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 garden structures, but a growing awareness of the importance of healthy soil biota is challenging its use.
A raised bed is an excellent vegetable gardening format and is even advised for crops where success factors include soil temperature control and adequate drainage. Raised garden beds are available in several forms, offering different heights, shapes, and grown garden bed materials.
Essential Raised Garden Bed Materials Considerations
When choosing raised garden bed materials, consider the well-being of your plants and their environment first. Below is a list of considerations:
- Some plants are unsuitable for taller raised beds. Sweet corn, beans, indeterminate tomatoes, and similar plants can be grown in raised beds, but they should be low for effective management.
- A healthy soil biota is essential to growing plants resilient to diseases and pest attacks. While hydroponic gardening shows that plants can be grown without soil, much effort is required to keep these environments disease-free. A single infection can decimate a whole crop.
- For optimal photosynthesis, most plants need between six and ten hours of direct sunlight daily. Ensure you choose raised bed materials that are UV radiation intolerant.
- Ensure that the raised bed materials can tolerate extended moisture exposure without rotting. If the material used is organic and reportedly rot-resistant, what is being used to prevent the decay and will the preservation chemicals destroy your soil biota?
- While wood has been a default choice for building garden structures for years, it is becoming increasingly clear that it’s not the best material for raised garden beds or planters.
- 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 adequate plant anchorage, the growing medium should balance organic content, inert materials, topsoil, and a healthy, diverse population of microorganisms.
Why Switch from Wooded Raised Beds?
You may think I’m against wooden products or trying to sell an alternative product, and neither is true. Wood is a beautiful material that can add significant value to a garden – but not as a planter or raised bed material, and plants need a healthy root system to grow well.
Healthy roots depend on healthy soil, which depends on a diverse population (billions) of microorganisms. Remove the microorganisms, and you will have dirt, not garden soil.
I love cedar wood with its natural dark color that pops when treated with a stainer and varnish, and it’s exquisite. But cedar oil, an ingredient of tanning oils, is toxic to fungi, and using it to create raised garden beds is unsuitable for plant growth.
Untreated wood may be preferable to grow plants resilient to diseases and pests. Unfortunately, commercially available dyes or sealers aren’t biota focused. Their products focus on aesthetics, with little consideration that they may harm biodiversity.
For several years, people have questioned the safety of common commercial wood preservatives, including creosote and copper-based pressure-treated products (for example, green stained wood used for decks).
Recycled railroad ties and utility poles should never be used for beds where edible plants will be grown because of the dangers creosote poses. The use of pressure-treated wood has also been met with skepticism, even though recent formulas have shown no ill effects on human health or food safety.
According to the standards the USDA sets for organic certification, no pressure-treated wood items may come into touch with edible crops in organic gardening. As a result, there aren’t many viable choices for protecting wood used in flower beds. Linseed oil and tung oil are the two most widely sold items, and there is scant evidence that either treatment significantly increases the lifespan of wood when placed in soil.
Building materials contain chemicals in defense against pests that could destroy buildings. The Environmental Protection Agency (EPA) reviews the uses of chromated arsenicals, including chromated copper arsenate (CCA).
CCA is a group of pesticides containing chromium, copper, and arsenic that protect wood against termites, fungi and other pests that can degrade or threaten the integrity of wood products.
Linseed oil from flax seed can prevent rot in unprocessed wood. The difference between raw and boiling linseed oil is significant. Natural linseed oil is combined with synthetic solvents that may not be allowed in a food-safe environment to create boiled linseed oil. Compared to creosote or artificial wood preservatives, raw linseed oil’s effectiveness as a wood preservative is limited.
Remember that wood treated with linseed oil is a mildew buffet. As a wood preservative, tung oil (an extract of the tung tree’s seed) is frequently diluted with hazardous solvents to aid application and absorption into the wood.
Stay away from treated wood to prevent chromate copper arsenate from seeping into your garden and tainting your produce. Building a raised bed out of untreated wood is the only option, but don’t expect durability.
Five Alternative Raised Bed Materials
If we accept that all the wood formats are not the best materials for raised beds, what are the other options? Below is a list of five materials to build a raised bed.
- Cinder blocks
- Plastic or resin
Metal Raised Beds
Some metal raised garden beds are sold as kits, while others are constructed from repurposed corrugated steel. Reclaimed, corten, or powder-coated steel can be used to build raised beds at a lower cost. Some are exceptionally well made with durability in mind, while others aren’t.
Space Saving Metal Raised Beds
Because steel beds have narrower edges, they take up less room in the backyard, garden, or field. Unlike wooden beds, they only need as much as raised ones. Alloy steels, in particular, are constructed to last for an extended time.
Despite common belief, steel-raised beds are not negatively affected by high temperatures. Raised beds made of steel are more stable in temperature extremes than other materials and can be used year-round.
The durability of Metal Raised Beds.
While metal raised garden beds may seem pricey, their visual appeal, durability, and superior functionality fully justify the investment. Considering the cost of replacing less costly items, you’ll realize that metal beds are less expensive overall.
This is especially true for powder-coated galvanized steel or corten steel beds. Depending on the coating, corrugated metal raised beds can survive more than 20 years, while untreated wooden beds hardly reach the 5-year mark.
Metal Raised Garden Beds Value Proposition
The actual price may vary slightly between different retailers. Beds made from coated aluzinc or corten steel can be purchased from select stores at between $120 and $300. The soil in a garden stays in them for decades, barring chemical imbalances such as excessive salt or chemical contamination. Because of this, they are currently one of the most popular options for use in raised bed gardens.
Metal Garden Bed Kits
Most metal raised beds are sold as garden bed kits, and these can easily be assembled with essential hand tools and pilot holes provided. If you decide to invest in powder-coated or alloy (aluzinc) raised bed kits, they’re easy to maintain, requiring minimal upkeep and easy dismantling, making relocation possible.
DIY Corrugated Metal Beds
Used water tanks and other galvanized steel beds that haven’t been coated or treated won’t last as long as their coated or heat-treated counterparts. Because of their susceptibility to rust, stock tanks have a shorter lifespan than untreated wood-raised beds. Despite their low price, a chemical used in production could seep into garden soil and affect vegetables.
These beds will corrode even quicker if you use an acidic soil mix such as sphagnum peat moss. If you don’t want to purchase a quality steel raised bed, consider the other options below. DIY steel raised beds should only be considered if you’re a metal worker with access to quality new galvanized, epoxy pre-coated sheets.
Fabric Raised Beds
You may know my success with grow bags if you’ve watched my YouTube channel. While there are many positives to using grow bags or cloth beds, there are also some drawbacks that novice gardeners may overlook.
Because of their modular design benefits, grow bags can be arranged in various ways to suit different needs and decor styles. You may choose from multiple sizes and colors to give you more flexibility, and sizes range from 5 to 100 gallons.
Fabrics used for grow bags may include recycled billboard vinyl, but whatever is used, fabric-raised beds are among the least expensive and most adaptable solutions for a garden. Whether a grower has a large backyard or merely a balcony to cultivate on, these systems are effective.
Standard five and ten-gallon grow bags are accessible for people using mobility devices so that everyone can enjoy the benefits of indoor gardening. They are more manageable in size and portability than enormous raised beds.
Because it’s so easy to bring a grow bag inside during the winter or move it out of direct sunlight, plants are happier, too. Fabric-raised beds provide roots with ample aeration, an expected deficit for most containers.
Challenges of Using Fabric Beds
Grow bags require more frequent watering than other gardening formats. A thick layer of mulch may be necessary to keep your beds moist in extremely hot or cold climates. Another challenge is to line areas where you want to use grow bags.
Grow bags leach chemicals and can boost weed growth. Due to poor nutrient retention and evaporation, you may need to replenish your raised beds more frequently with soil and organic matter.
Brick and Mortar Beds
Raised beds can be constructed using repurposed bricks, cinder blocks, cement blocks, or fiber planters. Raised beds can be built quickly and easily from bricks if laid correctly. You can take it to the next level by mortaring or cementing the beds together. Even prefabricated kits, complete with concrete nooks and wood siding, are available online.
Building materials like bricks and concrete blocks are widely available, and the size and contour of a raised bed can be customized with relative ease. Bricks and blocks are the simplest ways to create bespoke modular designs.
Among the materials we’ve discussed, brick has the highest cold resistance. When made from high-quality brick, it is the most efficient heat insulator. Antique bricks are typically more durable than newer ones because of the higher quality of the materials used to make them. If you’re building something, using bricks implies you can recycle the materials afterward.
The potential toxicity of concrete is a significant worry when working with cement and cinder blocks. Concrete may release harmful chemicals into the soil that pose a risk to plants and those who eat them. Fly ash is a typical aggregate used to produce concrete blocks. Fly ash is unfit for growing in any plant due to the prevalence of heavy metals and other contaminants.
Low-quality bricks tend to break in damp, chilly climates. Materials made from cement, cinder blocks, or concrete can also serve this purpose. Because of this problem, they are not rot-proof. If you use them, your hard work could be undone in a few years.
Plastic and Resin Beds
There has been a dramatic increase in the use of plastic and resin beds for home gardening. Some are sold as DIY kits, while others are ready to use right out of the box. Plastic and resin are the most common choices for modern raised garden beds.
Many of the plastic or resin beds on the market now are BPA-free and manufactured from polyethylene that doesn’t leach into the soil since their manufacturers realize the importance of human health and safety. The beds should be recycled according to the instructions given by the manufacturers.
Remember that some upcycled and reused materials may contain BPA and cause soil contamination, which could then be ingested by the food you cultivate. However, many plastics claim to be recyclable, whether or not they depend on the capabilities of your local recycling program. Plastic is unsuitable for plants that need regular drainage unless there are significant enough drainage holes.
Natural Stone Beds
Natural stones are another option for building your very own above-ground beds. These could be stones you find on your property or flagstone and mossy rocks you acquired from a hardscaping materials distributor. Let’s discuss the benefits and pitfalls of these.
Stone Bed Benefits
When it comes to natural stones (whether you’ve sourced them within your garden space or acquired them elsewhere), you’re working with one of the most natural materials. As they break down, they provide essential micronutrients to the soil.
Locally-sourced stones are the most environmentally friendly materials on this list. Like cement blocks or bricks, there’s a lot of modular potential in them too. You can place them directly on the ground or landscape fabric if necessary. If you’re sourcing from your property, they’re cheap as well.
Stone Bed Disadvantages
Much like concrete and brick blocks, you’ll have to move these around, and they can get heavy. They can be expensive and difficult to transport if not sourced locally. Even though they have a lot of modular capability, they could be thick and disadvantageous to those trying to maximize space. They could also fall over if stacked precariously on loose soil, making maintenance a consistent concern.
FAQs on 5 Modern Alternatives to Wooden Raised Beds
Is it OK to use treated lumber for raised garden beds?
Using treated lumber for raised garden beds is not recommended. Treated lumber contains chemicals that can leach into the soil and harm plants, which may not be approved for organic gardening. It is better to choose untreated wood or alternative materials like metal, fabric, cinder blocks, plastic, or stones for building raised garden beds.
What is the cheapest material to use for raised garden beds?
The cheapest material for raised garden beds varies depending on the location and availability of resources. However, some low-cost options include cinder blocks, untreated pine, and recycled materials like old pallets. It’s important to consider the durability and safety of the material before choosing the cheapest option.
What is the best of the raised garden bed materials?
There is no single “best” material for raised garden beds, as the ideal material depends on various factors, including plant type, environmental conditions, and personal preferences. However, materials like metal, fabric, cinder blocks, plastic, and stones are excellent alternatives to wood and offer durability, easy maintenance, and long-term value. Ultimately, the best material for raised garden beds meets your needs and promotes healthy plant growth.
There are many forms of the raised bed, and although wooden beds work fine, they do not last, causing you much more work and expense further down the line.