It depends, really

the plants you mention are not fussy,

is Coneflower Echinacea purpurea? That Echinacea likes somewhat richer soils than the other E.

Problem could be the water supply. Would you build it on regular soil or on concret? It is basicly like a big flower pot and probably needs much watering in summer. The mentioned plants would prefer full sun, so 9inches could dry out fast.

the good thing about perennials is that the robust ones are really low maintenance.

in regular or lean garden soil, they would need next to zero maintenance in the growing season.

if you put them in a shallow bed, that changes everything.

why do you want to use a raised bed or don't you have soil otherwise?

And soil to fill into the bed would be an imports t point, don't just buy peat based potting mix,

That is useless for longterm use and too rich in year 1

if you can fill in some details that would be helpfull, bye, Lin

Welcome, Pinsk - your question sounds straight forward enough. 'Will this be too shallow?' But to answer such seemingly simple questions we often need to delve down for more information, so please don't be offended if we bombard you with requests for more details, starting with Linaria's 'why do you want to use a raised bed?'

The plants you list are fairly unfussy and could be grown in the ground in pretty much any soil. It would come out a lot cheaper than buying a raised bed kit and bringing in soil. And in the ground maintenance would be a lot less hassle.

The second important question, also raised by Linaria, if you are wedded to the raised bed idea, is will it be on the native ground or on concrete? If it's on the ground plant roots will be able to go down into the soil so the depth of the bed is not that important.

The makers of raised bed kits and soil mixes want us to believe that is the way to garden but it really isn't necessary under most circumstances.

Ok, thanks for the feedback. This is the story behind the raised bed idea:

I recently had bushes and a small tree removed and replaced with pine fencing. The bushes had been in place for 20+ years. The removal was cutting them to ground level but a lot of the roots remain. There was also ivy that I fought back all season this year. I poured mixtures of vinegar, ivy killer, salt, and dishwashing liquid into the soil. I now have the soil covered with weed barrier and mulch. I planned on putting the garden bed over this soil/barrier/mulch for a couple of reasons; I didn't want to have to battle thru the roots from the old bushes and I don't know if the soil is suitable after all the ivy killing stuff poured into it.

It would be nice to plant directly into the ground just because it's so much cheaper. A raised garden bed project with soil can easily run hundreds of dollars. I would rather spend that on my flowers! The space that I'm planning on planting is full sun and receives direct afternoon sun, so drying out would be a problem.

What do you think about the soil I'm working with?

if you can dig ... you can plant.. imo .. and the smaller you buy.. the less digging need be done ....

no clue about all the stuff you poured on ...

ken