Many grasses and annual weed seeds have a relatively short life, two to five years, but researchers are finding other seeds to be more resilient. The Weed Science Society of America (WSSA) recently released a fact sheet with information about weed seed dormancy.
Research into weed seed longevity began in 1879 when Michigan Agricultural College’s William Beal kicked off agriculture’s longest running experiment. Beal buried seeds from more than 20 weed species in glass bottles to be recovered in later years. The 137-year-old experiment has been passed down to younger generations and has seen weed seeds germinate after more than 100 years. In the most recent dig, Moth mullein germinated after 121 years. Read more about this experiment here.
WSSA provides clues into what could make some seeds more resilient.
Seed coats are one of the more important factors in seed germination and long-term viability. The harder the seed coat, the longer the seed can survive without germinating. Harder coats provide a protective barrier, can camouflage seeds from predators and allow the seed to be buried deeper in the soil which further protects it from predators and other stressors.
However, seed coats can also make germination more difficult when the time comes. If the outer barrier is too thick and hard, the seed might not be able to access the moisture and oxygen it needs to germinate. Some seeds require physically scratching the seed coat to weaken it and allow germination.
In addition, soil itself can inhibit seed germination. They need light penetration to kick off growth, so deep planting or dense soils can force the seed into a dormant state. That means tillage can both help and hurt. When tillage pushes seeds deeper, farmers might see fewer weeds germinate, but if it brings seeds up farmers might see more weeds than they expect.
Finally, some seeds use a biological phenomenon called allelopathy to influence seed germination. Allelopathy involves on organism producing a biochemical that has a positive or negative influence on growth, survival and reproduction of other organisms like weeds. For example, rye, sorghum, rice and wheat release a biochemical that suppresses weed seed germination.
Learn more about common weeds in farmers’ fields, their germination patterns and control methods here.