As title, there are 1 897 features with this tagging. it should be changed to the approved landuse=flowerbed.
if there are no objections, i will do this 3 days after posting this.
https://wiki.openstreetmap.org/wiki/Tag:landuse=flowerbed
https://taginfo.openstreetmap.org/tags/garden:type=flowerbed
Sorry is this proposal for UK or worldwide?
I feel 3 days is a bit short for an automated edit if you’re planning on doing this worldwide - that is, in areas you’re not deeply familiar with.
To be explicit, please consider my post an objection to doing this automated edit worldwide.
landuse=flowerbed has never been approved. This is exactly what it says on the corresponding wiki page for the proposal.
https://wiki.openstreetmap.org/wiki/Proposal:Flowerbed
I strongly assume that this tag is not uncontroversial. I avoid it as much as possible because a flowerbed is not landuse for me.
Please follow the usual procedure for whatever automated edits are to be performed. Posting here and then waiting 3 days isn’t enough.
If I was suggesting this change I’d definitely want to look at examples where some other landuse tag is already used, and suggesting what to do in those cases.
I’d also look at data consumers for both tags to see if there was anyone that should be warned that data on their map was going to “disappear”.
I’d also check for unfeasibly large flowerbeds** to make sure that objects hadn’t been mistagged.
** that one doesn’t look like a “flowerbed” in the traditional sense but looks like commercial growing.
Both using leisure=garden for non-functional area’s and landuse=flowerbed is something to avoid. As landuse=flowerbed has changed meaning to not be a landuse anymore.
Picking a random example, how would you tag https://www.openstreetmap.org/way/995951730?
Edit: Here’s a Mapillary picture: https://www.mapillary.com/app/?lat=53.9537982566535&lng=-1.0769156699988116&z=17&pKey=756239081731450&focus=photo
Considering the aerial image I’d tag this as landuse=grey_area … 
Im not sure what i would tag that, i would have to check that in person. Don’t get me wrong there is definitely a gap in tagging, we have some tags for grasses, and we have tags for wooded plants, but not a lot for herbaceous and semi-herbaceous plants.
This leaves a situation where this “other” category is begin pushed onto tags that had a different but distinct purpose. For leisure=garden that is visit able and named gardens. And for landuse=flowerbed the full area where flowers are grown for decorative purposes. Aka keukenhof
This retagging is imo a result of a lack of tags in the herbaceous and semi-herbaceous plants catagory.