Having dealt with a both oenothera speciosa and ceratostigma plumbaginoides around our house, I recommend the ceratostigma. O.s. is indeed a thug, at least in my climate (Z7, harsh desert). It spread by over a foot in all directions in one year of extreme drought, and I found patches of it springing up in other parts of the property a long way away.

C.p. also spreads, but more gradually. I've been able to keep it within bounds without a lot of work so far. I love the vivid shade of its blue flowers and deep glossy green leaves. I'm using it to spread down along a walk and around the base of a big sycamore.

Cheryl

Oenothera speciosa in it's native area...which is well, here. It's hardy, but you can't grow it where you want it. It dies in patches and spreads wildly into new ground in all directions.

That's the behavior that might make it unsuited to your need (to keep it confined in a tight area).

Thanks jadeite and dbarron,
it is in an urban situation, the strip is fenced in by a wall on one side and by a pavement/ walkway on all others.

The ground cover needs to be resilient. Reseeding or runners would be an advantage in this situation.
"it dies in patchesâ¦" in winter or while growing?

Not sure yet whether it is too rampant, I have to confess I would love to try it somewhere, but go for something else if it seems to thuggish. I checked the (European) list of invasive plants, but it is not on it.

Thanks, so I will do some more research, bye, Lin

Typically doesn't return in spring might be the better wording.

Perhaps OS does better in very dry climates like ours? We never had a problem with it not coming back! I would guess from the masses of OS roots that we dug up when we took it out, that it likes having dry feet. So it may be more controlled for Lin if you have wetter conditions. BTW the flowers are simply gorgeous. Nurseries sell this by the hundreds here every spring.

The CP is completely neglected but it has grown along the walk and in the crack between steps and a patio. I'm encouraging it to edge a bed but we will have to put in a border to stop it invading.

I had a clump in a flower bed where it was starting to expand too vigorously so I ripped it out and stuck it into the ground under the sycamore. That was about 6 weeks ago. It's settled down nicely and started to flower. The tree base is circled by driveway and a walk so it can't go far.

Cheryl