You could set the linewidth to zero (lw=0), which makes the edge of the polygon invisible but does not affect the hatching.

API control of the hatching is something that needs work

Thanks.
The workaround suggested by @anntzer however currently fulfills my aim.
So let me know if you prefer to keep the issue open or whether I can close it.

Leave it open, at somepoint we are going to have to go through and collect all of the hatch related issues into a single tracker issue.

API control of the hatching is something that needs work

API control of every hatching is implemented now (something like set_hatch_color)?

There is control at the graphic context level, but there is not an API at the artist or user facing levels.

This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!

This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!