Questions & Answers about Бур'ян росте на клумбі.
In Ukrainian, the apostrophe shows that the consonant before it is not softened, and the following я is pronounced as a separate ya sound.
So бур'ян is pronounced roughly like bur-yan, not like a softened бурян.
After б, п, в, м, and ф, this is a very common pattern. The apostrophe helps you read the word correctly.
Yes, бур'ян is grammatically singular. But very often it is used in a collective or mass-noun sense, meaning weed/weeds as a general thing.
So this sentence can describe weed growth in a general way, not necessarily just one single weed plant.
If you want to talk about multiple individual weeds more explicitly, you could say:
Бур'яни ростуть на клумбі.
There, both the noun and the verb are plural.