Plants don't need a bottom feeder to survive. If your plant is healthy, then you can cut a bit of stem off to plant in the substrate. Well done, you've just taken your first cuttings! Cuttings are a great way to propagate your plants, and If I know Hornwort it grows like WEED! Also, if it came in a bunch or pot, you should take all the stems out of the pot/bunch and plant them in the gravel. This prevents to lower stems dying off because the big stems stop them.
PS. Hornwort is a great choice for a first plant - you'll find it's in all your tank sooner or later!