Question

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 ...

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   

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 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."  :-)