deadheading

Several questions were posed about deadheading, and "is it useful for plant
grow or rebloom," etc. This is a fun topic, and touches on plant physiology,
plant evolution, natural selection, and other interesting areas.

Q1: Is there data for the idea that developing fruits put a damper on plant
growth.
A1. I don't have scientific data and will try to find what is published.
Maybe I can come up with data rather than just "the accepted explanation," which
I present here.

Q2: Why would seed production be harmful to the bulb development?
A2: The oft given reason is that developing seeds are a "sink." They are a
site where photosynthate is shunted. The plant physiology-type idea is that
while seeds are developing the plan defers sending much photosynthate to
shoots, roots, and storage organs.

Q3: If seed production were harmful, why would bulbs produce so much seed
when they could vegetatively propagate as well?
A3: As I understand evolutionarily theory and sexual reproduction, it is
thought that seed production (sexual reproduction) has benefits overall for just
about any species. A plant can propagate its genes more effectively in an
evolutionary sense when the genes are "mixed and matched" with those of other
individuals. The idea from many studies is that just about any species that
doesn't reproduce sexually will eventually reach a dead end (but it may take many
centuries).

Q4: What about flowering, does deadheading enhance flowering?
A4: This concept is absolutely demonstrated in some plants that can rebloom
(e.g., roses, some annuals). What happens is that developing fruits send a
message to the rest of the plant (hormonal or hormone-like). The plant senses
the developing fruit and "decides" that it has reproduced successfully for the
season, and it makes no more flowers. Deadheading is useful in some plant
species because the practice promotes rebloom; i.e., more flowers.

This is not a general phenomenon of much bulbous plant, as far as I know.
They bloom once and that is it. However, some tuberous gesneriads benefit from
deadheading (e.g., Sinningia species).

As a side note, I understand that probably seed production is not "harmful,"
but it does temporarily (if the theory is correct) put food aside for the next
generation rather than for the current. Many species of plants are not
harmed (per se) as opposed to losing a bit of food for several weeks. But the idea
is that the species would be harmed if sexual reproduction did not occur.

Q5: What about hybrids, why don't sterile hybrids flower vigorously and
propagate more vigorously?
A5: Some sterile hybrids do just what is suggested, but many do not.
However, in general, hybrids establish their own rules as they try to express the
sometimes-conflicting information from two very different gene sets; hybrids
don't seem like a good test of the deadheading ideas because, by definition, most
hybrids are different from each other and comparisons don't work.

Also, quite often, hybrids are selected for color or shape, etc., with no
regard for vigor or bloom quantity; thus the hybridizer often throws away
vigorous bloomers because they might not be large-flowered or the correct color, etc.

Q6: Where is the evidence?
A6: I don't know, but I'll try to find out what is published. Maybe bulbs
will have patterns of photosynthate movement that are independent of fruit set,
maybe not. Such information is probably out there in the scientific record
for a variety of bulbs, and collectively may support general statements.

Comment: I don't deadhead, it is not in my nature.

C.J.