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The secret to good potting soil (or why you should NOT pay $1.99 for your bag of potting soil)

By Julie Boudreau

Last fall, a little something happened to me that inspired this text. In a garden center, upon seeing bags of potting soil sold for $6.99 each, a woman who was passing right next to me was offended: “Come on! It’s so expensive! I can get potting soil for $1.99 at “that big surface store that sells lots of products imported from China”! ” It’s true. She’s right. But…

Never, ever would I encourage a gardener who wants to be even remotely successful in their gardening project to get “cheap potting soil”. And there are many reasons why there is such a big difference in price.

The ingredients of potting soil are like the ingredients of a good cake: the better the ingredients, the better the cake! Image: Julie Boudreau

#1 The Bag Is SMALLER!

I mean, really smaller! This famous, very economical bag is sold in a 10 liter format. A beautiful bag of quality potting soil is a 30-liter format. It’s three times bigger!

#2 The Secret Is in the Ingredients

The best cakes and muffins are made with the best ingredients (the same could be said for spaghetti sauce). The best substrates too! I often compare a potting mix to a muffin mix: it’s full of ingredients! There is peat moss which forms the bulk of the contents. There is perlite, a small stone of volcanic origin, very porous. Perlite can trap 4 to 5 times its weight in water. It is also rich in minerals and has the advantage of having an approximately neutral pH. Potting soil also contains vermiculite, another mineral that keeps water trapped in its folds. Sometimes there are even slow-release fertilizers in the mix. And depending on the specialization of the mixtures, the potting soil will contain lime, bark, coconut fiber or sand. The whole thing forms a clever recipe with a well-calibrated dosage. The mixture should be light and airy. It must be both draining and able to retain water!

In less good quality soils, they’re selling illusion! Sometimes, the perlite is completely replaced by Styrofoam balls. Even though these little white balls have the appearance of perlite, they serve no purpose. In fact, their only use is to take up volume, because they are less expensive than peat or perlite. It helps to lower prices!

#3 A Potting Soil That Can Do Everything… That Doesn’t Exist!

It’s amazing! There is a direct correlation between the price of potting soil and what it can do! The cheaper it is, the more it does EVERYTHING! Everything, everything, everything!

Which is extremely unlikely. There are as many potting soil recipes as there are plants! For example, cactus potting mixes contain more sand and are very draining. Potting soils for tropical plants retain water better. And for flower boxes, we look for a potting soil with a high water-retention capacity. If someone offers you the miracle recipe… be wary!

There is always a reason why a product is more or less expensive. Potting soil is no exception to this rule! Image: Julie Boudreau

And finally, dare I say it, too often, lower quality potting soils come with their share of small harmful insect eggs and a nice handful of weed seeds! To offer such ridiculous prices, you have to cut corners.

This is why spending two big dollars more on good potting soil is a wise decision.

Julie Boudreau is a horticulturist who trained at the Institut de technologie agroalimentaire in Saint-Hyacinthe, Québec. She’s been working with plants for more than 25 years. She has published many gardening books and hosted various radio and television shows. She now teaches horticulture at the Centre de formation horticole of Laval. A great gardening enthusiast, she’s devoted to promoting gardening, garden design, botany and ecology in every form. Born a fan of organic gardening, she’s curious and cultivates a passion for all that can be eaten. Julie Boudreau is “epicurious” and also fascinated by Latin names.

6 comments on “The secret to good potting soil (or why you should NOT pay $1.99 for your bag of potting soil)

  1. Suzanne Armstrong

    One common ingredient seems to be peat. In the UK they are eliminating peat from potting soil. I hope in North America we will see more good quality peat-free options on the market too.

  2. Excellent article, extremely helpful. I could not understand why some composts say they can be used for everything and others are plant and/or seed growth specific ‘now it all makes sense’ Thank you!

  3. I enjoyed this informative article. I don’t really understand all the chemical terms and don’t know how to tell good peat from something that may be adulterated. If a producer of poor quality soil simply charged more, I would by the logic of more money is better quality, be completely duped. I expect you would prefer to not to list good soils by brand, but perhaps some of your readers can share Canadian brands that have given them success. And, I suppose, this is where shopping at a reputable greenhouse or garden supply company with knowledgeable staff is the real answer to my dilemma LOL.

  4. Why not make your own potting soil?

  5. Thank you very much for this information, sometimes cheap is expensive.

  6. Siri Zwemke

    Unfortunately here the difference in price is almost $20 a bag for the very top stuff at a good garden center. Even Miracle Gro seems to have changed their soil composition in the last few years, so I have been splurging on the ultra expensive stuff. And yes, while it is so expensive, it sure does make a difference to the plants. I’m moving back to roses after 30 years, and have put many of my new purchases in pots. While each pot takes one entire bag of soil, it’s definitely worth the investment!

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