There are many options when it comes to construction materials for your raised beds. If you choose to use wood, opt for non-treated, rot resistant lumber like cedar, oak, or locust as there is concern that treated wood may leach heavy metals into the soil that could be taken up by plants. If you happen to have treated lumber at your disposal, you can always line the beds with thick plastic to form a barrier between the soil and wood.
Other worthy materials to consider for raised beds include bricks, rocks, cinder blocks, and plastic decking material. Instead, most gardeners elect to fill their raised beds with a combination of quality garden soil and compost. Some mulch yards sell topsoil and compost blends, or you can use soil from your property and mix in compost yourself.
As in any other vegetable garden, raised beds should be sited in a spot that receives at least six hours of direct sun daily. If you decide to build more than one raised bed, make sure there is a wide enough path between them for easy travel, harvest, and upkeep.
Got questions? Call toll free at , Monday to Friday, 9 a. Home Blog What are the benefits of raised beds and how can I construct one myself? In all likelihood, the roots and foliage will be regularly making contact with your material surface.
Secondly, the soil you place in your bed will need to remain fairly moist, and the exterior surfaces of your bed will be spending a lot of time in the hot sun. Most materials degrade when exposed to constant moisture and sunlight.
The best types of untreated wood are black walnut, cypress, cedar, redwood, oak, black locust, or osage orange. These are known for their rot-resistant properties and last for many years, even under moist conditions. These woods can be difficult to find available for purchase in some areas. They are also expensive. Untreated pine is a less expensive untreated option, but it will also have a shorter lifespan.
Another consideration: Aside from pine, these woods are not as sustainable as other materials. Often, these woods are harvested from old-growth forest. If you choose to use one of these woods, check that it is coming from a sustainable source. The FSC is an international organization that has developed standards for responsible forest management. All types untreated wood will need to be replaced at some point. The lifespan of your wood will depend on wood type and your environment. If you live in an arid climate, untreated wood can last for several years.
If you live in a hot and muggy area, untreated wood may only see you through a couple of years. A robust raised bed garden form built with wooden structures. Replacing your wood does not signify failure.
The untreated wood is decomposing and even adding some nutrients to your garden bed in the process. You may opt to extend the life of your untreated wood by staining or painting it. I recommend using a natural treatment like raw linseed oil or raw tung oil. The chemicals are added to speed up the oil drying process, so by using the raw versions, allow for additional drying time. Another thing to bear in mind is that linseed oil is a food source for mildew, so if mildew is a problem in your area, that may not be a good choice for you.
Paint and stain ingredients vary, and overall, the impact is relatively unknown. But common sense should remind you that these all include chemicals of some nature, and those chemicals may impact your crop. I recommend against painting the exterior only of your raised bed structure.
Treated wood has been infused with chemical elements to preserve the wood. The primary concern with treated wood is that those infused elements leach out of the wood.
The arsenic in CCA led manufacturers of CCA-treated wood to discontinue its availability for residential applications in Raised bed garden structures being built of treated wood and ready to be filled. So to put this into an interesting perspective, studies exploring the impact of treated wood when used for raised beds have shown that the greatest risk is actually in touching the exterior of the bed.
When you or especially, your kids sit on or lean on treated wood, your skin or clothing is most likely to absorb the copper or arsenic leaching out of the wood to remain on the surface.
In other words, really healthy soil with lots of organic matter does not take up arsenic by plant roots. Yet the more acidic or alkaline your soil, the more likelihood of those elements being taken up by your plants.
So, just another reason for getting a soil test to get your soil closer to a neutral pH 6. Ditto for soil with a low amount of organic matter, so make sure your soil analysis tests for organic matter percentage as well.
Even if copper levels are high and being taken up, the plants will die before you ever have a chance to think about eating them. At any rate, that would be a good indicator of a potential problem — in which case you might want to think about having your soil tested for metal concentrations. Studies further show that those root vegetables are impacted most on their surface.
So by thoroughly washing all the impacted soil off and peeling the skin off your potatoes, beets, etc. Your tomatoes and your eggplant could absorb copper or arsenic into their roots, but it is generally not shown to affect the fruit.
Leafy greens are an exception and can take up arsenic in their leaves. In short: Keep your soil near neutral and add lots of compost more on both of these later , thoroughly wash off the soil and peel the skin from your root vegetables, and avoid contact with the exterior surface of the treated wood.
A final note: When building treated wood beds, make your cuts somewhere that allows you to contain the sawdust. Wear a dust mask and gloves, and remove and dispose of the sawdust promptly. The truth is, these days the terms are used interchangeably. What are your concrete blocks made from? That depends somewhat on your area, but there are consistencies. So, yes, those metals are in the concrete blocks that line your vegetable garden too.
A concrete block raised garden bed under construction. While that might sound scary, the risk of those metals becoming available in the soil only happens if part of the concrete block is pulverized.
First, the proximity of plant roots to the damaged area. Next, soils higher in organic matter are always beneficial but especially in this case, because they help chemically bind the metals — making them unavailable for absorption into the plant. Just as with CCA-treated wood, root crops and leafy greens are most susceptible when exposed to higher concentrations.
So, how much fly ash is absorbed by soil held within a concrete block structure? Well, if the block is intact, little to none. But not much research has been done on this specific subject. If you have beds made from concrete blocks, just avoid anything that would cause them to break to the point that the dust from pulverized pieces can come in contact with plant roots. A raised bed garden built on a concrete area.
There is so much information out there on the subject, and it will quickly take you in many directions. So, just be mindful of the reliability of the sources of these articles. Composite wood is made of recycled materials and can last for years.
Some composite material, when used in long side walls can buckle a bit. Are there any chemicals or elements released by the composite material? Railroad ties are made with creosote, an oil distilled from coal tar. Creosote is used as a wood preservative for industrial use and is the black, oily stuff you see oozing from the sides of the ties. The heft of railroad ties has made them a popular choice for raised beds and garden retaining walls. Creosote is a possible human carcinogen and has no registered residential use.
What I can tell you is that the galvanization process typically involves dipping the metal in molten zinc or zinc-based coating. If using wood, it is advisable to use untreated form. Typically supported raised beds are created using untreated rot resistant lumber like cedar. Pieces are usually of 2" x 6" ht. Site selection. Site selection is important.
Vegetables require a lot of sunlight; a bed for these plants should be located where it will receive full sun. Select a location that receives at least 6—8 hours of direct sun.
If that is not possible, select a site that receives morning rather than afternoon sun. If it is challenging to locate a spot with adequate sunlight, try growing cool season vegetables that tolerate shade, such as broccoli, cabbage and lettuce.
The soil or the growing medium in the raised bed and the location determine how well a raised bed will drain. Always locate the raised bed in a location with proper and adequate drainage. Setup the raised bed in a level area or one where minor modifications will make it level. Site preparation and dimension. Till the soil in the spot where the frame will be placed. Next, determine the size and height of the raised bed. It should be no wider than 4 ft. The length of the raised bed varies according to space but is typically ft.
Growing medium. Fill the raised bed with growing medium. Standard potting soil or commercial container mixes can be used as growing medium for vegetables, but are usually too expensive for filling large beds. The growing medium could be soil from a different location or a blend of soil, compost, and soil-less mix. If bringing soil from other location, ensure that the soil is not infested with soil borne plant pathogens or contaminants like lead, pesticides, etc.
Likewise ensure that the compost is well done, mature, and does not carry too much salts. Mixing compost with the native soil in the beds will help create structure, add nutrients, improve drainage, and enhance the biology. When filling the bed, grade the soil so that it slopes slightly away from the center of the bed to the edge, and away from adjacent structures.
Use mulch around plants in raised beds to conserve moisture and to control weeds.
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