**Edit** :

As of 2021, the preferred solution would be to use the [{sf}][1] package, even when using {sp} classes :

    library(sf)
    library(RPostgres)
    
    con <- dbConnect(Postgres(), user = "PG_USER", password = "PG_PASS", host = "192.0.2.0",dbname = "dbname")
    st_write(st_as_sf(my_layer), con, Id(schema = "public", table = "my_layer"))

---------

**Former answer** :

The package [PostGIStools][2] can help. See for example the [vignette][3].

Another way could be to transform your Spatial*DataFrame geometry to WKT, insert into PostGIS using the classic RPostgreSQL package and re-create the geom there.


  [1]: https://r-spatial.github.io/sf/index.html
  [2]: https://cran.r-project.org/web/packages/postGIStools/index.html
  [3]: https://cran.r-project.org/web/packages/postGIStools/vignettes/postGIStools-vignette.html