Choosing the Best Potting Soil and Raised Bed Soil

When looking for the best potting mix, remember that this growing medium isn’t the same as garden soil. Garden soil is for in-ground use and is made of clay, silt, sand and organic material. Any soil labeled for in-ground use is heavily compacted and not suitable for potting plants. Use a designated potting mix instead.

Potting soil mix is a blend of mostly organic matter, such as peat or coconut coir, as well as various amendments to promote drainage or help the soil retain moisture, such as perlite or vermiculite. Twigs, bark, sand and lime are sometimes incorporated as well, depending on the type of plant. The best potting soil for a container project is one designed for the type of plant you want to grow.

To learn more about container gardening, read How to Plant a Container Garden.

Plant soil labels contain various ingredients for essentially three main categories of potting soil: all-purpose potting mix, orchid mix and soil (for palm, cacti and citrus plants) plus a few other specific types. See the choices below on how to decide which soil is best for your planting needs.

Organic soil for raised planting beds come pre-mixed with the right blend of soil, soil conditioners and nutrients for optimal outdoor growing of herbs, flowers, fruits and vegetables. Organic raised bed soil contains the optimal pH balance that’s rich and nourishing, allowing plants to grow freely, ensuring they have access to the right amount of water for drainage and the nutrients they need to sustain healthy growth.

For a raised bed of your own, check out our video How to Build a Raised Garden Bed and also see Build a Stone-Raised Planting Bed.

As the name suggests, soilless potting mixes use inorganic and organic substances, instead of soil, as a base. A soilless medium protects plants from some types of diseases associated with transplanted soil and can assist with pest control. Because soilless mixes contain few nutrients, combine them with fertilizer to maintain plant health. Some soilless blends contain a small amount of starter fertilizer, but you'll need to regularly fertilize according to the plant type.

Sphagnum peat moss is a major component of soilless and many other potting mixes. It’s both lightweight and absorbent, so it helps maintain root aeration and moisture.

Coir is an absorbent medium made from the fibers between the inner and outer layers of coconut shells. Coir, as well as other soilless substances, is also used in hydro gardening.

When using a soilless alternative, wet the material before lightly packing it into containers. Plant roots need aeration and room to grow. Always thoroughly water plants after potting. Use fertilizer a few weeks after the initial planting, or you can mix in a slow-release fertilizer when potting. Check the product label for details.

Soilless seed-starter pots, pellets and strips are simple, convenient ways to start a new container garden, and they have the added benefit of minimizing transplant shock. For more help, see Starting Seeds.

When potting new plants for your container garden, start with potting soil recommendations specifically labeled for the type of plant. For example, find the best potting soil for outdoor plants. If after repotting you aren’t getting favorable results, add soil amendments to change the pH, moisture level or level of aeration of your soil. Here are some common potting soil additives:

• Vermiculite increases soil aeration and facilitates water retention.
• Perlite also increases aeration but promotes drainage.
• Sand reduces water retention. Cacti and succulents do well in sandier soils.
• Bark (a primary component of orchid mix) helps with both root aeration and drainage while maintaining the right amount of moisture for orchids, so the roots stay nourished but don’t sit in excess water.
• Lime raises the pH of soil. You can purchase soil test kits and add some lime to your growing medium, if necessary, to ensure your plants are growing in optimal conditions. See Test and Improve Your Soil for more information.
• Compost and manure add nutrients back to soil and also helps promote root growth.
  

To learn more about this topic, see our Soil and Soil Amendments Guide.

Interestingly enough, perlite and vermiculite simultaneously serve both similar and different purposes. This often leads to confusion but isn’t as hard to grasp as it might seem. Essentially, both amendments help aerate soil, so plant roots aren’t too compacted. Vermiculite is added to potting mix to help retain water, so the soil itself stays moist longer. Perlite, on the other hand, helps promote drainage, so plant roots don’t sit in an overly saturated environment for too long, which can lead to root rot. In terms of appearance, vermiculite is a softer, brownish substance and is a derivative of mica. Perlite is hard, white substance created from volcanic glass.

You can amend pre-blended potting soil with perlite or vermiculite if you aren’t getting the results you want. If your potting soil is drying out too quickly, add vermiculite. If it doesn’t drain well enough, add perlite. Many potting mixes contain both to achieve the optimal moisture level for the plants for which they’re intended.