The Seed Garden (Seed Savers Exchange, 2015) by Micaela Colley & Jared Zystro and edited by Lee Buttala & Shanyn Siegel brings together decades of research and hands-on experience to teach both novice gardeners and seasoned horticulturists how to save the seeds of their favorite vegetable varieties.
You can purchase this book from the MOTHER EARTH NEWS store: The Seed Garden.
Carrots are a popular garden crop, but they pose several challenges for seed savers—the most notable of these being their ability to cross-pollinate with wild carrot, or Queen Anne’s lace. Ubiquitous in the Northeast and Midwest and common in most other regions of the United States, the weedy form of the species forces gardeners to carefully manage the isolation of cultivated carrots grown for seed. Carrots also require vernalization; however, because of their small size, carrot roots can be vernalized in a refrigerator, which is not as feasible for many other biennial crops.
Beyond the many hues of orange that seed catalogs typically offer, carrot varieties can be found in a wide range of root colors including white, yellow, red, purple, and black. Carrot roots can be a single color throughout or display one color on the exterior and a different color in the interior.
Carrots are broadly grouped into types based on shape: Imperator, Nantes, Danvers, and Chantenay. Imperator carrots are very long, with tips that gently taper to a point; these are the carrots most commonly found in supermarkets. Nantes carrots are slightly shorter than Imperator carrots and have tips that are blunt rather than pointed. Danvers carrots are about as long as Nantes, but thicker, and Chantenay carrots are the shortest and thickest of the carrot types. Widely grown by food processors to make canned and prepared food, Danvers and Chantenay carrots are often preferred by home gardeners because their sturdy roots can be grown more successfully in heavier soils than Nantes and Imperator types. In addition to the common market classes, there are also specialty types including small round carrots, such as ‘Thumbelina’, and the large ‘Oxheart’ carrot, which has wide shoulders and short roots that may weigh up to 1 pound each. As with most root vegetables, carrots have a history in the United States of being used for both forage and fodder.
Carrots originated in Afghanistan sometime before the tenth century CE. From Afghanistan, carrots spread west to Europe and east to China. Based on historical record, literature, and art, the earliest cultivated carrots are believed to have been yellow or purple rather than the bright orange primarily associated with them today. Carrots were grown in Europe for several hundred years before the orange carrot rose to prominence in the seventeenth century.
Carrots that evolved in the subtropical regions east of Afghanistan, such as ‘Kuroda’, tend to have fuzzier, grayer leaves than their western counterparts. Subtropical carrots also tend to bolt, or go to seed, much more easily than western carrots, and can even flower in their first growing season.
Growing Carrots for Seed
Carrots are biennial plants that require vernalization in order to flower and set seeds. Typically, carrots must be exposed to temperatures below 50°F (10°C) for up to 10 weeks to initiate development of their floral stalks. Before they are vernalized, carrots can be spaced as if they are being grown as food, with three-quarters to 2 inches (2 to 5 cm) between plants. After vernalization, carrots being grown for seed should be replanted with suitable spacing for seed production: 6 to 18 inches (15 to 46 cm) between plants in rows 24 to 48 inches (61 to 122 cm) apart, or 15 to 18 inches (38 to 46 cm) on center.
Where winter temperatures are cold enough to fulfill carrots’ vernalization requirement, but do not fall below 15°F (-9°C), plants can simply be overwintered in the garden. Straw mulch, leaves, or row cover can provide a bit of extra protection from the cold in borderline climates and also help mitigate widely fluctuating fall, winter, and spring temperatures. Even when carrots can be vernalized in-ground, many gardeners choose to dig them—either before or just after overwintering—to evaluate roots, cull off-type and diseased roots, and replant selected roots at a wider spacing that better accommodates the plants’ size at seed maturity. When carrots are to be overwintered in the garden, sowing should be timed so that the roots will be slightly smaller than full size at the onset of winter, because younger plants are less susceptible to damage from the cold than more mature plants.
In the northern United States, where winter temperatures frequently fall below 15°F (-9°C), carrots must be dug before the first hard frost and vernalized in storage. If possible, dig carrots when the soil is relatively dry; shake or gently brush the roots to remove as much soil as possible, but do not wash them. Trim tops down to just above the crown by making two or three diagonal cuts upward from the base of the leaf stems. Carrot roots can be stored in perforated plastic bags or any ventilated container: In bags, evenly disperse wood shavings around the carrot roots; in containers, line the bottom of the container with wood shavings, clean sand, or dry leaves, and then alternate each layer of carrots with a thin layer of whatever storage medium is being used. Cull out diseased or off-type roots prior to storage and again before replanting.
The optimal storage conditions for carrots are between 35 and 38°F (2 and 3°C) and 90 to 95 percent relative humidity. A more practical goal—and one used by seed-saving farmers and gardeners for ages—is to meet the plants’ basic vernalization requirements and prevent stored roots from freezing or desiccating. A traditional root cellar is ideal for this, but garages, sheds, and other unheated structures can be equally useful in some climates. Given the size of carrot roots, a refrigerator can provide a suitable space for storing and vernalizing this crop. Carrot roots stored at optimal conditions can remain viable in storage for four to six months or longer.
In the spring, roots should be removed from storage and prepared for replanting. Cutting off the bottom third of the carrot root facilitates transplanting and also provides seed savers with an opportunity to check interior root traits. To discourage rot, the cut ends of the roots should be allowed to scar over for a day before they are planted back in the garden. Each root should be set so the plant’s crown is just above the soil line, mimicking the height of the crown during its first season in the garden.
Flowering, Pollination, and Seed Set
Individual carrot flowers are quite small, but when tightly arranged in the compound umbels characteristic of the Apiaceae, they provide a showy floral display that is readily visited by a variety of pollinators, including flies, wasps, and bees. Cross-pollination is encouraged, as each perfect flower is protandrous and sheds its pollen before its stigma is receptive. However, carrot plants produce many compound umbels, some containing upward of 100 flowers, and self-pollination occurs when insects transfer pollen between flowers on the same plant.
Carrot plants flower in a sequential pattern. The central flower stalk first produces a terminal umbel, called a primary or king umbel. Flowering then progresses to branches that grow from the main flowering stalk; these lateral branches produce secondary, tertiary, and sometimes quaternary umbels. Each order of umbel is smaller than the last and the lower orders may not develop in tightly spaced plantings. Depending on the variety, carrot plants in flower may grow to 5 feet (1.5 m) tall and often require staking.
Carrots are insect-pollinated, so the recommended isolation distance between varieties—or between a variety and a population of wild carrot—is 800 feet to one-half mile (244 to 805 m). Gardeners who share seeds with others or who garden in settings that do not provide many landscape barriers may choose to use the upper end of this range as a starting point when determining an isolation distance. Large-scale commercial seed growers separate different varieties by 1 to 2 miles (1.6 to 3.2 km). The foliage of Queen Anne’s lace or wild carrot is fine and low-growing while in the vegetative stage, thus wild carrot plants growing near gardens may not be apparent until they begin to flower, but they can easily cross-pollinate with a domesticated carrot variety. Gardeners in areas lacking wild carrots can likely manage isolation for one variety each season because other nearby garden carrot plantings are unlikely to be in the flowering stage, unless they too are being grown for seed.
Other than isolation by distance, options for controlled pollinations are limited because carrots are insect-pollinated, and caging plants requires the use of introduced pollinators. Additionally, isolation by flowering time is impractical because the multibranched plants flower for a month or longer.
Although carrots are self-compatible, population size recommendations are similar to those for other outcrossing species. Viable seeds can be collected from 5 plants or fewer, although a population size of 20 to 50 plants is recommended to maintain a healthy variety. The upper end of this range best captures a variety’s genetic diversity, and since carrots are prone to inbreeding depression, the upper end of this range is also preferable if the intent is to save seeds for multiple generations or to share seeds with others. For those saving seeds for genetic preservation, a population size of 80 plants or more is recommended. Some loss can be expected from rot or disease during overwintering, so gardeners should consider growing more plants than the desired population size.
Routine selection is necessary simply to maintain some open-pollinated carrot varieties. As always, off-type and especially weak or diseased plants should be rogued any time before flowering, and again before seed harvest, but plants that show undesirable root traits, such as forked roots or prolific root hairs, should also be removed from the population. When roguing or selecting, important carrot traits to consider are root color (exterior and flesh color), root shape, and core size.
Seed Maturity and Harvest
During seed development, carrot fruits are small, green, and tightly packed together on each umbel, and most gardeners are probably unaware of their development until they are close to maturity. The fruits, called schizocarps, split into two mericarps at maturity; each single-seeded mericarp is commonly referred to as a seed. Carrot seeds also have spiny appendages called awns that aid in seed dispersal, but these appendages are often removed as part of the cleaning process.
Carrot seeds can be expected to reach maturity approximately four to six weeks after pollination, but the sequential flowering pattern of carrots means that umbels continue to mature over a long period of time. The earliest-flowering umbels—the primary and secondary umbels—are also the first to reach seed maturity, and gardeners may reasonably choose to harvest only these umbels, sometimes preferring to limit seed collection to just the primary umbels. This practice requires cutting individual seed heads as they mature, but it allows for an early harvest. A single primary umbel can yield hundreds of seeds, and primary umbels tend to produce the largest and most vigorous seeds.
As carrot seeds mature, they turn from green to tannish brown; fully mature seeds detach easily from the plant. Individual seed heads can be harvested by cutting stems several inches below the umbels. The harvested material should be moved to a well-ventilated space that is protected from rain for further drying for 5 to 14 days.
For a once-over harvest, seeds are collected in the same manner as above when approximately two-thirds of the umbels have turned brown.
Cleaning and Storage
Carrot seeds can be easily threshed by rubbing the seed heads between one’s hands or against a fine mesh screen. Because each pair of seeds is held on a thin stem, dislodging the seeds into a container by gently brushing the tops of the seed heads results in a cleaner seed lot containing fewer dry flower stems.
Carrot seeds have appendages called awns that attach to animal fur as a method of seed dispersal, but these awns are typically removed to make planting easier. The seeds can be debearded by rubbing the seeds between one’s hands until the awns break off or crumble. If the awns are not easy to remove, the carrot seeds probably require further drying. After they are debearded, carrot seeds can be screened and winnowed to remove chaff.
When stored under cool, dry conditions, carrot seeds can be expected to remain viable for six years.
LIFE CYCLE: Biennial
SUGGESTED SPACING: When growing for seed, increase spacing to 6–18 inches (15–46 cm) between plants, in rows 24–48 inches (61–122 cm) apart. Staking is recommended.
OTHER REQUIREMENTS: Carrots require a vernalization period of temperatures below 50°F (10°C) for 10 weeks or less in order to flower and set seeds.
FLOWER TYPE: Perfect, self-fertile flowers are protandrous and shed pollen prior to stigma receptivity. Clusters of flowers are held in compound umbels.
MATING SYSTEM: Mixed. Protandry facilitates cross-pollination. However, carrots self-pollinate when insects transfer pollen between flowers on the same plant.
ADDITIONAL CROSS-POLLINATION CONCERNS: Wild carrot, or Queen Anne’s lace, is also Daucus carota.
FRUIT TYPE: Dry, paired fruits (schizocarps) split at maturity into two single-seeded, indehiscent mericarps. The mericarp is considered a seed.
SEED MATURITY: Seed maturity occurs in the second growing season, when green fruits turn brown.
SCREEN SIZE: 5⁄64–15⁄64 inch (2–6 mm)
EXPECTED SEED LIFE: 6 years
ISOLATION DISTANCE: 800 feet–1⁄2 mile (244–805 m)
For Viable Seeds: 5 plants
For Variety Maintenance: 20–50 plants
For Genetic Preservation: 80 plants
For more on seed saving, see our Seed Saving Guide.
Reprinted with permission from The Seed Garden, by Micaela Colley & Jared Zystro, edited by Lee Buttala & Shanyn Siegel and published by Seed Savers Exchange, 2015. Buy this book from our store: The Seed Garden.