Are Galvanized Steel Garden Beds Safe?
Are galvanized steel garden beds safe for growing plants? We demystify these metal raised beds and look into the safety concerns about them.
Raised beds are gaining in popularity. By using a raised bed, you can have perfect soil quality. Weeds are easier to prevent, and a quality raised bed can last for a long time. Many are constructed of wood, others of brick or rock. But galvanized steel is becoming a popular option, too, which raises a rather important question:
Are galvanized steel garden beds safe?
The short answer to this is yes, they’re absolutely safe for gardening use. Since it requires acidity to break down the zinc coating that galvanized steel has, and most garden soils are neutral, there’s little to no impact. Plus, zinc is an essential plant micronutrient and a normal part of the soil. We’ll go into more detail on all this stuff in a bit!
We love metal raised beds so much that they’re the first product we chose to kick off our web store. There’s a wide variety to choose from, and we think you’ll like these high-quality galvanized garden beds.
Our Favorite Galvanized Steel Raised Beds:
|The Original 6-in-1 raised garden bed is the perfect customizable garden solution. Get one here!|
|Need more depth? The Tall 6-in-1 raised garden bed provides 30″ of depth to grow in and is also customizable. Buy one here!|
|For a more unique planting option, this tall round metal raised bed is a real winner. Click for more information!|
|With a classic weathered iron look, this sleek planter is perfect for decks or balconies, porches or as an urban garden fixture. Find one here!|
|A tall pot for a single plant or a few trailing vines, this has the same sleek look as its companion planter. Get yours today!|
What Is Galvanized Steel?
Galvanization is the process of bonding a layer of zinc to the surface of steel or other ferrous metals like iron. This process prevents the steel or iron from rusting when it is in contact with moisture.
Most galvanized steel is made with a hot-dip process. Sheet steel, either corrugated or smooth, will be fully submerged in molten zinc. This creates a uniform layer on the steel’s surface. Sometimes, the metal will be cooled to allow the material to fully bond and then re-dipped for a secondary coating.
Not all galvanized steel is coated in pure zinc. Some galvanized metal is hot-treated with an alloy. Aluzinc, for instance, is an aluminum and zinc coating which is commonly used for hot-dipped galvanization. The aluminum creates an exterior layer that protects the zinc and steel inner layers from moisture damage.
What’s Galvanized Steel Used For?
A better question would be what galvanized steel isn’t used for. Galvanized steel is the preferred material for watering troughs for livestock, exteriors of grain silos and water storage containers, shed construction, roofing, gutters and downspouts, and a number of other products. It’s sometimes used as durable fencing panels.
For decades, galvanized steel pipes were the standard for home water pipes, too. While this is no longer the case as galvanized pipes have been replaced with PVC and copper, most older homes still have galvanized fittings in use. As long as the zinc coating remains intact, these pipes will continue to last for years to come.
In food usage, galvanized metals are less common for cooking, and more common for storage containers. As zinc is heated to high temperatures, it can off-gas into food and the surrounding air. This makes it unwise to use for cooking vessels. Containers made of galvanized steel are quite effective for storage, though!
Is Zinc Leaching From Galvanized Metal?
Yes and no. If you have extremely acidic water, such as acidified water from a well that has not been treated to neutralize the pH, the zinc will gradually break down. This process can take literally decades if the coating is thick. Most municipal water sources neutralize the pH of water through their facilities, which means that it’s unlikely to be a major concern. Alkalinity does not cause any problems for galvanized steel, as it can handle alkalinity up to pH 12. Only acidity at 5 pH or below can cause this slow and gradual corrosion.
Zinc is a normal component in most soils. Plants and humans both need a small quantity of zinc to survive. You’ll find it in your daily multivitamins too! Plants need less zinc than we do, but it still is a necessity. The microscopic amounts which they may absorb from your beds won’t harm any food you’re growing, nor should it be harmful to the plants themselves.
Zinc itself may not be a danger to human or plant health, but impurities in the zinc can be. Concerns have been raised about lead pollution in zinc. This has led to steps taken by manufacturers to use only pure zinc or aluzinc-type alloys to reduce the risk of lead pollution. You are less likely to have problems with lead from galvanized containers than you are to find it naturally in your soil.
So yes, acidic conditions may cause some zinc leaching. But it will be extremely minimal, and some plants may actually prefer the slight zinc boost in the soil. As long as the steel is from a reliable manufacturer, there’s no need to be concerned that your beds will leach toxic materials.
Is Aluminum Leaching From Galvanized Metal?
While one can never say never, there has not been a significant risk for aluminum from aluzinc galvanization leaching into the environment. The aluminum used for aluzinc galvanization is lighter-weight than the zinc when molten, and will rise to the outer surface during the heat-dip process and provide a super-thin protective coating for the zinc. This protective coating prevents the more soluble zinc from leaching off, and if there’s any additional coating such as paint, that adds even another layer of protection over the aluminum surface.
Aluminum itself is not anywhere near as soluble as zinc is, which is why it’s used so consistently in food storage. In addition, it’s resistant to acid conditions, an important thing to note when paired with the more soluble zinc. If it weren’t for aluminum liners in canned goods and aluminum cans for beverages, we wouldn’t have most of the long-term food storage options we currently have! There were some concerns back in the 1960s and 1970s about the safety of aluminum cookware, but intensive research has determined even that’s not a risk to humans. Since your garden beds will never reach the multiple hundreds of degrees of heat that cookware does even in direct sunlight, the very limited aluminum in the aluzinc coating is perfectly safe and protects the zinc from degradation.
What About Heavy Metals?
We can’t speak to the quality of other beds on the market, but per the Australian manufacturers of Birdies raised garden beds, their product does not contain any heavy metals of concern. Their steel is used for water tanks in Australia (among many other uses, such as gutters and roofing) for years, and meets ASNZS standards for Australia. These standards are set by Standards Australia, a non-profit, non-governmental organization that establishes health and safety standards for products.
Can Galvanized Steel Be Used For Raised Beds?
Absolutely! Galvanized metal raised beds are becoming some of the most popular garden beds out there. They’re durable, sturdy, resistant to damage, can’t rot out like wood, and will last for decades. Plus, they look great and can evoke a ranching or industrial vibe. A galvanized planter won’t swell or contract, doesn’t need to be oiled or painted to maintain it (although you certainly can if you want to), and will take anything that nature will throw at it.
Shallower raised beds are easy to fill with your preferred pH neutral, well-draining soil of choice. However, deeper beds may require a little more fill material. We’ve got a great piece on how to fill tall raised metal garden beds which goes into more depth on that topic!
Do Metal Raised Garden Beds Get Too Hot?
Not at all! It’s true, most metal will heat in the sun. But damp soil is a miraculous cooling agent for the hot metal. As a general rule, your vegetable garden or flower planter won’t become too hot, especially if you’re watering consistently.
Because metal can conduct some heat, the soil which is immediately against the sides of the raised bed may be warmer than the center of the bed. This actually acts as a beneficial thing, especially in the spring. The soil in raised beds warms up more quickly than the ground does, enabling you to start that vegetable garden even earlier. Your young plants will appreciate the warmer soil on their roots!
In mild climates, a metal raised garden bed can help you to maintain a more consistent soil temperature year-round, provide good drainage of excess water, and more. The rigid, sturdy material will provide a good base for a cold frame over plants you’re overwintering. And when using soaker hoses, these beds can maintain moisture extremely well.
Raised Garden Bed Selection
Choosing a commercially-made galvanized garden bed can be complex. There’s a surprising number of options out on the market, from large vegetable garden styles to the basic planter.
I’m very partial to the beds designed by Birdies, an Australian manufacturer. These sturdy galvanized raised beds are extremely effective. They are galvanized with aluzinc, a material which is comprised of 55% aluminum and 43.4% zinc with a small amount of silicon. Each container is designed with utility in mind. Some even offer multiple configurations, allowing you to choose the exact size and shape you need!
Those of us with limited growing space may be interested in their line of galvanized planters and pots. The courtyard-balcony-deck line (shortened to CBD) is a fantastic line of products. These don’t use corrugated metal, instead opting for a smooth, sleek and streamlined design that fits seamlessly on porches and patios.
But if you have lots of space for your garden, don’t fear! Their original line is perfect for you. Both 15″ and 30″ depths are available. These beds offer a great amount of square footage and are configurable to your space. I’m partial to their long narrow configuration (which works out to be roughly 5.25′ x 2′). But there are options for squares or other widths of rectangles as well. These are perfect to grow vegetables in, and you’ll use them for decades.
Do you have an area where only a circular bed will do? The tall round bed provides the perfect habitat for your potato plants, and its depth allows you to keep adding soil and expanding your potato harvest. You can fill it with concentric rings of leaf lettuces to make an eye-catching salad garden, or make an herbal display. The options are endless!
DIY Build: Raised Galvanized Steel Garden Beds
If you have galvanized sheeting available to you, you may want to consider building your own DIY bed. Be sure you have a good grade of galvanized steel that’s meant for roofing or other exposure to the elements. You’ll also need wood corner posts to secure the steel to, and some corner flashing to protect the edges from wear.
There’s a lot of designs on the web for this style of bed, and a quick search will get you patterns and materials lists that you can work from. We’ve got a few in our list of over fifty raised bed patterns, too! However, one thing I do recommend is to reinforce the sides of deeper beds with galvanized pipe. A short length of pipe pounded into the soil against the outside of the bed will prevent the steel from bowing outward when filled with soil.
One consideration for these DIY beds is that they do require wood as well as metal. The wood has a shorter lifespan than the zinc-coated steel does, so you may eventually need to replace the corner posts and any other wood used in their construction. If you paint the post with an exterior paint first, you may be able to prolong its lifespan, but be careful to select one which won’t leach chemicals into your soil.
Also, the sheet steel may have sharp edges, so you’ll want to prevent potential injury. Creating a topper to cover the bare edges of the steel is necessary. You can create a bench-like surface by securing a 6″ or 8″ wide board on the top of the bed, screwed into the corner posts to anchor it. This will also hide the open end of your reinforcement pipes.
Keeping Your Metal Raised Beds Safe
Zinc-coated steel is sturdy stuff and will hold up to most garden uses. But there are ways to ensure your containers are safe for decades to come!
Avoid using fresh chicken manure in your garden. While it’s amazing stuff, its acidity will break down the zinc surface more quickly, opening the steel up to a risk of rust. Instead, use composted chicken manure or other organic options.
Opt for plants that will grow in neutral soils, and keep the soil pH on the neutral side. At a neutral level, the zinc is less likely to break down into the soil.
If you’re planting acid-loving plants, consider a liner. Heavy plastic can keep acidic soils from making direct contact with the metal. Just be sure that the plastic only covers the sides to allow for good drainage.
Amend heavy clay soils to loosen them up. Well-draining soils are necessary for raised beds to ensure they don’t turn into muddy ponds. In addition, clay is such a fine particulate that it can cling to the sides of your bed, and the caked-on layer of clay will do more damage to the zinc finish than a sandy soil would.
So what have we learned? The zinc coating is safe enough that it’s been used for livestock feeding and watering. It’s unlikely to leach into your food. Steel garden containers aren’t likely to become too hot for your plants. And best of all, you’ll be able to grow healthy food in them. Commercial containers are available and, with easy assembly, can be ready to plant in quickly. If you’re handy with tools, you can DIY them too. And there are ways to extend the lifespan of your beds, which will already last for decades.
Growing plants in galvanized steel beds is not only safe, but you’ll be growing better quality food than you can get at the market. So consider gardening in these lovely containers! You’ll be happy you did.