The goal of our project was to build a retaining wall with a culinary herb garden for the Campus Center for Appropriate Technology (CCAT) on Cal Poly Humboldt. This design is intended to support the growth of annual and perennial plants on a steep incline by creating step-wise levels for them to grow and to collect water and nutrients.
The earthship building method is discussed at length here: Earthships
Recycled materials such as tires and wood are used with the clay found at the site to shape the swale garden.
Benefits of Tire Retaining Walls[edit | edit source]
- Freezing and thawing will NOT cause the wall to crack.
- Moisture passes through the wall without effecting structure, eliminating expensive drains.
- Plants can grow in the wall, camouflaging it and not effecting the stability.
- Scrap tires are used effectively.
Project Requirements[edit | edit source]
- Finish top row of clay packed tires
- Excavate behind tires to make a planting bed for culinary herbs
- Make a redwood retaining wall to hold the hill up behind the bed
- Bring in topsoil and amend it
- Cover top row of tires with gravel to make a walkway
Design[edit | edit source]
Our design includes three layers of reclaimed tires packed with clay and gravel. In the middle layer annuals will be planted to hang down over the first stack of tires. The plants to be eaten will be grown on the soil (with manure, bat guano, and green sand) on the top. Gravel covers the top and bottom tire layers for aesthetics and walking/planting substrate. Donated Redwood constitutes the wall for the top planting area. The wood is held in place by bolts and wire. A rain barrel collects water at the end of the wall to be used for drainage and irrigation.
Costs[edit | edit source]
- The tires were free from Les Schwab Tires in McKinleyville.
- The redwood was free (on the side of the road). A nice man chopped it up with his chainsaw for free.
- We had to buy the soil and amendments. I purchased these at Mad River Gardens and they delivered the top soil. I don't know how much it cost because I gave the receipts to CCAT for reimbursment.
- We also had to buy the metal cable, screws and washers to wire. These were purchased at ACE in McKinleyville. Again I don't know the cost because CCAT has the receipt.
- The Gravel cam from Eureka Ready-Mix on Bode Rd. It was $20 for all I could take in my truck.
Tools Needed[edit | edit source]
- Shovels - For digging and moving stuff
- Wheelbarrows - for easy transport
- pick axes - to break into the hard clay soil
- sledge hammers - for packing tires
- Screw gun - for screws holding wire to redwood
- Hoes - for mixing in soil amendments
- Strong backs for all the hard work
Discussion[edit | edit source]
Though we did not get to the actual planting, we are proud to present a mighty fine start to a culinary herb garden for CCAT. The wall is solid and ready to go!
Next Steps[edit | edit source]
Plant perennials or wait till spring to plant annual and perennials. If we wait till spring (left for a future group) we will need to cover the soil to prevent the nutrients we added from leaching out with the coming rains.
Also in the future: A second swale above the redwood wall with fruit trees.
Conclusions[edit | edit source]
Earthen construction is hard work! But that is part of what makes it an appropriate technology. We used common gardening tools to fill tires and cut a garden bed into the hillside. This required a lot of hard labor. We used waste materials, such as the used tires and small logs to build the retaining walls. We used great compost from CCAT, which mixed in with our top soil and amendments will be dynamite for the herb garden CCAT is planning on planting in the growing season. The whole project was not overwhelmingly technical and that is why I think it was so successful. I think that anyone who would like to build a sturdy retaining wall and/or garden bed, with recycled materials, and a limited budget, will find this project a useful inspiration.
Timeline[edit | edit source]
After designing the project and submitting our budget we could start the work, I mean the fun!
- 9/20/08 - Some of the group went with a truck and hauled some logs to be used for the retaining wall.
- 9/26/08 - We began the project. We started pick-axing and shoveling clay to cut a garden bed into the slope. We got a lot of work done with the help of the class. It was mostly filling the tires and shoveling clay out of the way.
- 10/10/08 - I can't remember all the days we spent working on the wall, but this was one of them. More shoveling to shape the bed and wall. This is most likely the day that we finished placing the logs for the retaining wall.
- 10/17/08 - We mixed together some really happy soil and prepared the herb bed.
- 10/29/08 - Last day of work. Secured log retaining wall with wire and screws. Made a gravel walkway along herb bed. We finished the earthship retaining wall, that is also part of a garden bed for herbs. Decorative plants can be grown in the soil inside the tires in the earthship wall. CCAT is building a rainwater catchment system and we incorporated the tank into our wall. The herbs when they are planted will have water conveniently available. Yay!
Contact details[edit | edit source]
The group consists of:
- Dan Hughes
- Stephani Pescitelli
- Thallia Bird
- Krystal Ocean
- Jamila Ghoul
- Azad, our awesome contact at CCAT
- Richard Hansis, HSU Professor who gave us the redwood
- And especially...Special thanks to the rest of the class who donated three hours on a Friday to help us conquer that clay wall. You guys rock.
- Also, thank you to other Friday volunteers such as Karly.
Update October 2014[edit | edit source]
The project is a success and after six years of the end of construction is still working. The initial goals as retaining wall and build a garden on top were hit. the second swale above the redwood wall with fruit trees hasn't been built yet and was in their plans for the future construction. They don't know when they gonna realize this second part. However, they are really satisfied with this project.
Members of CCAT informed us that they only plant non-edible seeds. According to them, sunlight reacts with rubber and toxic components may be released to the roots.