PPDL Picture of the Week
November 13, 2017
Blooming Out of Sequence is Cool!
Rosie Lerner, Extension Consumer Horticulture Specialist, Purdue University
is that crabapple doing reblooming in October and November? Actually, it might
be more correct to think of it as jumping the gun on next spring rather than
Although it happens to some extent many years, there seem to be more reports
than usual of landscape plants blooming out of sequence this fall.
Rhododendrons, crabapples, and saucer magnolias are the most commonly reported
species blooming this fall.
Spring-blooming woody plants initiate flower buds on previous year’s wood and
rely on chilling to stimulate the buds to mature. In other words, the flower
buds require a certain amount of chilling before they break out of dormancy to
open their flowers. Cool nights — like we’ve enjoyed recently — can provide
enough chilling to cause plants to bloom out of their “normal” sequence. And in
some cases, stressful conditions (such as summer drought) can substitute for
some of the required chilling.
Different species and even cultivars within a species vary in their requirement
for chilling units. In general, the earlier the plant flowers in spring, the
fewer chilling units it requires to bloom. Plants such as magnolia and some
rhododendron commonly rebloom sporadically in summer and into the fall. There
are some cultivars of rhododendron and other species that have been cultivated specifically
for their ability to rebloom like this. Similarly, some herbaceous perennials (such
as iris and daylily) may also rebloom outside their expected sequence.
factor for some plants is that the flower buds they initiate in late summer do
not develop the proper plant growth inhibitor hormones that normally keep the
buds dormant. In such cases, autumn warm spells can induce these flower buds to
Although blooming out of sequence may reduce the total amount of bloom for the
following spring, it is not harmful. Usually, there are still plenty of buds
left to provide a spring show.