In April of this year, I noticed some grape vines in the bargain bin
at the grocery store. Just out of curiosity, I looked at them, and
found one which had two buds which were closed but firm (neither dried
out nor rotting), so I gambled $1.95 on it.

The variety is Niagara. It was from one of those mass-market
nurseries.

I washed off the 'soil' it came in and let it sit in water overnight.
Next day, the buds had opened, and I planted it in the worst possible
place, a corner which gets no sun and the soil is building rubble in
clay.

My only thought was to have "something" in that corner. I figured if
it ever grew to 5 feet tall, it'd get some light (narrow porch has
windows on both sides). And if it didn't grow, well, it was only 2
bucks.

It sat for about a week, doing nothing, and I thought I'd wasted my
effort digging a hole for it.

Then it took off.

By July 1st, it was up to the windows.

I'd run strings from the sill down to the ground for it to climb, so I
put a trellis over the window for its further growth.

Now, each stem goes 5 feet up to the window, 2 feet horizontally
across, a foot up, 2 feet across, a foot up, and they're beginning
their third pass across.

From what I've read about growing/training grapes, you're to trim it
back at planting to only one stem and then hope it reaches a 36-inch
high wire the first year.

This has two stems, each about 12 feet long, with no sign of slowing
down!

I didn't have a distinct plan in place because I didn't expect it to
survive, and I've just been puttering, pinching off side shoots as I
tie it to the trellis to train it to go back and forth across the
window.

I know I'll never get grapes off it (besides lack of light and lousy
soil, the squirrels pass over it on their way to the feeder). I only
want something reasonably attractive.

I'm almost afraid to prune off the tips because if it sends out side
shoots, the way it's growing, it'll probably engulf the house!

I've looked at more than a hundred sites, and I haven't found a thing
about how to train grapes to a trellis purely for decoration, and
there's nothing, anywhere, about one which is growing like Little
Audrey!

At this point, I don't even know what I don't know, so I'm not sure
what to ask!

One thing I do need to know -- is it safe to just keep weaving it back
and forth across the trellis, or will that leave me with nothing but
bare trunks next year?

Any help appreciated!