In addition to TensorBoard scanning subdirectories (so you can pass a directory containing the directories with your runs), you can also pass multiple directories to TensorBoard explicitly and give custom names (example taken from the --help output):
In addition to TensorBoard scanning subdirectories (so you can pass a directory containing the directories with your runs), you can also pass multiple directories to TensorBoard explicitly and give custom names (example taken from the --help output):
More information can be found at the TensorBoard documentation.
I found the answer to my own question on github (https://github.com/tensorflow/tensorflow/issues/1548).
You need to put your logs in a subfolder e.g. /logs/run1/ and then run tensorboard on the root folder e.g. /logs/.