Vegetable gardening: Lining plastic pots to prevent leaching?

April 19, 2016 2:02 PM

What would be the best way to line a pot made of non-food-safe plastic so that I can grow tomatoes in it? Got the pots without thinking about the material and they're not returnable...

Explanation...

I'm growing tomatoes this year and went with a large plastic pot, since the previous tenants sprayed tons of Round-Up in our yard and I prefer not to use that soil.

Problem is, I'm on a budget and found some cheap plastic pots in Chinatown. When I got them home, I realized they're made in China and could be made of all kinds of nasty, leachy plastic (see these...websites...for notes on why certain plastics aren't good to grow food in).

Anyone have suggestions about something I could use to line these containers so they don't contaminate the soil so much, especially on hot summer days? Perhaps jute or burlap sacks? The shop doesn't allow refunds, so I'm stuck with the pots.

If you have any science background, all the better!

Thanks much

posted by manzanita to Home & Garden (25 answers total)

Maybe you could grow something ornamental in there? Beauty is important, too. Maybe some giant Dahlias, or some trumpet flowers or sweet peas for pollinators.
posted by amtho at 2:08 PM on April 19, 2016

Response by poster: True, I'll definitely use one of them for my trumpet flowers! They are huge, though, so was thinking they'd be so good for tomatoes!
posted by manzanita at 2:19 PM on April 19, 2016

If you use jute or burlap, would the roots go right through those and end up touching the plastic anyway?

I don't know the right answer, but maybe something else that is food grade, like those bags that you cook your turkey in for Thanksgiving?
posted by CathyG at 2:32 PM on April 19, 2016 [1 favorite]

Response by poster: That's an idea. I'm so icked out by the idea of cooking food in plastic (heat + plastic seems like such a dicey idea!) that I didn't even know they had such things. Hmm, I wonder if the roots could make it through a burlap sack in one season.
posted by manzanita at 2:43 PM on April 19, 2016

Polyethylene garbage bags
posted by flimflam at 2:46 PM on April 19, 2016

Burlap is often treated with chemical solutions, plus it's really permeable so I think you'd get a double dose of unknown ick. Maybe set another clay pot inside? Otherwise, I'd put ornamental plants in it and go with something like Grow Bags for your tomatoes. I guess you could put a grow bag in the pot, but with water, it might just allow unwanted stuff to pass through to the soil.
posted by cecic at 2:47 PM on April 19, 2016 [1 favorite]

Even if the roots don't make it through burlap, burlap is essentially a huge collection of wicks, so the burlap would be wicking any toxic stuff from the wall of the container and transporting it. I think it needs to be impermeable to do anything.
posted by misterbrandt at 2:48 PM on April 19, 2016 [1 favorite]

Food safe drum liner. A bakery or large restaurant would probably sell you just a couple instead of having to buy a whole roll. They may also have food safe buckets available that might fit inside your pots.
posted by Mitheral at 3:00 PM on April 19, 2016 [4 favorites]

A nice thing about growing ornamental plants in large pots is that you can put more than one plant in there, so it can be a really nice "little garden". Golden Creeping Jenny is great for this, because it doesn't have huge roots (so it won't affect other plants much), and it will cascade down the side.

I grew some awesome tomato plants in large terra cotta pots one year (terra cotta tends to be inexpensive, but it doesn't always survive winter outdoors); the roots ended up being very very large -- they packed in all the way tight to the sides and out the bottom.
posted by amtho at 3:06 PM on April 19, 2016

Response by poster: Great suggestions! Yeah, I might have to throw our ornamental plants in all of these. It's too bad, because two of them are really big - great size for tomatoes. :-/
posted by manzanita at 3:17 PM on April 19, 2016

Aluminum foil? Might take a big of origami to seal the edges without tape but I bet if you do a couple of layers, it'll be pretty waterproof once the weight of the soil is in place.
posted by teremala at 3:34 PM on April 19, 2016

What about placing terra cotta pots inside the planters?
posted by oceano at 9:07 PM on April 19, 2016

You know that big 50L plastic bag the potting mix comes in? Use that. It works perfectly well to just cut a hole in the top and plant your tomatoes in the bag, no roots escaping, so it will work just as well lining a pot. Plus you have it already if you're buying your soil. You can even buy bags specifically designed for growing vegies in (with marks for where to cut holes etc), and they'll be as food-safe as anything.
posted by shelleycat at 10:23 PM on April 19, 2016 [1 favorite]

And yeah, you need something impermeable so food-safe plastic is the way to go (I'm a biomedical scientist). Material like burlap etc won't form a barrier to anything water soluble.
posted by shelleycat at 10:27 PM on April 19, 2016

To allay your fears:

I've tested soil and other items for glyphosate residue while I worked in a lab. It was nigh impossible to extract any glyphosate from any surface or soil after 24 hours, so surely there wouldn't be any left from the previous tenant. Also your links say that you shouldn't grow food in a few specific plastics, but it doesn't mention why not to grow in those plastics. I think you might be unduly chemophobic.

That being said, I think the simplest thing would be to just line the pots by getting the smaller bags of potting soil and cutting open the top and poking a hole in the bottom. That way you would be only using the pots for vertical support of the soil and it wouldn't come into contact with the "hazardous" pots. The bags of soil though are themselves made of potentially "hazardous" plastic so it might not "work".
posted by koolkat at 8:41 AM on April 20, 2016 [3 favorites]

As an option for the tomatoes, Lowes sells food safe buckets. They also sell them in small numbers for (comparably) reasonable prices and shipping. 5 gallon buckets are also a great size for tomatoes.

Another option would be to ask at local restaurants and food stores if they have any food safe buckets they are getting rid of. My parents own a bakery and they have tons of food safe 5 gallon buckets they wash and put out front with a 'free' sign on a regular basis. Often they have way more than they know what to do with (honey and other liquid ingredients come in the buckets) and they love it when people ask for them since they would rather they get used as opposed to being thrown out. And hey, it's hard to beat the cost of free!
posted by scififan at 11:56 AM on April 20, 2016

Response by poster: @koolkat, Actually, I'm totally open to hearing that these plastics are completely safe--I don't know enough about the science to answer the question, which is why I was hoping that those with some chem knowledge (like you, it sounds like) would answer!

As someone annoyed by pseudoscience but with basically no science background, I try to go by whatever peer-reviewed studies I come across in the news. (As an aside, I happen to have a lot of cancer in my nuclear family at young ages, so I figure a little extra caution won't hurt, since I already may be susceptible.)

I've read about higher levels of endocrine disruptors being found in the body based on various environmental exposures (teens/cosmetics, eg: http://news.berkeley.edu/2016/03/07/cosmetics-chemicals/), http://www.niehs.nih.gov/health/topics/agents/endocrine/
But I don't think adequate studies have been done as to whether those higher levels are actually linked to higher rates of disease.

Anyway, tell me more about this test for herbicide! Sounds like any Roundup really would be long gone by now? That's great news!

Unfortunately, the part of our garden with free, open soil is also heavily shaded by the neighbor's trees, so it's still not ideal to plant there... :(
posted by manzanita at 7:48 AM on April 21, 2016 [1 favorite]

Response by poster: @shelleycat Oh right--I have seen people growing their veggies straight out of those soil bags. It didn't occur to me to put them right in the pot. That's an idea!
posted by manzanita at 7:49 AM on April 21, 2016

Response by poster: @shelleycat - Ah, good, I like to hear from someone with bio/chem bonafides! So those bags they come in are food safe, I take it?

And...am I being too paranoid about growing in pots made of mystery plastic in the first place?
posted by manzanita at 7:52 AM on April 21, 2016

Response by poster: @scififan Ooh, free is the BEST price. Will ask around.
posted by manzanita at 7:53 AM on April 21, 2016

Response by poster: @amtho that's a great idea. creeping jenny is nice, too. yeah, terra cotta is so heavy when you get to these huge sizes, though it's more pleasing to look at. i think it doesn't retain water as well as plastic, either, and the less i have to water, the better, in case laziness ensues for a couple days.
posted by manzanita at 9:11 AM on April 21, 2016

While I don't have specific evidence of food-safeness, given the bags of soil are made and sold specifically for growing vegetables in I don't see how they could be anything but. I used to work in a plastic bag factory sealing those exact bags and the bags are made specifically for that task and the plastic content tested and controlled, they're not just whatever random plastic thrown together. People all over the world have been eating veggies grown in this soil for many years, including me all my life (I'm 40). So personally I wouldn't have a single problem with using it, particularly if you're buying that soil in the first place anyway.
posted by shelleycat at 11:30 AM on April 21, 2016

And...am I being too paranoid about growing in pots made of mystery plastic in the first place?

Whereas this I wouldn't do. Any random pot bought from an actual garden store, yes, but unknown whatever pots from some place in Chinatown, no.

But then Roundup breaks down pretty fast in the environment so I'd have no problem re-using the actual garden a too. Particularly if it was a few months after the treatment, definitely if it was the next year.
posted by shelleycat at 11:35 AM on April 21, 2016

In terms of the glyphosate, it is broken down in the soil with a half-life that is measured in days if not hours. It is a combination of glycine and phosphate. Glycine is an amino acid and is ubiquitous in all life, and the phosphate is essentially what you are adding to the soil when you add bone meal. (It isnt exactly that because there is a methyl-group in between, but those things aren't much trouble for the soil bacteria to chew through and use as food.) I worked in the State of Vermont Agricultural labs while I was going to university. Someone had maliciously sprayed roundup somewhere (IIRC this was a while ago) and we were given soil samples to try and detect it to help prove that this was done. Unfortunately the soil samples were taken about a week after the spraying, and we were unable to detect any glyphosate in the soil, but we were able to detect it in our spiked sample, but not after the spiked sample had been left out for two days. This was with using quite powerful equipment, so powerful that we needed to pre-wash the cotton sampling pads to remove the miniscule level of pesticide residue left from spraying the cotton because it was above our detection limit. (I think the cotton pads had something like 1.2 part per trillion of diazinon or something like that.)

As for the pots themselves I really wouldn't worry. It seems to me that you are most worried about endocrine disruption via the plasticizers present in different types of plastic (such as bis-phenol A). Firstly the main reason I wouldn't worry is that plasticizers are added in to a specific plastic formulation to increase pliability, and I am guessing that your pots aren't very flexible so therefore the manufacturer is unlikely to incur the expense of adding in something to make it flexible. Secondly soil microbes are very good at removing and using as a food source, things that would leach from the pot. Especially if the containers are made of PVC and you are concerned by the phthalates that would be present. The esters in the phthalates wouldn't last a day in soil before being metabolised into fatty acids to be used by the soil microbes. If you're worried about the potential presence of formaldehyde, simply recognise that there will be an order of magnitude of formaldehyde in the tomatoes that you will enjoy that would ever leach out of the pots. In actuality there would be more naturally occurring phyto-estrogens in the tomatoes as well than anything that would be possibly taken up through the root system.
posted by koolkat at 2:00 AM on April 22, 2016 [1 favorite]

Response by poster: @koolkat @shelleycat Thanks for easing my mind!
posted by manzanita at 1:55 PM on April 23, 2016