something comes along and breaks it off...like a storm, or a child's ball, or something 
I had to put a wire fencing around some of mine to keep that from happening. We had some, what I call horse wire, its welded wire about 5 feet tall, I took some wire snips clipped it to just fit around the plant (in my case it was a rose bush) clipped the bottom wire totally off, leaving the little sharp points of wire to stick in the ground. If you'd like to try this, I'll post a picture of exactly what I'm talking about, it really does well on protecting plants, and welded wire is fairly cheap, and you can do about 20 to 30 plants with one roll that's 50 feet long (here it cost under $50.00) for a 50 foot roll. I also think it comes in 25 ft. rolls which I've seen at Lowes.
