My friend's garden is fairly large, wide borders around the sides, with many
trees and shrubs in the borders.

The problem is with the soil in the borders. You can't get a garden fork or
a spade into the soil at all. It's absolutely impossible to plant bulbs or
even the smallest perennial. The soil is rock hard and full of shallow (but
thin) roots, which I presume are from the trees or shrubs. The soil is so
bad that several spades and forks have been broken trying to dig into it.

My friend wants flowering perennials and bulbs in the borders, but when she
does manage to hack a hole and plant something, it soon dies.

I suggested adding more soil on top, but the borders are already built up
about a foot or so, so that's not a practical solution.

So the question is -- if it's impossible to dig into the soil to improve it,
then what's the solution?

Thanks.