Types and Varieties of Mint
Soil and Nutrition
Propagation and Planting
Irrigation and Drainage
Diseases and Nematodes
Condensers and Receivers
Economic Factors in Mint Farming
Yield of Oil
Price of Oil
Capital Investment and
Types and Varieties of Mint
Soil and Nutrition
Propagation and Planting
Irrigation and Drainage
Diseases and Nematodes
Condensers and Receivers
Economic Factors in Mint Farming
Yield of Oil
Price of Oil
Capital Investment and
Figure 1. Three types of mint
commonly grown in the Midwest.
Review ed by Dr. D. D. Warncke, Dept.
of Crop and Soil Sciences, and Dr. E. .J. Grafius, Dept. of
Entomology, Michigan State University
Donations from the A. M. Todd Co.,
Kalamazoo, Ml and Wm. Leman lnc.,Bremen, lN,helped defray
the costs of color reproduction and are gratefully
Figure 2. Mint production areas of the
Mint was introduced into the U.S. in colonial times and was first
grown in Massachusetts. Mint growing gradually moved westward with
the early settlers. The soils and climate of southern Michigan and
northern Indiana were so well suited to mint culture that these areas
became the major mint-producing areas of the United States by about
In 1924, Verticillium wilt was diagnosed in a field near Mentha,
Michigan. This disease gradually spread and became more severe,
eventually causing many midwestern growers to abandon mint
production. After 1950, peppermint acreage increased greatly in
Oregon and Washington, until this area is now the largest
mint-producing area in the U.S. All mint on the west coast is grown
on mineral soils (most of them light-textured) under supplemental
irrigation. Midwestern mint is grown almost entirely on drained
organic (muck) soils, usually with some supplemental irrigation.
Wisconsin now has a significant acreage of mint on mucklands which
were cleared and drained fairly recently.
The end product of mint culture is the oil produced in special
glands on the mint leaves and stems. This oil is collected in pure
form by steam distilling the mint hay. Peppermint oil is used to
flavor chewing gum, candy, toothpaste, and medicines. Spearmint oil
has a smaller market, and is used mostly to flavor toothpaste and
The main types of mint grown in the Midwest are peppermint
(Mentha piperita ) and two species of spearmint: the so-called
"native" spearmint (Mentha spicata ) and Scotch spearmint
(Mentha cardiaca ) (Fig. 1). There are no improved varieties
of native or Scotch spearmint at this time.
There are three varieties of peppermint: the Black Mitcham
variety, named after its place of origin (Mitcham, Surrey County,
England); Todd's Mitcham, named after the A.M. Todd Co., Kalamazoo,
Mich., buyers of mint oil; and Murray Mitcham, named after Dr. M. J.
Murray who was the leader in developing the Todd's Mitcham and Murray
Mitcham varieties. These last two varieties arose from some 100,000
pieces of stolon exposed to ionizing radiation to induce mutations,
and were selected after much field testing for their tolerance to
Verticillium wilt and acceptable oil flavor and quality. Murray
Mitcham is generally considered to be more vigorous, especially the
first year after planting in the Midwest, and to be slightly more
resistant to Verticillium wilt than Todd's Mitcham.
Geographical Location: In the Midwest, most mint is grown
on organic (muck) soils in Indiana, Michigan and Wisconsin north of
the 41st parallel (roughly the latitude of Fort Wayne, Indiana) (Fig.
2). Mint needs a midsummer day-length of at least 15 hours for
satisfactory yields and oil quality. This day-length cannot be
achieved south of the 40th parallel (roughly the latitude of
Soil and Nutrition: The mint plant is shallowrooted and
needs abundant water and a well- drained, rich, loose-textured soil
for good growth. Since drained muck soils meet these criteria better
than most other soils, they are most commonly used for mint
production in the Midwest. Drained muck soils have an additional
advantage: the water table can be controlled in the fields by raising
or lowering gates in the drainage ditches. This practice reduces the
need for supplemental irrigation. Maintain the water table about two
feet from the soil surface until just before harvest, and then lower
it to three feet below the surface. Loose-textured mineral soils with
abundant humus can also be used for mint production, but will require
Muck soils are subject to wind erosion during dry, windy periods
in the spring (Fig. 3). Windbreaks, usually willow, are often planted
in north-south rows at field margins to help prevent wind erosion.
Since mint is grown as a perennial crop, it is important to have
the soil as weed-free as possible prior to planting, especially of
troublesome weeds such as Canadian thistle, field bindweed, and red
root pigweed. Fall-plow the soil and disk and harrow thoroughly
before planting to reduce weed populations.
Figure 3. Wind erosion on muck soils.
Keep the pH of muck soils between 5.5 and 6.5 for mint production.
If the soil pH is below 5.5, add lime to raise the pH. Have soils
tested by a soils testing laboratory to determine fertility levels
and appropriate fertilization rates. If soil test levels are lower
than 100 pounds available phosporus per acre or 400 pounds available
potassium per acre, fertilize prior to planting first year mint.
With favorable soil fertility conditions, the equivalent of
300-500 pounds of 5-20-20 fertilizer is usually applied per acre for
first year mint on Midwest muck soils. Nitrogen is sidedressed at 20
to 25 pounds per acre when plants are 8-12 inches tall. On
established plantings, the equivalent of 250- 500 pounds of 5-20-20
fertilizer are applied broadcast and harrowed-in prior to the time
growth begins in the spring. Add additional nitrogen as a top
dressing if needed.
Mint is seldom responsive to additions of micronutrients except on
newly reclaimed acid mucks where copper applications (5 pounds per
acre) may be beneficial. Mint grown on muck soils above pH 6.5 may
benefit from manganese (5-6 pounds per acre) included in the
drilled-in fertilizer or from foliar manganese applications (1-2
pounds per acre).
Propagation and Planting: Mint is planted in late
April-early May by dropping pieces of mint stolons (also called
runners or roots) in the row with a mechanical planter (or
occasionally by hand), and covering with 2-3 inches of soil. Single
stolons laid end-to-end in the row provide a sufficient stand for
good row mint establishment. Roots and shoots soon grow from the
nodes on the stolons and establish new p lants.
Stolons are generally dug from a nursery bed or from an existing
planting in the spring, using a stolon digger (Fig. 4) or potato
digger. Dig stolons just before planting in the spring or late in the
fall. Do not plant stolons if they have sprouted beyond 2-3 inches.
The quantity of stolons required to plant an acre depends on row
spacing and how thickly stolons are planted within the row. An acre
of well-established mint that has not had significant loss due to
winter damage or other factors will usually yield enough stolons to
plant 10-l 5 acres, or sometimes as much as 20 acres.
If stolons are dug and not planted immediately. place them in
piles of moderate size and cover with soil until used. Stolons
exposed to sun or wind will wilt and lose vigor. Cover stolons as
soon as possible after they are dropped in the row, and do not plant
in dry soil. Do not make furrows too far ahead of time so that they
remain moist when stolons are planted.
Figure 4. Mint stolon harvester
Figure 5. Crop damage due to terbacil (Sinbar)
residues in soil.
Fields may be started with young plants if a late planting is
made, or if planting stock is scarce. When mint shoots are 4-6 inches
tall, loosen the soil around the base of the plants with a spading
fork, and pull the shoots (with some roots attached) from the soil.
These plants can be set in the ground with a celery or vegetable
transplanter. Heavily irrigate plants immediately after
Transplants allow later planting of the crop, which insures
against frost damage. However, transplants are more apt to be damaged
by hot, windy, or dry weather. If the soil is infested with
Verticillium, transplants are more susceptible to wilt damage in the
young bed than are plants growing from stolons. Transplants are also
more likely to become infected with rust in first year plantings.
Irrigation and Drainage: If mint is grown in muck or heavy
mineral soils in the Midwest, the soils must be well-drained. While
mint requires great amounts of water during the growing season, it
does not tolerate water-logged soils.
Mint requires about 5 acre-feet of water per year for grovvth in
the West where there is little rainfall. In the Midwest, sprinkler
irrigation is used to supplement rainfall, or at times to reduce
frost damage or wind erosion of muck soils. Mint is a very
shallow-rooted crop, so irrigate whenever the top 4 inches of soil is
so drv that it will not adhere and retain its shape when squeezed in
the hand. The water table can be controlled by adjusting the height
of the headgates in the drainage ditches.
Mint is usually plowed under after the first killing frost to
protect the stolons from winterkill. Do not plow stolons deeper than
4-5 inches, or they will not survive. Try to plow at a speed that
turns under stolons and stubble cleanly with a minimum exposed on the
The year before mint is planted, it is advisable to either (1)
plant the field to a crop which can be kept weed-free with tillage
and/or herbicides, or (2) to fallow the field with frequent disking
to eliminate as many troublesome weeds as possible. Excessive weed
populations compete with mint and reduce yields, and may contribute
off-flavors to the mint oil at harvest, resulting in lowered oil
Two herbicides, terbacil (Sinbar®) and bentazon
(Basagran®) are currently registered for use in mint crops.
Terbacil can be applied as either a preemergent or postemergent spray
in the spring. For best results, terbacil must be applied before
weeds are more than one-inch tall and followed by at least 1/2 inch of rainfall or
irrigation within 10 days. Terbacil will control most common weeds
found on muck soils if applied at the recommended rate before weeds
get too large. Redroot pigweed, for example, can be very hard to
control if terbacil is applied after plants are more than 2 inches
Terbacil has a very long residual life in soil. While this makes
season-long weed control possible with only one application of
material, it can also cause toxicity and damage in other crops
following mint (Fig. 5). Do not use terbacil within 24 months of the
planting of crops other than mint. Never apply more than 11/2 pounds
of terbacil (active ingredient) in any one year.
A simple test for terbacil residues can be done before planting a
different crop. Collect soil from various parts of the field to be
planted. Plant either oat or cabbage seeds (very sensitive to
terbacil [Sinbar] ), in small containers of these samples, and place
them in a warm (60-75°F) well-lighted place. Plant some seeds in
soil which has never had an application of terbacil
Figure 6. Diagnostic symptoms of Verticillium
for comparison. If the test seeds germinate normally and seedlings
are green, there should be no residue problem. If seedlings
germinate, and then the leaves become scorched looking, there may be
a terbacil residue problem, and sensitive crops should not be
For some of the troublesome broadleaf weeds that may escape
control with terbacil, bentazon (Basagran®) may be used
postemergence. It will control such weeds as Canada thistle, field
bindweed, ladysthumb, Pennsylvania smartweed, wild mustard, and
nutsedge. For best results, make two applications about 10 days
apart, applied when soil moisture is high and temperatures are warm.
Weeds must be relatively small and actively growing for good results.
Apply herbicides in 30-50 gallons of water per acre at 40- 60
pounds pressure using flat fan nozzles.
Diseases: Verticillium wilt, caused by the soilborne fungus
Verticillium dahliae , is the most serious and destructive pest faced
by mint growers. This fungus can survive for 10 years or longer once
its numbers have been built up in the soil, even if the soil is
continuously fallowed. The fungus can also survive indefinitely on
the roots of many plants on which it does not cause disease,
including many weed species. Thus, crop rotation is only effective in
preventing the buildup of Verticillium wilt if it is practiced from
the beginning of mint production -before the fungus is widespread and
wellestablished. Profitable mint production may be maintained almost
indefinitely by using short rotations of three years in mint followed
by three years of other crops (onion is a particularly good rotation
Verticillium wilt can be recognized by its rather distinct
symptoms. Plants are stunted because of shortened internodes, leaves
turn yellow and may eventually turn red, and opposite leaves bend
toward each other because of asymmetric growth (Fig.6). When the stem
is split with a knife, dark, discolored areas can usually be found
inside. Stands become thinned out as individual plants are killed by
the disease (Fig. 7).
Two peppermint varieties (Todd's Mitcham and Murray Mitcham) are
tolerant to Verticillium wilt and are available, in addition to the
standard Black Mitcham variety. Murray Mitcham seems to thrive better
in the Midwest, and is recommended for midwestern muck soils. These
new varieties are not immune to Verticillium wilt and may show wilt
symptoms when planted in infested soil. especially the first y ear.
However, the level of disease will be less than if the field were
planted to Black Mitcham. Murray Mitcham usually yields better than
Todd's Mitcham in first year plantings.
Figure 8. Mint rust lesions on spearmint
If mint is to be planted on soil which has never grown mint. use
disease-free planting stock. Small amounts of this stock can be
obtained either from Michigan State or Purdue Universities for
multiplication until you have sufficient rootstock to make a
commercial size planting. Also, rootstock certified to be
disease-free can be purchased from certified rootstock growers in
Oregon by contacting the Oregon Department of Agriculture, Salem,
Mint rust (Puccinia menthae ) may be damaging to spearmint
plantings in the Midwest. The rust fungus causes light-yellow,
blister-like lesions on young shoots in the spring, and brownish-red
spots surrounded by a yellow halo on the leaves later in the season
(Fig. 8). Rusted leaves may eventually drop off and defoliation of
plants can be severe. If rust has infected young shoots, the shoots
are usually twisted and distorted and break off easily at the point
of infection. In late summer and fall, leaf spots become a deep-
chocloate brown as the overwintering spores of the fungus are
There are two different types of mint rust. The rust that infects
peppermint will not infect native (common) spearmint, nor will the
rust which infects native spearmint infect peppermint. Either type of
rust can infect Scotch spearmint. However, in the Midwest. rust
unexplainably occurs only in spearmint.
Clean fall plowing of mint beds is the key to rust control in the
Midwest. The overwintering spores on the stubble, on regrowth, or on
the soil surface will be buried so that these spores cannot germinate
and infect mint shoots or leaves the following year. Eliminate wild
mint or volunteer mint in field borders so it will not serve as a
source of infection for commercial mint. There are currently no
fungicides registered for rust control in mint. An application for
label of one fungicide on mint is now pending. Consult your county
agent for most recent rust control recommendations.
Mint anthracnose or leopard spot, caused by the fungus
Sphaceloma menthae , is occasionally damaging to peppermint,
especially in Indiana. Small. sunken brown spots appear on the lower
leaves, stems and stolons, and these enlarge to form oval lesions
with light gray centers and reddish-brown borders (Fig. 9). The spots
may unite, causing defoliation (Fig. 10) and large cankers which may
lead to splitting of the stem. Similar brown spots appear on the
lower leaves, and develop light brown centers with a dark border.
Heavily infected plants are weakened and oil yields are reduced.
Anthracnose may become severe during wet seasons when mint foilage
becomes rank and remains wet for long periods.
The anthracnose fungus overwinters mainly in mint refuse rather
than in the soil. Clean fall plowing will usually prevent disease the
Figure 9. Mint anthracnose
Figure 10. Defoliation by mint
Septoria leafspot (Septoria menthae ) may cause minor
damage but is usually not a major problem.
Nematodes: The root lesion nematode (Pratylenchus
penetrans ) is commonly found on peppermint and spearmint in the
Midwest. These small microscopic eelworms feed on the roots of mint
plants, which inhibits root and plant growth. Large numbers of these
nematodes may not only stunt plant growth, but often cause plants to
show more severe Verticillium wilt symptoms than they would without
nematodes. A nematode problem is often indicated b_ localized areas
of stunted, unthrifty plants in a field. To determine if nematodes
are present, collect samples of soil containing roots from suspected
areas and submit to a nematode diagnostic laboratory for analysis.
If root-lesion nematodes have been a problem on any crop in a
field which is to be planted to mint, use a recommended soil fumigant
prior to planting. It is also important to use clean, healthy
planting stock from an area as free as possible from the root lesion
Several insect pests are troublesome on mint in the Midwest. Most
are sporadic and unpredictable. Regular scouting of fields is
necessary to observe the presence of most of the following pests:
Mint flea beetle: This beetle was first discovered in mint in
Michigan in the early 1920's. Annual production in a field with heavy
infestation of flea beetle larvae dropped from 44 pounds to 24 pounds
to 2.7 pounds. By 1929, mint flea beetle had become a serious problem
throughout mint fields in Michigan and northern Indiana. Flea beetle
problems continued in severity through the 1930's and early 1940's,
although calcium arsenate was being used as a foliar treatment for
By the mid-1940's, mint fields, especially peppermint, were
planted in 2 year rotations due to the severity of Verticillium wilt.
This short rotation had a definite effect on flea beetle populations.
From 1945 until the early 1970's, flea beetle problems were almost
nonexistent in the Midwest, due to short rotations and the widespread
use of DDT. The advent of Verticillium-resistant mint varieties made
longer rotations possible and increased the severity of damage from
The adult flea beetle is very small, about 0.25 cm
(1/10 inch) long and light tan to bronze
(Fig.11). It can usually be found in mint fields beginning about the
middle of July and appears in increasing numbers until early August.
Egg laying begins after a 2 to 3 week feeding period, most of which
is spent on the lower leaves of the plant. Because most of the adult
flea beetle activity is confined to the bottom half of mint plants,
their presence and damage may not be noticed until they are quite
numerous. Adult feeding damage appears as small, 1 to 3 mm
(1/25 to 3/25 inch)
holes, scattered across a leaf (Fig. 12). When these feeding holes
are numerous, the damage appears as shot-hole type damage. Because
these beetles feed on lower leaves, it is quite difficult to get an
accurate assessment of flea beetle populations. However, if 5 or more
adult beetles are taken per sweep with a sweep net, a field probably
has a serious problem.
Female flea beetles lay eggs in the soil near the crowns of plants
sometime in late July to early August, and continue laying eggs until
late fall. The eggs do not hatch in the fall, but remain dormant in
the soil until late April or early May. After hatching, the young
larvae feed first on the fine hair roots and then tunnel into stolons
and underground parts of the stem, where they continue to feed, for
about 4 to 5 weeks. Damage on underground parts is easily visible as
distinct tracks or tunnel marks (Fig. 13). In June, the larvae stop
feeding and pupate in the soil with adults emerging 3 to 4 weeks
The larval damage is far more serious for mint production than
adult feeding. In addition to interfering
with water and nutrient uptake, the feeding damage provides
entrance for plant pathogens and produces generalized stress on the
plants. As with other stress factors on mint, aboveground symptoms
include stunting, perhaps some wilting under extremely dry
conditions, and a general reddish-purple discoloration of new growth.
This reddish discoloration is not, however, restricted to flea beetle
feeding, nor does spearmint characteristically show this reddish
Because larval control is currently impractical, the adult stage
must be controlled in order to minimize damage. Crop rotation will
generally reduce buildup of populations of mint flea beetle. Also, if
volunteer mint on roadsides, ditch banks, and other areas is kept
down, flea beetle populations will not build up and move into new
When chemical control is used, timing is critical. Apply labeled
insecticides to the crop when the majority of adults have emerged
from the soil, but when a minimum number of eggs have been laid.
While the complete details for this have not yet been worked out, the
timing of sprays for adult flea beetle control probably falls between
July 25 and August 10. Make applications in late afternoon or evening
to reach the adults when they are most actively feeding, usually at
night and early morning. Sprays may be applied before harvest, but
insecticides may not be applied beyond the legal cut- off date
specified on the label. Sprays may also be applied after harvest.
Treat stubble within 3 days of harvest if the field had a flea
beetle problem before harvesting. Adult beetles will leave a field
soon after it is cut and migrate to adjacent volunteer mint or fields
in production. They will return as new growth appears or when
adjacent fields are cut and resume egg- laying.
Figure 13. Mint flea beetle larval
Figure 14. Mint looper larva.
Malathion is currently registered for control of flea beetle on
mint. It should be used at 1 pound active ingredient per acre. It has
a 7-day preharvest interval. Methomyl (Lannate, Nudrin®) is
registered and effective for control of variegated cutworm, looper
and flea beetle on mint. Methomyl cannot, however, be applied closer
to harvest than 14 days. Consult your county agent for the latest
pesticide recommendations on this and other insect pest problems.
Mint Looper: Several caterpillars, called loopers because
of their inchworm or looping habit, can be found feeding in both
spearmint and peppermint fields (Fig. 14). These include the mint
looper, the celery looper, and the cabbage looper. The adults of
these caterpillars are dark, nondescript moths which fly at night.
Eggs are laid singly on the leaves. Upon hatching, larvae feed on
leaf surfaces. When the larvae are larger, about 1 to 2 cm, they
begin to eat ragged-edged holes through leaves distributed from top
to bottom of the plant.
Often, the damaged leaves seen on the tops of mint plants are from
loopers. Because of the feeding damage to the leaves, large
populations may seriously affect oil accumulation and yield. While
some loopers may be found throughout the summer, the mint looper, the
most common and serious of the caterpillars, appears first about June
20 with a second brood appearing around August 10-15. The first brood
larvae of the mint looper can do serious damage in this preharvest
When fully grown, a mint looper may be as long as 5 cm with
alternating light and dark green (almost black) longitudinal stripes.
The head is likely to be dark brown to black. Other loopers are less
strongly marked than the mint looper. When necessary, loopers may be
controlled effectively with Methomyl (Lannate, Nudrin®). If
treatment is necessary closer than 14 days before harvest, Dipel will
probably give satisfactory control.
Cutworms: While several species of caterpillars, called cutworms,
can be found in peppermint and
spearmint, the most serious of these in the Midwest is the
variegated cutworm (Fig. 15). This species undergoes 3 to 5
generations per year and attacks a number of crops, including mint,
potatoes and tomatoes. The moths of this caterpillar fly at night,
laying eggs in bunches throughout the field.
Thus, caterpillars are found infesting circular areas throughout
the field. When infestations become more serious, these patches run
together giving the appearance of a uniform infestation.
Figure 15. Variegated cutworm larva.
The first generation of larvae usually appears in fields about May
25 to June 5.
After completing development, these larvae pupate in the soil with
a second group of moths appearing and larvae showing up in fields
about the first to second week in July. A third generation may be
present from the middle to the end of August.
The larvae feed on all portions of the plant, but are usually
found under the canopy rather than on the top of the plants. It is
not uncommon, however, to find larvae feeding on the terminal buds.
The mature variegated cutworm larva is about 5 cm long and varies
from pale gray to dull brown. Larvae are marked with distinctive pale
cream to yellow spots down the middle of the back. Cutworms must be
controlled before they become more than 3/4 of an inch in
Figure 16. Two-spotted spider
Two-spotted Spider Mite: Spider mites are not true insects,
but are more closely related to spiders, having 8 legs instead of 6.
They are only occasional pests in mint, but in hot, dry years may be
quite severe in some fields. Spider mites are tiny (about 0.5 mm, the
size of a period on this page) (Fig. 16). Adult mites are pale yellow
and have 2 dark spots on the body. Spider mites in low-to-moderate
populations are generally found on the undersides of leaves and feed
by sucking out cell contents. As chlorophyll is removed, the plant
takes on a mottled appearance, and eventually bronzing and browning
occurs. Heavy infestation results in leaf drop and reduced plant
When mite buildup is heavy, it is often possible to see silken
webbing on leaves and stems. The mites may be almost impossible to
see without examining the leaf surfaces with a hand lens or
microscope. One way to detect mites is to hold a white piece of paper
under the leaf or plant and strike the plant sharply. The mites will
be dislodged and can be observed crawling about on the paper.
Mites overwinter in mint fields in soil and in debris as females.
In the spring, these females begin laying eggs on undersides of
leaves. Eggs hatch in 4 to 5 days and the resulting larvae mature in
1 to 3 weeks depending upon temperature. With this rapid development,
many generations of mites may be completed in a single season and
numbers can reach damaging levels under ideal conditions. Research
data from Oregon suggest that if an average of 5 active mites are
found per leaf on a 45-leaf sample taken from 5 sites in the field,
miticide should be applied to avoid significant mite damage.
Materials to be used
for mite control are Kelthane at 1 pound active ingre per acre
applied no closer than 30 days before harvest, with one application
per season; or Metasystox-R, 3 pints per acre. It will generally take
2 applications of Metasystox-R 10 to 14 days apart to clean up
infestations, and the second or last application should not be
applied closer than 14 days before harvest. Malathion, if used for
flea beetle control, can be expected to give only partial mite
A number of other insects may be found at one time or another in
peppermint and spearmint crops. European corn borers can be found in
growing terminals of mint plants in mid- to late June and in late
August. In such cases, the top 3 to 4 inches of a stem will be found
laying over and wilted. If the stem is split at the point where
wilting is started, a European corn borer larva will often be found.
Corn borers are seldom damaging in fields and therefore no control is
A number of leafhopper species are commonly found in mint,
including the potato leafhopper and the six-spotted leafhopper. No
information is available on the damage these species may cause to
mint nor are recommendations for insecticides available. Any of the
insecticides used for control of other insects in mint should also
control leafhoppers. One problem with leafhopper that may occur is
their movement to other crops when mint is harvested. A serious
problem can arise in potatoes, alfalfa, beans, carrots, or some leafy
vegetables when leafhoppers migrate after a mint crop is cut.
Mint is cut and windrowed in much the same fashion as alfalfa hay,
generally with a swather or sickle bar windrower. Recently, some
growers have begun using a rotary windrower imported from Germany
(made by Klockner-Humboldt-Deutz AG) (Fig. 17). The rotary windrower
is said to have three advantages over the conventional windrower: it
moves through the field at a high rate of speed (up to 7 mph) so that
cutting is accomplished quickly; it cuts closer to the ground so that
oil yields per acre are increased; and it leaves the mint hay in
smaller windrows so that it dries faster and is ready to distill
sooner. Also, the rotary windrower is tractor- mounted and requires a
lower initial investment. It remains to be seen if this new equipment
will be widely accepted.
After the mint is cut and windrowed, it is allowed to cure until
the leaves are thoroughly wilted and partially dried (24-36 hours).
The hay should not be allowed to become too dry or leaves will
some of the oil will be lost. If the hay is too green. it will be
difficult to distill. The hay is picked up, chopped, and blown into
the distilling tub by a conventional field chopper (Fig. 18). Growers
have gradually shifted from coarsely chopped to finely chopped (1/4
inch pieces) hay for faster and more complete distilling of oil.
The Murray Mitcham and Todd's Mitcham varieties are ready to
harvest 3-6 days earlier than the older Black Mitcham variety.
Carefully observe the state of maturity and cut the hay before the
plants are in 10% of full bloom. Biosynthesis of mint oil decreases
with the onset of flowering, and the rate of oil degradation
increases at the same time. Menthone, a major component of mint oil,
can be lost during bloom due to conversion to a water- soluble,
nondistillable glucoside. Also, oil glands become leaky as bloom
progresses, which can result in loss of oil during rainy periods.
Harvesting after 10 percent bloom can thus result in both lower
yields and lower quality of oil.
Figure 18. Mint being picked up,
chopped, and blown into the distillation tub.
Figure 18. Mint being picked up,
chopped, and blown into the distillation tub.
Mint distilleries consist of mint distillation tubs, condensers,
receivers, and (often) redistillation units (Fig. 19).
Mint tubs are, for the most part, custom built by growers. They
are fabricated from 10-gauge steel plate on heavy-duty wagon running
gears with large balloon tires (Fig. 20). Tubs are rectangular in
shape, measuring about 6- feet deep, 71/2-feet
wide, and up to 12-feet long. Tubs are made about 6 inches wider at
the top than at the bottom so that the chopped mint is self-packing
as it is blown in. This also allows the entire charge to settle in
the tub when steam is applied and the charge shrinks. This helps
prevent formation of channels for steam along the sides of the tub.
These channels prevent good steam penetration of the entire load.
Figure 20. Mint tub hooked up to the distillery.
A series of perforated pipes for steam are fitted beneath the
perforated false bottom of the tub for introduction of steam. Total
surface area of the perforations in the steam pipes should not exceed
the surface area of a cross-section of the steam line into the tub,
or there may be difficulty in maintaining pressure. A gasketed door
fitted with an 8-inch flexible hose is clamped to the opening at the
top front of the tub where the chopped hay was blown in. This is
where the steam plus water vapor and oil exits the tub and is taken
to the distillery condenser. Large doors in the rear of the tub,
opening either from the top or the side, are used to dump the spent
charge from the tub after distillation is completed (Fig. 21). The
doors are fitted with gaskets made of close-celled neoprene.
Figure 21. A spent charge of minthay being dumped after distillation.
At least two tubs are needed for each station at the distillery;
one tub is being filled while one tub is being distilled. If the tubs
have to be transported any distance from field to distillery, three
tubs per station may be needed. A tub generally will hold the hay
from 3/4 to 1 1/4 acres
of land, depending on how well the crop has yielded.
At least one grower has designed an automated hitch for his tubs
so that the tractor operator can hitch and unhitch tubs from the
tractor without dismounting from the tractor. This requires a
spring-loaded tongue on the wagon chassis to keep the tongue in an
upright position, a sheet metal device to guide the tongue into the
hitch, and a hitch that can be released from the tractor seat.
A high pressure boiler is needed for generation of steam in a
distilling unit. The size of the boiler will depend on the number of
tubs to be distilled at any one time. The rule of thumb used is to
provide 100 horsepower for each tub. Thus, a 4-station still should
be powered by a boiler of about 400 horsepower (Fig. 22). This leaves
some surplus steam capacity for distillation of wet or green hay,
which is harder to heat to oil evaporation temperature than cured
Boilers are generally run at 100-125 p.s.i. at the boiler; 60-80
p.s.i. is applied at the tub until condensate begins coming through
the condenser, and then the pressure is cut to 10-15 p.s.i. to
complete distillation of the charge. Excessive amounts of steam after
the charge is heated will cause some oil to pass through the
condenser without condensing. About one hour is generally required
for distillation of a tub, but this time varies with tub size, hay
condition, and steam pressure.
Figure 22. A modern 4-tub distillation unit.
Condensers and Receivers
Once the mint oil is vaporized from the mint charge, it passes
through the vapor hose, along with vvater vapor, into the condenser
(Fig. 23). The condenser is a continuous series of pipes immersed in
water so that vaporized oil and water will recondense for collection
in the receiver. Condensers are usually either of the horizontal tank
type, which is most popular, or the tubular, upright type. Horizontal
condensers provide more condensing capacity per unit volume of space
occupied. Usually, one horizontal condenser tank will serve three or
four stations (one tub per station). A tubular, upright condenser is
usually needed for each station or for every two stations. The
header- type horizontal condenser (Fig. 23) is replacing the
worm-type horizontal condenser. The temperature of the water in which
the condenser is immersed should be maintained at 110°F This is
done by means of a thermostatically controlled valve which
automatically controls the flow of cold water into the condenser
tank. Aluminum is the best material for construction of both
condensers and receivers because of its heat transfer properties and
resistance to corrosion.
Receivers are designed to collect the water and oil from the
condenser, and to allow the lighter mint oil to separate and float on
top of the water so it can be drawn off in relatively pure form (Fig.
24). The level of the oil in the receiver is controlled by raising or
lowering the level of the end of the drain pipe where water leaves
the receiver. At the top of the receiver, oil can be periodically
drained off through a spout. BN7 raising the end of the water drain
pipe, the water level is raised, causing the oil to flow off. Care
must be taken to stop collecting oil before the water level in the
receiver is reached.
To prevent churning of the oil in the receiver. which affects oil
separation, baffles are usually installed below the inlet where
condensate enters the receiver. The baffle plates direct the
separated drops of oil toward the surface. If the receiver is
properly constructed and care is taken, the oil will be entirely
clear and can be placed directly in.drums for shipment.
Boilers, condensers, and receivers are built commercially and can
be obtained from several sources (see appendix).
Buying a used boiler can often mean considerable savings.
Many growers now install a small unit on their distilleries
consisting of a small steam-heated distillation chamber and a
condenser to recover additional oil from the effluent from the
receivers. The effluent from the receiver is fed into the
redistillation chamber, re-vaporized by steam heat, and re-condensed
to encourage separation of oil which passed through the receiver on
the first distillation (Fig. 19). The condensate is fed back into one
of the receivers for col lection. Most growers feel that they recover
1-3 pounds of oil per tub by redistillation.
Figure 24. Mint oil being collectedfrom the receiving can.
Yield of Oil: The yield of oil from mint varies with the
season, geographic location and cultural conditions. The average oil
yields per acre for peppermint and the spearmints in the major
Midwest mint growing states usually fall in the 30-35 pound per acre
range (Table 1). As indicated earlier, a midsummer day-length of at
least 15 hours is required for maximum yields. Also, periods of
clear, sunny weather. especially as the crop approaches harvest, are
essential for maximum yields. By contrast, cloudy, wet weather for
periods of several days prior to harvest will reduce yields. A
particular problem occurs if there are heavy rains when the mint hay
has been cut and is drying in the field. Such rains can actually wash
oil from the foliage, causing further losses in yield.
Table 1. Acres of mint in production
and average yields per acre.
Type of Mint and State
Other factors which may reduce oil yields include poor or
irregular stands, dense stands that prevent full leaf development and
encourage premature leaf drop, rough handling, weed competition,
damage by insects and diseases, drought, and other weatherrelated
Price of Oil: Prices received by farmers for peppermint and
spearmint oils depend on demand, quality and carryover from previous
crops (Table 2).
Capital Investment and Production Costs: The equipment and
machinery needed to grow the crop and distill the mint oil are
expensive. The distilling operation, in particular, requires
specialized equipment that may have no other use on the farm. This
presents a special problem for the new grower, so that it is often
advantageous to have the first crop or two distilled by established
The cost of the distillery varies considerably depending upon
location and availability of used equipment from other growers. For
example, much of the equipment, such as the portable tubs, are custom
built either by local tradesmen or on the farm. The most costly item
is the boiler, which can often be purchased secondhand at
Table 2: Average price per pound of mint oils received
by farmers in the principal Midwestern oil producing states
Estimated cost for new equipment for a 2-tub distillery, including
four portable tubs, condensers, receivers and other necessary
equipment (less the boiler) are currently as follows: four portable
distillation tubs, $20,000; two condensers and tank, $2,000; two
receiving cans, $800; pipe fittings, fuel tank, pumps, valves, hoses,
gauges, wiring, and labor, $3,000; building to house the distillery,
$6,000; and well and pump, $1,500. Total estimated cost, $33,300.
Larger distilleries are expensive because the multitub unit requires
a correspondingly larger boiler; however, the boiler should be large
enough to handle any anticipated expansion.
Production costs vary greatly among farms, depending upon acreage,
labor, cropping program and other factors. In an Indiana study in
1980, the total cost of producing oil from first-year peppermint
ranged from $345 to $460 per acre. This cost included land, stolons
for planting, fertilizer, pesticides, labor and equipment costs to
plant, cultivate, weed, harvest and distill the crop along with all
overhead costs. Second and subsequent year costs ranged from $300 to
$410 per acre, since there is considerable reduction in labor costs
and the cost for planting stock (stolons or plants) is a
The cost as determined from this study are as follows:
Cost per acre
$ 60 - 75
Land and improvements
80 - 110
65 - 75
20 - 25
25 - 30
Equipment and machinery
35 - 50
Harvesting and distillng
30 - 50
Overhead (taxes, insurance, repair and maintenance,
30 - 45
345 - 460
To increase production, supplemental sprinkler irrigation has
become increasingly common on mint in the midwestern region. Growers
may apply from 4 to 10 acre- inches of water, depending upon the
season. In the Indiana study, the cost for irrigation was
$7/acre-inch of water when water was drawn from existing wells or
Appendix 1: Some manufacturers of equipment for mint
culture and distillation.
General distilling equipment: Cobb Mfg. Co.,
Jefferson, Oregon 97352.
Mint planters and distilling tubs: Gmeinder Welding,
215 Deerfield Road, Marshall, Wisconsin 53559.
Condensers: Plummer Supply, P.O. Box 177, 1180 -
129th Street, Bradley, Michigan 49311; Hal Mullett, Palms,
High-speed windrower: Klockner-Humboldt-Deutz AG
(consult your nearest Deutz tractor dealer).
North Central Regional Extension Publications are
prepared as a part of the Cooperative Extension activities
of the 12 North Central State land grant universities in
cooperation with the Science and Education
Administration-U.S.D.A. The following states cooperated in
making this publication available.
University of lllinois
Urbana IL 6180l
W. Lafayette. IN 47907
lowa State University
Ames IA 50011
Michigan State University
East Lansing, Ml 48824
University of Minnesota
St. Paul MN 55108
Ohio State University
Columbus. OH 43210
University of Wisconsin
Madison. Wl 53704
For single copies of this and other North Contrul
Regional Publications, write to: Publications Office,
Cooperative Extension Service, in care of the university
listed above for your state.
If you live outside the North Central Region, write to
any of the above universities for single copies. For
quantities of any regional publication or general
information, write to: NCR Educational Materials Project,
111N Curtiss Hall, Iowa State University, Ames, IA
Programs and activities of the
Cooperative Extension .Service are available to all
potential clientele without regard to race, color, sex
national origin, or handicap.
In cooperation with NCR Educational
Issues in furtherance of cooperative
Extension work, Acts of Congress of May 8 and June 30, 1914,
in cooperation with the U.S. Department of Agriculture and
Cooperative Extensions Service of Illinois, Indiana, Iowa,
Kansas, Minnesota, Missouri, Nebraska, North Dakota, Ohio,
South Dakota, and Wisconsin. Gordon E. Guyer, Director,
Cooperative Extension Service, Michigan State University,
East Lansing, Michigan 48824.