The ` Nagami ' kumquat needs a hot summer , ranging from 25 Â C ( 77 Â F ) to 38 Â C ( 100.4 Â F ) , but can withstand frost down to about 10 Â C ( 14 Â F ) . The ` Nagami ' kumquat requires a hot summer , ranging from 25 Â C to 38 Â C ( 77 Â to 100 Â F ) , but can withstand frost down to about -10 Â without injury .