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LOTS OF REASONS WHY SEEDS FAIL TO GERMINATE
It doesn't take a lot of coaxing to get a bean seed or corn kernel to germinate. Pop it in moist soil and it emerges faithfully three or four days later.
Many types of flower seeds, on the other hand, can be a challenge.
If you're a seed starter, chances are you have had your share of disappointments with poor seed germination.
The list of reasons seeds don't germinate is long. The most common causes are seeds planted too deep or too shallow in soil that is too wet, too dry, too warm or too cold.
Light can also influence germination. On February 18, I planted impatiens, vinca and asarina. The impatiens seed packet says, "Cover seed lightly because light enhances germination." The asarina packet says "Do not cover seed since light aids germination." The vinca packet says "Cover seeds completely since darkness aids germination."
I planted liatris seed and achieved about 25% germination. Liatris, commonly known as Blazing Star, propagates in nature when the seed rests in the soil all winter under the snow. To start liatris indoors requires stratification -- storing seeds in the refrigerator for two months before planting.
I learned later that the right way to do this is to mix seeds with equal amounts of damp sand, vermiculite or other sterile media. Place the mixture in a sealed plastic bag and store it in a refrigerator at 33-38 degrees. The cold treatment I used was three months in the freezer, and the seeds were stored dry in an envelope. I'm sure germination would have been higher if I had done it the recommended way.
Over the years, I have learned that my best germination results are achieved when I place containers in a tray and cover the tray with a plastic hood. The soil in the containers must be moist before the hoods are placed on top.
These covered trays become tiny greenhouses where humidity approaches 100%. I can tell it is moist inside because shortly after the morning sun warms the trays, condensation forms on the inside of the plastic hoods.
I recently read results of a seed propagation research study conducted by the USDA that affirms this approach. It also may also cause some rewriting of seed germination textbooks. The report is titled "Vapor -- not liquid water -- spurs seeds' sprouting."
The news release states, "A new finding by Agricultural Research Service soil scientist Stewart B. Wuest has stunned many plant scientists. Until recently, it was generally believed that seeds must be in direct contact with soil to obtain liquid water needed for germination. Then Wuest discovered the importance of water vapor.
"From his research on wheat seeds, as well as from studying previously published data, Wuest concluded that water vapor in the soil is actually what makes seeds germinate. With a relative humidity of close to 99 percent in soil, the seeds didn't need to be tightly compacted in the soil to grow. In fact, seeds that were separated from the soil by crop residue still germinated, because the vapor was able to reach them."
Wuest also found that, thanks to water vapor, seeds separated from soil by a layer of fiberglass cloth germinated just as well as those touching the soil. He was even able to germinate seeds suspended in air above water, using just the vapor rising from it.
Water vapor is all around us, measured as humidity. That's what makes a dry cracker left out in a room with high humidity turn soggy from absorption of water from the air. Similarly, seeds are able to absorb their needed water from vapor in the soil. In fact, liquid water is not nearly as important as previously thought and may only account for 15 percent of water taken up by germinating seeds, according to the study.
An environment that provides high humidity and water vapor would explain why seeds that need light to germinate -- impatiens and asarina, for example -- are able to germinate when the seeds are placed on the top of the soil rather than in the soil. It also explains why my best results are obtained when I cover the seed trays with a plastic hood.
The same principles apply to seeding outdoors. Seeded lawns that fail to germinate completely and end up looking sparse and spotty can generally be attributed to seedbeds that weren't kept constantly moist for the several weeks prior to emergence. This is why lawn seed bags recommend covering seed with straw and sprinkling two or three times a day.
If your indoor seeding hobby this winter or outdoor seeding this spring don't result in 100% germination, you can take consolation in the fact that germinating seeds is a complex process. Everything needs to be just right. Good luck, and happy gardening.
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