How to plant Walking Apostle Iris. When is the best time to plant?

Welcome to ATP!
Most walking iris (Neomarica) are only hardy to zone 8, so I'm going to assume you are planting this in a pot to be taken indoors for the winter.
Like most iris, this one should be just barely covered with soil. Unlike most iris...this can handle moist soil and actually prefers shade. That's probably why it makes such a good houseplant. I used to move a potted one outdoors for the summer, placing it under a tree. Once in a while, it would jump from the pot to the ground and root there. Those could be divided and potted up at any time.
IF you are asking about seeds for Apostle iris, spring is the best time.
One year, a friend gave me a walking iris that she swears is hardy here in zone 6/7. It grew well in her yard, but not mine! She must have had it in a courtyard up against a brick wall. If you have the hardy one, plant it now, plant shallow, and keep it moist until winter. They do go dormant during the winter, so you probably want to give it some time to settle in before it sleeps.

Hi DJ, to ATP!

I glad Cindi has offered advice for growing the Neomarica (Walking Iris) since she's had experience with this particular plant. I don't grow Walking Iris so I'm not real familiar with it's growing conditions other than that it isn't cold hardy below zone 8 so would probably be considered an annual if grown in the ground in your area.

There are a few Neomarica's listed in the database: http://garden.org/plants/searc... and probably all require the same type of growing conditions!

Thanks you guys, I had never heard of a walking iris before now, so you info really helped. I was going to plant it outside with my other flowers, but not now. I think I'll just take your advice and put it in a pot.

Thank you, I really appreciated the help!
dj54