Carrot Seed Production: Quick Reference - Organic Seed Alliance

Carrots are a biennial so seed production must take into account a 2-year reproductive cycle.

Production

Year 1: Producing the carrot crop

Carrot production is most successful with dry, warm to hot summers in sandy or silty loam soils with high nitrogen and phosphorus but without excess nitrogen. Carrots prefer a soil with a high water-holding capacity and need a consistent water supply. They should be direct seeded in early summer and thinned to 1-2 inches apart. Once some roots have reached market size, selections can be made for desirable root characteristics.

Above ground characteristics (foliage and crowns) can be selected for during the growing season. Similar to onions, carrot populations need to be maintained with at least 120-200 plants, so initially select 225 or more since some may be lost to rot during the winter storage. Roots can be harvested when the soil is moist, but not wet. Any soil clinging to the root should be wiped off by hand. Do not wash the roots or rub them with a brush. Save only disease-free, true-to-type roots. Trim the tops to ½ inch above the root crown, taking care not to remove the apical bud. Store the roots at 34-38°F and 90-95% RH.

Year 2: Producing the carrot seed

Carrot is highly outcrossing and insect-pollinated. It must be isolated from other carrot varieties as well as wild carrot (Queen Anne’s Lace) by at least 0.5-2 miles unless the flowering plants are enclosed in a cage. Time planting so that seed set will happen when temperatures between 75-90°F. Before planting the stored roots, cut the bottom third of the root to select for root color or core structure (this can also be done at the time of root harvest to avoid storing roots with undesirable internal characteristics). Allow the cut roots to heal over for a few hours before planting. The roots should be planted 12 inches apart with the crown just above the soil’s surface. Avoid overhead watering to reduce the potential for disease. Carrots flower over an extended window of time, with the first and largest umbels (known as the primary or king umbels) at the top of the plant opening and maturing first, followed by increasingly smaller and later maturing sets of flowers down the plant. If feasible harvest the primary umbels when they have begun to brown and the seeds are visibly brown and fully formed. Continue to harvest as umbels mature until either all umbels with fully mature seeds have been collected or until a satisfactory amount of seed has been gathered. Lay cut umbels out on landscape fabric, or other breathable cloth, and allow to fully dry.

Use a combine to harvest large acreage, aiming to cut the crop when approximately 70% of the umbels have mature seed. It is preferable to dry carrot seed to 7% moisture or slightly less. Thresh seed by rubbing the umbels by hand, against a screen, or by stepping on a pile of them.

Clean the seeds with a combination of winnowing and screening. To remove fine sticks, an indent cylinder may be helpful. Debearding with soft brushes can remove the fine hairs on the seed coat and prevent the seed from clumping. Seed stored at 40-60°F and <40%RH will last 3-4 years.

Selection and Variety Improvement

Selections for foliar traits, root characteristics (such as external and internal color(s), shape, size, skin smoothness, and flavor) and resistance to disease and bolting should be made in year one when roots are fully mature. Plan to make selections during and after storage as well, selecting roots that have maintained quality, have not grown excessive root hairs, and have not succumbed to disease or rot while in storage. Always discard and never replant any diseased or rotten roots.

Trait	Timing
Seedling vigor	2-3 weeks after seedling emergence
Top height	Shortly before root harvest
Top density	Shortly before root harvest
Top strength	Shortly before root harvest
Root tip fill	At or shortly after root harvest
Root smoothness	At or shortly after root harvest
Degree of root forking	At or shortly after root harvest
Shoulder quality	At or shortly after root harvest
Root uniformity	At or shortly after root harvest
Root shape & color	At or shortly after root harvest
Disease resistance	During growing season and after harvest
Insect resistance	During growing season and after harvest
% Marketable roots	At or shortly after root harvest
Marketable yield (whole plot & weight per root)	At or shortly after root harvest
Storagability	Periodically throughout winter, 2-8 months after harvest
Flavor – sweetness	At harvest, and periodically for the next several months
Flavor – harshness (bitter)	At harvest, and periodically for the next several months
Flavor – pineyness (acidic)	At harvest, and periodically for the next several months
Flavor – perfumeyness (floral)	At harvest, and periodically for the next several months
Texture	At harvest, and periodically for the next several months

Disease

Plant disease-free seed. Use furrow or drip irrigation. Use a 3-year crop rotation. Bury carrot residues. Diseases are classified by severity with a class of 1 being the most severe and 3 the least severe.

Disease	Type	Severity class	Favorable conditions	Control measures
Bacterial leaf spot (Xanthomonas campestris pv. carotae)	Seedborne	1	Warm (77-86°F) temperatures and rain or overhead irrigation	Hot water (20 min. at 122°F)
Black rot/Black crown (Alternaria radicina)	Seedborne	1	Warm/hot (above 65°F) and extended wetness of foliage
Alternaria leaf blight (Alternaria dauci)	Seedborne	1	Warm and moist with wide temperature range (57-95°F)	Hot water (20 min. at 122°F)
Cercospera leaf blight (Cercospera carotae)	Seedborne	2	Warm and moist with wide temperature range (57-95°F)	Hot water (20 min. at 122°F)
Itersonilia canker (Itersonilia perplexans)	Seedborne	3
Aster Yellows – virus	Foliar
Carrot Rust Fly (Psila rosae Fab.)	Insect

Also see Principles and Practices for Organic Carrot Seed Production in the Pacific Northwest.

This resource was made possible thanks to the Montana Department of Agriculture’s Specialty Crop Block Grant Program.