Make sure you have read the legal bit on my home page.
For inanimate things (specifically including plants), presence or existence uses the patterns:
NOUNgaPLACEniarimasu.
PLACEniNOUNgaarimasu.
You can also make the PLACE the topic:
PLACEnihaNOUNgaarimasu.
arimasu is the present/future polite form of the existence verb aru, which is group 1 and almost (but not quite) regular.
ga indicates the grammatical subject in those cases where it is not the topic.
ni has several uses; here, it indicates a place where nothing is happening (simply being present does not count as something happening).
Examples:
shyokudoniyuushyokugaarimasu. "There is a dinner in the dining room."
shyokutakugashyokudoniarimasu. "The dining table is in the dining room."
Negations arimasen, past tenses arimashita and negated past tenses arimasendeshita are all straightforward.