There are times when rusty containers seem to be the best option for growing your plants. However, since rust looks ugly and is often equated with tetanus and decay, there are concerns about health and safety, and many ask if a rusty planter is safe for growing plants.
Plants can thrive in rusty containers and they’re safe to eat. This is because plants cannot absorb the rust of metal containers released into the soil . The only possible exception is for rust in a very acidic soil where iron becomes available to plants and negatively affects them
Unlike clay, ceramic, or plastic planters, metal containers used as planters can last long despite knocks and accidents. Even in heat waves, strong winds, hail, snow, rain, or flood, metal containers don’t chip, crack or break. But the fact is, metals rust, so you should know these three safety tips.
But wait. First, let’s settle the question: can plants absorb iron from rust or not? It seems that there are conflicting opinions about this.
Science says plants cannot absorb iron from rust because it’s not water-soluble. However, many gardeners disagree because a couple of rusty nails in water can quickly revive plants.
Iron is abundant in most types of soils. However, plants cannot absorb iron from normal and alkaline soil (pH greater than 7.0). The trick of using rusty nails cannot not work here as iron solidifies in normal soil conditions and thus can’t be absorbed by plant roots.
In alkaline soil, oxygen with hydroxide and carbonate ions can quickly turn iron nutrients into solids that roots cannot absorb.
Also, plants cannot absorb iron in soil that contains lime, poorly-drained soil, compacted soil, soil with little or no air movement, and very low temperatures.
On the other hand, many gardeners swear that adding some rusty nails to water can revive wilting plants, fruit trees bear more fruits, hydrangeas and blue spruce become bluer than blue, leaves turning yellow can turn green, and so on.
One explanation is this: when soil is highly acidic (pH less than 7.0), iron becomes soluble in water and can therefore be absorbed by plant roots and then benefit them in case of an iron deficiency in the soil. However, if iron deficiency is not a problem, then the plant will suffer from iron toxicity.
Very minute traces of iron in soil or water helps plants to respire (move oxygen) and transfer energy throughout the plant as well as develop chlorophyll, proteins, and enzymes. However, in the rare case where iron is water-soluble, too much iron can kill plants.
Iron is toxic for plants when (a) soil pH level drops below 7.0 and creates excess of available iron in the soil, (b) when zinc is deficient in the soil, and (c) when the soil is always very wet or often flooded.
Using rusty containers or too much iron fertilizer is unsafe for your plants when the soil is (1) warm enough (not cold), (2) alkaline, (3) well-drained, (4) well-aerated (not compacted), and (5) contains no lime. This is when plants can absorb too much iron from rust.
If you must use iron fertilizer, use very little on your plants. For example, to treat yellowing leaves (iron deficiency) apply an iron fertilizer at 1 ppm (part per million). That’s equivalent to 1 milligram of liquid chelated iron per liter of water.
Soil application is once a year, but liquid foliar sprays can be done at least thrice a week, depending on need.
FACTOID: Plants that absorb too much iron show stunted tops and roots, as well as unusually dark green leaves (bronzing disease).
To sum up: Avoid using rusty containers and iron fertilizer on plants that are growing in soil with pH levels of 6.9 or lower. Plants can absorb too much iron from rust and die of iron toxicity.
PRO TIP: Be careful and read instructions on labels of fertilizers with high iron content such as ferrous sulfate (20% iron), ferrous ammonium sulfate (14% iron), iron DPTA chelate (10% iron), and iron HEDTA chelate (5 to 12% iron). Too much iron fertilizer can harm plants.
Have you been captivated by your neighbor’s fancy-looking rusty container? Fair enough, I like them as well. However, what to do now? Which soil and rusty container to use? Here are some selected tips!
If using rusty containers for your plants is unavoidable, use alkaline soil or soil with a pH higher than 8.0 so that plants will absorb little or no iron. Don’t use soil with less than 7.0 pH (acidic) because plants can absorb too much iron and die.
So, if you love them go for it. However, only normal pH or alkaline soil is fine. If you must use acidic soil, you can lower soil acidity in different ways: (1) lime the soil with agricultural limestone, (2) mix well-decomposed organic compost into the soil, or (3) add sulfuric acid, ammonium sulfate, or elemental sulfur to the soil.
However, if your plants are growing on alkaline soil, go ahead and use rusty containers. Your plants won’t be able to absorb any iron from all that rust.
FACTOID: One problem with alkaline soil is that plants get very little micronutrients and can suffer from iron deficiency.
People who recycle often reuse food packaging containers as planters because these are durable, have wide mouths for easier planting, and holes can be easily made for water drainage. However, many non-rusting options are available.
Using food tins as planters makes ecological and financial sense: you’re helping the environment and saving on planters and plant pots.. And, unlike glass, you can quickly punch drainage holes and avoid root rot.
The thing is, metals rust when oxygen and water touch them for a while. They can be made waterproof (more on this later), but if you’ve got no time for that, what are your options?
Despite the fact that rusty containers have their own charm, I do not use them often. Small kids coming to visit us or small pets might get injured or accidently ingest rust and I do not want that. In this case, there are many alternatives.
Waterproof food packaging includes styrofoam and waxed paper or cardboard, which lasts long enough for seedlings to grow and rooting cuttings for transplants.
And then there are plastic food containers. The best ones have deep covers that can be placed beneath the plant to catch excess water. And punching drainage holes is like cutting butter – any hot, pointed object will do (make sure you don’t burn your fingers, though).
These options are better than metal, not only because they don’t rust but they also keep the soil and root area cool, even on hot days. When the sun overheats metal, plants can be burned.
PRO TIP: You can even use large chips bags (silver inside). Use a sharp pair of scissors strategically for easy drainage holes. Turn the bag inside out first if you want a silver planter. Then, tuck in the lower two corners so that the bag stands. Fill with soil, and voila! A light, long-lasting planter that’s easy to repot and never rusts.
When working with metal containers for planting, use thick garden gloves. Always work carefully and avoid touching any sharp points or edges.
As I mentioned at the onset, tetanus from rusty points or edges can be a painful and expensive experience. If you must use metal containers for your plants, be very careful and follow safety precautions at all times. Nowadays most people are vaccinated against tetanus, but it’s still something you do not want to risk.
When handling metal planters, whether you’re planting in them, painting them, or moving them from one place to another, always wear safety gloves (this one on Amazon is quite good). Thick garden gloves should protect your hands and fingers for maximum safety.
Can a new metal container become rusty if I plant in it? Yes. As you know, water and oxygen on bare metal result in rust. However, if you plant air plants that don’t need water, your metal planter won’t rust if it’s always dry.
Is it safe for the plant if I use a rusty metal container? Yes, unless the container was used to store something toxic before, or the soil pH allows the plant to absorb too much iron. See Option 1 in this article.
Is it safe to eat a plant that grew in a metal container? If a plant thrives in a rusty metal container, that’s a healthy plant that’s safe enough to eat.
How can I remove rust to make a metal container usable? You can soak the metal in white vinegar for a few hours, then wipe away all the rust. You can damp the metal with a little water, let baking soda stick to the damp surface, and after a few hours, scour with a metal brush or steel wool. For faster results, you can also try a chemical rust remover.
What if the container is rusty outside but not inside? It’s safe to plant in that container. If you don’t want the rust to spread inside, you can remove the outside rust and apply paint or other waterproofing.
Can I place a plastic bag or liner in a rusty container before planting? Yes. In fact, this is a common-sense technique that is used for easier transplant to a prettier planter later. Make sure that the plastic bag or liner has enough holes for water drainage, all right?
What type of food packaging containers doesn’t rust? Waxed paper, styrofoam, cardboard, metallic chip bags, and plastic won’t rust. Galvanized (shiny) metal containers won’t rust too. Tin containers that are fully painted don’t rust either.
Can I use a tin (metal bin container) for a planter? Yes, you can. Actually, they can be perfect decor touches for your indoor spaces.
And that’s what you need to know about growing plants in rusty containers. Before you go, here’s a summary of the top takeaways:
Rust in acidic soil: To sum up, if your kitchen herbs or house plants love acidic soil, you don’t need to worry. They’ll grow well in rusty containers, and they’ll be safe to eat.
Rust is safe: It’s quite common to see rust on plant containers, particularly when you grow plants on your porch, garden, indoors or outdoors. Unless the container was used to hold toxic chemicals, rust doesn’t affect plants. Always verify if containers are toxic-free.
Plants don’t absorb rust: In many cases, iron from rust does not dissolve in water. Therefore, plants cannot absorb this type of iron in soil or water.
Don’t use rusty containers for alkaline soil: Plants can absorb too much iron from rust when the soil is alkaline, well-drained, well-aerated (not compacted), warm enough (not cold), and contains no lime. Too much iron can kill plants (iron toxicity).
Congratulations! You’ve just completed a thorough review of how rust doesn’t affect your plants. Happy gardening!
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- “Control of Iron Chlorosis in Ornamental and Crop Plants” by R. Koenig & M. R. Kuhns, Utah State University Extension
- “Iron uptake and transport in plants: The good, the bad, and the ionome” by J. Morrissey and M. L. Guerinot in Chemical Review
- “Oxide” by Z. C. Kornblum in Encyclopedia Americana
- “Soil pH” by Queensland Government
- “Soil pH – South Australia” by Soil Quality Australia
- “Soil Quality Indicators: pH” by USDA Natural Resources Conservation Service
- “The pH of your soil can affect plant growth and health” by E. Ward in Naples Daily News
- “The Relations Between Concentration of Iron and the pH Ground Water” by N. I. M. Ibrahim, International Journal of Environmental Monitoring and Analysis