Chris Sherwood is a project manager by day and avid home and garden scholar by night who loves to share his trials and success with others.
The popularity of raised-bed gardening continually picks up speed as more people turn back to nature as a source of cheap, safe, healthy, and reliable food. With popularity comes innovation, and with innovation comes blog after blog featuring different building materials for developing raised-bed gardens. However, not all building materials are equally suited to this endeavor, and some can actually end up harming both you and your soil if you're not careful.
No matter what type of native soil you have, building raised beds allows you to create the perfect soil mix for whatever you want to grow without worrying about adding seemingly impossible amounts of amendments to the soil below. No matter if your soil is clay, rock, or sand, anyone can grow vegetables, herbs, and flowers in this way with one less obstacle. In fact, you can even put raised beds over unused concrete areas and on rooftops, making small or urban sunny spaces potential spots for a garden. Raised beds also help reduce weed issues, make gardening more accessible for those that have trouble bending over and taking care of their plants, and the beds provide and overall pleasing look that can fit most any landscape or design aesthetic depending on which material you use.
Materials to Avoid Using in Raised Beds
Recycling is great for the environment, and in some cases can be great for your raised bed as well, but certain recycled materials should be avoided when building your raised bed.
Railroad ties are found throughout the United States as garden beds, stairs, and other landscape features. However, the look is not worth the cost when you look deeper into how the wood is treated before use. The most important factor to look at is the use of creosote, which is often made up of over 300 different chemicals, many of which are potentially harmful to humans and can leach into surrounding soil. The EPA has released several warning regarding the use of railroad ties in landscapes and gardens, making it even more clear that you probably shouldn't use them even if you like the look.
Tires are often utilized for growing potatoes or as easy ways to add circular elements to your garden or yard. This has the added benefit of doing something good for the environment by saving tires from the landfill. However, tires contain heavy metals that may leach into the surrounding soil. There is some debate regarding this, as the rubber in the tire bonds these metals to the tire making it more difficult to leach out. Regardless, if you want to recycle tire in this way, stick to planting flowers in them that you don't plan on eating, just to be safe.
Pallets can be a great source for garden bed materials, as long as you know where they came from. Pallets are developed for shipping materials, and can often take on the remnants of whatever is shipped on them. Some pallets are also treated with a chemical called methyl bromide, a known endocrine disruptive chemical which can impact your reproductive health. Most pallet producers stopped using the chemical in 2005, but many old pallets are still out there. Look for a stamp on the pallet that says "HT" or heat treated. If there is no stamp, or you can't verify an HT on the surface, don't use the pallet for your garden.
Certain types of new materials should also be avoided.
Many new gardeners, and even experienced ones, turn to treated lumber when sourcing materials for raised beds due to its added protection against moisture and the associated rot and bug damage. However, while treated lumber will hold up better over time, it can also leach harmful chemicals into your soil. For many years, pressure treated lumber was created using chromated copper arsenate (CCA), which over time releases arsenic into the surrounding soil. Most newer treated lumber has removed CCA from the process and instead uses copper azole (CA-B) and alkaline copper quat (ACQ). While less toxic than arsenic, copper can still leach into your soil which has disqualified it for use in organic gardening. Note: If you're already using older pressure treated wood for your raised bed, ensure that you're plants are getting enough phosphorus through rich compost or other means, as plants are more likely to take in arsenic if the soil is phosphorous deficient.
Great Materials to Use for Raised Beds
Cedar or Redwood
Both cedar and redwood add a beautiful look to your raised bed garden while also employing a natural resistance to moisture, bugs, and rot. While these materials will still break down over time, you'll easily get five or more years from a properly built cedar or redwood bed, with some even lasting a decade or more depending on the climate.
Untreated wood in general can make beautiful, rustic-looking raised beds. The only thing to keep in mind with using these products is that they will break down much faster than other options. However, even with untreated wood, raised beds can last three or more years before sections need replaced, making it a great economical option for those looking for solutions with temporary cheap and easy raised beds while you slowly add more longstanding beds to your garden over time.
If you have a lot of natural rock in and around your property, put the rock to good use by creating a natural raised bed. While you'll get quite the workout moving the rocks to your garden site, the initial effort will result in long-term gains with rock raised beds that will last nearly indefinitely with little maintenance. You will most likely need to use some sort of mortar to hold the rocks together, at least enough to get height on the walls.
Note: This is not a very economic option unless you already have rocks on your property, as purchasing them will quickly add up and is not advised unless you're doing it more to fit the look of your property versus just function.
Brick or Cement Block
Brick is another beautiful option, but can also be price prohibitive depending on what type of brick you're looking at and whether it's new or recycled. Like rock, brick garden beds will stand for many generations of gardens once built. A cheaper alternative is cement block, which has also grown in popularity thanks to YouTube. However, the cinder block form of concrete blocks, especially older ones, can fall under the do not use category if they contain fly ash mixed in with the concrete. Fly ash often contains heavy metals like mercury, arsenic, and lead, which can leach into your garden bed and contaminate the soil.
Using Pots Instead of Raised Beds
For those in apartments, don't overlook pots as a great raised garden material for your small space. Even large gardens can benefit from pots placed in nooks and crannies of wasted space, especially for notorious plants that love to spread, like mint and certain cane berries in larger pots. Remember to drill extra holes beyond what the manufacturer has provided for better draining.
Note: Look for pots that are BPA-free to prevent BPA from leaching out of the plastic over time. You can usually find this information by looking at the bottom of the pot.
No matter the size of your outdoor space, raised beds provide the perfect solution to growing healthy, productive plants at any age and any skill level. With the right raised bed building materials you'll be well on your way to a more self-sufficient, active, and healthy lifestyle for many years to come.
Bountiful Harvest From Your Raised-Bed Garden
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.