Ask-a-Dave's-Gardener: best thing to do with this flower box, 1 by jpt101garden

jpt101garden wrote:
hi folks - a bit of a garden engineering question/problem here. I just moved into this house and have this popout sort of flower box along about 10ft of the front, coming off the front of the house 8-10 inches. It was long neglected, filled up with old dead soil and tons of dead roots, etc, major job cleaning it out. But I got to the \"bottom\" of it, which is a pretty solid mix of 1-inch driveway stone and dirt starting about 2ft down (empty space now from cleanout) and going all the way to the ground, see my picture with markups. The previous people did a lousy job of protecting the facing of the house (basically the siding) inside the box, all of which has rotted off, leaving a sheet-plastic covering on the wood to try to do the job. What I\'d like to know is:

1- what are some good showy (I want color!) perennial bush-flowers, or flowers that will stand up to blistering sun half the year, and cold nights the rest of the year (north coast CA). I know crepe myrtles are really good candidates, but I fear it would grow too big for the box, see #2 below. Bird of Paradise maybe? I have lots of irises in the back yard already, could always use more \"impossible to kill\", my arbor guy told me.

2- what is the best way to keep the plants from putting down roots too deep so I or later people can clean out the box again easily if needed. I was thinking of putting down a thin layer of concrete over the stone bed to limit the depth, but that would probably be stupid as I\'d lose the drainage. Not sure what I can use to \"stop\" the root travel.

3- what is a good method to face-protect the siding wood inside the box (back of the box that is). Someone suggested concrete board, or whatever that really tough stuff is...no more plywood, the water will just rot it. In non-drought times this area gets avg 30 inches of rain a year, so there could be a hell of a lot of water going into that box.

Really appreciate any input, I\'m a brown-thumb sort of gardener but want to get it greener! jt, Lakeport CA