Can't set grow zone on sand even though fertility is better than needed for crop

[Infalliblemistakes]

Colony has researched trees and can grow cactus (5% fertility requirement) on soil. However, can't add a grow zone in sand (10% fertility) to grow cactus there.

[Kirby23590]

You can't add grow zones in Sand, but you can add grow zones in soil or in stony soil.

However the Cactus part in sand, is mostly randomly grown by itself in the desert, and trying to grow one and making a cactus grow zone in the sand which you can't is mostly an oversight that the devs kinda missed...