I constructed the first bed of recycled plastic lumber. The cost of two planks (2 x 6 inches x 12 feet) was $89.00. Plastic planks can be cut with regular saws and nailed with ordinary nails. I used brass wood screws for a better hold. The cost is high, but plastic lumber is supposed to last forever.
I prepared the second bed using peeler cores. This required eight 8-foot cores at a cost of $15.68. I drilled these and used rebar to hold them in place at an additional cost of $6.84. The peeler cores are not entirely uniform in size, and the finish is only "skin deep." It is an inexpensive bed, but I feel it may have a short life.
The third bed came as a commercial kit from Gardener's Supply that cost $79.95 plus $10.50 shipping. This brown plastic kit was easy to put together, and assembly required no tools. It was lightweight but awkward to move. I felt it needed outer staking for added stability.
I built the fourth bed from three used railroad ties at a cost of $38.87. This cost included cutting one tie for the crosspieces, a job best done with heavy equipment at the seller's location. The weight of an 8-foot tie is challenging, but once the tie is in place, it is permanent and will not require further support. The useful life span is long. Ties are treated with creosote, an effective wood preservative. But creosote is a restricted-use pesticide, and questions have been raised about its safety around plants. The seller said their soil had been tested, and no significant leaching of creosote had occurred.
Pressure-treated lumber formed the fifth bed. Three 8-foot planks cost $28.00. This material offered no problems in construction and needed no reinforcement. The life span is stated to be long. During the past year, gardeners have debated the possible hazards associated with pressure-treated lumber.
Questions yet to be answered: Is the high cost of recycled plastic lumber justified? How long will the peeler cores last? Will the plastic kit withstand normal garden use? How long will treated lumber really last with soil contact? Time will best answer these questions.
For further information contact your local WSU Extension Office.
From The Gardener Vol 6, No. 1, Spring 1995.