How to Choose the Best Soil for Container Gardening

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A question we get asked repeatedly from newbie container gardeners is, “Why can’t I use soil from my garden for my containers?” Even very experienced conventional gardeners don’t fully realize how different container gardening can be.

Ground soil typically gets drained and aerated naturally. (There are exceptions to this, which anyone with clay soil or other soil problems can attest to.) But ordinary garden soil in a planter quickly gets compacted to the point where water and air can’t get through. Container soil mixes are designed mainly to solve these two issues.

If that sounds way too technical, bear with us a moment. We’ve put together a few notes to hopefully encourage you to persevere with what could turn into a lifelong passion. So without further ado, let’s take a look at the best soil for container gardening.

What Should a Good Container Soil Mix Contain?

The right container soil mix will depend on what you’re planting and sometimes on the type of container you’re using. For hanging baskets, you want to keep the weight down, and different mixes can vary significantly in weight.

Potting, or container, soil mixes will typically be constituted of some mixture of the following:

  • Peat or peat moss – Peat is decayed organic matter from under bogs, while peat moss is peat mostly comprised of mosses. It’s free of microorganisms and weed seeds. Peat helps with water retention and preventing soil compaction. It also adds acidity.
  • Bark – Shredded bark allows for rapid drainage of excess water to avoid attracting fungus, mold, and bacteria.
  • Coarse builder’s sand – Coarse sand adds air space and facilitates drainage.
  • Vermiculite – Vermiculite is a mineral that helps with water retention.
  • Coco coir – Coir fiber from coconut hulls is used instead of peat. It is less acidic and a more renewable material (peat takes ages to be created.)
  • Common soil – Ordinary soil is sometimes used in potting mixture to add texture. Be aware that garden soil can contain insects, weed seeds, and disease organisms. It is also quite heavy, making it an excellent ingredient to prevent planters from being blown over in windy conditions. Garden soil can be used to stretch expensive commercial potting mixtures – add 25% of good quality, weed, and disease-free soil.
  • Perlite – Perlite is a volcanic rock (or glass) popped in heat like popcorn and looks like Styrofoam. It helps soil hold air.
  • Slow-release fertilizers – These are designed to release nutrients slowly into the soil. But remember, if you are making up your own mix, fertilizers won’t last as long as they do in the garden because containers need watering more often.
  • Wetting agents – These reduce the surface tension of water, helping it spread from particle to particle. Wetting agents are often used to enhance the effects of pesticides.
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Best Soil for Succulents

Succulents need well-drained soil, so look for a mixture with higher percentages of bark, perlite, or sand. Or make your own – we like a three-ingredient mix made up of two parts sand, two parts common soil, and one-part perlite.

Best Soil for Herbs

Herbs also like well-drained soil and thrive with the addition of some compost. If you want to try your hand at mixing your own, try the following—one part each of coir (or peat moss), compost, perlite, and topsoil.

Best Soil for Perennials and Woody Plants

Perennials are another group that doesn’t like moisture for extended periods. Choose a coarse soil mixture. Mature plants will appreciate extra compost but don’t use too rich a mix for young plants as it can damage their roots. A good mix to make yourself is one part each of peat moss, composted bark, compost, builder’s sand, and perlite. Add extra perlite if the mix clumps.

Best Soil for Tropical and Foliage Plants

These guys like moist soil, so look out for higher percentages of peat and vermiculite and less of the coarse materials. These mixes should be moistened before planting. Break down any clumps and generally “fluff” the mix to ensure the moisture gets all the way through.

Can Soil Mixes be Reused?

Over time the organic materials in soil mixes will break down and lose their properties. But this usually takes a few years. So if your container plants were healthy, there’s no reason you shouldn’t reuse their potting mix. Now that you know the various components of soil mixes, you can always top-up what you feel is missing.

Final Thoughts

The science behind soil mixes can be a bit intimidating at first, but it won’t take long for you to get the hang of things. Experienced container gardeners develop a feel for soil and intuitively adjust their mixes for any shortfalls.

If you have any doubts, your local nursery will be able to recommend a suitable commercial mix. They are generally quite willing to hazard a guess at what you could be doing wrong with your home mix. So take a leap of faith and give it a go!

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