In our gardening visits, I’ve often mentioned the importance of a high quality potting mix. Does it really matter what mix you use, or are they pretty much the same? Let’s go shopping.
Notice that some brands are labeled potting mix and some are labeled potting soil. “Soil” has a broad definition, and the terms potting soil and potting mix are being used interchangeably and few contain actual dirt-type soil. The better quality products I found are labeled potting mixes. Apparently no state or federal regulations govern quality of potting products, although the label must list ingredients in decreasing order of volume.
Today’s “soil-less” mixes contain one or more of the following. Sphagnum peat moss absorbs and holds water. Vermiculite is the golden flake-like material that holds air, water and nutrients. Perlite is the white crunchy bead-like component added for aeration. Forest products like ground bark increase moisture retention but can limit air. Larger bark particles increase aeration.
A good potting mix must strike a balance of being porous enough for drainage and root aeration while retaining the right amount of water and nutrients. The mix shouldn’t become hard-compacted over time.
How do commonly-available brands of potting mix compare? I purchased seven types from home improvement stores, mass merchandising marts, and locally-owned garden centers.
The ultimate deciding factor of a good potting mix is whether it grows healthy plants long term. But I’ve found you can separate a good mix from a poor mix by doing some easy observations before you use it for plants. Fill a pot with mix and try watering it.
Does water flow in easily, or is the mix difficult to wet? Once it’s wet, squeeze a handful. Can you crumble it back apart nicely, or does it stay overly wet in a squishy mudball? Does a handful of mix feel spongy and wholesome, or does the wet mix leave your hands feeling slimy, sticky and dirty? Shed the garden gloves and you’ll be surprised how much you can learn by hand-analyzing potting mixes.
Here’s my analysis of the seven types, with five stars being a high quality mix.
Vigoro Potting Mix. Available at home improvement stores, the mix seems composed mainly of bark without enough peat and vermiculite to develop the balance between good drainage while retaining the moisture plants need. Two stars.
Hyponex Potting Soil. Heavy in the bag, it looks like plain dirt with a little perlite added. Difficult to re-wet when dry, it’s too heavy and sticky. Use the package for a doorstop instead of for plants. One star.
Premium Potting Mix Custom Blend (a garden center‘s recommended blend.) Ingredients are peat moss, vermiculite, perlite and bark particles in a nice ratio that accepts water readily, drains well yet retains just the right amount of moisture. I like the wholesome, spongy feel. If it works for greenhouse growers, it‘s a keeper. Five-plus stars.
Miracle Gro Potting Mix. My personal old-reliable because it’s available at nearly every mass merchandiser and local garden center, and it grows nice plants. It’s a well-researched blend of peat, perlite, and processed forest products plus slow-release fertilizer. Five stars.
Miracle Gro Moisture Control Potting Mix. Supposedly prevents over-and-under watering because it contains coir, which is ground coconut fiber that retains moisture well. This is an advantage for outdoor containers, but I feel it stays too wet for indoor houseplants. Four stars.