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CRIMSON CLOVER
Trifolium incarnatum
Type: winter annual or summer annual legume
Roles: N source, soil builder, erosion prevention,
reseeding inter-row ground cover, forage
Mix with: rye and other cereals, vetches, annual ryegrass,
subclover, red clover, black medic
See charts, p. 66 to 72, for ranking and management summary.
With its rapid, robust growth, crimson clover provides early spring
nitrogen for full-season crops. Rapid fall growth, or summer growth
in cool areas, also makes it a top choice for short-rotation niches
as a weed suppressing green manure. Popular as a staple forage and
roadside cover crop throughout the Southeast, crimson clover is gaining
increased recognition as a versatile summer-annual cover in colder
regions. Its spectacular beauty when flowering keeps it visible even
in a mix with other flowering legumes, a common use in California
nut groves and orchards. In Michigan, it is used successfully between
rows of blueberries.
BENEFITS
Nitrogen source. Whether you use it as a spring
or fall N source or capitalize on its vigorous reseeding ability
depends on your location. Growers in the “crimson clover zone”—east
of the Mississippi, from southern Pennsylvania and southern Illinois
south—choose winter annual crimson clover to provide a strong,
early N boost. In Hardiness Zone 8—the warmer half of the
Southeast—crimson clover will overwinter dependably with only
infrequent winterkill. Its N contribution is 70 to 150 lb./A .
Reseeding cultivars provide natural fertility to corn and cotton.
Crimson clover works especially well before grain sorghum, which
is planted later than corn. It is being tested extensively in no-till
and zone-till systems. One goal is to let the legume reseed yearly
for no-cost, season-long erosion control, weed suppression and nitrogen
banking for the next year.
Along the northern edge of the “crimson clover zone,”
winterkill and fungal diseases will be more of a problem. Hairy
vetch is the less risky overwintering winter annual legume, here
and in northern areas. Crimson clover often can survive winters
throughout the lower reaches of Zone 6, especially from southeastern
Pennsylvania northeast to coastal New England (195).
Crimson clover is gaining popularity as a winter-killed annual,
like oats, in Zones 5 and colder. Planted in late summer, it provides
good groundcover and weed control as it fixes nitrogen from the
atmosphere and scavenges nitrogen from the soil. Its winterkilled
residue is easy to manage in spring.
Biomass. As a winter annual, crimson clover can
produce 3,500 to 5,500 lb. dry matter/A and fix 70 to 150 lb. N/A
by mid-May in Zone 8 (the inland Deep South). In a Mississippi study,
crimson clover had produced mature seed by April 21, as well as
5,500 lb. DM and 135 lb. N/A. The study concluded that crimson clover
is one of several winter annual legumes that can provide adequate
but not excessive amounts of N for southern grain sorghum production
(22, 36,
105). Crimson clover has produced
more than 7,000 lb. DM/A several times at a USDA-ARS site in Beltsville,
MD., where it produced 180 lb. N and 7,800 lb. DM/A in 1996 (412).
In field trials of six annual legumes in Mississippi, crimson clover
was found to produce the most dry matter (5,600 to 6,000 lb./A)
compared to hairy vetch, bigflower vetch, berseem clover, arrowleaf
clover (Trifolium vesiculosum) and winter peas. It produced
99 to 130 lb. N/A and is recommended for soil erosion control because
of its high early-autumn dry matter production (426).
As a summer annual in lower Michigan, a midsummer planting of crimson
clover seeded at 20 lb./A produced 1,500–2,000 lb. dry matter
and 50-60 lb. N/A by late November (270).
Mixtures. Crimson clover grows well in mixtures
with small grains, grasses and other clovers. An oats crop is a
frequent companion, either as a nurse crop to establish a clear
stand of crimson clover, or as a high-biomass, nutrient-scavenging
partner. In California, crimson clover is planted with rose clover
and medics in orchards and nut groves to minimize erosion and provide
some N to tree crops (422).
Beneficial habitat and nectar source. Crimson
clover has showy, deep red blossoms 1/2 to 1 inch long. They produce
abundant nectar, and are visited frequently by various types of
bees. The blooms may contain many minute pirate bugs, an important
beneficial insect that preys on many small pests, especially thrips
(422). In Michigan, crimson
increased blueberry pollination when planted in row middles. Georgia
research shows that crimson clover sustains populations of pea aphids
and blue alfalfa aphids. These species are not pests of pecans,
but provide alternative food for beneficial predators such as lady
beetles, which later attack pecan aphids.
Nutrient cycler. Crimson clover adds to the soil
organic N pool by scavenging mineralized N and by normal legume
N fixation. The scavenging process, accomplished most effectively
by grasses, helps reduce the potential for N leaching into groundwater
during winter and spring (181,
265). Mixed with annual ryegrass
in a simulated rainfall study, crimson clover reduced runoff from
the herbicide lactofen by 94 percent and norflurazon and fluometuron
by 100 percent (346). The grass/legume
mixture combines fibrous surface roots with short tap roots.
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CRIMSON CLOVER
(Trifolium incarnatum) |
MANAGEMENT
Establishment & Fieldwork
Crimson clover will grow well in about any type of well drained
soil, especially sandy loam. It may fare poorly on heavy clay, waterlogged,
extremely acid or alkaline soils. Once established, it thrives in
cool, moist conditions. Dry soil often hinders fall plantings in
the South.
Inoculate crimson clover if it hasn’t been grown before.
Research in Alabama showed that deficiencies of phosphorus or potassium—or
strongly acidic soil with a pH of less than 5.0— can virtually
shut down N fixation. Nodules were not even formed at pH 5.0 in
the test. Phosphorus deficiency causes many small but inactive nodules
to form (188).
Winter annual use. Seed six to eight weeks before
the average date of first frost at 15 to 18 lb./A drilled, 22 to
30 lb./A broadcast. As with other winter legumes, the ideal date
varies with elevation. In North Carolina, for example, the recommended
seeding dates are three weeks later along the coast than in the
mountains.
Don’t plant too early or crimson clover will go to seed in
the fall and not regrow in spring until the soil warms up enough
to germinate seeds. Early to mid-August seeding is common in the
northern part of crimson clover’s winterannual range. In southern
Michigan (Zone 5b - 6a) crimson clover, no-tilled into wheat stubble
in mid-July, not only grew well into fall, but thrived the following
spring, performing nearly as well as hairy vetch (270).
While October plantings are possible in the lower Mississippi Delta,
an August 15 planting in a northern Mississippi test led to higher
yields than later dates (228).
In the lower Coastal Plain of the Gulf South, crimson clover can
be planted until mid-November.
Nutrient release from crimson clover residue— and that of
other winter annual legumes—is quicker if the cover crop is
tilled lightly into the soil. Apart from erosion concerns, this
fertility enhancing step adds cost and decreases the weed-suppression
effect early in the subsequent crop’s cycle.
Summer annual use. In general, plant as soon as
all danger of frost is past. Spring sowing establishes crimson clover
for a rotation with potatoes in Maine. In Michigan, researchers
have successfully established crimson clover after short-season
crops such as snap beans (229,
270).
In Northern corn fields, Michigan studies showed that crimson clover
can be overseeded at final cultivation (layby) when corn is 16 to
24 inches tall. Crimson clover was overseeded at 15 lb./A in 20-inch
bands between 30-inch rows using insecticide boxes and an air seeder.
The clover established well and caused no corn yield loss (295).Crimson
clover has proved to be more promising in this niche than black
medic, red clover or annual ryegrass, averaging 1,500 lb. DM/A and
more than 50 lb. N/A (270).
In Maine, spring-seeded crimson clover can yield 4,000 to 5,000
lb. DM/A by July, adding 80 lb. N/A for fall vegetables. Mid-July
seedings have yielded 5,500 lb./A of weed-suppressing biomass by
late October. Summer-annual use is planned with the expectation
of winterkill. It sometimes survives the winter even in southern
Michigan (270), however, so
northern experimenters should maintain a spring-kill option if icy
winds and heaving don’t do the job.
In California, spring sowing often results in stunting, poor flowering
and reduced seed yield, and usually requires irrigation (422).
Rotations. In the South, crops harvested in early
fall or sown in late spring are ideal in sequence with crimson clover.
Timely planting of crimson clover and its rapid spring growth can
enable it to achieve its maximum N contribution, and perhaps reseed.
While corn’s early planting date and cotton’s late harvest
limit a traditional winter-annual role for crimson clover, strip
planting and zone tillage create new niches. By leaving unkilled
strips of crimson clover to mature between zonetilled crop rows,
the legume sets seed in May. The majority of its hard seed will
germinate in fall.
Kill crimson clover before seed set and use longer season cultivars
where regrowth from hard seed would cause a weed problem.
Researchers have successfully strip-tilled into standing crimson
clover when 25 to 80 percent of the row width is desiccated with
a herbicide or mechanically tilled for the planting area. Narrower
strips of crimson clover increased weed pressure but reduced moisture
competition, while wider strips favored reseeding of the cover (236).
In a crimson clover-before-corn system, growers can optimize grain
yields by no-tilling into the crimson clover and leaving the residue
on the surface, or optimize total forage yield by harvesting the
crimson clover immediately before planting corn for grain or silage
(204). In Mississippi, sweet
potatoes and peanuts suffered no yield or quality penalty when they
were no-tilled into killed crimson clover. The system reduced soil
erosion and decreased weed competition (35).
In Ohio, crimson clover mixed with hairy vetch, rye and barley
provided a fertility enhancing mulch for no-till processing tomato
transplants. Use of a prototype undercutter implement with a rolling
harrow provided a good kill. Because the wide blades cut just under
the soil surface on raised beds, they do not break stalks, thus
lengthening residue durability. The long-lasting residue gave excellent
results, even under organic management without the herbicides, insecticides
or fungicides used on parallel plots under different management
regimes. Nancy Creamer at the University of North Carolina is continuing
work on the undercutter and on cover crops in organic vegetable
systems (96).
Mixed seeding. For cover crop mixtures, sow crimson
clover at about two-thirds of its normal rate and the other crop
at one third to one-half of its monoculture rate. Crimson clover
development is similar to tall fescue. It even can be established
with light incorporation in existing stands of aggressive grasses
after they have been closely mowed or grazed.
Reseeding. Overwintered crimson clover needs sufficient
moisture at least throughout April to produce seed (130).
Cultivar selection is critical when early spring maturity is needed.
DIXIE and CHIEF are full-season standards. AU ROBIN and FLAME beat
them by about two weeks; a new cultivar, AU SUNRISE, is reportedly
1-3 weeks earlier; the popular TIBBEE is about a week ahead of the
standards. Price varies more by seasonal supply than by cultivar.
Killing. Its simple taproot makes crimson clover
easy to kill mechanically. Mowing after early bud stage will kill
crimson clover. Maximum N is available at late bloom or early seed
set, even before the plant dies naturally. Killing earlier yields
less N—up to 50 lb. N/A less at its late vegetative stage,
which is about 30 days before early seed set (342).
A rolling stalk chopper flattens a mix of crimson clover, hairy
vetch and rye ahead of no-till vegetable transplanting at Steve
Groff’s farm in southeastern Pennsylvania. The crimson is
killed completely if it is in full bloom; and even early bloom is
killed better than vegetative crimson.
Pest Management
Crimson clover is a secondary host to plant pests of the Heliothus
species, which include corn earworm and cotton bollworm. Despite
its known benefits, crimson clover has been eradicated from many
miles of roadsides in Mississippi at the request of some Delta farmers
who suspect it worsens problems from those pests (106).
Crimson clover doesn’t significantly increase risk of Southern
corn rootworm in no-till corn, while hairy vetch does (67).
It is more resistant to diseases (422)
and to some nematodes than other clovers (337).
Crimson clover is said to tolerate viral diseases, but it succumbed
to virus in July plantings in Mississippi (228)
and to Sclerotinia in fall plantings in Maryland (108).
In lab tests, crimson clover, berseem clover and hairy vetch have
been shown to inhibit germination and seedling development of onion,
carrot and tomato (40). However,
this interference hasn’t been observed in North Carolina field
crops where strips are mechanically tilled, or in other studies
with crimson clover as part of a killed organic mulch. No-till vegetable
transplanting has been done successfully on the same day as mechanically
killing the cover crop mix on Steve Groff’s Lancaster County,
Pa., farm with no negative effects.
Wait two to three weeks after killing before planting seeds, to
allow the biomass to begin to decompose and the soil biological
life to stabilize. During this time, a flush of bacteria such as
Pythium and Rhizoctonia attack rapidly decaying
plants. These bacteria also can attack seedling crops. To plant
more quickly, mow the clover and use row cleaners to clear the tops
from the seed zone. The mow/wait/plant cycle also may be influenced
by the need to wait for rain to increase seedbed moisture.
Mixed with hairy vetch, crimson clover attracts beneficial insects,
provides nitrogen and suppresses weeds in Oklahoma ’s native
and plantation pecan groves. Both legumes go to seed and then are
harvested for forage. Arrowleaf clover provided more biomass and
N, but didn’t work as well for insect pest management and
is very susceptible to root knot nematode.
Crimson clover harbors flower thrips and is a more likely host
for tarnished plant bug than hairy vetch or subterranean clover
(56). Intensive screenings show
less abundant arthropod herbivores and predators on crimson clover
than on hairy vetch (206).
Tillage practices and residue management variations (no-till, incorporate,
removal) of cover cropped lupin, rye, hairy vetch or crimson clover
had little consistent effect on nematodes in north Florida corn
fields (264).
Other Options
Pasture and hay crop. Crimson clover is excellent
for grazing and haying. It will regrow if grazed or mowed no lower
than 3 or 4 inches before the early bud stage. Mixing with grass
reduces its relatively low bloat risk even further. Timely mowing
four to six weeks before bloom improves growth, reduces lodging
and will cause more uniform flowering and seed ripening on highly
fertile soils (120, 422).
Crimson clover can be grazed lightly in the fall, more intensively
in the spring and still be left to accumulate N and/or set seed
with little reduction in its soil N contribution, provided livestock
are removed before flowering (80).
COMPARATIVE NOTES
Crimson clover is:
 less
tolerant of mowing than are subclovers or medics (422)
similar
to hairy vetch and Austrian winter pea in the Southeast for total
N production
a better
weed suppressor in fall than hairy vetch
earlier
to mature in spring than hairy vetch Cultivars. See Reseeding
for cultivar comparisons.
Seed Sources. See Seed
Suppliers.
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