how close should I place a trelis to a plant (morning glory) so it can catch on and climb?

Answer 1

If you place the trellis right over the morning glories the plants should climb it on their own, but you could also wrap the shoots around the trellis a couple of times, when they are long enough, to "train" the stems. Morning glories are natural climbers and will attach themselves to almost any upward standing object.

Answer 2

I would put it right next to it. say within a few inches, then when shoots are long enough, stretch them out to the trellis

Answer 3

I put mine right over it. Make sure your trellis is firmly anchored.