Chemical Scarification

It seems that many seeds are blessed with an extremely hard and thick seed coat. Though this might seem like a great means of protection it is also a barrier to germination. You see, germination requires that the small embryo within the seed have access to both water and oxygen, a hard shell prevents such access. When this is the case the seed will remain in dormancy until the coat is altered to allow these essential makings of plant growth to reach the embryo.

Any action taken to alter the seed coat is known as scarification. In a natural setting this can occur in a number of ways. The seed can freeze (expand) and then thaw (contract) causing an alteration in the seed coat. Or, a seed can be consumed by an animal – often a bird – and the animal’s stomach acids will thin the seed coat just enough to allow access of even the smallest amount of water and oxygen, breaking dormancy and allowing germination.

Yes, I know acid does not sound like a growth enhancer! However, this artificial process is not a new idea; in fact, acid scarification has been a recommended method of improving successful plant germination and growth for more than 100 years. 

Further investigation taught me that commercial operations use sulfuric acid in their chemical scarification. If I were not fortunate enough to have a full lab at my disposal I would be taking a quick trip to Pep Boys – sulfuric acid is sold in the battery department of most automotive stores. Though, website authors recommend vinegar for home scarification; noting that although not as effective it is a much, much safer route for the novice. 

So, today we began to submit some of our seeds to a little pre-treatment with sulfuric acid, a forced method of chemical scarification, to see if this might improve the germination of our precious seeds of the lower Sonoran Desert.

For our scarification process we chose four different species and two different techniques.

First we counted 125 seeds of Lupinus arizonicus (Arizona Lupine) and 50 seeds of Cercidium microphyllum (Palo Verde) and bathed them for three minutes in sulfuric acid. After the short three minutes we washed them thoroughly with water (I wonder if the chlorine in water causes scarification?). Our little seeds were then divided (25 seeds per dish for Arizona Lupine and 10 seeds per dish for Palo Verde) and put into - paper towel lined and labeled - Petri dishes with 5mL of distilled water. The final step was sealing them with parafilm. 

Next we counted 125 seeds of Opuntia Phaecantha (Desert Prickly Pear) and 125 seeds of Encelia farnosaI (Brittle Bush) and bathed for one hour in sulfuric acid. After this long hour (It is emotionally hard to put a living thing in acid for such a long time!) we washed them thoroughly with water. The seeds were then divided (15 seeds per dish for Bursage and 25 seeds per dish for Brittle Bush) and put into - paper towel lined and labeled - Petri dishes with 5mL of distilled water. The final step was sealing them with parafilm.

All of the Petri dishes were left in full light.

As I have discussed in previous blogs, our project has been haunted by the presence of mold on our darling little seedlings. It seems that chemical scarification may also serve to kill fungi! We shall keep our fingers crossed!