Answer: What you propose is so unconventional that I'm not sure exactly how to guide you. Ivy, and most other vining plants, tend to root wherever they can as they run along the ground and scamper up walls. This is the way they stengthen and renew themselves. By restricting the roots to a single hole in a concrete footing, you'd be compromising the health of the plant. A serious consideration is the reflected heat from the wall and the concrete and the absorbed heat from the concrete. The roots can bake in such a small space, even with adequate water from a sprinkler. Third, roots will grow downward, but it would take several years for them to finally reach beneath the concrete to fresh soil.
Would you be willing to rethink the situation? How about a cascading plant to plant atop the wall? Bougainvillea will cascade, as will many other plants. Or, if that isn't an option, how about building a few narrow planters to place on the concrete? There would be adequate soil for a climbing plant in a planter and you could water from a hose or install a drip system.
Best wishes with your project!
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