Q. When trellising cucumbers or melons, should I cut all but one main
stem. And I don’t seem to see how to trellis Zucchini or yellow squash.
A. To grow cucumbers and small melons vertically, by all means, limit them to one stem. However, in removing the sucker stems you allow the stem to grow just long enough for the first female flower to form. This is usually at the first leaf. Keep the blossom and leaf, but cut or pinch off the stem at that point.
Zucchini and yellow squash are determinate plants, and can’t be grown vertically. No trellis or string is needed. However, it is imperative that you take off old leaves and those touching the ground. Keeping air and light into the interior of the plant will improve your yields, and it can reduce the likelihood of powdery mildew taking over the plant.