More About Dormancy in Seeds
Wed, 14 Jan 2004 20:17:04 PST

One part of dormancy in plants is very advantageous for hobbyists, the 
dormancy of seeds.  The ability of seeds to lie quiescent for long periods provides 
a means to easily and safely ship seeds around the world, knowing they don't 
need light or water while they travel.  

Many bulb seeds are orthodox, that is they tolerate drying and cold storage.  
Other seeds, such as those of Crinum, are recalcitrant.  Recalcitrant seeds 
do not accept much drying and resent cold storage for long periods, they seldom 
survive freezing.  The trick is to know about your seeds, are they orthodox 
or recalcitrant, or partly recalcitrant.  

The seeds of most plant species are orthodox, especially those from temperate 
or xeric climates.  Surprisingly, seeds of many tropical species too, can be 
dried and stored frozen.  If you have orthodox seeds there is abundant 
information about high-tech and low-tech methods for storage.  In general, you can 
enhance seed longevity in storage by a factor of 2 for every 1% reduction in 
moisture content that is achieved.  Similarly, another rule of thumb is that a 
doubling of storage life can be achieved for every 5 C drop in temperature 
during storage.  

For instance, seeds harvested from an Allium are black and dry-appearing when 
ripe.  If left to sit several days at room temperature and 70% relative 
humidity, they might equilibrate at 13% moisture content.  Reducing their moisture 
content to 10% could be expected to increase their storage life by 4-fold (3% 
drop = 2 x 2 x 2 = 8).   Similarly if you store them in the refrigerator (2 C) 
rather than at room temperature (22 C) you will increase their storage life.  
Dropping the temperature by 20 C gains a doubling of storage life for every 5 
C drop.  The drop of 20 C gains a 16-fold increase in storage life ( 2 x 2 x 
2 x 2 = 16).   

The gains are multiplicative.  Thus, if you drop the seed moisture content by 
3%, and store the seeds at 2 C, you can increase their longevity by about 
130.  Allium seed that might have survived 1 year before treatment can be 
predicted to survive well over 100 years.  Unbelievable!  But this is what theory 
predicts for orthodox seeds; I don't know anyone who has verified the 100 year 
prediction but high viability over 10 years is commonly and easily achieved for 
many seeds.  

The trick is to know which seeds can be stored, as well as how to achieve low 
moisture content coupled with cold storage.   Also, it is important to keep 
conditions constant in storage.   Fluctuations in humidity throw everything 
off, as do too many fluctuations in temperature (humidity changes are far worse). 
 One other important factor is cleanliness;  the seeds must be clean and free 
of debris, chaff, and insects for best results.  

A very simple way to store seeds reliably for years is to dry them at room 
temperature in a climate controlled building (air conditioned and heated).  With 
some luck, even in humid climates, the relative humidity indoors might 
average about 50-60%.  Spread the seeds out and let them dry for several weeks in 
thin layers (on paper plates or newspapers, etc.) in an open space where they 
will receive air (but not strong currents).  I leave them on a table or desk.  
After drying, store the seeds in airtight containers and place in the 
refrigerator or freezer.  Orthodox seeds will last years.  

Finally, some recalcitrant seeds can be stored for a while.  Gentle drying 
can help some (e.g., palms), and cool conditions can enhance longevity of others 
(e.g., Crinum).  Such treatment must be determined empirically, and cannot be 
predicted by the seed storage equation.  

LINK 1:  Seed Storage Practices for Native Hawaiian Plants… 

Link 2:  Seed Moisture and Drying Principles (slow to load) 

Link 3:  (book) Guidelines for the Management of Orthodox Seeds - This volume 
provides a source of practical ideas on orthodox seed storage. Available in 
English (1995), and Spanish (1997). Center For Plant Conservation ($14.00). 


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