All Things Gardening forum: Sterilizing used garden pots

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North Central TX (Zone 8a)
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tx_flower_child
Oct 7, 2016 3:07 AM CST
Someone else asked about re-using soil, but I'd like to know about re-using pots. (Note the 's' on the end of that word.)
I'm not especially worried about my 'regular' garden plants. Most, but not all, have moved to a perennial bed. I'm more concerned about plants like epiphyllums and others that I guess might be called 'esoteric'.
For clay pots, should I use the old bleach trip on them or just rinse them out? Really the same question about plastic pots.
My concern is that I might unknowingly give a new plant the nasties.
Advice?Opinions?
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
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RickCorey
Oct 7, 2016 12:27 PM CST
If you use the classic "bleach" method, look closely at the label on the bottle of bleach.

If the fine print doesn't say "Sodium Hypochlorite", it might not be what we used to call "bleach".
Some laundry bleach is now "oxygen-based" and does not work as a disinfectant.


scrub clean: remove visible dirt and mineral deposits. You can use a wire brush on clay pots.

soak at least 10 minutes in 1:10 dilution of CHLORINE bleach (household bleach, not "oxygen" bleach. Preferably unscented.)

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Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
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Weedwhacker
Oct 7, 2016 11:03 PM CST
I think it depends a lot on what type of plants you are growing; some years I get time to clean the pots from my veggie seedlings,-- other years... not so much. Even so, I've never had a problem.

However, this year I grew some Madagascar vinca (Catharanthus roseus) from seed, that eventually developed a fungus, so i will be more careful in regard to what I pot that up in, in the future.
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Name: Yardenman
Maryland (Zone 7a)
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Yardenman
Oct 9, 2016 1:04 AM CST
I usually fill up my laundry tub, add some bleach and soak them for an hour (trading them out as often are needed to process all my pots and usable 6-packs). I don't think bleach gets used up in a few hours.

Then I give them a few tubs of clean water. So far, I've never noticed any problems in germination the following year. And BTW, an aquarium expert told me that 2 ml of HO (hydrogen peroxide) per 25 gallons is really good at killing algae. And since the instructions say you can actually gargle with the stuff, it can't be very harmful. And it is cheap!
[Last edited by Yardenman - Oct 9, 2016 1:25 AM (+)]
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North Central TX (Zone 8a)
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tx_flower_child
Oct 9, 2016 9:41 PM CST
@RickCorey - I hadn't realized that there were differences in bleach. I'lll read the labels when I go to the store. And the thought of perfumed bleach is giving me the willies.

I think where I'm my plants worst (well worst is questionable - long list) enemy is that I take many small plants that are in 4" plastic pots and then set them in larger clay pots. I've even seen where I've put a pot in a pot in a pot. Sometimes for appearance. Mostly so the little guys don't get blown over or knocked over by Ms Clumsy here. I'm wondering if it might help to clean the clay pots that I'm setting the plastic pots in.

A few nights ago I had to bring most of the smaller ones inside b/c we were getting a hard rain. (Not complaining.) Now I can take them back outside for awhile. I feel like my plants have a mantra of sorts that goes, 'I'm your plant and I want to go out. I'm your plant and I want to come in. I'm your plant and I want to go back out.' and on and on.
I guess it would be good to give the clay pots a good scrubbing and use fresh pots when the little ones are ready to be potted up.

As always, thanks for your advice.
Name: Donald
Eastland county, Texas (Zone 8a)
Region: Texas Enjoys or suffers hot summers Raises cows Plant Identifier
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needrain
Oct 10, 2016 7:22 PM CST
tx_flower_child said:Someone else asked about re-using soil, but I'd like to know about re-using pots. (Note the 's' on the end of that word.)
I'm not especially worried about my 'regular' garden plants. Most, but not all, have moved to a perennial bed. I'm more concerned about plants like epiphyllums and others that I guess might be called 'esoteric'.
For clay pots, should I use the old bleach trip on them or just rinse them out? Really the same question about plastic pots.
My concern is that I might unknowingly give a new plant the nasties.
Advice?Opinions?


I quit bothering with cleaning used pots years and years ago. I haven't seen any bad side effects with simply reusing them. I don't even bother with washing them out with plain water. I'm a bit more careful with the planting medium when I'm starting seeds, but not a lot. I think I could be described as a very careless, but often successful, gardener. I do fail, but I can't think of a time when the failure could be attributed to my not cleaning and disinfecting a container. I'm not advocating you do what I do, mind you. Just relating my own experience.

Donald
Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
Charter ATP Member Celebrating Gardening: 2015 I was one of the first 300 contributors to the plant database! I helped beta test the first seed swap Garden Sages Million Pollinator Garden Challenge
Region: United States of America Region: Michigan Seed Starter Vegetable Grower Greenhouse Birds
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Weedwhacker
Oct 10, 2016 8:49 PM CST
" I could be described as a very careless, but often successful, gardener. "

LOL, Donald -- that is a very good description of me, too!
"Blessed is he who has learned to laugh at himself, for he shall never cease to be entertained."
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Name: Yardenman
Maryland (Zone 7a)
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Yardenman
Oct 11, 2016 3:38 AM CST
Well, I feel better giving the pots and cell packs a clean start every year. Mostly thinking that it can't HURT to do it. And it gets me going for the new season.

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annie5
Jan 11, 2017 5:57 AM CST
following this!


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Name: woofie
NE WA (Zone 5a)
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woofie
Jan 11, 2017 11:13 AM CST
I have about 500 4" square pots that I use in my greenhouse. I used to try to get them all washed before re-using them. "Used" to. I got tired and lazy 2 or 3 years ago. So far, I haven't had a single problem using them as is. Of course, they have been empty and dry for about 6 months by the time they get used again. And I always use fresh potting soil in the greenhouse.
Confidence is that feeling you have right before you do something really stupid.
Name: greene
Savannah, GA (Sunset 28) (Zone 8b)
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greene
Jan 11, 2017 2:49 PM CST
RickCorey said:
If you use the classic "bleach" method, look closely at the label on the bottle of bleach.
If the fine print doesn't say "Sodium Hypochlorite", it might not be what we used to call "bleach".
Some laundry bleach is now "oxygen-based" and does not work as a disinfectant.


Excellent information. Thumbs up Thank You! We need to get the word out.
Sunset Zone 28, AHS Heat Zone 9, USDA zone 8b~~"Leaf of Faith"
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
Frugal Gardener Garden Procrastinator I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest
Photo Contest Winner: 2014 Avid Green Pages Reviewer Garden Ideas: Master Level Garden Sages I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database.
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RickCorey
Jan 11, 2017 5:35 PM CST
Yardenman said:Well, I feel better giving the pots and cell packs a clean start every year. Mostly thinking that it can't HURT to do it. And it gets me going for the new season.


Me, too. I think it's better to clean well before putting away for the winter so fewer microbes have that long to turn into spores. But that depends on how busy I am in fall!

Mostly I have trays of small plastic cells or 4" pots, and they are only in use for a few weeks or one season. So they don't get crusty or baked-on.

It seems easy to me to rack them all up on "webbing trays" and stack them up so the runoff from one layer of pots washes the layers underneath. If it's the rainy season, I leave them out for while so rain will soften and pre-rinse them.

Then I use a hose-end sprayer on "hard spray" or "mist" to blast all soil or mix out of the top layer, and soften/rinse the layers of trays underneath. I use a webbing tray on top of the top layer so the hose spray doesn't blow them all around the yard.

When the top layer is "clean enough", I set it aside to dry and start spraying the next layer down. That's enough to get most of them visibly clean. Any that aren't visibly clean I pull out to soak and scrub individually.

This hose-end-sprayer pre-wash keeps the dishwasher from filling up with soil & mix.

One year I set up my dishwasher to run one full cycle, but I kept interrupting it to add detergent and replace the current load of clean-ish plastic trays and pots with the next load. That way, ONE dishwasher cycle let me give MANY pots and trays vigorous spraying with caustic dishwasher detergent. They continue soaking in the caustic detergent film until all are washed. Then I take them outside to rinse in one big stack.

But bleach is better for killing microbes.

I think that mere cleaning removes 99% or 99.9% of possible plant pathogens.
But what is 0.1% of a serious soil infection? It's still a serious soil infection!

So bleach (sodium hypochlorite - CHLORINE bleach) is needed to prevent ONE infected pot from infecting everything touched by water that passes through it (like every cell or pot in the same tray plus anything that any re-used potting mix contacts).

Maybe those who don't need bleach every year have almost no soil infections to worry about anyway.

But maybe the people who say "I usually can't grow plant X because of plant disease Y" have more need for bleach than they realize.

On the other hand, maybe someone with lots of soil diseases locally doesn't get much benefit, because no matter how well she cleans her pots, rain and dust re-infect every pot and seedling shortly after it goes outdoors.

I don't know. But I always clean well, and usually also soak in chlorine bleach diluted 1:10.


Name: Jai or Jack
Pennsylvania (Zone 5b)
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Jai_Ganesha
Jan 12, 2017 12:41 AM CST
I use Physan 20. I have used bleach before but it can get really rough on the lungs when used indoors on pots en masse.
Keep going.
Name: Gary
Wyoming MN (Zone 4a)
hostasmore
Jan 12, 2017 8:42 AM CST
Bleach and organics ie ammonia are a toxic combo!
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
Frugal Gardener Garden Procrastinator I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest
Photo Contest Winner: 2014 Avid Green Pages Reviewer Garden Ideas: Master Level Garden Sages I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database.
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RickCorey
Jan 12, 2017 3:20 PM CST
hostasmore said:Bleach and organics ie ammonia are a toxic combo!


Very true, and not just "toxic" in the sense that prolonged exposure might have some effect.
"Toxic" in the sense of "burn your lungs".

chlorine bleach + acids release chlorine gas (very toxic).

chlorine bleach + ammonia releases chloramine vapor, plus hydrazine if there's enough ammonia. Both are toxic or highly toxic.

At least there is no ambiguity: DON'T mix chlorine bleach with either acids or ammonia.
North Central TX (Zone 8a)
Million Pollinator Garden Challenge
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tx_flower_child
Jan 12, 2017 3:58 PM CST
@RickCorey - I'm familiar with the 1:10 formula but wonder about a couple fine points.

Do you soak the pots or just give them a quick swish?

Is the bleach still effective after cleaning X number of pots? (same day of course)

I realize there are probably different answers for clay v plastic as well as how dirty said pots are. Just asking for general guide.
Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
Charter ATP Member Celebrating Gardening: 2015 I was one of the first 300 contributors to the plant database! I helped beta test the first seed swap Garden Sages Million Pollinator Garden Challenge
Region: United States of America Region: Michigan Seed Starter Vegetable Grower Greenhouse Birds
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Weedwhacker
Jan 12, 2017 6:50 PM CST
hostasmore said:Bleach and organics ie ammonia are a toxic combo!


Good reminder!
"Blessed is he who has learned to laugh at himself, for he shall never cease to be entertained."
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Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
Frugal Gardener Garden Procrastinator I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest
Photo Contest Winner: 2014 Avid Green Pages Reviewer Garden Ideas: Master Level Garden Sages I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database.
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RickCorey
Jan 13, 2017 4:50 PM CST
tx_flower_child said: ...
Do you soak the pots or just give them a quick swish?

Is the bleach still effective after cleaning X number of pots? (same day of course)
...


Soak!

What I read says "dilute 1:10 and soak for 10 minutes".

I don't have any clay pots, but if I did, I would soak them longer during the pre-wash and also longer in bleach.

I think I read someone say that "hard water" or "lime" deposits are less harmful on clay pots than using harsh chemical "lime removers" like "CLR" or "Lime-Away". Scrub, yes, but CLR, no. I think.

But if I have a lot to do, and not much time, I skimp on the bleach step. Also, if I don't make up a 5 gallon bucket, I have to keep spraying or sprinkling bleach repeatedly. In that case, the whole batch gets sprinkled repeatedly every few minutes until I run out of mix. Then I hope that the bleach clings enough to kill 90%, 99%, or 99.9% of whatever microbes are still there.

That's why I think of it as: "clean VERY THOROUGHLY ... and then also get some bleach on them".

But I use every method I know to prevent damping off, and I don't know of any real soil disease problems in my few potted plants. So for me it's a preventative practice.

If I still had trays or pots where I KNEW I had damping off or soil disease problems, (or dirty ones I just brought home from a discard bin) I would "clean VERY THOROUGHLY", make sure they were immersed in bleach for more than 10 minutes, and then also leave them outside so that random microbes from rain and dust would have time to compete with and displace any remaining pathogens. Then clean them again.

Or, what's probably smarter : if you have a tray or pot where you KNOW there was an infection ... throw it away.

-
>> Is the bleach still effective after cleaning X number of pots? (same day of course)

With plastic, which is most of what I use, I think one bucket can disinfect MANY plastic trays and pots. If they are wet when I put them in, they might dilute the bucket, but I can always add another few ounces of bleach. With clay, I don't really know for sure how long one batch lasts.

BUT I always "clean VERY THOROUGHLY" before bleaching. If there is a pinch of dirt on each tray, I expect that to "consume" the bleach rather rapidly.

These are my practices and opinions. I don't know for sure how well supported they are.

But I trust the idea that CLEANING is needed to remove the first 99.9% of crud and pathogen spores. I would not trust bleaching without cleaning, at all.

And my opinion is that cleaning is desirable as a preventative measure, even if you have no "greenhouse diseases" or "pot ghetto diseases" YET.

Some others don't bother with bleach OR even cleaning, , and some of them get away with it just fine, as others have said.
North Central TX (Zone 8a)
Million Pollinator Garden Challenge
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tx_flower_child
Jan 15, 2017 12:19 AM CST
@RickCorey - you did indeed say 10 minutes. Guess I wasn't wearing my glasses. My bad.
London, United Kingdom
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ShannonBrady
Jan 16, 2017 3:21 AM CST
Hi there,
I was concerned about the same thing myself. Using the same soil is OK I think.... However it is better if you make a soil mix. The mixture could be organic blend of bone meal, poultry manure, feather meal, poultry manure. That stuff, to be honest, smells a little funny but is really good for the soils and the plant that is to be seeded. I hope it helped.

Best,
Shannon
I am Shannon and I work for a London garden clearance company: https://www.houseclearance.co/...

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