Tomatoes are the easiest plant to clone. A very low stress way to do it is to bury some connected stem in the ground and keep it dark. In about 2 weeks, you can cut the stem from the rest of the plant and put it anywhere you want.
If you just leave a tomato plant to grow, undoubtedly, some branches will touch the ground. Even with this casual contact with soil, roots will sprout. Tomatoes love to grow roots.
so i took a couple clones from my outdoor tomato plants. been in only 3 days so no roots yet but i'll put some pics up as soon as they do to let u guys see if it worked 4 me
I always sucker my tomatoes, and the suckers are perfect for starting new plants. I've had great success just sticking them directly in wet soil and keeping them in the shade for a week or so.