Stock flowers (Matthiola incana) are appreciated for their dense, spire-like blooms and distinctive sweet, clove-like fragrance, making them popular in cottage gardens and for cut flower arrangements. While many gardeners treat them as seasonal annuals, they can reseed themselves. This process is highly unpredictable, depending heavily on the specific variety, local climate, and the gardening environment. New plants appearing the following season are not guaranteed, so they are not considered dependable self-seeders.
Understanding the Stock Flower Life Cycle
The potential for reseeding is rooted in the life cycle of Matthiola incana, which can be an annual, biennial, or short-lived perennial depending on the climate. In mild winter regions (USDA Zones 7-10), the plant often acts as a biennial, flowering in the second year, or as a short-lived perennial. In colder climates, it is grown as an annual, completing its life cycle in one season.
After blooming ends, spent flowers must remain on the stem to mature into seed pods. These pods, called siliques, are long, narrow structures characteristic of the Brassicaceae family. As the seeds ripen, the siliques dry out, turning from green to brown. This drying leads to natural dehiscence, where the pods split open and scatter the mature seeds onto the surrounding soil.
Factors Influencing Reseeding Reliability
The consistency of self-seeding is unreliable due to external and genetic limitations. Climate plays a significant role, as Matthiola incana is a cool-season plant thriving in moderate temperatures. Seeds dropped in late summer or fall need time to establish a root system before hard frost; young seedlings often do not survive very cold winters. Conversely, prolonged high heat, especially nighttime temperatures above 60°F, causes established plants to decline and limits the seed production window.
Soil quality and moisture levels also dictate germination success. Seeds require well-drained soil with a near-neutral to slightly alkaline pH, struggling in compacted or overly acidic conditions.
A primary factor is the genetic makeup of modern cultivars. Many popular varieties are F1 hybrids bred for specific colors or high rates of double flowers. Offspring from these hybrids often revert to the less desirable single-flowered form with less intense colors, a phenomenon known as genetic drift.
Identifying Volunteer Stock Flower Seedlings
Gardeners hoping for self-seeded plants must distinguish desirable volunteers from common weeds. Stock flower seeds typically germinate quickly, often within one to two weeks in optimal conditions. The first leaves to emerge are the cotyledons, which are small and generally oval-shaped.
The first true leaves appear after the cotyledons, offering definitive visual cues. These true leaves are usually oblong or lance-shaped and possess a characteristic gray-green color. The foliage of Matthiola incana is often covered in fine, soft hairs, giving the plant a slightly fuzzy or “hoary” appearance that sets it apart from many other seedlings. Knowing these features allows a gardener to selectively thin the volunteer seedlings, giving the strongest ones space to develop.
Gardener’s Role in Seed Management
The gardener can significantly influence the self-seeding process by either encouraging or preventing natural seed distribution.
To maximize the chances of volunteer seedlings the following season, spent flower stalks should be left entirely intact. Allowing faded blooms to remain enables the full maturation of seeds inside the siliques. Limiting aggressive fall cleanup is also beneficial, as dropped seeds need contact with the soil surface to germinate, often with a light covering of soil.
Conversely, preventing reseeding is achieved through deadheading, which involves removing spent flowers before the seed pods ripen and dry. Timely removal prevents the plant from expending energy on seed production and ensures no seeds are scattered. Applying a thick layer of organic mulch after blooming can also act as a physical barrier, inhibiting fallen seeds from germinating.