Henbit, Lamium amplexicaule L.

Purple deadnettle, Lamium purpureum L.

Identification

Other common names:

  • Henbit: bee nettle, blind nettle, giraffe head, dead nettle, henbit dead nettle, henbit nettle
  • Purple deadnettle: red deadnettle

Family: Mint family, Lamiaceae

Habit: Henbit is a winter annual or summer annual, sprawling with upward curving stems that root at the nodes. Purple deadnettle is a sprawling winter annual with stems rooting at the nodes.

Description: Seedlings have stalked cotyledons with two lobes at the base and a flat to shallowly indented tip. Young leaves are opposite with large, rounded teeth and distinct stalks.

  • Henbit: Cotyledons are round to thumb shaped and 0.13–0.5 inch long by 0.1–0.2 inch wide. Seedling stems are purple. The upper leaf surfaces and prominent veins on the underside of the leaf are covered with fuzzy hairs. Young leaves are round in outline and have two to four teeth per side. 
  • Purple deadnettle: Cotyledons are oval shaped, red-stalked, hairless and 0.47 inch long by 0.43 inch wide. Fuzzy hairs are present on the blades and edges of young leaves. Young leaves are round to broadly egg or heart shaped, and they have two to four teeth per side with one large lobe at the tip.

Mature plants have square, green to purple-tinged, weak stems that branch in a prostrate or leaning manner at the base with tips curving upright. Leaves are opposite and heavily cross-veined, giving the surface a wrinkled appearance. The distance between leaves shortens near stem tips, especially flowering tips. The fibrous root system is shallow and supplemented by roots growing from stem-leaf junctions in contact with the ground. 

  • Henbit: Stems have downward pointing hairs and purple tinges; they can reach 4–16 inches tall. Lower leaves are stalked and similar in appearance to seedling leaves. Upper, stalk-less, fan shaped leaves encircle the stem almost completely. Leaves are broadly round-toothed to lobed, softly hairy, strongly veined, round tipped and 0.5–2 inch long (lower) or broad (upper). 
  • Purple deadnettle: Stems are hairless to lightly hairy, streaked purple and hollow; they can reach 4–20 inches tall. Lower leaves are stalked and similar in appearance to seedling leaves. Upper, small-stalked leaves are maroon, angle down to the ground and do not encircle the stem. Leaves are shallowly lobed, lightly hairy, pointy tipped and 0.4–0.5 inch long. 

Flowers are whorled in circles set just above upper leaf pairs. 

  • Henbit: Six to 10 pink to dark purple flowers are present per leaf pair. Flowers near stem tips are 0.5–0.75 inch long, with lightly hairy petals fused into a flared tube. Flowers on lower whorls never fully open; they are small, inconspicuous and self-pollinating.
  • Purple deadnettle: Three to six flowers are present per leaf pair. Flowers have 0.5–0.7 inch-long, fused petals that are partially wrapped by green structures and are hidden from view by leaf pairs.

Fruit and seeds: Four brown, egg- or thumb-shaped, 0.06 inch-long, nut-like seeds are produced per flower. Nutlets have two flat sides, one round side and white spots.

  • Henbit: Nutlets are long and tapered to a flat tip.
  • Purple deadnettle: Nutlets are bumpy, broader and rounder than henbit nutlets.

Similar species: Young Persian speedwell (Veronica persica Poir.) has similar leaves but is distinguishable by its round stems and blue or white flowers. Ground ivy (Glechoma hederacea L.) also has blue flowers and leaves that are long stalked, triangularly toothed and have a shiny surface. Ground ivy, however, is a strongly aromatic, mat-forming perennial with creeping stems. Spotted deadnettle (Lamium maculatum L.) has white spots on the leaves, and healall (Prunella vulgaris L.) has larger, round tipped, largely untoothed, egg-shaped or lanceolate leaves. 

Management

Tillage in late fall is effective for killing purple deadnettle and fall emerging henbit to prevent seed production the next spring. Unfortunately, soils are often too wet for tillage that time of year, and fall tillage leaves soil exposed to winter erosion. Flame weeding is an effective alternative. If the stand is dense, reduce ground speed to ensure that sufficient heat reaches the base of the plant. In areas where spring germinating henbit is a problem, tillage for late spring planted crops will destroy mid- to late-emerging cohorts, but early emerging plants may already have set seed. Thus, tillage or flame weeding in late April may be necessary in addition to tillage in May. In vegetable systems, an early planted crop of transplanted lettuce may become weedy with spring henbit, but the tillage before and after planting can be effective for breaking the weed’s life cycle.

Cultivation of cool season vegetable crops to control henbit and purple deadnettle will be more successful if these weeds are small. The spreading, fibrous root system of plants with several nodes holds soil well, and in cool weather the plants are slow to dry and can easily reroot. They are especially difficult to kill after stems begin to root at the nodes. For controlling purple deadnettle and fall emerging henbit in winter grains, till and plant midway in the planting window to allow a large proportion of seedlings to emerge first but still produce a competitive crop. Seed at a heavy rate to allow aggressive tine weeding after crop establishment, and try to rotary hoe or tine weed before crop emergence as well. Plant spring grains as early as possible to get the crop established before peak henbit emergence. Weed as for the winter grains. If planting of spring grains has to be delayed, consider planting a later crop species instead so that tillage will kill off the henbit after it emerges.

Management of winter cover crops is critical for effective long-term control of both species in a vegetable rotation. If fall rye or forage radish cover crops establish quickly and produce a high amount of ground cover, then henbit and purple deadnettle will be severely suppressed. However, fall cover crops that do not establish well and leave significant gaps in the leaf canopy will allow either of these weeds to establish and set seed before cover crop termination in spring. One alternative is to shift to an earlier planted cover crop of a winter hardy clover. Use buckwheat as a nurse crop so that the clover does not become weedy with summer annuals, and mow it before seeds form. The lack of late summer/fall tillage and the low light under the clover will reduce henbit and purple deadnettle emergence, and the clover will compete strongly with plants that do emerge. Use a high seeding rate of clover to ensure a dense, competitive stand. In regions with hot, sunny summers, solarization can effectively destroy the surface henbit seed bank to prepare the soil for fall crops.

Purple deadnettle is particularly adapted to the moist, protected soil environment of fields with incomplete crop residue cover left untilled over winter. However, complete ground cover by wheat straw reduced henbit density by 77% relative to a no-straw control following minimum tillage and completely suppressed henbit in an organic no-till crop of winter fava beans.

Ecology

Origin and distribution: Both species are native to the Mediterranean region of Eurasia and North Africa. Henbit has spread throughout Europe and much of Asia, and it has been introduced into Australia, New Zealand, North America and temperate and mountainous parts of South America. It occurs throughout the United States and southern Canada. Purple deadnettle is now a weed across most of Europe, North America and New Zealand. It is most common in the eastern half of the United States and along the Pacific Coast, including Alaska. It occurs only sporadically in the High Plains and Intermountain West.

Seed weight: Henbit population mean seed weight ranges from 0.5–0.6 mg. Purple deadnettle mean seed weight ranges from 0.65–0.92 mg.

Dormancy and germination: Henbit seeds are dormant when shed from the parent plant. After exposure to high summer temperatures for several weeks, seeds from Kentucky populations germinate well at any temperature regimen from 41°F to 86/68°F day/night. Both dormant seeds and seeds that have lost dormancy through warm summer temperatures become conditionally dormant during exposure to winter temperatures (e.g., 41°F) and then will only germinate well at temperatures below 68/50°F. Consequently, seeds germinate in hot weather in the late summer or in cool weather in the fall or early spring, but not in the warm weather of late spring or summer. This ensures that the plants will have time to grow during cool seasons of the year. In the cold climate of Sweden, dormancy was broken by a long (24 weeks) period of warm, dry conditions, and emergence in the field occurred almost entirely in the spring. Another study showed that non-dormant seeds of henbit germinated best at 68°F. 

Purple deadnettle seeds are also dormant when shed in the spring. Hot summer temperatures break dormancy of seeds from Kentucky by late spring or early summer, but germination is inhibited by hot summer temperatures of 86/59°F or higher. When temperatures cool in the fall to 68/50°F or lower, the seeds can then germinate. A few weeks of cold winter temperatures (e.g., 41°F) induce a secondary dormancy so that the seeds will not germinate in the same mild temperatures in the spring that allowed germination in the fall. This secondary dormancy is again broken by hot temperatures in late spring or early summer, and the cycle repeats. This dormancy cycle causes purple deadnettle to act as a strict winter annual, at least in the central United States. In Sweden, warm moist or dry conditions break dormancy as in the central United States. However, most emergence occurs in the spring, implying that cold temperatures during the winter do not induce dormancy. In Sweden, seedlings emerging in the fall often die without reproducing. Dormancy cycles in the northern United States and Canada require study.

Germination of non-dormant seeds of both species is generally stimulated by light, although one study found that light inhibited germination of henbit.

Seed longevity: Viable seeds of both species have been found beneath medieval ruins in Europe, but such sites are favorable for long-term seed survival. Roughly 20–50% of henbit seeds survived 20 years under sod. Purple deadnettle seeds in annually tilled winter wheat and oilseed crops declined by 39% and 60% per year. In another experiment, purple deadnettle seed density declined at an average of only 20% per year, with the decline faster in spring wheat than in winter wheat. Average seed loss over a five-year period from soil stirred three times per year was 43–60% per year for henbit and 43–53% per year for purple deadnettle. 

Season of emergence: Henbit emerges in mid-spring and in early autumn, but emergence is primarily in autumn in the South and primarily in spring in the prairie provinces of Canada. In Michigan, emergence occurs from spring to fall, with peak emergence in late summer. Purple deadnettle emerges only in autumn in Kentucky, throughout the growing season with a peak in autumn in England, and primarily in the spring in Sweden. 

Emergence depth: Most seedlings of henbit and purple deadnettle emerge from the top 1 inch of soil, though a few can emerge from as deep as 2.5 inches. One study sampled the effective seed bank of these species by taking cores only 0.5 inch deep, indicating that the researchers thought most seedlings emerged only from that shallow surface layer of the soil. 

Photosynthetic pathway: C3

Sensitivity to frost: Both species are frost tolerant. Henbit can tolerate temperatures down to 22°F but suffers some damage at that temperature. Fall emerging plants of both species can overwinter in the northern United States, but snow cover likely improves survival substantially. 

Drought tolerance: Henbit is drought-intolerant.

Mycorrhiza: Both species are mycorrhizal.

Response to fertility: Henbit response to N was intermediate among 24 weeds and crops studied and was roughly similar to wheat. Of the same 24 species, it was among the group of species most responsive to P fertility. In another experiment, however, four years of manure or compost either with or without additional sulphate of ammonia had negligible effects on late spring henbit density in vegetable crops. Eight years of application of various N fertilizers decreased henbit relative to plots that received no N, probably because increased vigor of fertilized winter grains suppressed the low growing henbit. On a sandy soil, henbit was insensitive to pH from 5 to around 7, but below pH 5 density decreased, although its proportion of the weeds present increased. 

Soil physical requirements: Henbit is often found in light, sandy soils but occurs on a range of rich agricultural soils. Purple deadnettle is usually found in rich, loamy or sandy-loam soils.

Response to shade: Henbit is shade intolerant. Purple deadnettle partially avoids shade through increased stem elongation in environments with competition from other plants. 

Sensitivity to disturbance: Fragments of purple deadnettle reroot readily after shallow tillage or hoeing. 

Time from emergence to reproduction: In warm climates, fall germinating henbit flowers in late winter to early spring. In the northern United States and southern Canada, fall germinating plants flower from April to June. Spring germinating plants emerging in early April in Wisconsin began flowering 36 days later, but some spring and summer emerging plants in the northern United States do not flower until September. Purple deadnettle flowers from late March/early April to mid-May in Ohio. A relatively short time is required for viable seed to be produced after flowering, because peak shedding of henbit seeds occurred in mid-May, within a month from when flowering began. 

Pollination: Henbit forms closed self-pollinating flowers on the lower nodes and sometimes on the whole plant, but it often produces open, cross-pollinated flowers at the upper nodes. Pollination is by solitary bees and honeybees. Purple deadnettle self-pollinates, but it is also pollinated by bumblebees and other bee species. 

Reproduction: A typical henbit plant produces between 200–2,000 seeds, but a particularly large plant produced 60,000 seeds. Purple deadnettle produces about 600 seeds per plant but can produce 27,000 seeds if grown without competition. Purple deadnettle spreads as a mat of stems that root at the nodes; if fragmented by tillage, rooted stem sections can re-establish.

Dispersal: Both species form persistent seed banks and probably commonly disperse in soil clinging to farm machinery and the bodies of cattle. Purple deadnettle seeds have been found in soil adhering to an automobile traveling in rural areas and also in commercial topsoil. Seeds of both species have specialized bodies that provide a food source attractive to non-seed-eating ants. These presumably encourage dispersal by ants.

Common natural enemies: Both species are favored food sources for a variety of slug species. 

Palatability: These species are sometimes eaten as salad or pot herbs, particularly in Japan. Henbit has digestibility, crude protein and mineral content similar to or higher than common forage grasses. Grazing on henbit can cause mild neurological problems in sheep, cattle and horses, but the condition is rare and reversible. Purple deadnettle has no reported toxic properties for ruminants.

Weed Characteristics Summary Table

Henbit
Purple deadnettle
Growth habitSeed weight (mg)Seed dormancy at sheddingFactors breaking dormancyOptimum temperature for germination (F)Seed mortality in untilled soil (%/year)Seed mortality in tilled soil (%/year)Typical emergence seasonOptimum emergence depth (inches)
short, sprawling0.5–0.6
0.65–0.92
Yeswst, li, at41–682039–60late summer to fall, spring0–1
Photosynthesis typeFrost toleranceDrought toleranceMycorrhizaResponse to nutrientsEmergence to flowering (weeks)Flowering to viable seed (weeks)Pollination Typical & high seed production (seeds per plant)
C3highlowyesmoderate2–52–4both1,000 & 50,000

Table Key

General: The designation “–” signifies that data is not available or the category is not applicable.

Growth habit: A two-word description; the first word indicates relative height (tall, medium, short, prostrate) and second word indicates degree of branching (erect, branching, vining).

Seed weight: Range of reported values in units of “mg per seed.”

Seed dormancy at shedding: “Yes” if most seeds are dormant when shed, “Variable” if dormancy is highly variable, “No” if most seeds are not dormant.

Factors breaking dormancy: The principle factors that are reported to break dormancy and facilitate germination. The order of listing does not imply order of importance. Abbreviations are:

scd = seed coat deterioration

cms = a period subjected to cold, moist soil conditions

wst = warm soil temperatures

li = light

at = alternating day-night temperatures

ni = nitrates

Optimum temperature range for germination: Temperature (Fahrenheit) range that provides for optimum germination of non-dormant seeds. Germination at lower percentages can occur outside of this range. The dash refers to temperature range, and the slash refers to alternating day/night temperature amplitudes.

Seed mortality in untilled soil: Range of mortality estimates (percentage of seed mortality in one year) for buried seeds in untilled soil. Values were chosen where possible for seeds placed at depths below the emergence depth for the species and left undisturbed until assessment. Mortality primarily represents seed deterioration in soil.

Seed mortality in tilled soil: Range of mortality estimates (percentage of seed mortality in one year) for seeds in tilled soil. Values were chosen for seeds placed within the tillage depth and subjected to at least annual tillage events. Seed losses are the result of dormancy-breaking cues induced by tillage, germination and deterioration of un-germinated seeds.

Typical emergence season: Time of year when most emergence occurs in the typical regions of occurrence for each weed. Some emergence may occur outside of this range.

Optimum emergence depth: Soil depths (in inches below the soil surface) from which most seedlings emerge. Lower rates of emergence usually will occur at depths just above or just below this range.

Photosynthesis type: Codes “C3” or “C4” refer to the metabolic pathway for fixing carbon dioxide during photosynthesis. Generally, C3 plants function better in cooler seasons or environments and C4 plants function better in warmer seasons or environments.

Frost tolerance: Relative tolerance of plants to freezing temperatures (high, moderate, low).

Drought tolerance: Relative tolerance of plants to drought (high, moderate, low).

Mycorrhiza: Presence of mycorrhizal fungi. “Yes” if present; “no” if documented not to be present, “unclear” if there are reports of both presence and absence; “variable” if the weed can function either with or without, depending on the soil environment.

Response to nutrients: Relative plant growth response to the nutrient content of soil, primarily N, P, K (high, moderate, low).

Emergence to flowering: Length of time (weeks) after emergence for plants to begin flowering given typical emergence in the region of occurrence. For species emerging in fall, “emergence to flowering” means time from resumption of growth in spring to first flowering.

Flowering to viable seed: Length of time (weeks) after flowering for seeds to become viable.

Pollination: “Self” refers to species that exclusively self-pollinate, “cross” refers to species that exclusively cross-pollinate, “self, can cross” refer to species that primarily self-pollinate, but also cross-pollinate at a low rate, and “both” refers to species that both self-pollinate and cross-pollinate at relatively similar rates.

Typical and high seed production potential: The first value is seed production (seeds per plant) under typical conditions with crop and weed competition. The second value, high seed production, refers to conditions of low density without crop competition. Numbers are rounded off to a magnitude that is representative of often highly variable reported values.

Further Reading

Baskin, J.M., C.C. Baskin and J.C. Parr. 1986. Field emergence of Lamium amplexicaule L. and L. purpureum L. in relation to the annual seed dormancy cycle. Weed Research 26: 185–190.

Defelice, M.S. 2005. Henbit and the deadnettles, Lamium spp.--archangels or demons? Weed Technology 19: 768–774. 

Hill, E.C., K.A. Renner and C.L. Sprague. 2014. Henbit (Lamium amplexicaule), common chickweed (Stellaria media), shepherd's purse (Capsella bursa-pastoris), and field pennycress (Thlaspi arvense): fecundity, seed dispersal, dormancy, and emergence. Weed Science 62: 97–106. 

Holm, L., J. Doll, E. Holm, J. Pancho and J. Herberger. 1997. World Weeds: Natural Histories and Distribution. Wiley: New York.

Lawley, Y.E., R.R. Weil and J.R. Teasdale. 2011. Forage radish cover crop suppresses winter annual weeds in fall and before corn planting. Agronomy Journal 103: 137–144.