Trifolium incarnatum L.

Soil Improvement (Green manure)
Soil Protection (Cover Crop)

Herbaceous winter annual legume with an erect growth habit. Can be used as a summer annual in northern areas (USDA Plant Hardiness Zones 3 and 4). Often sown in mixtures with other legumes, cereal grains, or annual ryegrass.  Crimson clover is used for pasture or hay, as a green manure or cover crop in rotation with vegetables or field crops, as a reseeding cover crop between rows in vineyards, berries, and fruit and nut orchards. It is a source of pollen and nectar for pollinators.

Identification Characteristics

Growth Season: 
Identification Characteristics: 

Inflorescence is a cylindrical or conic flower head 1-2 1/2 inches (2.5-6.5 cm) long containing many small (1/2 inch, 1.3 cm) bright scarlet (or occasionally white) florets that open in succession from the bottom to the top of the head. Plants are densely hairy. Unbranched stems reach 1-3 feet (30-90 cm) tall. Trifoliolate leaves are palmately trifoliolate, with egg- to heart-shaped leaflets 1/2 to 1 inch (1.3-2.5 cm) long, finely toothed near the tip. Stipules are elliptic, blunt, violet-veined, reddish-tipped, and mostly fused with the stem. Taproot and numerous fibrous roots extend 12-20 inches (30-50 cm) deep. Seeds are yellow and borne singly in small pods. Seeds are larger and more rounded than red clover seed, with approximately 120,000 to 150,000 seeds per pound (264,000-330,000/kg).

Growth Habit and Stand Life

Erect growth habit. Winter annual or summer annual in northern portions of the USA.

Life Cycle: 
Summer annual
Winter annual

Yield Potential and Production Profile

Seasonal growth is affected by temperature and precipitation. Early maturing species used in pasture systems based on warm-season perennial grasses.

Vegetative growth and forage availability by month have been stylistically drawn in various publications, with zones based on average annual temperature.  Crimson clover is shown here in comparison to other appropriate species for Zone A in the southeastern region of the USA, corresponding to northern Florida to southern South Carolina (mean annual temperature > 65°F, 18°C) (Ball, Hoveland, Lacefield, 2007. Southern Forages. 4th Ed. International Plant Nutrition Institute. 322 pp. ISBN 0-962-9598-6-3).

Zone A - Forage Availability


Cultivars 'Dixie,' 'Autauga,' 'Auburn,' 'Chief,' and 'Kentucky' were developed to self-reseed and have a high proportion of hard seed which is preferred for non-irrigated fall plantings. Early-maturing cultivars are best for over-seeding on summer grass sod to avoid competition, and also for green manure crops to allow early spring termination. Late cultivars have higher yields and can be grazed longer in the spring.

Climate and Soil Suitability Zones

Climate Tolerances: 

Crimson clover is a winter annual widely grown from Kentucky southward and from eastern Texas to the Atlantic Coast (USDA Hardiness Zones 6-9) and in the Pacific Northwest and California, or as a summer annual in the extreme northern US and parts of Canada (Hardiness Zones 3-4). It does not tolerate drought conditions, and requires 30 inches (760 mm) of rainfall during the growing season. Does not tolerate extreme heat or cold, with optimal growth in cool, humid conditions.

Soil Tolerances: 

Grows on poorer soils than most other clovers. Tolerates strongly acid to moderately alkaline soils (pH 5.1-8.4). Grows best on well-drained, fertile, loamy soils, but tolerates excessively drained to moderately well-drained soils. Tolerates only brief periods of flooding. Once established, it produces more biomass at lower temperatures than most other clovers.

Quantitative Tolerances: 

Crimson Clover Suitability Tolerance Values


Suitability Class

Ave Ann Extreme Min (°C/°F)*

July Max


Annual Precip (mm/in)**

Soil pH***

Soil Drainage 

Soil Salinity (dS/m)#








Moderately suited







Marginally suited







*USDA Plant Hardiness Zones 7a-9a - based on average annual extreme minimum temperature; as a winter annual in the southeast and west coastal areas; Zones 3-4 as a summer annual in northern US and Canada.  Heat zones <=88=92; 32°C/90°F.

Latitude and longitude delimitations: winter annual – 38 degrees N, 96 degrees W; summer annual from 40-50 degrees N.

** Precipitation requirements: 30 inches (760 mm during the growing season).

Rooting depth: 20 inches (50 cm).

*** Soil pH tolerance: NRCS Range and Pasture Handbook, Chapter 3 classification for crimson clover is strongly acid to moderately alkaline (5.1-8.4).

† Soil drainage: NRCS Range and Pasture Handbook, Chapter 3 classification for crimson clover is MWD-ED. Soil drainage class abbreviations: 1=VPD, very poorly drained; 2=PD, poorly drained; 3=SPD, somewhat poorly drained; 4=MWD, moderately well drained, 5=WD, well drained; 6=SED, somewhat excessively drained; 7=ED, excessively drained. Percent relative yield for crimson clover for the 7 classes: 0, 25, 50, 87, 100, 87, 75.

Flooding Tolerance: Brief (3-6 days).

# Soil salinity tolerance: NRCS Range and Pasture Handbook, Chapter 3 classification for clovers (alsike, Berseem, white, red, strawberry) is Moderately Sensitive (1.5-3 DS/m). No specific listing for Crimson. 




Suitability Maps

Historically, maps have been drawn based on primary use areas, showing broad geographic areas, e.g. Compendium of Common Forages maps within Forages: An Introduction to Grassland Agriculture, 7th ed. (2018), John Wiley & Sons, Inc.

(Crimson clover adaptation and use map.)

Crimson Clover SARE Cover Crop Map


(Crimson clover SARE cover crop map. Source: Managing Cover Crops Profitably, 3rd Ed., Sustainable Agriculture Research & Education.)

More highly detailed maps, based on quantitative climatic and soil factor tolerances and using GIS spatial grids, provide information on where species are suitable for a variety of intended uses.

The following collection of maps were developed by a group of Oregon State University scientists, using the PRISM-generated collection of climate factor grids and the NRCS soil characteristics database.

Quantitative Tolerances GIS-based Maps

Climate Factors Soil Factors Combined Factors

Minimum Temperature


Climate and Soil

Maximum Temperature


All Soil



All Climate


Quality and Antiquality Factors

Quality Factors: 

Highly nutritious forage, over 25% crude protein that can be 80% digestible in early spring growth, and even at full bloom may contain 12-14% crude protein and 60-65% digestible nutrients on a dry matter basis.

Anti-quality Factors: 

Use in mixtures with grasses to reduce risk of bloat. Bloat much less likely in animals grazing crimson clover than white clover or alfalfa. Flower heads on overly-mature crimson clover are problematic for horses, harvest hay promptly as it begins to bloom.


Species Selection Characteristics

Annual Precipitation (inches): 
36 to 40
40 to 50
50 to 60
60 to 70
70 to 80
80 to 100
100 to 120
120 to 140
140 to 160
> 160
Plant Hardiness Zones (cold tolerance): 
Heat Zone (July Mean Max Temperature): 
< 14 °F
14 to 18 °F
18 to 22 °F
22 to 26 °F
26 to 30 °F
30 to 34 °F
34 to 38 °F
38 to 42 °F
42 to 46 °F
46 to 50 °F
50 to 53 °F
53 to 56 °F
56 to 59 °F
59 to 62 °F
62 to 65 °F
65 to 68 °F
68 to 71 °F
71 to 74 °F
74 to 77 °F
77 to 80 °F
80 to 84 °F
84 to 88 °F
88 to 92 °F
Soil pH Tolerance: 
Strongly acid, 5.1–7.3
Moderately acid, 5.6–7.3
Moderately acid to moderately alkaline, 5.6–8.4
Slightly acid to moderately alkaline, 6.1–8.4
Near neutral, 6.1–7.3
Soil Drainage Tolerance: 
somewhat poorly drained
moderately well drained
well drained
somewhat excessively drained
excessively drained
Flooding Tolerance: 
3-6 days
Soil Salinity Tolerance: 
Moderately sensitive, 1.5–3 dS/m

Management Level Required

Suitable Management Level: 

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