So lately I’ve been growing new Eastern Redbud Trees every year. I’ve grown all of them from seed. The first year I just followed the instructions on the packet, which stated that I should soak the seeds in hot water (taken off a boil) for 24 hours. This soaking method is a way to scarify the seeds. Well, I’ve germinated hundreds of seeds using different scarification methods with different levels of success depending on the seed. So this year, I thought I would conduct an experiment to determine what was the BEST way to scarify the seeds of the Eastern Redbud Tree to get the highest germination rate. The purpose of this little experiment is to determine how different scarification methods effect germination rates of Eastern Redbud Tree seeds. Studies have shown various methods will increase the germination rates of the seeds. In particular, this study by Geneve (1991) showed that scarification by immersing seeds in sulfuric acid for 30 minutes greatly increases germination rates. However, since most of us don’t have sulfuric acid available, I’m going to attempt to see if any alternatives increase germination rates.
What is the outer shell of the Redbud Seed?
Certain types of seeds, particularly Legumes (and a Redbud is a Legume) have hard outer shells that prevent water from reaching the inner seed, which is necessary for germination. It is a feature on these seeds the has come through evolution. By having this outer shell, the seed won’t germinate late in the fall, or in the middle of summer due to some random rain. This outer-shell will protect the seed from premature germination, that could result in the young tender seedlings death due to frost or summer heat.
So, how does nature Scarify seeds? There are several other processes that can scarify a seed – digestion of the seed by an animal that ate it (deer, bird, squirrel). Or, even bacteria/microbes can breakdown the shell over time. Also, freeze/thaw cycles that occur during the Autumn/Winter with a seed in a moist environment can crack the outer shell and prepare it for germination.
A special note on how I stored my seed
A note on this experiment. When I gathered my Redbud seed last Autumn, I didn’t store the seed in a sealed container in the refrigerator. I thought that it was OK to just keep them in my basement, which is around 60 degrees F and dry. All seeds were stored together from approximately November until March in these conditions. So, I don’t think this would have had an effect on any particular method being better/worse than the others, since they all received the same treatment. But I do believe that it affected the overall germination rate in a negative way. So, now that I’ve stated that, let me get to the experiment………
The Scarification Experiment on Redbud Seeds
So, I gathered a large quantity of Redbud Seed last Autumn. This allowed me to be able to try out new methods and document the results. I didn’t get the idea until I had already soaked a large number of my seeds, so that is why the sample sizes are uneven. But in general, I performed four different scarification methods.
Immersing the seeds in water that had just been boiling, and allowing them to cool/soak for 24 hours
Soaking seeds in warm tap water for 24 hours
Rubbing the seed on sandpaper to ‘knick’ or mechanically break the outer coating
A combination #1 and #3. First by rubbing the seed on sandpaper to break the outer coating, but then immersing them in water that had just been boiling and allowing it to soak for 24 hours
So, after doing this I prepared and planted seed starter pots (6-packs) with moist potting soil. I planted 3 seeds per cell. Method 1 had three six-packs planted at 1/4″ deep, for a total of 54 seeds. Methods 2, 3, and 4 each got on six-pack with 3 seeds per cell. I then watered, covered the tray with a plastic dome (with holes poked in it for drainage and air movement). Next, I set the whole tray outside on a side of my house that faces North-West on March 11. Needless to say, at that time of year there is very little sunlight.
Once temperatures started to warm up to highs in/around 50-60 degrees F (12-16 C) I removed the dome, made sure it stayed moist. But moved the whole tray over to the South West side of my house (Mid-April). And lo and behold, I had my first germination on May 3rd. Annnnnd it was a seed from Method 1, the boiling water soak!
My Seed Scarification Results Table – aka Germination Rate, time to germination, etc
I tabulated and summarized my results in the table below.
So, all in all this was a fun little project / science experiment. Overall I was quite surprised by my results. I fully expected to get the highest number of seeds sprouting / germination rate by the Process 4, sand paper + soaking. I figured that mechanically opening up the outer shell by rubbing it on sandpaper would just allow the water to enter that much quicker. But, I can’t argue with my results. What do you think? Did I damage the seed by first removing part of the shell, then putting it in very hot water?
To answer these questions I would probably have to do this experiment several more times in the coming years (and do better at storing my seed!).
But, I am pleased with the results. Going back to when I first grew Eastern Redbud from seed I bought, the instructions then told me to soak in boiling water for 24 hours. And, well, I guess that company knew what they were talking about because that seems to be the best method to scarify seeds. And thus, should give you the highest germination rate.
Well, I hope you enjoyed this article. Got any questions or suggestions? Ask me in the comments.
Also – I made a video describing this whole experiment, and you can have a look at it below. Hope you enjoy!
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