Hoop Arch Removal Report
Published: February 28, 2025 | Revised: March 21, 2025
Overview
Hoop houses, also known as high tunnels, are used in fresh fruit production around the world. Hoop houses are temporary structures used to cover an entire field with a thin sheet of white plastic. Hoop houses are used extensively by raspberry growers, where a planting may be harvested sees multiple harvests without disassembling the structure. In the Santa Maria, California area, limited strawberry acreage is also covered with the hoop house system. Both conventional in-ground production as well as the newer tabletop production systems utilize hoop houses. The plants and fruit are protected from direct sunlight, rain and wind (Holmes 2024). Further the hoop houses accelerate transplant growth and fruit production by maintaining higher temperatures inside the houses (Santos et al., (2011). The hoop houses allow growers to continue harvesting fruit throughout the late fall and winter months when prices are typically higher (Carey et al.). Strawberries in hoop houses are often grown organically to capture premium prices and cover the additional costs associated with the hoop house installation process and materials. With the in-ground production, the ground prep, planting and harvesting is done in the same fashion as conventional
strawberry growing for the region. The difference is that after the ground prep is done, the hoops are erected and after harvest is over (perhaps six months later), the hoops are disassembled and placed into storage. This relatively short six-month turnaround contrasts with that of caneberry or tabletop strawberry production, where the same hoop houses may remain in place for multiple years. Thus, in-ground strawberry growers face a unique challenge in the volume of labor required and the high replacement rate of the materials themselves, which are at an increased risk of damage during the installation and removal processes.
Figure 1. Typical hoop house structure covering strawberries in the Santa Maria, California Region.
The “Hoop House” is an assembly made up of several parts, shown in figure 2. The ’platform,’ is a steel post with two prongs welded on one end and a pointed end with an auger-type feature welded on the other. The platform is driven into the ground with a specialized implement that applies down-pressure on the while also spinning the post like a screw. The platform drives itself into the soil approximately 3 feet deep. The platform can be driven into the bed top or a furrow, based on grower preference. The platforms are spaced approximately 8 feet apart down the row and about 22 feet apart from row to row. Typically, a single hoop house section is centered about and covers three (3) complete strawberry beds, and the platforms are driven into the center of the outside two (2) beds. In the Santa Maria, California area, the beds are spaced 64 inches apart. When all the platforms have been installed, the hoop arches are brought into the field. The ‘hoop arch’ is a long, slender steel pipe which has been formed into an arch shape and had its ends bent such that it has a short straight section at either end where the hoop arch connects to the platform. Both ends of the larger diameter hoop arch pipe slide onto the smaller diameter platform prong and the arch will span about 22 feet across three (3) complete strawberry beds as referenced above.
Figure 2. Hoop arch steel structure dimensions (left) and platform to hoop arch connection (right).
Due to natural variability in the placement of the platforms and dimensions of the arches, each connection between platform and hoop arch is unique. Thus, each hoop arch and platform will have an unknown combination of forces holding the two together. This scenario presents a challenge for hand labor and for future mechanical removal solutions. Once the platforms and arches are connected, bracing is added between the first few arches at either end of a row. A row is typically about 300 feet long and contains forty (40) arches. With the bracing installed, the plastic is draped over the top of the steel structure and tied down with ¼” rope. The plastic is a translucent white polyethylene, 6 mil (0.006 inches) thick and usually comes in 32-foot-wide rolls.
Problem
Strawberries, being an annual crop which require extensive ground prep prior to each planting, provide growers with the unique challenge of installing and removing hoop houses before each planting and after each harvest season. The installation and removal process is labor intensive. Adding to the challenge of removing the hoop houses is that they are often used in areas with high winds and hilly terrain. High winds can cause significant damage to the steel structures which adds to the difficulty in separating the hoop arch from the platform. Damage to the plastic covering leads to increased replacement costs and difficulty removing the plastic from the steel structure. The behavior of each hoop arch as it’s removed is highly unpredictable. When a laborer is removing a hoop arch, they must stand up on the strawberry bed and lift with a great deal of force on the hoop arch. The laborer is frequently lifting at or above chest height, and the hoop arch may spring away from or towards the laborer, depending on condition of the hoop arch to platform connection.
Figure 3. Three workers struggle to remove a hoop arch from platforms in the Santa Maria, California area
Objective
At the request of the California Strawberry Commission and its grower members, The Cal Poly Strawberry Center set out to develop a machine that would reduce labor requirements for the Hoop Arch removal process. Internally, it was determined that the machine should be tractor mounted, relatively low cost, and easy to operate for an average tractor operator employed by a strawberry grower. The initial goal for the machine was that it should be in continuous motion throughout a 300-foot row, completely removing and storing the hoop arches as it traveled. At the end of the row, a forklift should unload approximately 40 hoop arches from the machine and the machine should turn around and drive down the next row.
Summary
A variety of prototypes were built and tested at Cal Poly Strawberry Center facilities. Two different machines were also tested in commercial strawberry fields. The second of the two machines showed potential for commercial adoption but ultimately was not able to economically outperform conventional practices. At project completion, the scope had significantly narrowed from the initial objective. The final version of the machine removed the right side of each hoop arch and left the other side connected. As the machine drove down the row, the hoop arches behind the machine were left hanging from the left side platform. A two (2) person labor crew would follow the machine to complete the removal of the arch and place it on the ground.
Figure 4. Two machines designed and tested by the Cal Poly Strawberry Center in commercial strawberry fields. The Roller Remover, left, was an earlier version of the hoop arch remover which suffered from reliability issues and difficulty in positioning the rollers. The Umbrella Remover, right, was the final product of multiple years of development.
Results
The one-sided Umbrella Remover machine was able to consistently remove the right side of the arch from the platform. The new process utilized two (2) hand laborers, one (1) tractor operator, and one (1) tractor. This process was compared to the conventional practice of two (2) hand laborers. Although the new process with the machine did reduce the difficulty and actual time required to remove the hoop arch compared to the conventional method, it was not fast enough to reduce the total labor hours required when factoring in the additional tractor operator. Additionally, the operating cost of the tractor further reduced the economic viability of the new mechanical removal process. Operating costs and time required per acre are tabulated below. The data below are averaged from three (3) separate trials, each carried out on a different ranch in the Santa Maria, California area.
Discussion
The determination to reduce the scope of the project such that only one side of the hoop arch is removed by the machine was a large contributor to the lack of economic viability of the machine and its accompanying process. However, the researchers still see potential in this approach. As discussed previously, removing the hoop arches is physically demanding for the typical laborer. Much of this difficulty is directly attributed to the unpredictability of the hoop arch to platform connection. This unpredictability is largely a result of the hoop arch’s tensile and compressive forces which are induced as the hoop arch is forced onto the platforms during installation. Damage incurred from the elements or from physical impacts throughout during the growing season compounds the issue. Thus, by mechanically releasing one side of the hoop arch, the job of completing the hoop arch removal becomes far easier. In testing performed with the prototype machine, the tractor traveled very slowly and stopped frequently. The frequent stops were primarily due to the arch getting stuck on the machine after removal. This issue could be mitigated in at least two ways:
- Stationing a laborer on the ground behind the machine ready to clear jams as needed.
- One of the two laborers that are following the machine removing the second side of the hoop arch should be able to manage this, thus this recommendation should not add additional cost to the scenario outlined previously
- Future revisions to the machine would incorporate covers and rounded corners to prevent jams
The speed of the machine could also be significantly improved in future revisions and with more operator confidence. An immediate improvement in speed would come from improved operator controls for positioning the end effector. With the variability between each hoop arch to platform connection as discussed earlier, the operator must make minor positioning adjustments as the tractor approaches each platform. Because the operator needs to wait until the umbrella wheel gets close to the platform to make the adjustment, there is a small window of time for the operator to correctly position the umbrella wheel. The existing three position levers could be replaced with an ergonomic X-Y joystick which would make it easier for the operator to position the end effector. Furthermore, if the umbrella wheel was repositioned such that it was out in front of the driver’s seat, the operator would have a better line-of-sight to the platform and would be able to begin positioning the umbrella wheel at a greater distance than with the current machine layout.
References
- Carey, E.E., L. Jett, W.J. Lamont Jr., T. T. Nennich, M.D. Orzolek, and K.A. Williams. 2009. Horticultural Crop Production in High Tunnels in the United States: A Snapshot. HortTechnology 19:1, 37-43.
- Holmes, G.J. 2024. The California Strawberry Industry: Current Trends and Future Prospects, International Journal of Fruit Science, 24:1, 115-129. DOI: 10.1080/15538362.2024.2342900
- Santos, B.M., D.N. Moore, T.P. Salame-Donoso, C. D. Stanley, and A. J. Whidden. 2011. Evaluation of Freeze Protection Methods for Strawberry Production in Florida. Proc. Pla. State Hort. Soc. 124:188-190.
Downloads
3D CAD model (download and open HTML file)
Testing
