We all want to ensure we’re using the best potting soil possible for our plants, whether we’re growing flowers, vegetables or houseplants, but with so many brands to choose from, the decision can be difficult. The ultimate deciding factor of a good potting mix is, of course, whether it grows healthy plants long term.
Recently, scientists with the University of Arkansas’s Department of Horticulture conducted a side-by-side comparison of Magic Dirt’s Premium Organic Potting Soil versus another leading organic potting soil. In each image you see below, the left-hand plant or set of plants were grown using Magic Dirt, and the right-hand plants used the other organic potting soil.
A good potting mix should strike a balance of being permeable enough for drainage and root aeration while retaining the proper amount of water and nutrients. It’s also important to note that the quality of potting soil is not directly related to its weight. It’s very easy to incorrectly assume that the heavier your potting soil is, the better it will be for your garden. In actuality, though, potting soil only becomes heavy for two reasons: it’s wet, or it contains a lot of sand.
At the initial stages of the experiment, Magic Dirt required fewer intervals between watering. The other potting soil, which contained organic matter such as rice hulls and hardwood compost, was more difficult to judge water content by sight. After about three weeks, all plants required about the same number of waterings. However, up front, fewer waterings means reduced labor and the decreased possibility of over-watering causing disease problems.
Tomato – The Magic Dirt plants are visually more vigorous with a larger leaf area and a better green color. The plants grown in the other soil are showing obvious signs of mobile element deficiencies such as phosphorus and potassium, and they’re generally unhealthy looking overall.
Marigold – There aren’t any significant visual differences between the two brands of potting soil, but the Magic Dirt plants do seem to be more uniform in height and fuller. Most plants of either treatment are showing flower buds.
Radish – Both potting soils produced vigorous plants and have actually formed radishes. At the termination stage, the plants grown in the other potting soil are showing marked chlorosis and other signs of nutritional stress on the older foliage. In the images you can see the yellowing foliage indicative of nutritional stress. In other words, the potting soil is “running out of gas.”
The tomato plants definitely performed better using Magic Dirt versus the other organic potting soil. This better performance seemed to show up toward the end of the growing time when the plants are filling the pots with roots and an increased growth rate.
As previously mentioned, the marigolds were about even so Magic Dirt performed just as well as the control potting soil.
The radishes performed well in either substrate (visually), but the plants grown in the other soil are definitely showing foliar deficiencies as the radishes began to “bulb” up.