New Crop FactSHEET
Contributor: Desmond R. Layne
Copyright © 1995. All Rights Reserved. Quotation from this document should cite and acknowledge the contributor.
- Common Names
- Scientific Names
- Origin and Botany
- Description of the Plant
- Crop Status
- Crop Culture
- Seedling Production
- Field Planting
- Vegetative Propagation
- Commercial Seed Sources
- Commercial Seedling Sources
- Commercial Named Variety Sources
- Key References
- Selected Experts
Poor Man's Banana
Species: Asimina triloba (L.) Dunal
Family: Annonaceae (Custard Apple Family)
Eaten in-hand as fresh fruit or processed into desserts. Twigs are source of
annonaceous acetogenins which are being used in the development of anti-cancer
drugs and botanical pesticides.
The pawpaw is the only temperate member of the tropical Annonaceae family and
is the largest tree fruit native to the United States. Pawpaws grow wild in
the rich, mesic hardwood forests of 25 states in the eastern United States
ranging from northern Florida to southern Ontario (Canada) and as far west as
eastern Nebraska. Pawpaws flourish in the deep, rich fertile soils of
river-bottom lands where they grow as understory trees or thicket-shrubs. In
addition to the tropical Annona relatives, there are eight members of the
Asimina genus that are native to the extreme southeastern states of
Florida and Georgia. These include A. incarna (flag pawpaw), A.
longifolia, A. obovata, A. parviflora (dwarf pawpaw), A. pygmaea, A.
reticulata, A. tetramera (opossum pawpaw), and A. X nashii.
Pawpaw is a small, deciduous tree that may attain 5 to 10 m in height. In the
forest understory, trees often exist in clumps or thickets. This may result
from root suckering or seedlings developing from fruits that dropped to the
ground from an original seedling tree. In sunny locations, trees typically
assume a pyramidal habit, straight trunk and lush, dark green, long, drooping
leaves that turn gold and brown in color during the fall. Flowers emerge
before leaves in mid spring. The blossoms occur singly on previous year's wood
and may reach up to 5 cm in diameter. Flowers are strongly protogynous,
self-incompatible and require cross pollination although some trees may be
self-compatible. Pollination may be by flies and beetles which is consistent
with the presentation appearance of the flower: dark, meat-colored petals and a
fetid aroma. Fruit set in the wild is usually low and may be pollinator or
resource-limited but under cultivation, tremendous fruit loads have been
observed. Fruits are oblong-cylindric berries that are typically 3 to 15 cm
long, 3 to 10 cm wide and weigh from 200 to 400 g. They may be borne singly or
in clusters which resemble the "hands" of a banana plant (Musa spp.).
This highly aromatic, climacteric fruit has a ripe taste that resembles a
creamy mixture of banana, mango, and pineapple. Shelf-life of a tree-ripened
fruit stored at room temperature is 2 to 3 days. With refrigeration, fruit can
be held up to 3 weeks while maintaining good eating quality. Within the fruit,
there are two rows of large, brown, bean shaped, laterally compressed seeds
that may be up to 3 cm long. Seeds contain alkaloids in the endosperm that are
emetic. If chewed, seed poisons may impair mammalian digestion but if
swallowed whole, seeds may pass through the digestive tract intact.
Pawpaws are not yet a commercially important crop in the U.S. but they have
tremendous potential based on the following reasons: 1) adaptation of trees to
existing climatic and edaphic conditions; 2) nutritional/cosmetic value of
fruit; 3) valuable natural compounds in plant; 4) nursery wholesale and retail
tree production; and 5) as a component in residential 'edible' landscapes.
Pawpaw is well adapted to the 25 states to which it is native and where it
already grows in the wild. It is hardy to zone 5 (-25°C) and requires a minimum
of 400 hrs annual chill units, 160 frost-free days, and 80 cm of annual
precipitation with most falling during spring and summer. Pawpaw is an
excellent food source. It exceeds apple, peach, and grape in most vitamins,
minerals, amino acids, and food energy value. Pawpaw fruits are best eaten
fresh when fully ripe. The intense tropical flavor and aroma may also be
useful for developing processed food products (blended fruit drinks, baby food,
ice creams, etc.). The flesh purees easily and freezes nicely. Pawpaws easily
substitute in equal part for banana in most recipes. Aromas may be used
commercially in cosmetics and skin products. Pawpaw plants produce natural
compounds (annonaceous acetogenins) in leaf, bark and twig tissues, that
possess both highly anti-tumor and pesticidal properties. Current research by
Dr. Jerry McLaughlin at Purdue University (personal communication) suggests
that a potentially lucrative industry, based simply on production of plant
biomass, could develop for production of anti-cancer drugs (pending F.D.A.
approval) and natural (botanical) pesticides. The high level of natural
defense compounds in the tree make it highly resistant to insect/disease
infestation (R.N. Peterson, The PawPaw Foundation, personal observation). With
proper management, organic commercial fruit production may be possible.
Currently in the U.S., there are more than 40 commercial nurseries selling
pawpaw trees. Seedling and grafted trees in the retail nursery trade are
currently selling briskly for as much as $18.50 and $26.50 apiece,
respectively, versus $3-4 for a 2-year old, grafted apple tree. Standing
orders are currently in excess of 40,000 trees in the wholesale market (Jim
Gilbert, manager, Northwoods Wholesale Nursery, Molalla, OR, personal
communication). Pawpaws are ideally suited for the residential 'edible'
landscape due to their lush, tropical appearance, attractive growth form, size,
fall color, and delicious fruit. In addition, Asimina spp. are suitable
for butterfly gardens as they attract the zebra swallowtail (Eurytides
marcellus) for whom they are the exclusive larval host plant.
As soon as flesh is soft, fruit should be collected for seed. Seeds are easily
extracted following maceration of fruit in water and floating off of pulp. The
seed can be sterilized by shaking seeds with a 10-20% Chlorox solution for 1-2
minutes followed by several rinses of distilled water. This aids in reducing
fungal and bacterial contamination during storage. Seeds should not be allowed
to dry out. Once cleaned, they should be stored refrigerated in Ziplock-type
polyethylene bags with slightly moist sphagnum (or peat) moss. Seeds have a
dormant immature embryo and require stratification. Storage under refrigerated
conditions (5°C) for 100 days is recommended to overcome embryo dormancy.
Provided that desiccation and microbial contamination do not occur, seeds may
be stored for several years under refrigerated conditions with little loss in
Stratified or afterripened seeds are planted either in a prepared seedbed or in
containers. Scarification of the seed coat is not necessary. Pawpaw seed
germination is hypogeal. Seeds should be sown to a 3 cm depth in a moist, well
drained soil or other medium that has good aeration in containers that are
20-25 cm deep. Following radicle emergence, tap root growth proceeds to the
bottom of the container and lateral roots begin to develop. Typically, under
soil temperatures of 24°-29°C, the shoot does not emerge from the soil until 9
weeks following sowing. Shoot emergence is hastened 10 days by elevating soil
temperature to 29°-32°C from sowing date thereafter. The optimal conditions for
greenhouse production of robust, container-grown seedlings include the
following: average day and night temperatures of 27° and 24°C, respectively, max.
light intensity 1000 µmolm-2 s-1 photosynthetic photon flux density
(greenhouse whitewashing recommended during summer months, especially), 16 h
photoperiod (extended by high pressure sodium lamps), fertilization 2x/wk to
runoff during shoot growth phase, and soil temperature of 29°-32°C. For
seedlings with 2-12 unfolded leaves grown in 740 cu. cm containers, 250 ppm
20N-20P-20K water soluble fertilizer plus trace elements is recommended. After
12 or more unfolded leaves are attained, seedlings require transplanting to a
larger container. Seedlings will continue actively growing once 'potted-on' if
transplanted before they exhaust the existing soil volume; otherwise, they will
set a terminal bud and stop shoot growth. We transplant into 40 cm deep 2
gallon pots and then boost the fertilization rate to 500 ppm 20N-20P-20K water
soluble fertilizer plus trace elements. If root spiraling in containers is a
problem, containers can be coated with a latex paint mixture containing copper
compounds of low solubility. By utilizing photoperiod extension, light
intensities not exceeding 50% of full sunlight, temperature regulation, soil
warming and fertilization, we have produced pawpaw seedlings with up to 1.5 m
of top growth in one season in the greenhouse. Trees of this size are ideal
for field transplanting and have sufficient caliper for chip-budding.
Field planting should be done when trees are not actively growing. Trees can
be planted in fall or spring. Spring-planted trees should have had their
chilling requirement met at or before planting. Ideally, a dormant tree is
planted in early Spring, although similar considerations as noted below should
be adhered to for Fall planting of a dormant tree. Planting holes should match
the existing containerized root system. For 2 gal. containers, a hand-held
power auger works nicely for hole drilling. Care should be taken not to plant
trees when soil is too dry or wet. Hole drilling in wet, clayish soils will
result in glazing of the hole walls which may impede root penetration into the
soil. Soil should be well drained, deep, fertile and slightly acid (ie. pH
5.5-7). Preplant soil tests are desirable in order to make necessary
amendments. Spring planting should be done during the local pawpaw budbreak
period (April in Kentucky). Trees should be planted such that the soil line of
the pot is even with the soil line of the field. It is essential that
seedlings receive adequate water in the year of establishment. Pawpaw trees
establish and grow best when they are given shelter the first year in the
field. This is reliably accomplished by utilizing tree shelters that are used
in reforestation. Weed control is necessary especially in the establishment
year. Fertilizer application can be accomplished by broadcasting granular
fertilizer in spring. Fertigation with liquid fertilizer can be useful if drip
irrigation is installed in the orchard. We do not currently have
recommendations for feeding field planted trees but we fertigate with 500 ppm
20N-20P-20K water soluble fertilizer plus trace elements once a month in May,
June, and July during the active growth phase. Fertilizer recommendations
based on foliar and soil analyses will be developed in the future. Recommended
tree spacing at present is 5.5 m between rows and 2 m apart in the row. Row
orientation should be North-South.
Transplanting trees from the wild is usually unsuccessful. Young trees dug
from a thicket or grove are often root suckers with few, brittle roots that
have very few root hairs. Due to the poorly developed root system and frequent
absence of shelter following transplanting, transplanting shock is usually
severe resulting in the death of the root sucker. Transplanting of seedlings
from the wild is most successful when done in the Spring during budbreak. If
many roots are lost in the digging process, it is desirable to prune the shoot
to bring it into balance with the existing root system. Unlike transplanting
seedlings collected from the wild, containerized seedlings transplant with high
success if the guidelines described above are adhered to.
Pawpaws are easily propagated by several grafting and budding techniques.
These include whip-and-tongue, cleft, bark inlay, and chip budding. Chip
budding is most successful when the seedling rootstock is pencil thick or
greater in diameter and actively growing. Winter collected, dormant scion
budwood should have had its chilling requirement fulfilled. When performing
chip budding, it is desirable to try to match the diameter of the budwood with
that of the stock plant. It is recommended to wrap the graft with parafilm
laboratory film using strips cut to 2 cm x 15 cm. Parafilm is flexible,
moldable, self sealing and moisture resistant. When stretched, it applies
adequate pressure to stimulate callus production and it maintains good humidity
for union formation. Within 2 weeks, buds will begin expanding and may
penetrate the parafilm or just enlarge under it. In the latter case, parafilm
is easily removed by using a sharp budding knife and making a shallow incision
along the length of the wrap on the side opposite the bud. Care must be taken
not to damage the scion bud in the process of removing parafilm. Once scion
growth commences, we recommend cutting back the top of the stock to 30-60 cm in
height leaving 6 or more functional lower leaves and rubbing off all competing
buds on the rootstock. We have found that cutting the stock back to just above
the bud reduces scion growth. Once the scion is 30 cm or more in length, the
lower leaves on the stock can be removed and the stock can be cut back to a
height of 20-25 cm above the union. Under greenhouse conditions, we have also
found that leaving the stock as described above is extremely helpful because
the stub of the stock projecting above the union then provides a `stake' to
secure the growing scion. Some scion varieties appear to grow more
horizontally from the graft union than others and using this technique ensures
uniform habit and development of a strong union and vertically oriented scion.
We use masking tape to tie up the scion as it grows. Once the scion becomes
woody, this tape is no longer needed. Starting with a large, healthy
rootstock, up to 1.5 m of scion growth can be attained in as few as 3 months
under optimal greenhouse conditions described above. Whip grafting is
successful on seedling rootstock material that is as small as 3-4 mm in
diameter, provided the scion is of similar diameter (Jim Gilbert, Northwoods
Wholesale Nursery, Molalla, OR, personal communication).
Other vegetative propagation techniques such as root cuttings, hard and
softwood cuttings, and tissue culture have met with poor or marginal success.
Propagation by hardwood cutting techniques has never been attempted for pawpaw
indicating a need for research to evaluate the commercial potential thereof.
However, pawpaw propagation by softwood cuttings has been successful although
at a low percentage. Micropropagation techniques have been developed for many
Annonaceous relatives of pawpaw indicating potential promise of this technology
Kentucky State University, Frankfort, KY (USDA National Clonal Germplasm
Repository for Asimina spp., satellite site of Corvallis, OR
The PawPaw Foundation (University of Maryland property).
F.W. Schumacher Seed Co., 36 Spring Hill Rd., Sandwich, MA 02563.
Sheffield Seed Co., 273 Auburn Rd., Locke, NY 13092.
Edible Landscaping, P.O. Box 77, Afton, VA 22920.
Oikos Tree Crops, P.O. Box 19425, Kalamazoo, MI 49019.
Sherwood Greenhouses, P.O. Box 6, Sibley, LA 71073.
Northwoods Retail Nursery, 27635 S. Oglesby Rd., Canby, OR 97013.
Hidden Springs Nursery, Route 14, Box 159, Cookville, TN 38501.
Desmond R. Layne, Assistant Professor of Horticulture, Department of Horticulture, Poole Agriculture Center, Box 340375, Clemson University, Clemson, SC 29634-0375
- Kral, R. 1960. A revision of Asimina and Deeringothamnus
(Annonaceae). Brittonia 12:233-278.
- Layne, D.R. 1996. The pawpaw [Asimina triloba (L.) Dunal]: A new fruit
crop for Kentucky and the United States. HortScience (in press).
- McGrath, M.J. and C. Karahadian. 1994. Evaluation of physical, chemical, and
sensory properties of pawpaw fruit (Asimina triloba) as indicators of ripeness.
J. Agric. Food. Chem. 42:968-974.
- McLaughlin, J.L. and Y.-H. Hui. 1993. Chemotherapeutically active acetogenins.
U.S. Patent No. 5,229,419.
- Peterson, R.N., J.P. Cherry, and J.G. Simmons. 1982. Composition of pawpaw
(Asimina triloba) fruit. Ann. Rpt. N. Nut Growers Assoc. 77:97-106.
- Peterson, R.N. 1991. Pawpaw (Asimina). In: J.N. Moore and J.R.
Ballington (eds.) Genetic resources of temperate fruit and nut trees. Acta
- Ratanyake, S., J.K. Rupprecht, W.M. Potter, and J.L. McLaughlin. 1992.
Evaluation of various parts of the paw paw tree, Asimina triloba
(Annonaceae), as commercial sources of the pesticidal annonaceous acetogenins.
J. Econ. Entomol. 85:2353-2356.
FAX: (864)-656-4960, phone: (864)-656-4964
Contributor: Desmond R. Layne, Community Research Service, Kentucky State
Copyright © 1995. All Rights Reserved. Quotation from this document should cite and acknowledge the contributor.
Last update Tuesday, February 24, 1998 by aw