If you’ve recycled old metal drums or mesh into planters or trellises, it won’t be long before they start to rust. It’s a worrying sight, and you’re probably wondering if rust is bad for plants.
Rust is not bad for plants, though it might look unpleasant. The reddish-brown flaky substance is iron oxide and is the result of a chemical reaction of iron with water and oxygen. Rust isn’t harmful, so it won’t affect plant health.
Given how ominous rust looks and its association with neglect and decay, it may seem counterintuitive to say it won’t hurt your plants. So, to explain further, we’ve rustled up some additional information for you below.
What Does Rust do to Plants?
If you’ve planted in iron or steel containers, it’ll only be a matter of time before they start to rust.
Rust occurs when you expose iron or steel to oxygen and moisture. You’ll soon see that familiar reddish-brown, rough or flaky material where previously there was shiny metal.
It’s caused by an electrochemical reaction called redox, though typically, we refer to it as oxidation.
In scientific terms, rust is iron oxide, and it can eventually coat all the exposed metal on your planters over time.
Now, don’t confuse this type of rust with the fungal disease of the same name. While the fungal disease can kill your plants, metal rust won’t affect their health.
In fact, you could argue that rust might do your plants good. It seems logical since iron is one of the micronutrients that plants need for healthy growth. Iron occurs naturally in the soil.
However, iron in the soil occurs in two forms. The form that plants can use is ferrous oxide. The other form of iron in the soil is ferric oxide like hematite.
Hematite is the mineral that colors soils red in some areas. However, ferric oxide is an insoluble form of iron which means that plants can’t take it up through their roots.
Rust, like the insoluble iron found in soil, is also ferric oxide. That means it’s insoluble. So, unfortunately, the rust on your containers or tresses isn’t something that plants can take up to meet their iron needs. Consequently, while rust isn’t bad for plants, it probably isn’t beneficial either.
Can You Grow Plants in a Rusty Container?
Since rust doesn’t harm your plants, there’s no reason to avoid planting in a rusty container. Just make sure it has drainage holes.
However, if you’re concerned about the rust, try double-potting the plant. That simply means planting your plant in a non-metallic pot and burying that pot into the soil in your rusty container.
This will prevent your plant’s roots from coming into contact with any rust inside a rusty container.
One drawback of a rusty container is it may stain plant foliage or flowers if there’s contact between the plant and the rust when wet. If that happens, you can simply pluck off the affected foliage, or support the plant so that it doesn’t come into contact with rusty parts of the container.
Keeping plants from coming into contact with the rusty container can also reduce the risk of plants getting scorched by hot metal on sunny days.
It’s also best to avoid placing your rusty container directly onto a surface like a patio. Whether the rust is outside or inside your container, it may discolor water. That can run-off onto your patio, leaving rust stains. You can avoid this by placing the container in a saucer or tray to hold water draining off or through it.
Can You Safely Grow Vegetables in a Rusty Container?
As you’ve seen above, there’s no harm in using rusty containers for planting.
However, as with your ornamental plants’ foliage or flowers, you don’t necessarily want your vegetables coming into contact with the rust. That’s especially the case with the edible parts.
It’s not that it will make the vegetable inedible, but rust may damage vegetables, as it’s often flaky and uneven.
So, a vegetable rubbing against rust may end up looking worse for wear. You may also get rust flakes embedded in the vegetable. Wounds caused by flakes breaking the vegetable’s outer layer can create vulnerability to rot and disease.
So, use supports to keep the edible parts of your vegetable plants away from the rust.
Can You Safely Grow Herbs in a Rusty Container?
As with vegetables, it’s also safe to grow herbs in a rusty container.
With herbs, you’re generally growing them for their edible foliage, so keep the foliage away from the rust.
Again, that’s because rust might damage the foliage, making it look unsightly. It probably won’t make it inedible.
However, if small particles of rust cling to foliage, you might get a metallic taste to your herbs. So, if you use rusty containers for herbs, pay particular attention when you wash the herbs before using them.
Does Rust Affect the Soil?
As iron rusts, it may affect the color of the soil in which it is present as a result of iron oxidation.
Remember, oxidation occurs where iron or steel comes into contact with water and oxygen. A relatively high level of iron in the soil in some southern states is why the soil in those states is reddish in color.
As mentioned above, the reddish color is from hematite. This iron oxide occurs where the soil is hot with plentiful oxygen. Other colors can appear depending on the environmental conditions.
Apart from possibly changing the soil color, it’s unlikely that rust will have any other effect on the soil. As mentioned above, rust on your containers is a ferric oxide, which is insoluble. So, it’s unlikely to add to the nutrients in your soil. At the same time, it’s not harmful to the soil either.
Does Rusty Water Help Plants Grow—Fact or Fiction?
You’ll probably have worked out from what we’ve said above that watering your plants with rusty water is unlikely to help them grow.
Rusty water is just water that’s discolored by rust. As mentioned above, rust is a form of iron oxide that’s insoluble. So, if you soak rusty nails in water, the water will soon turn reddish-brown. However, that doesn’t mean the rust has been absorbed into the water.
Remember, it’s soluble ferrous iron that plants can take up from the soil. As well as occurring in soil, soluble ferrous iron is naturally present in water.
However, unlike ferric iron, you won’t be able to see it. It’s that ferrous iron content in the water that plants can use for healthy growth, not ferric iron like rust.
That’s not to say that watering your plants with rusty water will do any harm. Just don’t water them from above if you want to avoid the risk of discoloring the foliage or flowers.
Is it Okay to Use Rusty Tomato Cages?
If you’re supporting your tomatoes with rusty metal cages, don’t worry. It’s not a problem but be aware of the risk of damage to leaves and fruits if they’re left to rub against the rusty parts of the cage.
Especially after rain or watering, those parts of your tomato plants touching the rusty metal may discolor from the rust.
Also, tomato skins are quite flimsy, so they could be damaged if left to rub against rusty cages.
None of this necessarily affects edibility, but you might find the discoloration or damage unappetizing.
So, protect tomatoes by putting something like garden fleece between them and the rusty metal.
To recap, rust isn’t bad for plants. While you might think it looks like something that can’t possibly be good for your plants, it won’t do them any serious harm.
The worst it can do is discolor or tear leaves, flowers, or edible parts that rub against the rust, but it won’t adversely affect your plants’ growth or health.
So, if you were thinking it’s time to take your old metal containers to the scrapyard to let them rust in peace, there’s no need. You can rest assured the rusty metal won’t damage your plants.
Here are Some of my Favorite Gardening Products and Tools
Thank you for reading this article. I hope you found it helpful for growing some new plants in your home or garden. Here are some products I like that I hope you’ll also find helpful. These are affiliate links, and I am compensated for referring traffic. But in all honesty, these are the exact product that I use or recommend to everyone.
Soil: For high-quality soil, I really like Fox Farm Ocean Forest. I do all my growing in containers and this soil has worked great for me. I like how they use nutrient-rich contents like earthworm castings, bat guano, and composted crab and fish.
Fertilizer: Currently I am using a seaweed-based organic fertilizer call Neptunes Harvest. This is a great milder fertilizer option if you want to use something organic. If you want a more powerful fertilizer, I recommend Fox Farm Liquid Nutrient Trio, lots of people have had great growing success with this product.
Pruning Shears: Pruning shears are one of the most useful gardening tools to have because it’s important to prune your plants to keep them healthy. The pruning shears I recommend are the Gonicc 8’’ pruning shears. I like them because they are built sturdy and work both on bigger and smaller plants, so you don’t need to have multiple pruning shears.
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