Re:Bloom Time Shift
You asked several difficult questions about how one can delay flowering
of early cultivars such as sieboldianas so that they will correspond to
dates of flowering of the late fragrant cultivars or species. I have
never attempted this but I think I understand the various methods one
can use and the reasons why. The reasons involve an understanding of
photoperiodism, the morphological structure of the hosta plant, the
manner of growth of the cultivars involved and a consideration of all of
the major environmental factors affecting growth throughout the growing
season. I don't want this to sound too complicated but it is very
difficult to give simple answers to complex questions.
I'm sure you have read up on photoperiodism and its influence on the
growth and development of the various hostas. But let me summarize
briefly for those who may not be very familiar with it. Hosta are
responsive to length of day, especially in regards to the dates of
flowering. In "Photoperiodism in Hostas" (see Journal 27.1), I described
how I believed hostas responded to the varying day lengths. I predicted
that the "critical photoperiod" for hostas was probably 13 1/2 hours
which occurs approximately in late April or early May in mid US
latitudes. Long day plants such as the sieboldianas bloom in late May
and June, the short day types of hostas such as the longipes,
pycnophylla, plantaginea, etc. bloom when days become shorter in late
summer and fall and the remaining hosta types which are intermediate in
their blooming dates are those which are perhaps hybrids which are not
responsive to the length of day, but flower as a response to other
I made a point of suggesting that the stimuli to control flowering may
not be functional with small, immature plants. I also discussed
"re-blooming", suggesting that this term is a misnomer because a given
growing point of a division only blooms once. When different, young
shoots branch off from the division, they may grow and develop flower
scapes but this is not re-blooming. Each division blooms once as the
growing point differentiates from vegetative growth into flowering
tissues and organs. When this differentiation takes place the hormonal
relationships (between auxins and cytokinins) change and influence
apical dominace of all axillary buds on the division. Those that then
become dominant grow...those less dominant ones do not grow. This change
in apical dominance is expressed in the new flush of growth in the sides
of the division after the scape developes. Whether you cut it off or
leave it on is not a significant factor affecting the hormonal
relationships in the division, in my opinion.
With that brief summary, lets go to your questions, Norm.
1.At what point should you cut off the bloom scapes?
I SUGGEST WHEN IT FIRST EMERGES.
2. How many times can you do this before the plant gives up?
AS LONG AS IT HAS LEAVES, IT NEVER "GIVES UP", ANTHROPOMORPHOLOGICALLY
3.How late can you expect to have blooms given this method?
PROBABLY UP TO FIRST FROST OR FREEZE DATE
4. What chemical does blooming produce that causes the plant not to send
up another bloom scape?
AS EXPLAINED PREVIOUSLY, ONE GROWING DIVISION PRODUCES ONLY ONE SCAPE.
THEN THE DIVISION MAY OR MAY NOT BRANCH. EACH BRANCH HAS THE POTENTIAL
TO BLOOM.THE HORMONE INVOLVED IN CONTROLLING APICAL DOMINANCE IS AUXIN,
PRODUCED IN THE ACTIVELY GROWING CELLS, ALSO KNOWN AS INDOLEACETIC
I realize this sounds very complicated...that's because it is. My
discussion is a very simplistic one but I am sure you get the gist of
the processes involved.
Jim Hawes Oakland MD
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