Garden Questions

I know there is a wealth of gardening information out there, and in the hopes that gardeners out there might pass by my little blog -- here are some of the questions I have been pondering:

SHRUBBERY:

Should I avoid planting near evergreen shrubs because their roots suck all the moisture/nutrients away from other plants? i.e. I noticed that the Siberian irises near a juniper looked smaller than the others (then again, these ones may get a bit more shade too). Also, the Polemonium next to a globe cedar looks puny compared to its lush compadres lounging around the raised beds.

DOES SIZE MATTER?:

How high of a structure do you need to grow pole beans? I stuck my steel obelisk (about four and a half feet tall) in the garden, but then jammed a rough piece of 7 foot lumber in there too just to be sure.

UGLY VISITORS:

How do I deal with pear slugs? I noticed these on the sandcherries and tart cherries last summer but didn't know what they were till I read the Sherwood greenhouses blog about these little monsters. I sprayed them with insecticidal soap and maybe some permethrin last year, but they didn't look deterred by this effort.

GOING CATTY:

What is a good replacement for a drift of catmint (Nepeta cataria, no particular variety)? The catmint looked really nice in front of some pink tulips for the first two years, but now looks a bit tired (after it spread its seed all over the raised bed). I was wondering about Veronica spicata. My criteria: blue/purple flowers, about 8 to 18 inches tall, flowers in June, hardy to zone 3, and does not become invasive. I especially hate the plants that spread quickly by their roots, like the ladybells I am still trying to eradicate from the yard. Also, I prefer plants that I can grow from seed because these are usually easier for me to obtain.