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effect of rust (iron oxide, not the disease) on plants?

The only decent sunny spot for me to plant a containerized veggie garden is underneath a rusting fire escape. There is obviously rust run-off when it rains. I can see rust stains built up on the walkway. Will the rust have any harmful effects on the plants or on the food they produce?

Public Comments

1. A little rust won't hurt, but too much of it can in turn cause a lack of manganese in the plants. Also some plants are more sensitive to iron than others so just give it a try - at worst the plant wont grow. I'd also be worried about Aluminum runoff from the ladder, are there aluminum parts on it? It can really mess the substrate up. As for consumption, once you've made sure the fire escape isn't made up of aluminum for a large part you are safe to eat the products of the plant. Even if there is more iron in it than usual, you'd practically live off that patch exclusively, which is impossible. To check for aluminum oxide, it is white rather than red and aluminum parts feel warmer to the touch than iron.
2. Iron toxicity is very rare. Ferric iron (rust) is insoluble unless the pH is well below 6 and is only very slightly soluble at pH6. Toxic levels can occur in sandy, very acidic soils but the pH must slip below 5.0. Very few domestic vegetable plants can grow at such a low pH except blueberries. If the pH is this low iron is less a problem that that major nutrients are all restricted. http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex6607 http://www.extension.org/pages/Soil_pH_and_Nutrient_Availability In a case where the pH is very low the presence of soluble iron salts can prevent the uptake of manganese. Iron toxicity symptoms on the plants are dead spots on the leaves. This appears first as lots of yellow pin prick sized lesions all over the leaf surface. The spots then turn brown as they die from the center out. Finally the whole leaf is brown and dead. I use rebar or welded, rusting steel with all my larger roses, in acidic (pH 6 at the lowest), sandy soil, with no problems. At this time there are more than a dozen ranging from Bourbon, Hybrid Musk, and Floribunda, to a couple of species roses climbing over iron frames. Belleview Botanic Garden had sets of heavy gauge custom steel bars made for their large freestanding shrub roses so I copied it using rebar. I also use rebar uprights for the tomato cages in soil that has a tested pH of 6.5.