Hello Vladimir,
they look fine for the purpose. What's the span that you plant them in? I just got an idea, okay, don't laugh if it sounds foolish to you or if you got the same idea a million years before me. What about planting them a bit farther from each other at the lowest part of your cold bed and tying them to a horizontal bar or wire so that they grow horizontally rather than vertically? Sure, it would be a tough job for your back but it might be worth it. Trying to be helpful.
Milan