Answer: What a beautiful choice for covering lattice! Morning glories usually don't grow much until the weather moderates and the soil warms up, so they should start growing more actively in June.
These vines can grow quite large and that is why the suggested spacing is so far apart. I am a bit concerned that the pots are too small and will cramp the growth of even one vine. Is there any way you can plant them in the ground and let them grow up to the deck? If not, I would suggest moving them to much bigger pots, at least 12 or 15 inches or even larger if possible. ( Do this carefully and gently, taking the entire rootball, as morning glories sometimes resent being moved. For this reason move all three, in case some die.)
After they have settled into the new pots and are growing, thin to two in each pot because you obviously want the maximum fullness possible to cover the lattice. Be sure to maintain a vigilant watering and fertilization program to compensate for the restricted root run within the pot and enjoy!
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