Ooh I had to tell you gardening folk about these things. I don't know whether or not they have been around for years, but I found them yesterday. The local garden centre had a display really tall tomatoes in a grow bag held up by these metal frames.
I'm growing my tomatoes at the shop this year in the back yard, and because the grow bags are on concrete I couldn't put the canes right into the ground to support them, I was about to make a bizarre contraption with bits of wood to hold up the canes when I found these frames.
The frame goes under the grow bag round both side and you put the cane through the loops in the middle, ingenious! and far better than my bits of wood stuck together ever could have been
Grow Bag Cane Frame (3)