Sometimes I think my garden survives on string. I'm always tying things together and holding things up with string. Here I used a 4' bamboo pole at both ends and in the middle. This will keep the 8' poles the correct distance apart to keep the onions from falling through. Some are spaced more closely together for the small onions. And some are farther apart for the larger onions. Everything is tied together with string. When I buy string, I buy a honking big piece of it. The spool was 5000' long when I bought it in 2012. It is still going strong.