Tony O’Neill, gardener and author of the popular “Composting Masterclass” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify the art of gardening. His mission? Helping you cultivate a thriving garden. More on Tony O’Neill
Wood has long been the default material for creating structures, but new trends emphasize aesthetic appeal, practicality, durability, and time-saving.
Raised beds offer the gardener several advantages. They enable gardeners to structure a growing medium of their choice, best suited to the needs of different plants. The height gained provides better accessibility, allowing gardeners to tend their gardens with less strain on the back or haunches.
Raised Garden Beds
Raised beds are an excellent choice for almost every garden environment, especially with limited space.
Raised beds are frequently more productive than ground beds because the soil is less compacted, has better drainage, and heats earlier in the spring, allowing plants to begin growing earlier in the season.
Raised beds are also sometimes easier to manage, especially for persons with restricted mobility, and generally have less perennial weed pressure.
The main drawbacks are that they require more frequent irrigation and have a high initial building cost. It makes sense, therefore, to make an investment that offers a durable, beautiful, and practical product.
This article explores why gardeners are moving away from wooden raised beds to more durable alternatives, exploring what some of those alternatives are.
Gardeners cultivating in raised beds can better manage their soil, preventing compaction and ensuring optimal root health—happy roots equals happy shoots.
In raised gardens, the soil also warms up faster and stays warmer, which helps seeds germinate and allows them to be planted earlier than they might otherwise.
The warmer and looser soil in raised bed gardening, combined with increased air movement for disease prevention and decreased pest pressures, gives you a bigger harvest of delicacies during the growing season.
Raised Garden Bed Considerations:
- For optimal photosynthesis and the resulting plant resilience, ensure your raised bed gets at least 6 hours of direct sunlight.
- Lettuce, Swiss chard, kale, mustard, parsley, and chives are suitable to grow if your planter gets dappled shade.
- Planning the position of your raised garden bed should also consider the water supply.
- Consider drip irrigation, as it limits the spread of pathogens caused by wet foliage and allows you to monitor your water applications more closely.
- Drip irrigation is relatively inexpensive and makes mid-summer watering easier.
- Raised beds can be built as low as 6 inches, but galvanized raised garden beds are so quick to erect that you should consider heights that benefit your gardening posture.
- Stick to the standard four feet wide if you want to reach all of your plants.
- If your beds are longer than 6 feet, lateral supports may be needed to prevent bulging in the middle.
- While wood has been a default choice for building raised garden beds for decades, it is becoming increasingly clear that preserving the wood comes at a price unacceptable to those concerned with the vitality of our essential soil biota.
- Even untreated, longer-lasting wood like cedar harms the soil biota needed for resilient crop production.
- For optimal growth, plant moisture and nutrient availability, and effective plant anchorage, the growing medium should balance organic content, inert materials, and topsoil. More on this later.
Why are Wooden Raised Garden Beds Becoming Less Popular?
Wood is a renewable commodity, so why are gardeners moving toward alternatives? The problem is twofold:
- Untreated wood has a replacement cost, lasting only about three years. Longer-lasting wood is either treated or contains natural bacteria and fungi deterrents.
- The treatments used for wood preservation are, by definition, anti-bacteria and fungicidal. This bodes poorly for the well-being of the microorganisms we need in our root zone.
For many years, wood has been a mainstay in landscape design. It is frequently used to outline a border, frame various flower or shrub beds, build compost bins, and construct raised beds for flower and vegetable gardens.
Several questions emerge when deciding what wood to use in the landscape. Before we learned the value of soil biodiversity, our main concerns about utilizing wood were how long it would last before rotting and whether we could eat the produce grown in this bed.
The Goal of Treatments
In numbers, bacteria and fungi are the most ubiquitous inhabitants of this planet, followed by trees. Microorganisms are essential for our existence; without them, organic material would not be recycled.
For microorganisms to be active, they need a food source and some moisture—the rest is nature. When boards and timbers are accessible to microorganisms, they do what they do—recycle organic material.
When evaluating wood materials for outdoor structures, it is typical to consider using the most decay-resistant material with the greatest life expectancy at the lowest possible cost.
Naturally slow-decaying natural woods include redwood, cypress, cedar, and oak; however, these can be costly. They contain natural species-specific fungicides as defense mechanisms in forests.
Treated wood used to be a popular alternative to natural decay-resistant woods. Treated lumber is commonly accessible and frequently the most cost-effective option.
It’s essential to note that all wood, whether treated or untreated, will eventually decay. Treated wood has a detrimental impact on soil biota, a critical element of successful gardening.
The Challenge of Dated Wood Finishes
Treating wood with chemical preservatives makes it more effective at destroying organic recyclers such as fungi, bacteria, and actinomycetes.
This extends the usability of wood in outdoor settings. I am not against wood treatment, merely resistant to the idea that it’s suitable for building an environment where microorganisms matter.
Consumer wood products were previously dipped or pressure treated with inorganic (waterborne) preservatives such as chromate copper arsenate (CCA), ammoniacal copper arsenate (ACA), and acid copper chromate (ACC).
Copper (Cu) had fungicidal activity, arsenic (As) had insecticidal activity, and chromium (Cr) linked the preservatives to the structure of the wood. The possibility of these preservative components seeping into soils has long been a source of worry.
Twenty years ago, the wood preservation industry voluntarily resolved to phase out using arsenic and chromium-containing preservatives in wood products. There is now Federal legislation that prohibits its use.
Residential landscape wood obtained from lumber yards is treated with micronized copper azole (CA) or alkaline copper quaternary ammonium (ACQ).
The look of copper azole-treated timber is similar to that of CCA-treated wood but has a green tint giving it the general term “green wood.”
Treatment is performed by either dipping, with provides a cosmetic surface treatment, or by pressure treatment, which forces the preservatives to penetrate the product uniformly.
When dipped, treated wood is not generally recommended for ground contact. Boards and timbers may be labeled as standard for ground contact use when fully pressure treated.
Boards with an American Wood Protection Association (AWPA) label provide usability information and a warning against burning treated wood.
What are Corrugated Raised Garden Beds Made Of?
Several materials are now being used to manufacture durable alternatives to the dated wooden garden bed. Let’s look at three and see why they’re a better option.
- Galvanized Steel Raised Garden Bed
- Powder-Coated Galvanized Raised Garden Beds
- Zinc, Aluminum, and Magnesium (ZAM) Alloy Coated Steel Raised Garden Beds
- Aluzinc Steel Raised Garden Beds
Galvanized Steel Raised Garden Bed
Corrugated galvanized steel has been a reliable commodity since 1742 the process was first invented. Zinc is stable to oxidation, even in the presence of water. Metal is most definitely not.
While it’s popularly believed that the Romans were responsible for the advent of the arch bridge, the mathematical prowess of the Greeks was accountable for its formulation centuries before.
But, as we’ll see later, execution triumphs over conceptualization. The Romans took what the Greeks argued and put it into practice, thus providing civilizations through the millennia with the means to defeat gravity.
Corrugated iron and even corrugated carton boxes all capitalize on the principles of an arch to strengthen the material. In addition, corrugated iron provides a means to channel water, even in our raised garden bed example.
The popular word for iron oxide is rust. The most common kind of rust is the reddish coating that forms on iron and steel (Fe2O3), but rust can also be yellow, brown, orange, and even green! The various hues represent the diverse chemical compositions of rust.
Even though rust is considered the product of an oxidation reaction, it is essential to note that not all iron oxides are rust.
Iron and oxygen react to generate rust; however, merely combining iron and oxygen is insufficient. Even though approximately 21% of the atmosphere is oxygen, rusting does not occur in dry air.
Rust is a product of iron and oxygen, but the source of that oxygen must be bound in elements like water or CO2. Saline water even further accelerates the process.
Remember that oxygen is also present in carbon dioxide. Carbon dioxide and water combine to form carbonic acid, a weak acid. Water is a poorer electrolyte than carbonic acid. Water disintegrates into hydrogen and oxygen as the acid eats away at the iron.
Free oxygen and dissolved iron combine to form iron oxide, freeing electrons that can move to an adjacent metal part, causing the rust to spread.
Preventing Rust – The Galvanizing Process
Immersing steel sheets do hot-dip galvanizing in a bath of molten zinc to create a corrosion-resistant, multi-layered coating of zinc-iron alloy and zinc metal.
A metallurgical reaction occurs between the iron in the steel and the molten zinc. Because this is a diffusion reaction, the coating forms perpendicular to all surfaces, resulting in a homogeneous thickness across the item.
There is a shift from this process to more energy-efficient ways of creating anodic-protected steel sheets resistant to acids and rust.
The goal of surface preparation in the hot-dip galvanizing process is to get the cleanest steel surface possible by eliminating all oxides and other polluting residues.
Surface preparation is critical because zinc will not react with dirty steel. Steel cleaning for hot-dip galvanized coating consists of three steps:
First, the steel is immersed in a degreasing bath, such as an alkaline, acidic solution, to remove organic impurities from the surface, such as dirt, oil, and grease. The steel is cleaned with water after it has been degreased.
The steel is next pickled in a weak hydrochloric or sulfuric acid solution to remove oxides and mill scale. Once all oxidation has been removed from the steel, it is rinsed with water before proceeding to the final surface preparation step.
The flux aims to clean the steel of any oxidation accumulated since the pickling process and establish a protective covering to prevent oxidation before entering the galvanizing kettle.
When the steel has been thoroughly cleaned, it is ready to be immersed in the 98% pure zinc bath. Other metals may be added to the kettle to enhance specific desirable qualities in the galvanized coating.
The galvanizing kettle is heated to a temperature of 820-860°F/438-460°C to a liquid state. Steel goods are left in the bath until the steel reaches the bath temperature.
Several of the current galvanized raised garden beds on offer have additional treatments to improve durability even more and improve aesthetics.
Current offerings of galvanized raised garden beds are pretty exquisite. I prefer the powder-coated galvanized raised garden beds.
Powder-Coated Galvanized Raised Garden Beds
Several steel coil merchants produce a range of galvanized pre-coated steel coils in various colors for appliance manufacturers and other industries. These are now being used to manufacture raised garden beds.
In addition to the protective zinc coating, another heat-responsive epoxy adds protection and visual appeal.
Powder coating is a dry finishing technique that has grown in popularity since its introduction in North America in the 1960s. The powder is used on many items and accounts for over 15% of the industrial finishing market.
Powder coatings are increasingly being specified by businesses for a high-quality, long-lasting finish, enabling increased productivity, enhanced efficiency, and simplified environmental compliance.
Powder coatings, used as functional (protective) and aesthetic finishes, are available in various colors and textures, and technological improvements have resulted in exceptional performance attributes.
How Does Powder Coating Work?
Powder coatings are made from polymer resin systems mixed with curatives, pigments, leveling agents, flow modifiers, and other additives.
These components are melted, cooled, and milled into a homogeneous powder resembling baking flour.
Powder coating is often applied to a metal substrate using a process known as electrostatic spray deposition (ESD).
A spray cannon is used in this application to apply an electrostatic charge to the powder particles, which are subsequently attracted to the grounded side.
Following the powder coating application, the parts are placed in a curing oven, where the coating chemically reacts with the addition of heat to generate long molecular chains, resulting in a high cross-link density.
These molecular chains are complicated to break down. This is the most commonly used method of applying powders. Non-metallic substrates such as plastics and medium-density fiberboard can also be coated with powder coatings (MDF).
Preheated components are dipped in a fluidizing powder hopper, where the coating melts and flows onto the part.
Post-cure may be required depending on the mass and temperature of the item and the type of powder employed.
Powder coatings are simple, environmentally friendly, cost-effective, and durable regardless of the application procedure.
The Powder Coating’s Durability
Powder coating is a high-quality finish that may be found on thousands of objects you come into contact with daily.
Powder coating protects the most rugged gear and the home goods you rely on daily. It delivers a more durable surface than liquid paints while remaining visually appealing.
Powder-coated objects are more resistant to coating quality degradation caused by impact, moisture, chemicals, UV light, and other extreme weather conditions.
As a result, the likelihood of scratches, chipping, abrasions, corrosion, fading, and other wear issues is reduced.
Aluzinc Steel Raised Garden Beds
Aluzinc steel, or galvalume or zincalume steel, is a cold-rolled galvanized steel with a metal coating of 55% aluminum, 43% zinc, and 1.6 percent silicon.
Aluzinc steel is distinguished by its unique composition, which combines aluminum’s physical protection and great durability with the electrochemical protection of zinc.
Aluzinc outperforms galvanized coatings by 2 to 6 times in terms of long-term corrosion resistance.
The density of 55% aluminum is less than that of zinc. The area of a galvalume steel sheet is 3 percent or greater than that of a galvanized steel sheet with the same weight and thickness as the plating layer.
Zinc, Aluminum, and Magnesium (ZAM) Alloy Coated Raised Garden Beds
As I mentioned earlier about the bridge arch, the Greeks and the Romans. The ZAM process is similar in that the Americans theorized, but Nippon Steel commercialized it.
Several companies now manufacture Zn-AL-MG alloy-coated steel. The zinc-aluminum-magnesium coating is an alloy coating with zinc as the major component and aluminum and magnesium levels ranging from 1.5 to 8%. The magnesium content is not less than 0.2 percent and boosts the formability.
Compared with the coatings mentioned above, ZAM alloy-coated steel is known for its superior corrosion resistance, formality, wear and scratch resistance. It is used for cars, HAVC, solar photovoltaics, agriculture, high-speed guardrails, and greenhouse structures.
Gardeners garden better if they work in harmony with microorganisms. Using wood, unless it’s untreated softwood, is detrimental to your soil biota.
Untreated wood doesn’t last, but several environmentally friendly options exist for constructing a raised garden bed in one afternoon.