I'm totally inexperienced too but thought I might add that I read recently on the sfg forum that someone recommended to someone else (a friend of a friend) who's vining plants were outgrowing the trellis to train the new growth down the other side of the trellis...they also suggested going horizontal but well, I guess that depends on whether that would throw too much shade to the plants below.

I have a jungle!! Tomatoes and cucumbers fighting. Think I am going to try to go taller then ??? But I am so proud how well this is working.

I appreciate the responses, but what I really wanted to know was whether it is safe/appropriate to prune off the end tips of the vines so that they'll stop growing out. I'm having problems with both the cukes and my honeydew - the vines are getting way too long for the space available to them. I'd like to prune back the ends, but I don't want to do that if it will damage the plant or jeopardize the still-growing fruits.

Alan

Hopefully next season you'll get a much bigger trellis, appropriately sized for each vining fruit. What likely will happen is that the axils will start growing and you'll get lots of side shoots that will elongate and try to continue growing. I doubt too much will happen with the fruit proper.

Dan

Mine have far outgrown their trellis also. I take which ones I can and train them back down (actually to the side and back again so it makes a bit of a basket weave) which is a task since they always want to go back up. Eventually, I'll pick a few and trim the leading vine back and like Dan said, they'll send out smaller, but still productive side shoots.

So, train as many back down as you can.

Here is a link that might be useful: TCY

I am citing Douglas Green from Canadian Vegetable Gardening:

"Train the central leader, the fastest growing and original shoot, straight up the fence until it gets to the top. Then prune it off level to the top of the fence. This 1.3-m vine will then develop multiple side shoots which will bear profuse amounts of fruit."

Having said that, I have a trellis about 7 feet long, so I don't think my cukes will ever grow over it. I also have watermelons and cantaloupes along the same trellis, and I am really hoping that once the melons outgrow the cukes, whatever room the cukes will not climb up to will be free for the melon vines to roam.