For tomato plants, a conical cage that looks like this is the best way to go. This way, you provide support at each stage of the plant's growth and there are multiple points (on each circle) for you to tie the fruits to.
However, this requires that you plan in advance and set up the cage before the plant gets too big. There is no way you're going to be able to fit that onto a full grown plant.
Supporting your cane
Now coming to supporting your 6' cane, here's one cheap way using some twine and some turnbuckles. You'll need:
- Some mason's line or strong twine (costs around $3-4 for a 100-feet roll. You'll need a lot less!)
- 3 small turnbuckles (costs around $1.50 each for the small ones)
- 3 6" nails (costs around 10¢ each)
Now I'm not at home and don't have a picture of how it looks like, but here's a hand drawn drawing that shouldn't be too hard to follow (also not too clear because of the scanner, but it's readable).
- Drive in the three nails at the points marked X. Make sure that you drive it in at an angle so that the head is tilting outward as in the second figure.
- Tie some twine from the cane (probably around less than half way down from the top) to the loop of the turnbuckle.
- Next tie a smaller piece of twine from the nail head and through the hook of the turnbuckle. Pull it till it is tight and then make a knot.
- Make sure that the turnbuckle is screwed out most of the way so that later if and when you need to adjust tension, you can (last figure).
- Repeat for all three nails and adjust tension till the cane is as vertical as you'd like it to be.
- Check periodically (every week?) to see if it is leaning and increase tension in the string(s) opposite to the direction in which it is leaning.
This is a neat way to keep it vertical without having to build additional supports/structures and is my preferred method of training young trees to grow vertically.