Hidcote and Munstead plugs
While they're in those cells and then in pots you need to make sure they're watered regularly to keep their roots growing and the tops too. Don't let them sit in water but don't let them dry out either as teen roots are susceptible to drying out.
Once they're big enough to plant out they will send their roots down as far as they need for moisture and nutrients but for now they need you to care for them. Think baby, toddler, teenager process before adult leaving home to fend for itself.
As FG indicates, perennials and sub shrubs like this don't have to do all their growing, flowering and seeding in one year so grow at a much more measured rate. Slow and sturdy is what you want.
Vendée - 20kms from Atlantic coast.
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw