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.
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Whether one is cultivating celery or celeriac, growing Apium graveolens for seed presents some challenges for new seed savers and is perhaps better suited to those with more experience. The small seeds of these tender biennials require care to germinate, and the plants themselves need ample fertility and consistent moisture during transplanting and vegetative growth in order to prosper and set seeds. And because the seeds mature unevenly, seed crops of Apium graveolens must be monitored carefully as the seed harvest approaches.
Apium graveolens is used culinarily for its roots, seeds, stems, and leaves, and the species consists of three crop types: celery, celeriac, and smallage. Celery seed, a common seasoning used in cooking, can be collected from any of the different Apium graveolens crops.
Celery is grown for its pale-green-to-white fleshy petioles (leaf stems), commonly referred to as stalks. Historically, celery plants were blanched to keep the stalks tender and prevent them from tasting bitter, but many cultivars available today are self-blanching. Red-stalked varieties, such as the historic cultivar ‘Red Celery’ or the newer cultivar ‘Redventure’, are topped with dark green leaves and do not require blanching.
Celeriac, also known as celery root or turnip-rooted celery, is grown for its large, edible root, which is actually comprised of both the root and the swollen hypocotyl (the base of the stem). Celeriac can be stored through the winter more easily than celery.
Smallage, also known as leaf or soup celery, lacks the swollen edible root of celeriac and the large fleshy petioles of celery; it is grown primarily for its edible fragrant leaves, which are used to season soups and stews. Smallage is thought to be the closest in form to wild celery but is not widely cultivated today.
Apium graveloens originates from Eurasia, and its use medicinally was recorded more than 3,000 years ago, although whether it was domesticated or foraged from the wild is unclear. There was a separate domestication of celery by the Chinese, who had been using the wild species since the fifth century. The first known mention of cultivated celery came from the French horticulturist Olivier de Serres in 1623. Cultivation of celeriac in Europe was documented in the seventeenth century.
Growing Celery and Celeriac for Seed
Celery and celeriac are biennials that require vernalization in order to progress from the vegetative to the reproductive phase. Juvenile plants first become receptive to vernalization when they have six to eight true leaves—plants of at least this size can be induced to flower by subjecting them to temperatures below 50°F (10°C). Vernalization proceeds more quickly at temperatures between 39 and 48°F (4 and 9°C). Plants may require exposure to these temperatures for up to 10 weeks, but cultivars vary drastically in their response; some varieties will initiate flowering with a shorter cold treatment.
If celeriac roots will be vernalized in storage, they can be grown to full size before overwintering, although small roots require less storage space. The plants should be lifted before the first hard frost, ideally when the soil is relatively dry. The roots can be shaken or gently brushed to remove as much soil as possible, but they should not be washed. The tops must be trimmed down to just above the crown by making several diagonal cuts upward from the base of the petioles. The roots can then be stored in any ventilated container: Line the bottom of the container with wood shavings, and then alternate each layer of celeriac roots with an inch (2.5 cm) of wood shavings. Diseased or off-type roots should be culled before storage.
Celery plants have fibrous root systems and, compared to celeriac, require some additional effort for successful winter storage. The leaves and petioles must be trimmed down, making sure the growing point in the center of the rosette is left intact—the cut stalks can be used in the kitchen. Plants should be replanted into containers filled with slightly moist potting mix or sand before storage. Celery is often grown to a smaller size than celeriac before vernalization.
The optimal storage condition for Apium graveolens is 34°F (1°C) and at least 75 percent relative humidity. A more practical goal—and one used by seed-saving farmers and gardeners for ages—is to meet the species’ basic vernalization requirement and prevent stored plants and roots from freezing, desiccating, or rotting. A root cellar is ideal for this, but garages, sheds, and other unheated structures can be equally useful in some climates. Celeriac is more likely to survive less-than-optimal storage conditions than celery. Following winter storage, set plants back out in the garden after the danger of hard frost has passed, burying the root mass up to the crown.
Before vernalization, plants can be grown at regular garden spacing, but in the second season plants should be replanted or thinned to at least 24 inches (61 cm) on center. Seeds usually begin to develop by midsummer of the second season in the northern part of the United States.
Flowering, Pollination, and Seed Set
Apium graveolens is pollinated by a variety of insects, including flies, wasps, and bees. The species bears numerous small, white, protandrous flowers that, as in other members of the Apiaceae, are held in compound umbels. Each flower is perfect and self-fertile, but cross-pollination is common because pollen shed occurs before stigma receptivity.
Apium graveolens is insect-pollinated, and the recommended isolation distance between varieties—including varieties of the different crop types—is 800 feet to one-half mile (244 to 805 m). Gardeners who plan to exchange 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 isolate varieties by 1 to 2 miles (1.6 to 3.2 km).
Given the biennial nature of the species, it is uncommon to see it flowering in gardens, which makes it relatively easy to grow one variety in isolation. Other options for controlled pollination are limited for this insect-pollinated species because caging requires the use of introduced pollinators. Typically growing to only 3 feet (91 cm) tall, Apium graveolens plants are smaller in stature than some of their Apiaceae relatives, but they still have a multibranched habit with numerous umbels blooming in succession, which makes isolation by flowering time impractical.
Apium graveolens is self-compatible, but growing a large population helps to ensure a successful seed set and to conserve genetic diversity within a variety. Viable seeds can be collected from 5 plants or fewer, though 20 to 50 plants is the recommended population size for seed saving. The upper end of this range helps prevent inbreeding depression and is preferable if a gardener’s 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 at least 80 plants is recommended. As some loss can be expected from rot or disease during overwintering, it may be necessary to grow more plants than the desired population size.
Off-type and especially weak plants should be rogued before seed production; seed crops of celery may also be selected based on stalk color and plant habit.
Seed Maturity and Harvest
The highly branched plants of Apium graveolens produce numerous umbels that mature fruits over an extended period of time. The fruits, called schizocarps, consist of a pair of mericarps that separate at maturity. Each single-seeded, indehiscent mericarp functions as a seed. During development, the immature seeds are green and small. As the seeds mature, they turn brown and easily detach from the plant.
Depending on the seed quantity desired, seeds can be gathered by harvesting individual umbels, whole branches, or entire plants. Similar to carrots and dill, Apium graveolens has a predetermined flowering sequence. The central flower stalk first produces a primary umbel, and then numerous umbels are successively produced on the lateral branches. However, unlike other crops within the Apiaceae, this species has a relatively small primary umbel that is often obscured by the numerous lower-order umbels held at the top of the floral canopy. An effective harvest method, even on a small scale, is to cut whole branches or plants when approximately two-thirds of the seeds are mature. The harvested branches or plants should continue drying for 5 to 14 days in a well-ventilated space that is protected from rain.
Cleaning and Storage
Celery seeds are easily threshed by rubbing umbels between one’s hands or by gently brushing fruits from the seed heads. Careful work minimizes the amount of tiny floral stems and other chaff mixed in with the seeds, resulting in a seed lot that is easier to clean. The dry umbels can also be threshed by rubbing them against a fine-mesh screen to separate the seeds from the seed heads. The tiny, lightweight seeds can be challenging to winnow.
When stored under cool, dry conditions, celery and celeriac seeds can be expected to remain viable for six years.
LIFE CYCLE: Biennial
SUGGESTED SPACING: When growing celery or celeriac for seed, increase spacing to 18 inches (46 cm) between plants in rows 36 inches (91 cm) apart, or to 24 inches (61 cm) on center.
OTHER REQUIREMENTS: Celery and celeriac require a vernalization period of temperatures below 50°F (10°C) for 6–12 weeks 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, plants self-pollinate when insects transfer pollen between flowers on the same plant.
ADDITIONAL CROSS-POLLINATION CONCERNS: None
FRUIT TYPE: Dry, paired fruits (schizocarps) split at maturity into two single-seeded, indehiscent mericarps. The mericarp acts as a seed for propagation purposes.
SEED MATURITY: Seeds mature in the second growing season, when fruits change from green to brown.
SCREEN SIZE: 3⁄64–5⁄64 inch (1–2 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.