Ask a Question forum: Reusing planter soil

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JudyS
Sep 25, 2016 3:48 PM CST
The zinnias I planted in a raised planter on my patio developed serious powdery mildew. After discarding the plants for the fall, can I keep the soil to reuse next summer? And if so, can I just cover the planter for the winter? Or should you always discard used soil every fall anyway?


Name: Yardenman
Maryland (Zone 7a)
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Yardenman
Sep 25, 2016 3:54 PM CST
You can cook the soil in your oven but it smells. I forget the temperature because I don't bother. I use 'used' potting soil (uncooked) for transplanting tomatoes to larger pots and for new flower pots. It seems to work OK.
Name: Laurie Basler
Western Washington (Zone 7b)
Houseplants Region: Pacific Northwest Sedums Orchids
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lauriebasler
Sep 25, 2016 4:43 PM CST
I would not with that powdery mildew issue.
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
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sooby
Sep 25, 2016 4:46 PM CST
Welcome! You'd be OK if you're not planning on growing zinnias or anything else susceptible to that particular powdery mildew, which unfortunately has a wider host plant range than many. Some zinnias are more resistant to powdery mildew, I've never seen it on the Profusion ones for example.
Name: Yardenman
Maryland (Zone 7a)
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Yardenman
Sep 25, 2016 5:12 PM CST
My used potting soil generally sits in buckets of aridity for a year, then gets added to healthy transplants the next year.

Plus, since it exists on lawn grass and is blown around by wind, its pretty hard to avoid.
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
Image
sooby
Sep 25, 2016 5:27 PM CST
There are different species of powdery mildew and many are quite specific to certain plants although unfortunately the zinnia one (Erysiphe chichoracearum, which I think has had a name change but many references still use the former) can affect many other plants. The powdery mildew on grass is a different fungus, Erysiphe graminis.

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