What should you do with your containers at the end of the season?
Q uestion: We grew many plants in containers this year on our deck. I had some tomatoes, peppers, basil and even a cucumber plant, along with lots of flowers. My question is this. Do I have to dump out all of the potting soil before replanting those containers next year or can I reuse the soil? The pots are still sitting out on the deck and we were planning to leave them out there all winter. Is there a reason not to let them out there?
Answer: Congratulations on growing a successful container garden! Growing in pots is very rewarding and a whole lot less work that growing an in-ground garden. Despite the need to regularly water the containers, you can grow almost any vegetable or flower in a pot, as long as you choose a container that’s large enough and you set the plant up for success by using a high quality potting mix, which, of course, leads us to your question.
Whether they’re organic or not, most commercial potting soils contain enough nutrients in slow- release form to fuel one year’s growth for the plants growing in that container. Because of this, it’s essential that you replenish those lost nutrients at the start of every new growing season.
I know potting soil can be expensive and lugging bag after bag of the stuff from your car to the deck can be a hassle, but ideally, 100 percent of the potting soil in your containers should be replaced with new potting soil each season. I recommend filling containers with a blend of 50 percent high quality potting soil and 50 percent finished compost, as not only does the compost improve the water-holding capacity of the potting soil (leading to a reduction in watering needs), but it also adds another source of slow-release nutrients, as well as beneficial soil microbes that help plants acquire nutrients and thrive. You can use finished compost from a home compost pile, but I prefer to use bagged compost from a local nursery, as I know it will be weed and pathogen free because, unlike most home compost piles, commercially produced compost is turned regularly and heats to a high enough temperature to kill weed seeds and pathogens.
Using a new potting soil and compost blend each season supports exceptional plant growth. It also helps limit disease prevalence, too, as several fungal and bacterial diseases can easily over-winter in used potting soil. If you grow tomatoes or other disease-prone plants in your container garden, always empty the container at the end of the growing season and scrub it out with a 10 percent bleach solution before refilling it with new potting soil at the start of the following growing season. Several tomato pathogens can overwinter both on the pot and in the soil. For flower growers this isn’t quite as much of an issue.
That being said, I know for many gardeners who have physical and/or budgetary restrictions, replacing 100 percent of the potting soil is difficult. For those gardeners, the lost nutrients can be replaced by adding a few tablespoons of organic granular fertilizer to the old potting soil at the start of a new growing season. Before adding the fertilizer, however, remove 1 ⁄ 3 to 1 ⁄ 2 of the old potting soil and then top the pot off with a mix of new potting soil and compost. That will give you a blend of old and new potting soil, plus the nutrition from the compost and fertilizer.
As for leaving your pots outside all winter long, there are several pros and cons to this practice. First, it’s essential that your containers be frost-proof so the freeze-thaw cycles don’t cause them to crack. Traditional terra cotta pots crack and flake if left outdoors for the winter, plastic pots become brittle after a few seasons, and glazed ceramic pots often crack, too. But, if your containers are made from Fiberstone, fiberglass, metal, wood or another frost-resistant material, it’s fine to leave them outside. Do be aware, though, that leaving soil-filled containers outdoors also means that every time it rains or snows, more nutrients get washed out of the potting soil, making it more important than ever for you replenish those nutrients before adding new plants next spring.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.