I grew tomatoes in 15 gallon containers last year for the first time.
My plan is to grow tomatoes in those containers again this year.
Can I reuse the soil in those containers as is, or should I amend it before planting tomatoes in them again?
The list of soil borne tomato diseases is legendary! Verticillium Wilt, Fusarium Wilt, Corky Root Rot, Black Dot Root Rot, Rhizoctonia Root Rot, Pythium Root Rot, Sclerotinia White Mold, and nematodes…
IMO you risk accumulating a soil-borne tomato disease if you re-use soil, even if it is amended.
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Really? I’m glad I asked. Thank you – so I should start completely over? What should I do with the old soil?
keep it and set up a crop rotation if you can. grow something not vulnerable for a year or three and you can come back to tomatoes
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Try Burpee’s “On Deck” sweet corn. Says it’s the first you can grow in containers. Just be sure to fertilize well as corn needs a lot of nitrogen.
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Rotation is good . But
If you did not have any apparent root problems last year,
A good chance they will do good again.
I would reuse that soil . Maybe flood with water to leach out any soluble salts . ( Like a tea bag )several times , and recharge with fertilizer for this year.
Good luck
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Hmm. I like that idea but my family doesn’t like corn all that much. How would I determine what other veggie could go in the pot for “crop rotation”?
I’ve done that in my containers although disease pressures are light around here. It works. Adding at least some new media helps a lot. I’m trying to do crop rotation this year. No point in pressing my luck.
Based on internet scans I’m trying to grow Brassicas as my rotation crops where practical. Supposedly Brussels sprouts are the best crop in rotation to tomatoes. Looks like a PITA to grow though. I don’t count Eggplant or peppers as being a significant rotation from tomatoes.
I’ve done before and after soil tests on container media. I was surprised at how played out the nutrient profile was at the end of the season of growing tomatoes. Even P was down significantly ( although still in the OK range).
If you assume that you are starting from scratch and almost growing hydroponically that would not be overdoing it too much.
At a minimum I would pull out the soil turn it over, maybe amend a little to keep it from clumping together and give it ferts including micros a few weeks in advance of planting.
I am getting more careful about monitoring soil Ph. It’s more volatile in a container, especially after you add a considerable amount of ferts.
I don’t know that it’s good practice, but Ive been using old tomato potting soil as mulch for the trees. I’m sure you could use it for ornamentals at least.
PS. I’ve grown regular corn in containers like that. Maybe four or five stalks to a container. More of a curiosity than anything else though.
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Assuming that the resident plant is /was heathy in a pot.
I will reuse that soil.
Pots where a plant was unthrifty looking or died for unseen reasons, that soil gets put in a lower garden bed that would benifit from some amendment.
I say lower, meaning one where the water from that area will not reach propagation areas and other garden beds.
So that if there is a disease in that soil the water runoff will not take it to propagation areas. I plant a unrelated species in that soil.
Also should add…
Pots that had unthrifty plants or ones that died , get a good cleaning and 10% bleach before reuse
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I grow peppers in 5 gallon bucket and I reuse the soil every year for the past 10 years with little problem. I feed well and I get great harvests.
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Typically I dump pre-used soil into a mixing container and add bagged or scoops of mix and soil, and a little fertilizer, into a mix for
the next generation of plantings…at
the least, dump it around existing fruit or nut trees if not recycling in more potted plantings.
I attempted to grow “On Deck” corn last season. Squirrels got the kernels as soon as they went in the ground. Three separate plantings. Even after I moved the containers up onto the deck 
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I’m sorry. Squirrels Are my nemesis here in Ellicott city, Md. they seem even worse than they used to be in The part of Pittsburgh where I grew up, which is Squirrel-hill! 
Maybe you can create a wire mesh lid over the container out of chicken mesh. I have a bunch left over I could give you segments maybe 20 x 20”, and they could be even cut to be circular. Too bad I live so far away. Which would allow the corn to germinate and you could even theoretically keep it covered and definitely, because sometimes I notice squirrels dig around just for the hell of it and destroyed my pots on my deck
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I must be lucky all my squirrels seem to steal is bird feed and suet. I’m yet to loose any fruits or veggies to them even under a heavy presence. Now for rabbits and ground hogs that’s a different story.
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