Q: I have about 30 containers and am wondering if I can reuse the potting soil next year. It costs me a lot to refill the pots every year. I have to thank the Journal for your column every week. It is a great resource.
A: One question that keeps showing up in my email inbox at this time of year and every year is about potting soil and whether you can save it from one year to the next. I know we have addressed this issue in the past, but it may be time to talk about it again based on the number of queries I have received.
The answer to reusing potting mix is I’m not sure. How’s that for taking a firm position? Up until very recently, I was a proponent of the ‘do not reuse potting mix’ school of thought but a couple of things have begun to change my mind. Firstly, some of the higher organic content potting mixes just might have enough nutrient value to reuse them. One example of this type of soilless mix is Sea Soil Potting Mix. Sea Soil itself is high in organic content because of its makeup, which is simply fish refuse and ground-up forest fines. These ingredients would likely last through two growing seasons in terms of nutritional breakdown. Just add some fresh Sea Soil in the spring to the saved soil you have.
Secondly, I have been reading some research where old, tired potting mix (the regular peat moss type) really does not break down much over the growing season. If you dig around in the pot in the fall, you will notice that the soilless mix is still light and breaks up easily. This means that roots can still find their way into the mix without a problem. The studies also recommend adding organic matter to the soilless mix and working it in well. The organic matter can be compost (such as Sea Soil, as one example) or something like well-rotted manure. The other point I’d like to make is that with the advent of slow-release fertilizer pellets that are designed for containers, adding nutrients to the containers is easier than ever.
I always find the fall a great time to take inventory of the past growing season and make some notes about things you might like to change next spring. If you, like me, are concerned about the cost of potting soil you can always make your own. A good quality potting mix would be one part sphagnum peat moss, one part vermiculite and two parts of compost (sifted if possible). Many of the less expensive mixes contain only peat moss and a little vermiculite so you can see how much more you will have in the way of nutrients by using my formula.
Every week, Growing Things Outdoors runs online at edmontonjournal.com or, if you prefer an epaper format, epaper.edmontonjournal.com
Learn more by emailing your questions to filipskigerald@gmail.com, reading past columns or my book Just Ask Jerry. You can also follow me on X (Twitter) @justaskjerry01.
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