It's in a pot, right?

If so, now that it's a humongous vine that should be in the ground.

Yellowing leaf margins usually mean a nutritional deficiency. Try a spoonful of epsom salts.

Looks like magnesium deficiency. Try the remedies listed here.

Thanks so very much for your advice! I added the epson salts today!

I'll remember that hack to fix the colour if it ever happens here. No flowers??