Hornwort can be a bit fussy about changes in water parameters, but if it decides it likes your conditions it will grow nonstop. I always acclimate mine to its water slowly, just like a delicate fish.
Buy some from a pond supplier rather than an aquarium shop if possible; pond suppliers usually carry Ceratophyllum demersum, a temperate zone species, while aquarium suppliers carry C. submersum, a tropical species. C. submersum might do well too, as mild as your winters are, but C. demersum can definitely take the cold.