Topping the tomato plant allows it to finish ripening those green tomatoes that you see hanging, and preventing any further upward growth of the main stem. (If you don't top your plants, then they will continue to produce stems and leaves and green wimpy fruit that you won't enjoy.)
Pruning Tomato Plants, Indeterminate Varieties
Take off any blossoms on your plant until it reaches about 18 inches tall.
Indeterminate tomatoes produce several vines. Since you'll want to concentrate all that energy on tomato production, you'll want to eliminate all but 1 or 2, or possibly as many as 3 vines, but leave no more than that.
Pinch off any suckers you see that form between the main stem and the branches. This is the same procedure that you would perform for pruning determinate tomato varieties.
However, if you're planning to leave 2 or 3 vines, then you'll want to leave the stem(s) growing just above the initial fruit cluster.
Another method for pruning tomato plants is called "Missouri pruning," which means that instead of taking the entire sucker off, you remove the part of the sucker that is above the first two leaves nearest the main stem.
Missouri pruning allows the two leaves to remain, which allows additional energy to be harvested from the sun by these remaining leaves. However, new suckers will grow very quickly, meaning that your pruning chores will be increased.
Missouri pruning is also helpful if your plants have gotten out of control, and you think pruning suckers severely may hurt the mother plant.
A Few Additional Tips for Pruning Tomato Plants
You'll notice that as your plants get larger and begin producing fruit that the bottom leaves may start to yellow and drop off. Don't worry! This is normal. Feel free to remove them yourself if you like.
Topping your plants should typically be done about a month before your first anticipated frost. This allows the plant to put all its remaining energy into ripening fruits.
Remember to stake or support your plants. Plants that are kept upright and off the ground are healthier and produce better fruit.
If you're a smoker, don't prune unless you've washed your hands thoroughly. Mosiac Virus is spread to tomatoes through tobacco residue on your hands.
If you put a little energy and effort into pruning tomato plants, you'll reap a crop you'll be proud of!
The author Jack Griffith really enjoys his home and family and lives life to the full. He also loves to learn about everything. Feel free to see some of his interests at Natural Stone Flooring and Garden Watering System. http://cheaptile.org/natural-stone-flooring