It depends where your property line is. Generally (IANAL), if it's not a structure, you can do what you want on your property. However, DC controls everything from the street to the property line, which is often a lot more than you'd think: >"Public Space is defined as all the publicly owned property between the property lines on a street and includes, but is not limited to, the roadway, tree spaces, sidewalks, and alleys.

You may find some helpful information here: https://ddot.dc.gov/service/public-space-management

It appears that there's a $0 permit [1] for " The pruning of street trees, the planting or removal of trees or the planting of hedges on public space." that may apply to what you're talking about, called "Rain Garden (S.F. Home Yard Area)"

If you touch the "Tree Space," Requirements are laid out in DC 24-109[2], but I can't seem to find anything else about non-tree-space areas.

Unrelated to your question, did you use a kit for your raised bed? I'm thinking about doing the same this year and just looking into what it would take!

[1] https://tops.ddot.dc.gov/DDOTPermitSystem/DDOTPermitOnline/PermitTypes.aspx [2] https://www.dcregs.dc.gov/Common/DCMR/SectionList.aspx?SectionNumber=24-109