[Copied from Texas Gardening Forum]

Instead of starting all my Ipomoea alba seeds in flats this year,
as an experiment I placed some of the seeds directly in 3' x 8" x 6"
rail planters, confident only a few would make it. The fertility spirits
must have danced over last year's crop, because all these seeds have
germinated. Each 3' planter contains six growing moonflower seedlings. I
suspect moonflowers spaced 4-5" apart will choke each other out before
they reach maturity. Before I start thinning, what spacing would you
recommend?