Monday, April 16, 2012

The Dirt on Potting Mixes

Last year I learned an important lesson about the value of a good quality potting mix when planting vegetables in containers.

After searching around, I found a product called Earth Gro potting soil. It was made by Scott’s, and most importantly (or so I thought) it was CHEAP! For a little over $3 a bag, how could I go wrong? After all, it’s dirt.

You get what you pay for... in this case heavy sandy soil! It was OK, but who wants to waste the time and effort of seeding, planting, watering, and fertilizing just to have OK results?

Well, I was wrong on many accounts. First, potting mix really isn’t “dirt” at all. Usually it’s a mix of bark, peat moss, and perlite. As I was soon to discover, the cheaper mixes, such as the one I has just bought about 10 bags of, included a generous helping of sand. The result is a very heavy, very compact mix that turns into something reminiscent of a block of concrete as soon as you water it. Halfway through a hot day it would crack and pull away from the sides of the containers, making watering extremely difficult.

Not surprisingly, most of the plants didn’t grow all that well in it. The tomatoes did okay, but not great. The cucumbers died soon after plating. The peppers didn’t seem to mind it, though, nor did the tomatillos, which provided enough fruit for a small army—even when I planted a few extra tomatillo plants in a spare 1 gallon (at best) pot I had around just to see what would happen. The okra produced only a few pods here and there, and most of the rest of the garden seemed stunted the entire season. 

The plants did okay but needed constant attention. Sometimes even that was not enough.
This year I was determined not to skimp on the soil. For one thing, we moved to an upstairs apartment, so weight on the upstairs porch was more of a consideration than when everything was outside on a concrete slab. Also, I wanted a decent harvest this year. To that end, I bought two kinds of potting mix to try: Miracle Gro and Sta Green Moisture Max (which is a Lowe’s exclusive). Each seems good, but I decided to go with the Sta Green for a couple of reasons.

First, it is about $2-3 cheaper per 2 cu ft bag than the Miracle Gro, which when you need to buy many bags adds up quickly. Second, it is light, fluffy, and airy—all key qualities that you want in a potting mix. It seems to have a lot of pine bark, which adds to the lightweight quality of the soil. So far, the strawberries and broccoli seem happy in it, so I decided to go with it for the rest of the containers this season.

To compare, a 2cu ft bag (the biggest bag they had at Lowe’s) weighs about 33 pounds after it had been outside getting rained on, which is about 10-15 pounds lighter than the wet Miracle Gro. Multiply that by 10 bags, and you’re talking a couple hundred pounds less weight and about $20 cheaper. Since I fertilize anyway, I am not too worried about what the mix has in terms of fertilizer, but the Sta Green does come pre-fertilized.

This mix is light, fluffy, and seems consistent from bag to bag so far. I have never used moisture control mix before, but I have heard good things, especially when you have a hot sunny porch like we do.

 Either way, the difference between both of these soils and the Earth Gro mix is stunning. A little 5 gallon pot of the Earth Gro that I had left over from last year was heaver than the entire 2cu ft bag of Sta Green!

The lesson was simple and clear: if you are going to grow vegetables in containers, don’t skimp on the potting mix. If you go with the cheapest soil you can find you’ll waste time and money, and ultimately be disappointed in your experience and your harvest.


  1. Thanks.. feeling bitter with Earthgro and growing mint. it doesnt want to grow in it.. gonna replant it in a better potting mix..

  2. That's a good choice! If you're just growing mint and nothing else, I would buy the small bag of Miracle Grow for about $5. The consistency is so much better.

  3. That's because one is potting SOIL and one is potting MIX. Mix has no soil and is used for planting in pots.

  4. Hi Lisa, thanks for the comment! I am aware that Earthgro is "soil" but I would also point out that the bag says right on the front "Potting Soil.... A general purpose growing medium for indoor and outdoor POTTED plants."

  5. Made the mistake of buying Earthgro Potting Soil. Horrible. I would love to get it tested to find out what the big chunks of orange powder are. A lot of it is just dust or incinerator ash perhaps. Should not be allowed on the market.