this time of year, adenium are, or have entered dormancy ....leaves stop growing and old leaves yellow and fall off ....that's normal ....
some plants may drop all leaves, others might drop half their leaves ...while some plants may retain all leaves
can see if dormancy has or about to occur ...look at the very top of stems ....see any new leaf or stem growth ? ...if not dormancy, has or is happening ...
stop watering .... do not water again (not even a sip) for at least 30 days ....if a bunch of leaves fall off during that 30 day period ...extend the "no watering period" another 30 days ...
resist the temptation to water ... just a sip can cause root rot ...often fatal
if and when stems or trunk look a little shriveled, or raisin like....water, but only enough water for volume of pot ....then start water cycle all over again
do not let potted adenium sit in water ...ever !
and do not expose to cold temperatures below 40° ...or expose to freezing or frost - either will kill adenium
