What makes Amaryllis hybrids bloom?

Michael Mace mikemace@att.net
Mon, 24 Aug 2009 23:10:09 PDT

From time to time we've had discussions about what drives the difference
between a good bloom year and a bad bloom year for Amaryllis belladonna and
its hybrids.  Many of us in California and other Mediterranean-climate areas
have some of those bulbs in the neighborhood, and because they are so big
and colorful it's easy to notice when there is a good bloom.  They seem to
pop up all over the place.

We have a lot of anecdotal guesses from things people have observed, but
there's no consensus -- is blooming triggered by summer rains?  Fires?  Low
summer temperatures?  Etc...

I realized the other day that we might be able to get some evidence from the
archive of this mail list.  Those of us who live in California usually write
about the Amaryllis bloom season every year.  So I went through the e-mail
archives, checking every August, and looked for which years had the top

One year really stood out: fall of 2006.  Check the archives for yourself --
you'll see a lot of comments about the abundance of Amaryllis blooms that
year.  You'll also see a lot of comments that there was no significant
rainfall that summer.  "Warm, sunny, and dry" was a typical summary.

Here's a typical post, from Mary Sue:

The comments about summer rain were interesting, because some very
experienced growers say that a good summer drenching is the thing that
triggers large blooms of Amaryllis.  That may well work in their climates,
but in much of California significant summer rainfall (even one good storm)
is almost unheard-of.  If that were the trigger, we'd get heavy Amaryllis
blooms only about once every 20 or 30 years.

So I looked up the weather statistics for that year.  Sure enough, most of
the populated areas of the state had no summer rainfall at all:

But something else also stood out.  Winter of 2005-6 was a heavy rain year,
with totals in many places about 150% of normal.  The preceding winter,
2004-5, was also pretty good.

The years before then (going back to 2002) and after (up to last winter) all
had low to average rainfall.  And they also had average Amaryllis blooms.

This isn't much evidence to go on, but my preliminary guess is that
Amaryllis blooms in California are triggered by high rainfall in the
previous one (or two) winters.

We'll have to wait for a couple of wet winters to test my theory.  In the
meantime, based on the rainfall last winter, I'd predict an average to low
Amaryllis bloom season this year in California.

Oh, and if you want better blooms from the Amaryllis in your yard, maybe the
thing to do is give them extra water *in the winter*.  I may try that with a
few, just to see what happens.

San Jose, CA (zone 9, min temp 20F)

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