That's a lot of lavateras! How long/wide is the bed you intend for them? IME, with a few exceptions, lavateras get big fast. Growth in a single season can often reach 6'x6', sometimes larger. Good, nutrient-rich soil or not, leggy is the way they tend to grow, but I'd agree keeping them on the lean side will generate more erect growth. While these plants rapidly take on shrub-like proportions, they do not develop a truly woody framework. The stems are very fiberous and remain flexible, which is a good reason to cut them back hard each spring. Failure to hard prune each season often results in the plant becoming top-heavy and the stems splaying and splitting.

Prostanthera may be hardier than you expect, specially if in a somewhat sheltered location. I've grown it in a container and it has lasted several winters, although probably would have bit the dust in this past one. In the ground, it very likely would have survived with good placement. It too can grow quite large (4'ish) pretty rapidly. Needs very well drained soils and a lot of sun.

Hey gg, long time no talk :-)

The bed is fairly narrow (18" +/-)but they can grow through the fence on the backside (2x2x6' vertical cedar on 4" centers)and grow out over the curbing on the lawn. I'm OK with an overhang as long as I can get the mower by down low. It is probably a bit narrow for them but I figured that I could do some selective pruning to keep them in line. The bed is about 24' long. I was thinking the "fluff and aloofness" of the lavatera and the mint would be a nice counterbalance to the flat climbers behind and between. Besides, the rest of the front yard was getting too formal and serious for a happy go lucky guy like me. I've got a Darlow's Enigma coming for one spot and have a number of clematis ranging from dark blue to red to white called out for the other spaces. I have 8 of these 6' fence sections built now in this run and this 24' section is kind of in the middle.

I agree that maybe I won't feed the lavateras unless they tell me otherwise and just feed the mint like all the rest of my perennials.

While I've got you though, I'm still struggling with what to circle that fountain with. The pool is a 3 block high stackstone circle with about a 9' diameter. I'm wanting a long blooming mixed color blast with max height about 8-12". The last thing I've been considering is portulaca. This will get a little bit of oversplash but not a huge amount. Any suggestions? This is right across from the section with the lavateras. The lawn between is a small kidney shape that wraps around the backside of the fountain pool. This little bed is about 18" all the way around the fountain.

Where did you get your Australian Mint bush from? I am in Toronto now, after moving from Vancouver, and am having trouble finding one. Thanks!

You are most likely having difficulty finding one in Toronto because I doubt that there are any species of Prosanthera hardy enough for that climate. Most are going to require a zone 8 climate or higher.