Commercial Vegetable Recommendations Extension Bulletin £-1437 (Minor Revision) February 1986 Coopererative Extension Service CARROTS Michigan State University Bernard H. Zandstra, Department of Horticulture Edward J. Grafius, Department of Entomology Darryl D. Warncke, Department of Crop and Soil Sciences Melvyn L. Lacy, Department of Botany and Plant Pathology Production and maturity than open-pollinated Genetic resistance is the best pro- cultivars, but the seed is much tection against bolting. Approximately 7,000 acres of more expensive. Some growers carrots are planted in Michigan plant open-pollinated cultivars for There are four main types of car- each year. fall harvest because the roots do rots (Figure 1): The average state yield for fresh not oversize as quickly as hybrids, market carrots is 8.8 tons (350 50-lb thus giving the farmer more Imperator—long, small shoulders, bags) of usable carrots per acre. latitude in scheduling harvests. tapered tip; used primarily for Yields on good fields with no Bolting (formation of a flower fresh pack. Most carrots grown for nematode, water, or other limiting stalk the year of planting seed) is a fresh market in Michigan are of problems may exceed 15 tons (600 response to cold temperatures and this type. 50-lb bags) per acre. Minicarrots plant size. Plants that bolt do not Nantes—medium length, uniform yield about 11 tons per acre. form a marketable root. Plants that diameter, blunt tip; used for bun- Processing carrots can yield 35 to have reached sufficient size bolt ching, slicing, and mini carrots. 40 tons per acre on good fields with when exposed to temperatures Although not widely grown in irrigation. below 50°F for an extended period Michigan, Nantes type carrots of time. Although the most suscep- have a good eating quality, and are Use tible cultivars require less than 2 especially suited for local sales. days of cold temperature to induce They normally mature earlier than Approximately 85% of Michigan bolting, most cultivars used in Imperator types. carrot acreage is used to produce Michigan need about 10 to 15 days. Danvers—large, medium long, full size carrots for fresh market. Mini or baby carrot production for Fig 1: Four main types of carrots. fresh pack is increasing, but is still a minor part of total production. Imperator Danvers Nantes Chantenay About 15% of carrot acreage is used to produce processing carrots. Types and Cultivars The carrot is a biennial plant. During the season in which it is planted, the plant produces a storage root. After a period of cold temperature, the root begins to grow again and produces a seed stalk. Most carrot seed is produced in the western U.S. in areas that have relatively mild winters. Seed is planted in August and produces a small root before winter sets in. The next spring the plant resumes growth, flowers, and sets seed, which is harvested in August. Most carrot cultivars used in Michigan are hybrids. Hybrids tend to be more uniform in quality processing type; used for dicing Climatic Requirements periods of hot, dry weather often and slicing. Danvers cultivars re- and Irrigation cause a strong, unpleasant flavor. quire a long season (120 days) to Alternating periods of slow or develop tonnage and high sugar Carrot is a cool season crop. rapid growth caused by irregular content. Most carrots grown for Seeds germinate at soil temperatures or moisture often processing in Michigan are of this temperatures of 40°F cause rough carrots. Saturated soil type. or higher. Roots and leaves grow conditions after heavy rains often Chantenay—large shoulders, short, best at temperatures of 60° to 70°F. kill the tap roots, resulting in short, usually with a large, distinctly Carrot seedlings grow rapidly dur- stubby carrots. Good drainage is colored core; used for dicing. ing cool growing conditions in the therefore as important as a suffi- These are older cultivars and spring, producing their mature- cient water supply for good carrot usually not of the quality required length tap roots in the first 3 weeks production. by processors. They are now used of growth. primarily by home gardeners. Young carrot seedlings can with- Soil Requirements and stand light frosts, but hard frosts Tillage Qualities of Good Fresh heave the soil and break the tap Market Carrots roots, which results in stubby and Carrots grow best on deep, loose, forked carrots. Young seedlings are well-drained mineral and organic burned off easily by high soils with good water holding Carrot cultivars for fresh pack in temperatures that occur before the capacity. Most Michigan carrots plastic bags should have the follow- plants are 1 inch high. are grown on deep muck soils. ing qualities: Although mature carrot leaves Sandy and marl mucks can pro- can tolerate several nights of frosts duce good carrots, but require • long (9 to 10 inches), slender, with temperatures in the mid-20°F more careful management. Sandy smooth, with small diameter range, they will be killed when and clay soils crust easily after necks (point of attachment of temperatures fall below 20°F for rains, which reduces seedling leaves) several hours. Because leaves are emergence and air penetration. If • uniform deep orange or gold needed for harvest, recoverable crusting occurs, the soil between color (including the core) yields of roots decrease as leaves rows should be worked with a • mild, sweet flavor are killed by frost. Healthy tops cultivator as soon as possible. • vigorous, blight-resistant leaves resist frost better than blighted Carrot roots are very sensitive to • high percentage of usable yield tops. soil compaction. Rows next to the Carrots require about 90 to 120 wheel track often have more forked Good cultivars should also be days to mature in Michigan, and stubbed carrots than rows in consistent producers regardless of depending on cultivar and season. the center of a bed, and usable weather and season. Unfort- Harvest of early, fresh market car- yields are reduced. Therefore, limit unately, few cultivars meet these rots begins in late July or early movement of equipment in fields qualifications. The following August. Processing carrots are as much as possible. During the cultivars have performed better harvested in September and first 3 weeks of growth, stay off the than average in Michigan trials. October. Mini carrot harvest field completely. begins in early July. Some farmers grow carrots on Carrots should not be exposed to raised beds. This allows the soil to Recommended Cultivars water stress. When irrigating, soak drain better and warm sooner in the soil completely to avoid separa- the spring. It is of most benefit on Fresh market cellopack (Tm- tion between sub-soil and surface heavy and poorly drained soils. perator type): Spartan Fancy 80, moisture. A separation between Spartan Delite 80, Six-Pak, moisture sources with a dry mid- Fertilizer Requirements Chancellor, Debut, Fanci Pak, dle zone can cause differential Grenadier, Paramount, Trophy growth and cracking. Carrots need Add lime to muck soils to main- Nantes type: Pioneer, Nantes, about 10 to 14 inches of water dur- tain a soil pH of 5.5 to 5.8; main- Scarlet Nantes ing the growing season, depending tain pH of mineral soils at 6.2 to Mini carrots: Frantes, Scarlet on the soil type and water table. 6.8. Nantes The water table should be main- It is important to maintain active Processing: Spartan Bonus 80, tained below 30 inches. foliar growth throughout the Danvers 126 Weather has an adverse affect on season to minimize damage from several quality factors. Long leaf blights. Hybrids are less susceptible to cracking caused by banded fertilizer at planting, or 4 cases, up to 50% of the roots are excess fertilizer and water than lb manganese sulfate (1 lb Mn) in undersized and cannot be packed. open-pollinated cultivars. water as a foliar spray in mid-June Seed companies are trying to im- Therefore, it is often advantageous to early July. Include Mn with in- prove uniformity of germination. to increase the nitrogen fertilizer secticide or fungicide sprays 2 or They harvest the seed at an op- rate on hybrids if blight is a 3 times to avoid deficiency later in timum time when most of it is problem. the season. mature, grade it to remove large A good nutrition program main- Boron (B) deficiency causes and small seed, leaving seed of a tains moderate to high nutrient necrosis (plant tissue death) in the relatively uniform size, dry the levels in the soil with annual addi- growing tip or internal breakdown seed, seal it in airtight containers, tions of fertilizer based on a soil in carrot roots. To avoid this prob- and keep it in refrigerated storage. test. Soil should be tested at least lem, apply 10 to 20 lb borax (1 to Some seed companies are every 2 to 3 years. Soil test levels 2 lb B) per acre in the broadcast fer- developing a seed treatment ser- for good carrot production should tilizer each year. Boron deficiency vice called priming to improve be maintained at 150 lb phosphate occurs on both sandy and muck uniformity of germination of carrot (P2O5) and 350 lb potash (K2O) per soils. seed. This process includes soak- acre. Nitrogen (N) does not ac- Copper (Cu) deficiency ing the seed in an aerated salt solu- cumulate in soil over time, so it sometimes occurs on new muck. It tion, which brings it to a uniform should be applied annually for each results in poor orange-color level of pregermination. The seed crop planted. development in carrot roots. If Cu is then dried to an optimum A 20-ton carrot crop removes levels are below 20 ppm by soil test, moisture level and sealed and about 100 lb N, 25 lb P2O5, and 100 apply 12 lb copper sulfate or 4 lb stored like unprimed seed.