Ha! I spent 6 hours yesterday on my hands & knees digging out Four O'Clock tubers & seedlings from one bed (I love them, and they are rampant & staying in another bed, but decided that in this particular bed they were not good for my antique roses). I have been doing that every two weeks all Summer, after my husband did the bulk of the hard work at first and dug out the HUGE old tubers (some of which were the size of the largest sweet potato you could imagine). I go back every two weeks because by then the new seedlings and any tubers I missed have put out new leaves.

I am amazed that this plant won't grow in zone 7 - that's not that cold, and my seeds sprout in just a few days (drat!), so I agree that you should be able to grow them at least as annuals. Because after a year or so they produce such huge tubers that go fairly far down under the dirt, I would think they would have some cold hardiness, too.

I don't know what kind mine are - they have naturalized here in vacant lots and along the street, and are obviously all one kind. I have only found one kind in seed packets at the nurseries (when I took a cut flower in and asked what it was, they said "a weed"!). Mine have black seeds that are about the size of a green pea. They bloom here in mid-summer, and have already set seeds. We are dry here in the summer - maybe they don't like humidity? They love full sun. Here is a picture of mine, if that would help you figure out what kind they are.

Jackie

I planted seeds of Mirabilis longiflora and it didn't take off right away. Now I am trying to get rid of it. I pull it up and it grows back. I thought it would be fragrant and it may be but I notice the common four o clocks fragrance more. The plant is not attractive or showy.