Building Raised Beds
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WWW.ECOLOGYCENTER.ORG | 510.548.2220 X 233 | [email protected] Building Raised Beds There are many reasons you might choose Lining the Raised Bed to build structures to grow vegetables, herbs, and other plants: You can line your raised bed to make it more durable and to prevent toxics from • To avoid toxics in soil such as lead or leaching into the soil. For lining, use arsenic landscape fabric found at garden supply • To avoid drainage problems that some stores or cloth fabric from clothing. Avoid soils can present non-porous plastic, as it can retain too • To reduce back strain. Raised beds much water and discourage beneficial can be built at a good height for a insects and worms. A lining can make an wheelchair. existing raised bed safer, but if your raised • To add an aesthetically pleasing bed is made of creosote railroad ties or feature in the garden arsenic-treated wood, it’s best to remove • To make it easier to add nutrients to the wood from the yard altogether to the working layer of the soil prevent continued migration of the toxics. • To improve yields by reducing how To keep gophers and moles out of your much of the soil is walked on and plants, line the bed with metal hardware compacted cloth or staple gopher/rat mesh to the • To clearly separate the growing area bottom of the bed. from pathways for easier weed control • To enable gardening in paved spaces Treated and Untreated Wood Some pressure treated wood is toxic, while Choosing Your Materials some is not. The most toxic pressure- When choosing materials for your treated wood, chromated copper arsenate raised bed, consider durability, toxicity, (CCA), can often be identified by its environmental impact, affordability, staple-like indentations and greenish aesthetics, maintenance requirements, tint, but not all types of CCA wood have and how permanent or portable you want these identifiers. To make matters more your raised bed to be. confusing, wood pressure-treated with Alkaline Copper Quartenary (ACQ), which Reused materials tend to be the most is considered safe, also appears green. If affordable. Their environmental impact is the wood was bought or the structure built low because they don’t require forestry, prior to 2003, the lumber was most likely mining, manufacture, or long-distance treated with toxic CCA. To be sure, buy an Building Raised Beds transport. Find free or low-cost materials arsenic test kit from your local hardware on Craigslist or Freecycle, at your local store or online. salvage yard, or in your own backyard. The Ecology Center’s EcoDirectory If your existing raised beds were built with contains Bay Area resource listings, CCA-treated lumber, remove the structure including local salvage yards. to avoid the continued migration of arsenic through the yard. Even if the soil is One low-tech method that saves money replaced, the arsenic will migrate into the and has minimal environmental impact new soil. Dispose of the wood at a local involves building a mound of soil and waste facility as construction debris. If you straw directly on top of the existing choose to keep the bed, you may grow ground, without a structure to contain it. ornamental plants in it rather than food. This method, which permaculturists favor, builds nutrients and adds tilth to impacted If you use untreated wood for your bed, land. If your aim is to avoid toxics, this use natural wood treatments like flaxseed method might not be sufficient. oil or wax. Linseed oil can contain toxic additives, so it’s best to avoid it. A wide variety of borate-based “washes” exist that are safer to use near food plants. factsheet Building Raised Beds (continued) Determining Raised Bed Depth 6 - 10 inches: basil, beet, carrot short, chervil, chives, cilantro, lettuce, onion, greens, parsley, radish, Make your raised beds deep enough for healthy roots. peppermint, spinach, thyme, dwarf cherry tomato, Plants will be stunted and not produce well if their roots watercress, oregano, sage, marjoram. can’t reach down far enough into soil. If the raised bed is 10 - 15 inches: carrot, celery, cabbage, garlic, chard, built shallowly, the roots will venture into the ground below leek, lettuce, mustard, oregano, potato, strawberry, unless it is too compacted. A floor or barrier is needed if dwarf patio tomato. you don’t want roots growing into contaminated soil. The 15 - 18 inches: beans, collards, cucumber, kale, pea, recommended soil depths at right are taken directly from pepper, squash, short vine tomato. Golden Gate Gardening by Pam Peirce. 18 - 24 inches: broccoli, brussel sprouts, cabbage, corn, cauliflower, tomato. Common Materials for Raised Beds MATERIAL ENVIRONMENTAL TOXICITY/ DURABILITY COST NOTES IMPACT LEACHING Soil/straw mound Very low None Low Free to low Explore permaculture methods. Urbanite (broken Salvaged material See note High Free to low Concrete less than one year old concrete pieces) has low impact. can leach lime, affecting soil pH. Brick or Low if reused, See note High Low when Lining the bed can prevent lime cinderblock Medium if new. reused from entering the soil. Wood logs Low if scrap None Medium to Free to low high Bamboo Especially low None Medium Moderate when grown domestically Metal siding Low if reused Low Medium to Low to high Line with fabric to delay rusting. high Naturally treated Low Low Medium to Moderate Use nontoxic sealant on untreated reuse wood high wood (Flaxseed oil or wax) Plywood, High if new. Very high Medium Moderate Avoid. Contains toxic pressboard, and Lower if reused. components. painted woods Pressure treated High Can be high High High See section on pressure treated wood wood. Redwood or High, or lower if Low High High cedar (new) FSC certified. Stone (new) Can be very high Low High High Plastic lumber Medium ( does Moderate High High HDPE and LPE are best plastic not decompose or choices. recycle) Railroad ties Hazardous Very high High Moderate Avoid due to toxic creosote. Recommended Books, Websites, and Resources The Essential Urban Farmer – descriptions of building with Washington Toxics Coalition – tips on growing food at urbanite, brick, stone, corrugated steel, and wood. home in a way that avoids toxics. watoxics.org The Vegetable Gardener’s Book of Building Projects – Healthy Building Network – arsenic wood hazards and plans and building instructions for wooden raised beds. alternatives. www.healthybuilding.net/arsenic/hbn_ Berkeley Tool Lending Library – building and gardening wood_factsheet.html tools available for those with a Berkeley library card. Ecology Center EcoDirectory – salvage yards, soil and compost sources. www.ecologycenter.org/directory Please consider supporting the Ecology Center’s free educational resources at www.ecologycenter.org/donate. 2530 San Pablo Avenue, Berkeley, CA 94702 | 510.548.2220 x 233 [email protected] | www.ecologycenter.org Printed on 100% post-consumer recycled paper.