Getting Rain Lilies to Bloom

Monica Swartz
Sat, 23 Nov 2013 16:25:29 PST
I grew twenty or so species of rain lilies successfully in a place 
even hotter and dryer than Leo's Phoenix, AZ (the blast furnace of 
California's Coachella Valley) and learned a few things. The most 
relevant was flowering was NOT triggered by rain, but instead by the 
changes in pressure that accompany weather fronts. In most places, 
rain accompanies pressure changes so I imagine the observation that 
the lilies bloom after this trigger is what led to their popular 
name. The town of La Quinta, California has three inches of average 
annual rainfall, and many years see no rain at all. My rain lilies 
bloomed without fail in the days after pressure changes, and many had 
never seen water falling from the sky in all their lives. The naming 
of "Rain lily" has been confounding correlation with causation. It 
would be interesting it know if growers on the coast have fewer rain 
lily flowering events than interior continental growers with the 
interior's more frequent and greater magnitude pressure changes.
	I have also found that rain lilies and many other amaryllids 
will be kicked into flowering with a pulse of Phosphate. I have a 
salt shaker filled with decomposed bat guano and a big dash of that 
often does the trick, though it can take a year to see a flower from 
bud initiation in some species.
	On another rain lily issue, I now live in Austin, TX where 
two species are very common. Some older homes have rain lily lawns 
that they mow like grass and mass flower periodically from spring 
through fall. Other posts have mentioned taxonomic confusion with 
rain lilies, but I have never seen such a muddle as with these two 
very different species. I asked Scott Ogden to sort it out for me and 
took notes so you'all can go relabel your pots. The giant prairie 
lily, Zephyranthes drummondii (aka Cooperia pedunculata or 
Sceptranthes) has very broad grey leaves, perhaps the broadest leaves 
of any Zephyranthes so it is easy to ID on sight. It flowers most 
often in the spring. The other common rain lily from this area is 
also white night flowered (probably shares a pollinator) but it has 
narrow, more typical leaves and is properly named Zephyranthes 
chlorosolen (aka Cooperia drummondii). It flowers most often in the 
fall but both species will flower together, especially in summer. I 
hope this clears up some confusion, it did for me.

Monica Swartz   shivering in a week-long freezing rainstorm

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