The Search for the Ultimate Cycad Seed Cleaning Procedure
by Tom Broome

One of the difficult aspects of growing zamias is the chore of cleaning the seeds. Unlike the seed coat of other cycad seeds, zamias have a very rubbery seed coat that sticks to the seed. I have seen hundreds of thousands of seeds being wasted because people did not have the time or the method to clean them.

In my early years of growing cycads, I would only produce 100 seeds or less at a time. I would watch TV at night and scrape the seeds one at a time with my pocket knife. I had to find a better way than this. The next I tried was to put the seeds in an empty pot and place that pot near a fire ant mound. Within a week, the ants would pick the seeds clean. This worked pretty well, but the ants wouldn't clean more than a couple of hundred seeds before they would lose interest. 

Dr. Bijan Dehgan, at the University of Florida, told me his favorite method was using a wire brush on a drill. He instructed me to put the seeds in a coffee can, cut a hole in the lid, and insert the wire brush into the drill through the lid so that when it was placed in the can it would keep any extra material from flying out when the drill was turned on. This worked very well but I needed something that would clean 1000's of seeds at a time. 

I improved on this method by taking a length of "all thread" (a metal shaft with threads all the way up and down), and placing three large wire brushes on the shaft with nuts in between each brush. I would fill an entire five gallon bucket full of seeds, add water and a little sand, and 'brush' the seeds for almost an hour. I would then use a pressure hose to clean off most of the residue, but still not all of the seeds would be perfectly clean. 

I have seen other nurserymen over the years use rock tumblers, cement mixers, and potato peelers to clean their seeds, but they found that many of the seeds would be damaged. One nurseryman used to nick the seed coat, place his seeds on a bed of clean sand, cover with a screen, and pile oak leaves on everything. After a month or so the bugs and natural enzymes would clean the seeds. Even though it sounded bizarre, this was the only natural way I had ever heard of.

In 1992, an old groves man told me a story about a product he had used in the 1950's to separate the seeds from oranges so that they could be used to plant rootstock material for grafting citrus. He told me how they would throw massive amounts of oranges in a large cow trough and then cover the oranges with water. Next, he would pour a cup full of a liquid into the trough. In approximately a week the oranges would break down into pulp, and the seeds would sink down to the bottom of the trough. The most important aspect of this method was that the seeds were still viable. I wondered if something like this would work with cycad seeds. The man didn't even know how to read and could not give me any clues as to what this product may have been.

After months of searching (most people didn't even know what I was asking about) I discovered that the product I was looking for was a pectinase enzyme. From what I was told, the enzyme breaks down the cellular structure of fruit but won't harm other materials such as seeds or plant material. In Florida, this enzyme is still used to separate the orange seeds from the fruit in mass quantities. In North Carolina, it has been used to make apple juice. By using the enzyme, more juice can be produced from each apple because there is no wasted material, except for the seeds, to throw away. 

I thought I would check all this for myself, so I procured some enzyme and conducted a few experiments. I put some Zamia floridana seeds in three different cups, and added three different strengths of enzyme solution to test for speed of cleaning. I used 1/2, 1, and 1-1/2 teaspoons of enzyme per pint of water for the three different cups. After a week, there was what appeared to be a liquid wax floating on the top of the cups, and after 2 weeks only a few seeds were clean. I assumed the enzyme was having a hard time penetrating the seed coat. I tried scraping the seed coat a little for my next experiment. Eureka! The enzyme entered the scraped sarcotesta and broke it down from underneath. Depending on the size of the 'scrape', the seeds were perfectly clean in as soon as 5 days using the 1-1/2 teaspoon rate. All I had to do after that was to rinse them in water and I had perfectly cleaned seeds. Having to manually scrape each seeds still took too long, though. I found that if I soaked the seeds in a bucket for three days and then used the wire brushes for a couple of minutes, the seed coats would be damaged enough to let the enzyme work. For those who don't have a drill, I found that after the three day period, if I put some gloves on and worked the seeds through my hands for ten minutes I would get the same results.

The next question was still critical. How would the use of the enzyme affect germination? I found that even after soaking seeds for up to three weeks in the enzyme solution, I had no loss of germination. I then soaked some seeds that had recently germinated in the enzyme, and after three days, the radicles weren't adversely affected. I think the key is that this is a very specific enzyme and does not work like an acid that could damage seeds.

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