Morning glories, belonging to the genus Ipomoea, are popular climbing vines known for their trumpet-shaped blooms that open briefly each day. These attractive annuals are often planted on trellises and fences for their rapid growth and vibrant color. They reseed themselves with great efficiency. This ability to readily self-sow is why gardeners find volunteer seedlings appearing year after year in the same location.
The Mechanism of Seed Production and Dormancy
The prolific reseeding ability of morning glories is rooted in the structure and survival strategy of their seeds. Each spent flower develops into a small capsule that typically holds between four and six dark, wedge-shaped seeds. A single, vigorous plant can produce hundreds of seeds throughout a growing season.
These seeds possess a hard, protective outer layer known as the testa, which enforces physical dormancy. This hard seed coat is water-impermeable, preventing water from reaching the embryo inside, even when the soil is moist. This physical barrier allows the seed to remain viable in the soil for extended periods, protecting it from immediate germination.
Dormancy is eventually broken when this protective layer is compromised, a process known as scarification. In nature, this occurs through physical abrasion from soil particles, microbial activity, or chemical weathering. Temperature fluctuations and repeated cycles of hydration and dehydration also weaken the seed coat. Only once the testa is physically altered can the seed imbibe water and begin germination.
Environmental Factors Affecting Volunteer Growth
The success of volunteer morning glory plants is dependent on the external environment, which dictates when and where the seeds will sprout. Warm and fluctuating temperatures are significant environmental signals that promote dormancy release. The alternating heat and cool cycles experienced near the soil surface are particularly effective at breaking the seed coat’s dormancy.
Morning glory seeds remain viable in the soil seed bank for many years, sometimes decades, before conditions are right for germination. Major soil disturbance, such as tilling, can bring buried seeds closer to the surface where they are exposed to light and temperature changes. While they can emerge from depths up to four inches, most seedlings sprout from the top one to two inches of soil. Seedlings continuously emerge from late spring through mid-summer due to this staggered dormancy-breaking process.
Strategies for Managing Morning Glory Spread
Controlling the spread of morning glories requires preventing new seed formation and managing the existing seed bank. The most effective preventative measure is deadheading, which involves removing spent flowers before they develop into seed capsules. Since morning glories flower continuously until the first frost, this must be a consistent, season-long effort.
For controlling existing volunteer seedlings, physical removal is effective when the plants are young. Pulling the seedlings by hand is easy when they have just sprouted. Heavy mulching can also suppress germination by blocking sunlight and preventing the temperature fluctuations needed to break dormancy. A layer of organic mulch, four to six inches deep, can smother new sprouts.
Gardeners must distinguish between annual Ipomoea species and perennial weeds like field bindweed (Convolvulus arvensis), often mistakenly called “morning glory.” While the annual species are easy to control through seed prevention and pulling, bindweed is a tenacious perennial that spreads aggressively via deep, extensive root systems. Control methods for the annual reseeding plant are simpler than those required for perennial bindweed.