Q: What exactly is a tomato sucker? Is the stem smooth or rough?
A: The definition of a tomato sucker doesn’t have anything to do with smooth or rough. A sucker is just a young leaf that develops between the tomato stem and a mature leaf. If you allow a sucker to grow, it will eventually produce fruit but it will reduce the size of fruit on the vine above it, because it intercepts nutrients coming up from the roots. Gardeners who remove tomato suckers are just trying to maximize the number of leaves facing the sun, thus increasing the sugars produced by photosynthesis. Suckers would otherwise shade lower leaves. One method of tomato pruning is to allow suckers to grow to the 5 – 7 leaflet stage and then remove 3 leaflets from the tip. This stops sucker growth and minimizes shading but encourages extra photosynthesis in the remaining leaves of the sucker. You’ll get fewer but larger fruit this way. Of course you can do as many gardeners do and let the tomato vine ramble as it wants. You’ll have more, but smaller, tomatoes plus less maintenance work.