"Potřebujou hrušky."

Translation: They need pears.

[RobertPoll2]

"potřebujou" is only dialects, grammatically right is "potřebují"! Do not teach foreigners bad Czech!

[kacenka9]

Check with the Czech academy of science, Department of Czech. They do not agree with you

http://prirucka.ujc.cas.cz/?slovo=potrebovat

[va-diim]

When do I use potřebují versus potřebujou for "they need"?

[endless_sleeper]

It's the same with (já) potřebuji / potřebuju

-u/-ou are considered more colloquial, -i/-í more formal.

[va-diim]

So both "I need" and "they need" use potřebujou?

[endless_sleeper]

potřebuji/potřebuju = 'I need'
potřebují/potřebujou = 'they need'

Sorry, I made a typo. Edited now.

[Viviard]

It is very hard to me to tell the difference in the sound of "Potřebuju" and "Potřebujou" it would be really nice and helpful if someone could explain the difference to me a bit :)

[va-diim]

It's literally "Ou" the "O" is audible, like English "low" with the "-w" extended out to a "lowoo." Czech „-u” sounds like the "ou" in English "you"

[Pollyhs]

after reading the other comments. is Potrebuju wrong?

[VladaFu]

yes, that is first person singular (I need/já potřebuju).