About That Bag of Potting Mix

There’s nothing wrong with growing food indoors using hand watering or drip irrigation and the traditional container methods. However, you should be aware of just what you’re up against using ‘premium potting soil’ or ‘premium potting mix’ purchased from your favorite garden center or big box store.

Advertising is wonderful. As long as you are the manufacturer or retailer. But neither of these are from the plant world, and what is in most of their bags of product is fine for growing hot house flowers… seed geraniums, colorful petunias and a host of other container garden plants meant to toss a dash of color on your porch or patio. Truth be known, even your summer annuals could fare a lot better if you do a little customizing to their ‘professional’ potting mixes. Whats in that bag is designed to drain, not to optimize your growing efforts.

The first issue is the pH level. Something you should know is going to be an issue if you’ve done much reading up on indoor gardening. The given analysis tells you that the pH is 5.5-7.5 on any given brand of potting mix. Garden plants – both food or flower types – generally want a pH of 5.5-6.5. The majority of them will not be at their utmost best if the pH goes above 6.5. So what happens if the bag you bought actually tests out at 7.0-7.5? It might not even be the entire bag, but just a portion of the bag. So if you’ve got 40 new plants all growing in the same mix and a few of them just aren’t doing well, it could very well be what their roots are trying to deal with.

All potting mixes are made of peat moss, bark, perlite and dolomitic lime. Perlite doesn’t alter pH. It’s neutral. Peat moss is very acidic, and wood products like bark, wood chips or sawdust are there to create better drainage but they also feed on nitrogen that any plants need to thrive. The composition is created to deliver drainage for roots in a plastic container first and environmental balance second. While these blends have provided a solution to the container nursery and greenhouse grower for landscapes and flower gardens, they aren’t doing you any favors in providing the optimum conditions for growing your begonias on in pots around the yard or your indoor garden of edibles.

You can amend what’s in that bag and come out much farther ahead in terms of plant vigor and harvest volume. While you do need to exercise some caution on proportions, adding topsoil or worm castings to any bagged potting mix will do wonders for your results. Amend the purchased product by adding 25% of either. Be sure to blend it well and break up any chunks of soil to make sure it gets evenly distributed. Also, don’t forget that worm castings have at least nitrogen, if not other parts of the NPK analysis you’re giving your plants via nutrients. Most commercial brands of worm castings have an analysis of 1-0-0.

If you’ve grown in straight potting mix that is for the most part peat moss, you’ll quickly see that just this small amount of real soil has a solidifying effect. When hand watering, the weightier soil stops a lot of the float off effect you saw with the mostly peat moss mixes – keeping your plant’s roots more protected from air and drying out.

Be sure to use sterilized topsoil, or you’ll be weeding inside the house too.

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Tammy Clayton

Contributing Writer at Garden Culture Magazine

Tammy has been immersed in the world of plants and growing since her first job as an assistant weeder at the tender age of 8. Heavily influenced by a former life as a landscape designer and nursery owner, she swears good looking plants follow her home.