Wed, 05 May 2004 06:12:21 PDT

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 
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 

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.  


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