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How do I build a raised bed garden?


Raised bed gardens offer numerous benefits and are easy to build. In their simplest form, they can be created with a shovel, spade or rake by mounding soil up so that the level area for planting is higher than the sounding area for walking. Beds can be any length you'd like but shouldn't be any wider than 4' so that it's easy to reach into the middle. Some garden gurus like Eliot Coleman recommend narrower bed widths of 30" that can be easily straddled for planting. Although it's not necessary for raised bed gardens to have a frame, many people opt for one either for aesthetic or practical purposes. Frames help delineate which areas are for planting and which are for walking which can be very helpful for family and school gardens where little feet might not know the difference. Frames can be built from a variety materials depending on what you have on hand and the importance of aesthetics: logs, rocks, untreated boards, landscaping timbers, concrete blocks or corrugated metal. The video instructions above are for a 4'x12' frame made out of 2" wooden boards. There various ways to attach the boards to one another. You can use 4" deck screws, brackets or buy ready-made corners where all you need to do is slide the boards in and attach them with screws. Photo credit: Conomike Video credit:

Question details

Up until recently, I had been convinced that composit lumber was the right choice for raised beds. Unfortunately, someone recently suggested to me that the only composit lumber that is not toxic is the high density version. Versions made with some wood are toxic. I'm not sure how to tell if it is high density or not.   I'm now considering boiled linseed oil as it suggests in the video. Here's my question: Does linseed oil have toxicity issues, too? Also will boards treated with linseed oil last?
We built ~ 360' of raised beds in a landscaping installation at a house I owned. Because it was available, we used specially milled 4"X12" Cottonwood beams from a sawmill at the edge of town. It felt sort of like making a giant Balsa-wood model ... All the topsoil was imported since our reason for making raised beds was that our ground was old river-bed rock. We did not treat the beams at all. We knew the installation would be relatively temporary but we wanted to get on with it. Although the beams were from the same logs & had a similar garden exposure, they all reacted differently. About 50% remained sound over ~15 years. About 40% gradually showed rot deterioration that did not affect their function & was picturesque. And about 10% soon rotten away & got replaced. My favorite beam, right in the front of the main gardens, warped up into such a unique arch along its 30' length that i was tempted to incorporate it into the garden design with a rainbow painting! But we replaced it & stayed with geometric design.  :-)   My sense from observing raised beds made of harder woods is that the durability ratios would remain about the same but the deterioration time would be longer with harder wood. Bill, I am not sure what you mean by "composit wood." Any kind of composite particle board relies upon toxic adhesives for its form. I have never seen even one particle board advertised to be safe for leaching or offgassing indoors - another health hazard subect. In the indoor garden bed at this house we edged it with ~1-ft logs - shaped with a draw-knife- because I wanted the edge to be an inviting seat. I treated the inside of the logs with boiled linseed oil & they began to rot anyway in a year or so. So we spaded the fill soil back & coated the inside of the logs with an asphalt "paint" that my son, the master builder, assured me would be inert when "cured." It never seemed to leach into the soil, but the logs continued to rot on the inside where they were exposed to moist soil. The outside remained lovely. :-) If I had this to do again, I would line the logs with the heavy liner made for organic fish & lily ponds. I am thinking of researching the food-safety of that kind of deck planking that is made with recycled plastic. If I can find a food-safe-rating from a scientifically reliable source, that durable, no-splinter planking would be useful for raised beds. Has anyone else looked into this material? Would love to hear ...
Jessica -- I made a typo and wrote composit instead of composite. Sorry. What I should have said is wood-plastic composite. This is planking made from a combination of wood and plastic. Often recycled plastic is used. I think this is what you are calling deck planking above. I've seen it used instead of pressure treated wood on childrens' play structures. This is why I thought it might be safe. I've only seen one comment in another forum about this material. The person said that if it is high density plastic it is safe from leaching toxic materials. If it is made from wood and plastic, it is not safe. So, I'd realy like to know more about the safety of deck planking for raised beds. I have four beds using this material now and will make a change if it is found to be unsafe. I'm also looking to build two more in spring.
Hi Bill - enjoying your initiatives on KGI. I just did a Google Search for "wood & plastic composite boards." There are clearly a lot of different manufacturers & methods. So I would think you could ask your supplier for the name of the source company & see if they have a product spec sheet. If they are an established company their product might be specced in Sweets Catalog online, where spec details & details of uses are listed for a lot of construction products. Sweets is where I learned how to really apply drywall mud like a pro & then I had to give lessons to my neighbors.  :-)
Glenn is right on target.  It's all in the soil.  I've used borderless bed with great success at times, using heavy mulch for the pathways.  Mine were 3-4' square so I never had to walk on them.  Presently my beds are bordered with: 2'X10' recycled lumber treated with boiled linseed oil thinned with mineral spirits for penetration, and dried for about 2 weeks before using; plastic fence rails that will last forever, but are expensive to buy new; plastic composite decking boards that are also too expensive to buy new. The reason I'm using borders is just to create a barrier for lawn grasses.  After about 10 years, tons of compost, and weeding, I'm still getting sprigs of Bermuda Grass, even though there is none left in the lawn.  Bermuda Grass is popular in southern lawns, but is one of our most invasive weeds (weeds are only plants where we don't want them). My beds are amended with compost from the bins, rock powders, cornmeal, molasses, seaweed, and sprayed with a compost tea mixture.  Garlic spray is my main insect repellent, with an orange oil spray for heavy infestations. I will also post this in SMALL KITCHEN GARDENS. Stay natural, David   
'Although it's not necessary for raised bed gardens to have a frame, many people opt for one either for aesthetic or practical purposes.' I think this is the most important sentence in the above comment. A lot of beginners think that the boards surrounding the beds are the things that are going to make their gardening successful. This is not the case, it is what you put into the beds that is the most important thing. 'THE SOIL.'  If you are in a small space[garden] and you want it to look pretty and you have adequate watering facilites to hand and money for the boards, then a surround to your bed is OK. If not try it without the boards. then you don,t have to worry about how the boards are treated or lay out the initial expense. If you want to spend money then spend it on the best quality compost that you can, although i would also investigate to see if you can get free local community compost. Riding stables are a good place to look for compost, or the stuff that will make great compost next year. The term RAISED BED is also misleading, i prefer the term DEEP BED. A deep bed is a bed that is raised above ground level due to the addition into the soil of LOTS of compost on a regular basis. The perimeter of a bed like this can be defined with four pegs and some heavy duty string. The edges of the bed will form to a natural slope or batter. A lot cheaper and easier than wooden boards. Deep beds are also a lot easier to keep watered because they are nearer to the water table, and with the addition of the extra compost act like a natural sponge. This is a picture of my beds which are edged with plastic banding tape obtained from a car boot sale. The beds are not raised to the extent that they would be if they were enclosed, but the topsoil in the beds is now about 15" or more deep, after adding compost for the last ten years. The main thing to note with a deep bed / raised bed is not to walk on the soil, otherwise you will squash it back down to ground level. Always work from a board. Glenn
Gorgeous photo, Glenn! If a picture is worth a thousand words, this one is an intriguing book about your garden! One thing I would add about raised bed edges is their social uses: the ability to seat a group comfortably on the edges while teaching the garden; or doing light work in the garden; or enjoying conversation & tea with a friend; or with children playing alongside in the garden & running little trucks of soil along the edges - the edges can make a significant contribution to the overall usefullness & enjoyment of a sociable garden.  This past summer I helped set up the planting systems for a community garden at a shelter house for women clients, who may or may not know anything about gardening. A square-foot system worked well for all who took an interest & the garden was very productive. The garden-bed-installation worked well too, for all of the functions noted above. The large beds were edged with 6"x6" timbers, stacked two high. This made comfortable enough seating & looks like it will last "forever."
Hi Jessica Thankyou for your comments. This has reminded me of a visit to Harlow Carr Gardens in Harrogate last year. In the kitchen garden area they have used plastic boards to edge their beds. I,m not a great fan of plastic boards generally because i think they are flimsy and will go brittle in time. These boards though are substantial and are probably 6" x 1.5 " in section, made from recycled plastic bottles. To date this is the only product i have seen that directly makes use of recycled plastic in the garden. If anyone is thinking of installing edged beds then i would suggest looking for a similar manufacturer in your area. These boards look like they will last forever. The only drawback i can see is that they may soften at higher temperatures. Glenn
Boards from plastic bottles.
Harlow Carr Gardens looks wonderful. Did I miss a link to see the kitchen gardens area? The substantial plastic boards look natural in garden use & could be built with more of a seating edge in places, if desired. This is the kind of planking I see advertised in the US, usually in high-end decks in architectural settings. Our local lumber yard can get it "on order" & I haven't priced it yet. I too have thought plastic planking might be more flexible than wood for long, unsupported runs. There's an attractive structural solution to be seen in Maxine's raised bed garden design, over in the Small Gardens Group. Her garden beds look like they are edged with 1" cedar boards with a light stain & in the middle of the beds you can see a cross-piece that has been notched in as a brace to keep the longer sides from bowing out from the pressure of the soil. I like the notched construction at the corners! With our 4"x12" Cottonwood beam ends, my son made a big Z interlocking joint wherever they connected, with a 1' or more spike driven down to keep the Z from shifting. I appreciate his design/build expertise. I have photos, but the nearest good & free scanner is ~10 miles away in a busy landscaping office where I can use it after hours. To do.  :-)
Hi Jessica These are a couple of photo,s that i took of the kitchen garden area at Harlow Carr. It,s all made to look perfect. Being run by the Royal Horticultural Society money is no object to them. They probably have loads of people looking after it. I think the garden is designed more to inspire others rather than for just production of vegetables. The edgings look like timber but they are in fact recycled plastic bottles. Glenn
Your views of Harlow Carr are a treat! Thank you! I will add these to my collection for garden examples in a paved courtyard area - some raised, some Medieval with wattle edges & other detailing. Have you seen any interesting sculptural benches in garden or courtyard settings? Like concrete paved with tile? or?
Okay, we just built a raised bed yesterday. I filled it with compost and soil from my garden and we topped it with a greenhouse glass door! All we have to do is put brackets and some kind of levor for me to raise the glass, and im ready to plant. This one is going to be for lettuce and spinach, and radishes. We are building another for my herb garden! We have a 50 foot greenhouse and more than 1/2 acre vegetable garden, so I am new to raised beds, but am looking forward to a good growing season all year round with these. any tips, and Ill take them gladly. Ann
Jessica -- I didn't know about Sweets Catalog. I'll check it out. Thanks for suggesting it. I'm also going to see if I can get the supplier to give me contact info for the manufacturer of the material. I'll see what I can find out.
Hi Jessica -- I was able to talk with an authorized Home Depot spokesperson about Veranda composite deck planking for raised bed frames. The material is supplied by Fiberon. Home Depot said that Veranda does not leach toxic preservatives into the soil, but they couldn't guarantee that it would last 15 years when in the soil. Here's my post with the details:   I did try to find Veranda in Sweets directory. This is an interesting resource that I didn't know about. I couldn't find Veranda in the listing.
Hi Bill - Thanks for sharing your research. Here are my thoughts, based on the fact that if & when i use composite planking for some demonstration raised bed gardens, as I would like to, I will be not only using it but recommending it to others. i have researched composite planking, but long-past enough to need fresh input, since products can change over time. 1. What price difference are you seeing between wood options & composite options? Can you express that as a percent? With a % premium you can calculate the practical value of extra-service features, such as no splinters, or longer-life, or a stable finished color. 2. For the questions of composite water-absorbtion next to moist soil, which also affects any leaching issues, i would only want to talk to the manufacturer. Whether composite could leach undesireable elements depends upon [a] what kind[s] of recycled lumber are in the feed-stock; and [b] whether the finished composite plank is surface-sealed or can wick up water. Obviously, decking does not wick up water as decking. However, does the decking integrity depend upon a predictable wet/dry cycle, like wood? or upon a plastic-sealed surface? Only the manufacturer would know about the feed-stock - which wouldn't matter much for decking & they may not have anticipated continuously-wet garden uses - yet. :-) If a manufacturer is using leaching-safe stock, they should be willing to say so in writing & in a spec sheet.  :-) 3. Fiberon looks like a good supplier & Home Depot has a good, green product reputation overall. Fiberon website has a contact link. You could ask if they have a spec sheet & pose the questions re wood feed stock & surface seal. If they haven't already done this garden testing, I bet they would be willing to ship you some free samples for testing. 4. When I research for raised beds - not on the front burner this month - I will be dealing with a local lumber store - the nearest Home Depot is 90 miles from here. And we will look at nearest manufacture, for best shipping. The last manufacturer I researched was in the Seattle area. You may find there is a composite manufacturer in the Northeast. Then you could inspect the feed stock & view the process.   :-)  5. As Forrest Gump said, "That's all I know about that."  :-)
Wow this is kind an interesting. You know what guys planting has something to do with eating!So what you planted will reflect on your personality. That's why children should be very cautious about eating healthy and nutritious foods.The U.S. Department of Agriculture has been making an effort to make school meals healthier. The U.S. Senate on Tuesday, however, obstructed the USDA's ability to make many of these limitations. Article source: Potatoes will stay in schools, for now .Can you give me some tips on how to do this fantastic planting of yours?
I use boards on my raised beds because I have greenhouse doors made with heavy glass on top of them. We put brackets on the boards, and then put a handle on the door. It works great, because in the cold you start seeds and close the door and it has a great greenhouse effect, and the seeds germinate faster in the warmth. I can grow herbs and lettuce and spinach all winter long. I still have my 50 foot greenhouse, but Im just growing collards in there now, because we really don't want to keep the heat going at night all winter. It costs a lot. I might try cucumbers in there this winter.



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