germination

by

Dr. Beal’s Seed Viability Experiment

In 1879, Dr. William J. Beal buried 20 jars full of sand and seeds on the grounds of Michigan State University. He was hoping to answer questions about seed dormancy and long-term seed viability. Farmers and gardeners have often wondered: “How many years would one have to spend weeding until there are no more weeds left to pull?” Seeds only remain viable for so long, so if weeds were removed before having a chance to make more seeds, the seed bank could, theoretically, be depleted over time. This ignores, of course, the consistent and persistent introduction of weed seeds from elsewhere, but that’s beside the point. The question is still worth asking, and the study still worth doing.

When Dr. Beal set up the experiment, he expected it would last about 100 years, as one jar would be tested every 5 years. However, things changed, and Dr. Beal’s study is now in its 140th year, making it the longest-running scientific experiment to date. If things go as planned, the study will continue until at least 2100. That’s because 40 years into the study, a jar had to be extracted in the spring instead of the fall, as had been done previously, and at that point it was decided to test the remaining jars at 10 year intervals. In 1990, things changed again when the period was extended to 20 years between jars. The 15th jar was tested in 2000, which means the next test will occur in the spring of next year.

In preparing the study, Dr. Beal filled each of the 20 narrow-necked pint jars with a mixture of moist sand and 50 seeds each of 21 plant species. All but one of the species (Thuja occidentalis) were common weeds. He buried the jars upside down – “so that water would not accumulate about the seeds” – about 20 inches below ground. Near each bottle he also buried seeds of red oak and black walnut, but they all rotted away early in the study.

After the retrieval of each bottle, the sand and seed mixture is dumped into trays and exposed to conditions suitable for germination. The number of germinates are then counted and recorded. Over the years, the majority of the seeds have lost their viability. In 2000, only three species germinated  – Verbascum blattaria, a Verbascum hybrid, and Malva rotundifolia. There were only two individuals of the Verbascum hybrid, and only one Malva rotundifolia. The seeds of Verbascum blattaria, however, produced 23 individuals, suggesting that even after 120 years, the seeds of this species could potentially remain viable long into the future.

moth mullein (Verbascum blattaria)

In the 2000 test, the single seedling of Malva rotundifolia germinated after a cold treatment. Had the cold treatment not been tried, germination may not have occurred, which begs the question, how many seeds in previous studies would have germinated if subjected to additional treatments? Dr. Beal himself had wondered this, expressing that the results he had seen were “indefinite and far from satisfactory.” He admitted that he had “never felt certain that [he] had induced all sound seeds to germinate.”

There are also some questions about the seeds themselves. For example, the authors of the 2000 report speculate that poor germination seen in Malva rotundifolia over most of the study period could be “the result of poor seed set rather than loss of long-term viability.” The presence of a Verbascum hybrid also calls into question the original source of those particular seeds. A report published in 1922 questions whether or not the seeds of Thuja occidentalis were ever actually added to the jars, and also expresses uncertainty about the identify of a couple other species in the study.

Despite these minor issues, Dr. Beal’s study has shed a great deal of light on questions of seed dormancy and long-term seed viability and has inspired numerous related studies. While questions about weeds were the inspiration for the study, the things we have been able to learn about seed banks has implications beyond agriculture. Seed bank dynamics are particularly important in conservation and restoration. If plants that have disappeared due to human activity have maintained a seed bank in the soil, there is potential for the original population to be restored.

In future posts we will dive deeper into seed banks, seed dormancy, and germination. In the meantime, you can read more about Dr. Beal’s seed viability study by visiting the following links:

Advertisement
by

Onion Seed Viability, etc.

Seeds don’t remain viable forever. However, each species is different – the seeds of some species can remain viable for many years (decades even), while some species have seeds that will no longer be viable after a single year. This, of course, is something to keep in mind when planting seeds.

Recently I planted some onion seeds. I was curious to see if they would germinate because they were a few years old –  collected in 2007. My experience with onion seeds is that they germinate fairly quickly, within a week or so. However, three weeks have passed and my seeds have not yet germinated, despite being kept in moist potting soil in a sunny, warm corner of the house. This experience has led to me to think about seed viability.

Like I said, seeds of different species remain viable for different lengths of time. For vegetable gardeners, there are a variety of places to go to learn more about seed viability. Iowa State University Extension has a great chart which shows the number of years that the seeds of popular vegetable crops should remain viable. It is interesting to note that onion seeds only remain viable for one year. As it turns out, my seeds were far past their prime.

Seed storage can make a huge difference, though. Ideally, seeds should be stored in a cool, dry location. If they are exposed to too much heat or moisture, their metabolism will increase and their viability will decrease. This is because seeds are living organisms, despite appearing dead or dormant. Their metabolic processes are proceeding at an extremely slow rate,  but they are still proceeding. If metabolism increases (due to excessive heat or moisture, for example), the embryonic resources of seeds can become depleted, and viability (or germination potential) decreases.

Some sources recommend that you keep your seeds in the refrigerator, provided that they are sealed in plastic to keep them dry. Regardless, the ideal conditions for seed storage are cool and dry. I have always kept my seeds in a shoebox at room temperature (which isn’t always that cool because in the summer I refrain from using the air conditioner as much as possible). Thus, the viability of my seeds may in fact be reduced simply due to the conditions in which they are being stored.

There is a way to determine the viability of your seeds if you are curious. Just place some seeds on a moist paper towel, roll up the paper towel, and place it inside of a plastic bag. Wait a few days and then remove the paper towel from the plastic bag. Count the number of germinated seeds and divide that number by the total number of seeds originally placed on the paper towel. This will give you the germination percentage and will help you determine how many seeds to place in each hole or pot when you are planting them.

onion seed packet

This is the seed packet for the onion seeds that I planted. 2/15/2013 is the date that I planted them. After three weeks they had not germinated. I guess I’ll have to try some newer seeds.