Aluminum from containers goes readily into solution at pH levels around 5.0 or lower. Excess aluminum can damage root and leaf cells, but it's primary effect is inhibition of P to the top of the plant.

I can't comment about the potential health risks to humans because I don't know, but you may already have what you need to make your decision. ;o)

Al

Thanks, Al. I've been thinking, and if the aluminum was harmful to humans, then the various drinks that come in cans wouldn't be permitted.

I think I understand what you're saying.....depending on the ph level of the soil/water in the container, the aluminum could theoretically be absorbed by the plant, especially if very acidic. Is that right?

EG

The Landscape Architect types like Al containers for their urban designs and you can find them by high-end buildings often enough. I think old cigarette ash cans would be an interesting artistic statement...

Bottom line: if your potting soil pH is nearing 5, Al toxicity is the least of your worries.

Dan

Yes - that's why acidifying the soil of hydrangeas turns the blooms blue. "A soil pH around 6.0 will have the plant producing pink blooms, while @ a pH of soil pH that influences bloom color. It's the fact that when soils are acidic, aluminum becomes more soluble and is taken up by the plant. When aluminum binds to the anthocyanin/co-pigment complex, it changes the blooms from pink to blue (as pH falls).

Al

Ok...I got it, now! Whew....I don't feel like a big dummy anymore. :-)

EG

Aluminum in tropical soil is one of the reasons container gardening intrigues me & I value this forum.
Many believe tropical agriculture is highly productive. For suitably located sugar cane it is, but generally it has low fertility for food crops.
We get weathered soil, fast bacteria degraded organic matter & a stingy cation exchange capacity.
The pH is often low.
Oxides of aluminum & iron are common in the top layer with silica leached down underneath the profile.
The moderating effect of silica to raise the pH is thus remote. The benefits of silica to plant health are not available to most food crops.
The aluminum itself interferes with phosphorus utilization, as stated above. Since phosphorus is naturally not highly mobile from where it is located in the soil there is a compounded problem from the low cation exchange.
So I guess that makes me dis-inclined to start growing in aluminum.

So I guess that makes me dis-inclined to start growing in aluminum.

o Aluminum pots are sold all over the place.

o What fruits or vegetables would be affected by solubilization of the Al? That is: what plants would you be planting in a soil of pH 5 when you control the soil(?

o (I don't see a direct answer to the edible question above. )

Dan

Hi engineered,
Dan's correct, I didn't directly answer original query.
Some aluminum containers are of cheap quality & I suspect that alloy is vulnerable to a wider range of pH alteration, based on the pitting noticed.
Were a growing medium partially comprised of something like a tropical soil to be used I think the plan poses limitations, based on the factors I described above.
If you have no problems with pH, use an appropriate substrate & obtain a strong container alloy then a healthy edible annual vegetable crop is likely .
Should you do the same for a fruiting tree & notice pitting after a time in the aluminum container you should examine the arrangement for any detrimental changes.

Thanks for all of the information everyone! Sounds like if my ph is kept around 6.5-7, it shouldn't be a problem. I got me a plan, now! Gringojay and Dan...thanks for your input....

EG

Bottom line: if your potting soil pH is nearing 5, Al toxicity is the least of your worries.

You prolly should have looked into this before you posted.

First, a pH of 5.0 is not particularly unusual or undesirable in a container soil, and soil solution pH is far more important than media pH in container soils. You can easily grow in container soils with a media pH as low as 4.5. Check out Whitcomb's bible on container rearage if you doubt the link I provided below.

From NC State U - Co-op Extension - a direct quote. Find complete text here:

"Soils are placed into three classes, based on the amount of organic matter that is present - mineral, mineral- organic, and organic. Soils that have more organic matter tend to have lower aluminum content. Thus, for most plants, a lower pH level can be allowed. Mineral soils contain more aluminum, therefore, a higher pH is recommended to avoid aluminum toxicity. For most plants, the desired pH level in a mineral soil is 6.0, 5.5 for a mineral-organic soil, and 5.0 for organic soils."
Since the container would be AL, we must consider there will be LOTS of soluble Al @ pH 5.0.

It's very common knowledge that aluminum toxicity begins to be a problem at a pH around 5.0. Use a fertilizer with its N component from ammonium nitrate or sulfate, at ANY media pH level (in an aluminum container) and you practically guarantee an Al toxicity issue.

Al

The issue is whether typical edibles have an optimal pH less than ~5.5. Not whether potting soils ever reach a pH of 5.

»As we control pH in our containers, and typical container edibles like their pH more basic than ~5.5, there is a rather small chance that Al containers are an issue for edibles, and above 6.0 it should be close to zero chance of being an issue. .

EG: plz post pics if you go this route - imagine seeing nice looking containers on this site, rather than my dopey-looking 5-gallon buckets! Cigarette ash cans for sustainable adaptive re-use! Will the tobacco executives spin in their graves?! (hope so)

Dan

Scheesh. No need to reword anything or to phrase your own question to make your OP easier to defend. The issue IS: "Does anyone know if there are any health risks for the plant ....."

There are, and they are exacerbated by the use of acid forming fertilizers.

Al

My word, Al.

If you are making your soil pH 5.5-6.0, there are likely few health risks for the plant, and above 6.0 likely no health risks for the plant, as I asserted just above (emphasized with a »).

IOW, as I stated upthread if your potting soil pH is nearing 5, Al toxicity is the least of your worries . Why? because the edible plants will probably already be stressed at this pH. Fortunately, it seems as if others understand the pertinent issues involved with Al containers and will adjust their pH accordingly.

Dan

Dan,

I think you might be missing Al's point that it is the water/fertilizer that is more important than the pH of the potting mix.

If aluminum begins to leech at pH 5.0 and if the fertilizer results in the water being pH 5.0 or below then some aluminum is likely to leech into the soil, potentially taken up by the plant, potentially screwing with the availability of other nutrients in the potting mix, etc.

First, I never advised the original poster NOT to grow in an aluminum container. I only stated facts.

"Aluminum from containers goes readily into solution at pH levels around 5.0 or lower. Excess aluminum can damage root and leaf cells, but it's primary effect is inhibition of P to the top of the plant. I can't comment about the potential health risks to humans because I don't know, but you may already have what you need to make your decision." See? Short, sweet, to the point, and allowing the grower to make his own decision. WHY the argument? WHAT is there to even argue WITH? These facts cannot be disputed unless you rewrite the science.

No one ever stated or disputed that Al toxicity risks are not minimized as pH levels climb above 5.0 - that goes without saying, simply because toxicity issues become worrisome as pH levels drop toward 5.0, so that's another straw man set up to knock down.

You may find it interesting to learn that it's very difficult to maintain an even pH in containers w/o considerable effort, sophisticated equipment and a variety of chemical nutrient compounds that only a minuscule % of hobby growers have. Doubt the veracity of anyone that says he DOES maintain a certain pH level in containers w/o the equipment and chemicals to do so. This in itself makes it foolish to take the risk. Dan - do you REALLY think that anyone is going to "adjust their pH" (of what? media AND nutrient solution?) so they can safely grow in aluminum containers? That you admit they would specifically HAVE to maintain pH above certain levels to avoid Al toxicity levels is proof in itself that there IS risk. If there is any chance that the pH will drop below 5.0 - there is risk, and I simply left it to the grower to decide if he wants to take it.

I never even mentioned that it's illogical to assume that just because Al containers are offered for sale it somehow makes it a wise decision to grow in them. For crying out loud, there are hundreds if not thousands of products offered to gardeners that are either useless or potentially detrimental to the growing experience.

I think you're digging yourself a deeper hole, Dan. Why (specifically) do you think edible plants grown in container media will necessarily be stressed @ a pH of 5.0, and why do you differentiate between edibles and the pretty stuff?

Al

just:
it is the water/fertilizer that is more important than the pH of the potting mix.

Yes.

My point is that the unstated assumptions are:

o why would you want to take the pH of your system down that far?
o How likely is this to happen?
o is the solute going to enter the entire solution of the system?

The unstated presumption on this thread is that pHs will go down this far and it is uncorrectable.

And if we know the resultant deficiencies, what prevents someone from correcting just like someone would correct anything else detected (reaction time? Cost? Crop loss?)? Or when a deficiency is detected should it be left uncorrected?

The answer to these questions should help one calculate the value of aluminum containers, on some sort of scale or continuum; we should not presume this is a binary choice - esp. without any risk assessment offered to us.

»That is: are the likely issues arising from such containers too much to overcome wrt the benefits of such containers? Is the value of the Al containers greater than any additional effort expended on Al containers as opposed to other, non-Al containers?

[/systems analysis hat]

----------

Al: why do you differentiate between edibles and the pretty stuff?

I like to stay on topic. The topic was edibles. Why (specifically) do you think edible plants grown in container media will necessarily be stressed @ a pH of 5.0

Peppers and tomatoes grow better in soil more basic than 5.0 and may react to such a pH with difficulty in uptaking N or P, indicated by yellowing or stunted growth.

So,

What has been left out of the answer is context. Is the deficiency correctable? What is the chance any fert acidification will enter into solution and affect the entire plant at these unlikely pHs?

Dan

Umm....yeah....I didn't mean to cause a conflict between you 2, but I have to admit - it sure is informational! Ha!

Anyway, if either of you have ever visited my gardening blog, you already know that I come up with all kinds of crazy ideas/contraptions for gardening. Just look at my homemade propagation chamber, for instance.

Anyway, I've been trying to look at all of the options for modifying wicking baskets in self watering containers, mainly to decrease the surface area of it to slow down water capillary action into the growing medium. In my research, I've discovered that aluminum foil would work very well, but wanted to know all of the disadvantages that there may be, especially for a tomato plant. Henceforth...the question was asked.

EG

Dood: love your blog of the crazy *ss injuneer with the yield counter!

My crazy projects are limited mainly by the better half, so I can't go crazy like I want. The Sterilite SWCs might be my last one for a while.

I'd say an Al wick would have even less chance of toxification than a full-blown container, altho I can see it being a concentration point of the solute that drips down thru the shelf and cycles back up via the wick...but you are adding new water with a higher pH...nah. Even better situation than my ruined visual of a line of old ash trays, like sentries, with ripe red peppers like the ends of cigarettes.

Dan

Oh my. ;o) You want to stay on topic, so you rephrase the OP to suit yourself and then invent a bunch of "unstated presumptions (assumptions?)", so you can assume they're correct and hope everyone else does as well, and then use them to argue your point? How many logic laws does THAT break? Lolol

This is my original statement. "Aluminum from containers goes readily into solution at pH levels around 5.0 or lower. Excess aluminum can damage root and leaf cells, but it's primary effect is inhibition of P to the top of the plant." Let me know if you can refute anything I said w/science instead of assumptions and presumptions, please.

Take care.

Al

Ahem.

No one, Al, is disputing the bolded; rather, it is the confusing context and non-sequiturs that make for extra group effort in interpreting the answer (evidenced above).

Nonetheless, I personally enjoy the exercise of trying to interpret your prolix text to fit given fact patterns. Other people's mileage may vary. But I do such exercises for a living in order to give people concise, cogent, useful answers in unambiguous forms intended to be easily utilizable and actionable.

Best regards.

It looks to me like we are good, then? Keep the pH up there and edibles are fine, and any signs of P deficiency we correct appropriately?

Dan

It looks to me like we are good, then? Keep the pH up there and edibles are fine, and any signs of P deficiency we correct appropriately?

I don't know if you and Al are good or not, but I am kind of confused. Probably my fault, it happens easily.

If an acid forming fertilizer is used, how does the typical container grower know if any part of the media or water drop below pH 5.0 at any point in time?

Assuming this does happen, how does one correct it? How would one even know it occurred?

Some growers add vinegar to their water to purposely acidify it. It doesn't take much vinegar per gallon of water to drop the pH below 5.0 Should one avoid this if their container is made from aluminum?

Thanks for the compliment, Dan. I'm building a trebuchet this year! Ha!

Ok, i'll run back over to my gardenweb home (sqft forum)Thanks for everyone's input, it is greatly appreciated!

EG

Here is a link that might be useful: EG's wacky garden blog!

If an acid forming fertilizer is used, how does the typical container grower know if any part of the media or water drop below pH 5.0 at any point in time?

Assuming this does happen, how does one correct it? How would one even know it occurred?

Well, this is the issue.

I've been thinking about, for example, a localized area on the side of a container that acidifies to, say, ~4.5 for say 10cc, and that product goes into solution. Does the rest of the soil that is ~6.0 "fix" the localized acidification? I say yes, but I wouldn't bet the farm on it. Some solute may reach the roots and get translocated, which is an issue. But how much solute makes a difference? I'm not sure I know. If the product reaches the reservoir, it's likely the higher pH of the water will neutralize the product, but maybe not and we may have to correct the deficiency, which is easily done with a solution that goes into the water.

But it's an interesting question and I think what gringo jay wrote above makes a lot of sense and adds to the complication of Al containers. The Al planters I've seen in public spaces are huge and have large woodies in them, so they must work.

Dan

Dan,

I wouldn't argue with 'what works', but I wonder if these large aluminum planters you see have the potting mix in direct contact with them or if they are decorative containers with a less reactive container material inside?

Personally I have never even seen an aluminum container sold as being for growing plants, but that might be a local thing. I have seen all sorts of metal containers, but the all lack drainage holes which tells me they aren't intended as the primary growing area, just a decorative container to hold a more functional container inside.

Maybe justaguy... Next time I see one I'll poke around and I'll ask some of my designer friends.

Dan

I was told to plant a rusty nails aluminum nails with my hydrangeas to make them blue. Will crushed aluminum cans do the same thing?

Some of the accomplishments laid at the feet of the rusty nail myth are, plants will always profit from an extra kick of iron - they'll be greener and healthier, spruce will be bluer, green trees greener, a lower soil pH, better and bluer hydrangea blooms, more fruit on fruiting trees, ......., none of which actually happen.

Rust is iron oxide, and it's essentially insoluble in soils. The problem is that the iron produced by rusty nails is iron oxide, an essentially insoluble compound. Being insoluble, it's unavailable to plants. Even if you grew in a bucket of rusty nails with a little container medium to fill in the voids between nails, it won't work.

Only rarely is iron not found abundantly in garden soil, soils with pine bark have plenty of iron, and the low iron of peat-based media is easy to fix by way of basic fertilizing. If your soil pH is north of neutral (alkaline), iron will likely be fixed tightly to soil particles, in which case it's wise to consider lowering it or using an Fe chelate to ensure iron's availability when you see an iron deficiency's tell, interveinal chlorosis ......... even though iron isn't really what you're looking for here. You need aluminum for bluer hydrangea blooms, which is also normally very abundant in soils but sometimes unavailable, which is a good thing because it's toxic to most plants at even low levels. Like Fe, Al can be made available by lowering soil pH, so powdered sulfur or aluminum sulfate would be the go to chemicals for bluer hydrangeas. If there is a pH-driven insufficiency of aluminum, aluminum nails will simply add to the supply of unavailable aluminum, so that brings us back to soil pH. Too, finely powdered material is significantly more desirable than big chunks of aluminum or iron, as you would have with nails.

Al

Aluminum doesn't rust......it corrodes. Rust is ony associated with iron. The corrosion of aluminum is limited to alumium oxide but that is a hard, unflaky and insoluble material that actually forms a protective coating around the AL to prevent any further corrosion. So pretty much any solid AL added to the garden - nails, cans, tinfoil, etc. is a wasted effort.

Instead, use the aluminum sulfate Al mentoned above that is sold specifically for this purpose.......it has the common name of 'hydrangea bluing' and is often sold under that label. But there is also a limit to its effectiveness depending on the existing soil pH. Aluminum sulfate is not going to be sufficient to alter a high pH signficantly to achieve deep blue flowers.

I seem to remember reading somewhere that Aluminium is extremely difficult to assimilate through the human digestive system. If it were I'd be screwed by all the cans of beer I have ever drunk!