help me with my structure and posts

[tnkrer]

I have a 20' x 1.5' row where I plan to plant a bunch of beans and one tomato and one cucumber. My idea is to create a simple structure and then drop twine from the top to support the plants. The structure will consist of 5 posts 8 ft high. At the top of the posts I will attach 1/2" conduit (metal pipe). The Strings will drop down from this conduit.

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o are posts, The longer side of the C is 20' the shorter sides would be about 5-7'

What do you think about the stability of the structure, Any other ideas?

The posts will be in a 5 gallon bucket half filled with cement. (the remaining half will be grow media and bee attracting flowers will be planted in those buckets)
I am considering three options for posts
1. metal - would like it for strength, durability, light weight but cost is too high
2. wood - 2x4 - pros - strength, cheap - cons - heavy, would rot in 10 years
3. pvc pipe - 1.5 inch schedule 40 - pros - cheap, durable, light - cons - not strong enough, will bend easily

I am liking the pvc pipe option, may be going to 2 inch would give me enough strength? Anyone used pvc pipes as posts? Any other materials that might work?

Thanks