Exactly, Nantonos!
For short SPI wire runs, you ar elikely fine attaching the SD card directly to the hardware SPI port pins on the Teensy 3. However, for longer wire runs, you may either have to consider termination or reducing the speed of the SPI bus to achieve a good signal. FWIW, I am using 120Ohm source terminating resistors even though my wire run is relatively short.