I'm not sure where you live, so keep in mind I am in humid hot Florida and I keep my plants a bit different than alot of others. I recently found a "fir bark mulch"...it was going into a front yard area...and I helped myself to a bucket of it. When everything I planted in it began growing like crazy, my sedirea japonica went into a basket with the mulch as well. So far I have amazing new roots and it seems very happy. I will attach a picture of mine.