during a heat wave. Overwatering has not been much of an issue for me but it has happened on occasion. The plant will wilt and die quickly if not tended immediately. When over-watering occurs, carefully take the plant from the water-logged container and replant in drier, well-draining potting mix. Set in a partially sunny location to help it recover. Under watering will result in browning, dry brittle plants that look unwell. Now that I have more knowledge of what the container garden soil should be, I would repot the plant using a better system that contains the peat moss and perlite soil for moisture retention and drainage.

Purchasing the Right Potting Mix for Container Gardens

If you don’t want to mix your own potting soil mix, there are many commercial types available. Most garden centers, plant nurseries, and home centers carry quite a variety of bagged potting mix. Knowing the soil facts concerning the difference between garden soil and potting mix is important. Now that I understand the different needs of container gardens, I can look forward to healthier producing plants in my garden. Have you added perlite soil to your container garden potting mix? Let us know in the comments below.

Originally published in 2016 and regularly vetted for accuracy.