Germinating super old seeds

[Carol Deppe]

My method for dealing with old seeds in general. First, if seed has been stored for long without drying to dormancy it is usually dead. Most seed sold via seed companies in paper packaging is still actively respiring and is not going to last long. Unless you live in a very dry area.

Second. If seed has been dried to dormancy and held for years at room temperature it needs to be rehydrated gently. I put seed in an open container in an air-tight plastic box it shares with an open bowl of water filled with wet paper towels for a couple of days. The object is to let the seed skin gradually absorb moisture and regain its flexibility without ever touching liquid water. Then I move seed to a plastic box with a layer of paper towels to which I have added just enough water to barely wet paper towels. I cover seeds with a single-just-barely-wet paper towel. More can cut down oxygen and suffocate seeds. I open box once per day to exchange air and add additional water if needed. This gives seed some time to restore the flexibility of their seed coats, wake up, and germinate properly instead of seedlings tearing themselves apart by trying to imbibe and grow when seed coat is not moist and elastic enough.

You don't want seeds sitting in actual water because if one or more seeds have mold or bacteria the contamination will spread to many seeds instead of being limited to one seed. People sometimes use antibiotics or sterilization processes on outside of seeds. I haven't tried it.

I use Brawny paper towels for germination tests and all work with seeds. Some brands of paper towels actually smell like mold when you soak them in water. Paper towel brands can matter. The folks studying Juvenile hormones in insects at Harvard one year suddenly had their insects going into abnormal instars and refusing to metamorphose into adults. Turned out someone had changed the brand of paper towels in the growing bottles. The new brand was made from different trees. And it turned out that some trees produce juvenile hormone analogs as part of their insecticidal repertoire. The new brand of paper towels contained juvenile hormone activity.

[Kai Emerge]

I just wanted to add my own experience.

I had approximately 500 seeds of Hibiscus cannabinus, the 'Big Love' variety. The seeds were about eight years old and had been stored at room temperature in paper bags, with temperature fluctuations. My goal was not to develop a complete germination protocol, but simply to rescue at least a few plants from the old seed stock.

I first tried germinating the seeds on moist paper with water only. I obtained no germination.

I then tried soaking the seeds in hydrogen peroxide, potassium nitrate and sugar before placing them on moist paper. Again, there was no germination.

With hydrogen peroxide and potassium nitrate without sugar, I obtained one germination.

I then added mechanical scarification with a utility knife before the hydrogen peroxide and potassium nitrate soak. This produced approximately twelve germinations. However, only one plant survived, and three seedlings had their cotyledons trapped inside the seed coat.

For my final attempt, I used approximately 50 remaining seeds. Every seed was scarified with a utility knife. I soaked them for 24 hours in approximately 200 ml of solution containing:

180 ml of warm water at about 30 °C;
20 ml of 3% hydrogen peroxide;
0.4 g of potassium nitrate;
one capsule of white willow bark extract;
a very small amount of vitamin B complex.

The white willow capsule was a 34:1 Salix alba bark extract labelled as containing 50% salicin. According to the label, one capsule contained 240 mg of extract, providing 120 mg of salicin, together with approximately 40 mg of vitamin C.

The seeds were not rinsed after soaking. They were placed on moist absorbent paper in separate zip bags and kept at approximately 18–21 °C.

I did not record the exact total number of germinations in this final batch, but there were enough seedlings to select the strongest plants. I kept nine vigorous plants. These nine plants are now growing in my garden and have allowed me to renew my stock of fresh Hibiscus cannabinus seed.

I cannot say which individual ingredient was responsible for the improved result, because several treatments were combined. I am only sharing my personal experience and the final outcome: scarification and the combined treatment allowed me to recover nine vigorous plants from an old seed stock that initially appeared almost impossible to germinate.