It's December, but it's not yet too cold for me to work outside. One of my long range plans came to fruition today with the completion of a raised bed for our garden composed of 6 railroad ties and 5 straw bales.
Standard US railroad ties are 8' - 6" long (most of the time) and range in width from 8-10" and run about 8" deep for the most part. I picked up 6 this summer as part of a little horse trading with the idea that I would make the raised bed pictured above. I also obtained about a dozen straw bales for free from work after they had an outdoor festival and no longer needed the bales. The Wunder Wagun (tm) was crammed full to the ceiling to make that haul.
Raised bed gardening has been around for along time. From Portugal to ancient Peru, agronomists have recognized the favorable conditions obtainable in a raised bed where the soil is otherwise poor. Extreme examples can be seen at Machu Picchu. The famous terraces on the mountain tops there were not just aesthetic, they provided arable soil in which to grow high altitude crops for sustenance. A raised bed improves soil drainage and reduces infiltration from varmints. It can aslo provide an extended growing season when used as shown above with thick, insulating timbers which will keep the perimeter soil from freezing too soon while raising the crops up above the cold air that may settle on the ground during Spring and Fall frosts.
The straw is another story. Used as a planting medium, it provides both superior drainage and root depth. What it lacks, however, is high nutrient content. We will be adding that through a couple of successive steps of decomposition through natural processes. Right off, the straw is already sprouting and providing growth medium to wheat grass. I'll be adding some bone meal to provide phosphorus and protein to the mix. I might try to get some mushrooms established early in the spring by purchasing some spore or seeing what I can get ahold of locally through foraging that can be positively ID'd as safe to eat. A simple tarp and a bit of water will be all we need to add to this for growing mushrooms.
Once the straw has broken down over the course of the first year, we'll begin sowing seed directly into the straw. I will most likely start with crops that will be good to leave the roots behind, like swiss chard or beans. Regular crop rotation will apply thereafter, perhaps favoring those things we wish to grow for early and late crops.
To make the bed, I cut two of the ties into 51" lengths, then laid out the first level in a butt-and-pass fashion. The second level is the same, but flipped around to provide overlap at the corners. I then drilled holes and drove 12" galvanized nails into the corners and middles of the top timbers to keep things from falling over. I had considered more elaborate lap joints at the end, but decided the time to do those along with the need for additional fastening on the lower level before installing the second level was overly complicated for such a simple structure.
Railroad ties are incredibly heavy, and soaked in creosote. They are rot resistant but do decompose over time. Coal-tar creosote is generally considered toxic in high doses. It is used as a pesticide, with the proper license, and can cause kidney or liver damage or death when eaten. Why am I not worried about that here? These railroad ties are very old, to begin with, and have been exposed to the elements for 20 years or more already and much of the actual creosote has leeched away - they have practically no odor. The amount of creosote that can leach from these ties into the straw and then into the food we may grow here is extremely low. One good tell as to whether there is an appreciable amount of creosote entering my soil is the health of the plants grown there. If the plants become ill as they develop roots that reach the perimeter of the bed, we'll know the soil is not good for food stock and will switch to growing flowers there. I suspect, based on years of my own observations, that these will do just fine though for vegetables.
That said, the weight of the ties, the difficulty in obtaining and transporting them as well as building with them make them something of a novelty here. I'll probably not replicate this project. We will instead next time look at using red fir, which is naturally rot resistant, though in terms of cost, it may be more expensive.