Wider bandwidth transmissions are dynamically enabled in a wireless networking environment. During a transmit opportunity time interval for a wireless network device, a transmission is sent in a primary channel in a frequency band in which the primary channel and a secondary channel may be used simultaneously to send a wider bandwidth transmission. Activity is monitored in the secondary channel. A determination is made as to whether the secondary channel is free based on the monitoring. When it is determined that the secondary channel is free, the wider bandwidth transmission is sent in the primary and secondary channels.