It really depends on what kohleria you have. A few species have long dormant periods but most of the hybrids--and most of the cultivated plants are hybrids--have a very short dormant period, if any. The rhizomes will often begin to sprout even before the mother plant has finished blooming. In general kohleria rhizomes don't tolerate drying out and should be kept in barely moist potting mix until they sprout, then given plenty of light and water. If you try to keep them dormant by letting them dry out, they will often shrivel up and perish.

Thanks, johnnieb. Mine is a hybrid, 'Longwood,' so I guess keeping them til fall wouldn't work. Had tried collecting them and just storing them dry--that sure didn't work!