A Paw for You and a Paw for Me
The Autumn birding hike of October 10th was not very productive in terms of birds. However, during the course of the hike, several of the participants got their first introduction to the Pawpaw, Asimina triloba. The name of this plant is sometimes spelled Papaw - and in that form is often confused with another fruit that sometimes goes by that name, the Papaya, Carica papaya. (The latter is in a totally different family than our Pawpaw, and can only grow in tropical areas.)

Our Pawpaw, which grows as far north as New York and southern Ontario, out west as far as Nebraska and Texas, and south to Florida, is known by several other names including the American Custard Apple, the West Virginia Banana, and the Indiana Banana. There are about seven other members of the genus Asimina, all growing in the southeastern U.S.

The Pawpaw made some headlines in 1992 when it was reported that a Purdue University researcher had isolated a powerful anti- cancer drug, as well as a safe natural pesticide from the Pawpaw tree. The substances are said to be primarily found in the twigs and small branches. The researcher, Jerry McLaughlin, revealed that it was because of some childhood experiences with eating the fruit that he had a feeling that there was something biologically active in the plant.

In the book, Sturtevant's Edible Plants of the World, one finds the Pawpaw fruit called "...a natural custard, too luscious for the relish of most people. The fruit is nutritious and a great resource to the savages." Millspaugh, in American Medicinal Plants, describes the fruit as "soft, sweet and insipid, having a taste somewhat between that of the May-apple and the banana, tending to the former." The Peterson Field Guide mentions that the seeds, along with being an emetic, have narcotic properties.

As late as the early 1900's, fishermen in the Ohio valley were using strips of the inner bark for stringing fish. They likely learned this use from the Indians, who used these bark strips to make fabric and nets. It is also thought that the Indians may have been responsible for extending the range of the Pawpaw far beyond its natural growing area.

Closer to home, a West Virginian and DC resident, Neal Peterson, has been conducting a Pawpaw research study for the past eight years at the Western Maryland Research and Education Center near Keedysville. He has 600 trees planted on the Center's property and has been evaluating the fruit from the individual trees with an aim to choose the ten "best" trees in his orchard in order to begin producing the most tasty Pawpaws possible. Peterson hopes to bring Pawpaws to the mass market.

Note: October, 1997: I found a listing for Paw Paws on the NCSU Poisonous Plants of North Carolina Page. Apparently some individuals cannot eat them without severe stomach and intestinal pain.

Note: September, 2005. Pawpaws should gain in popularity because deer tend not to eat them. While they will eat the fruits which have fallen to the ground, it is thought that the unpleasant smell the stem emits when it is damaged keeps the tree from being palatable to deer. In fact, in certain areas anlong the C and O Canal, botanists feel that it is becoming a weed, taking over places that used to have a wide variety of species, but where seedlings of other trees are being gobbled up by deer, leaving the pawpaws to thrive.


--Kathy Bilton
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PAWPAW

Asimina triloba
Annonaceae
Common Name:Pawpaw, Paw Paw, Papaw, Poor Man's Banana, Hoosier Banana, etc. (In Australia the tropical papaya, Carica papaya, is also known as Pawpaw).
Related species: Asimina incarna, A. longifolia, A. obovata, A. parviflora, A. pygmaea, A. reticulata, A. tetramera, A. X nashii. These eight Asimina species grow in the southeastern United States.

Distant Affinity: Cherimoya (Annona cherimola), Soursop (Annona muricata), Custard Apple (Annona reticulata), Sugar Apple, Sweetsop (Annona squamosa), Atemoya (Annona squamosa X A. cherimola).

Origin: The pawpaw is native to the temperate woodlands of the eastern U.S. The American Indian is credited with spreading the pawpaw across the eastern U.S. to eastern Kansas and Texas, and from the Great Lakes almost to the Gulf. Fossils prove the pawpaw is indigenous to the U.S.

Adaptation: The pawpaw is adapted to the humid continental climate of its native habitat. It is seldom found near the Atlantic or Gulf coasts. It requires a minimum of 400 hours of winter chill and at least 160 frost-free days. Pawpaws appear to be sensitive to low humidities, dry winds and cool maritime summers. It has been successfully grown in parts of California and the Pacific Northwest that meet its growing requirements. It has grown well in the San Jose area (USDA Climate Zone 9 or Sunset Climate Zone 15). The climatic conditions of Southern California make growing the pawpaw there more difficult. The deep winter dormancy of the tree makes it highly frost tolerant, withstanding temperatures of -25° F or lower (hardy to USDA Climate Zone 5). Pawpaws can be grown as container specimens, although this is not often practiced. A deep pot is needed to accommodate the root system.

DESCRIPTION
Growth Habit: The pawpaw is a deciduous, often narrowly conical tree growing from about 12 feet to around 20 feet. Pawpaw trees are prone to producing root suckers a few feet from the trunk. When these are permitted to grow, the single-clone pawpaw patch comes into being. The prevailing experiences of many individuals is that the pawpaw is a slow grower, particularly when it is young. However, under optimal greenhouse conditions, including photo-period extension light of approximately 16 hours, top growth of up to 5 feet can be attained in three months.
Foliage: The dark green, obovate-oblong, drooping leaves grow up to 12 inches long, giving the pawpaw an interesting tropical appearance. The leaves turn yellow and begin to fall in mid-autumn and leaf out again in late spring after the tree has bloomed.

Flowers: Dormant, velvety, dark brown flower buds develop in the axils of the previous years' leaves. They produce maroon, upside-down flowers up to 2 inches across. The normal bloom period consists of about 6 weeks during March to May depending on variety, latitude and climatic conditions. The blossom consists of 2 whorls of 3 petals each, and the calyx has 3 sepals. Each flower contains several ovaries which explains why a single flower can produce multiple fruits.

Fruit: The pawpaw is the largest edible fruit native to America. Individual fruits weigh 5 to 16 ounces and are 3 to 6 inches in length. The larger sizes will appear plump, similar to the mango. The fruit usually has 10 to 14 seeds in two rows. The brownish to blackish seeds are shaped like lima beans, with a length of 1/2 to 1-1/2 inches. Pawpaw fruits often occur as clusters of up to nine individual fruits. The ripe fruit is soft and thin skinned.

CULTURE
Location: The young plant is very sensitive to full sunlight and requires filtered sun for the first year or two. The use of tree shelters is an ideal solution to the problem, permitting the plant to receive a full day of filtered sunlight. Once established, pawpaws prefer full sun. The large dangling leaves dislike strong winds. Overall the tree is an excellent edible landscape addition.
Soil: Pawpaws do best in deep, fertile soil that is moist, but well-drained and slightly acid (pH 5-7). The addition of compost to most western soils makes them more hospitable to the pawpaw. Avoid heavy, wet, alkaline soil.

Irrigation: The pawpaw needs regular watering during the growing season. The soil should be kept moist but avoid waterlogging.

Fertilization: The pawpaw responds to the application of an organic or granular fertilizer high in potassium twice a year. For container growing, 250 - 500 ppm of soluble 20-20-20 NPK plus soluble trace elements during growth phase is optimal.

Pruning: Ordinarily little pruning is required, except to remove dead, damaged or wayward branches. Periodic pruning may be used to stimulate some new growth each year on older trees, since it is new growth that produces fruit the following season.

Propagation: To break dormancy Pawpaw seed must receive a 90 to 120 day stratification, i.e. exposure to cold temperatures. To accomplish this, the seed should be placed in plastic freezer zipper bag containing a handful of moist sphagnum moss and refrigerated at 32° - 40° F. The over wintering of field planted seeds normally accomplishes this stratification requirement.

Germination of pawpaw seed is hypogeal--the shoot emerges without any cotyledons. Under ideal greenhouse culture, germination can be expected in about seven weeks. Seeds field-planted in the fall will emerge the following July or August. But before the shoot emerges, the seed will have sent down a 10 inch long tap root.

Hardwood cuttings are essentially impossible to root, while root cuttings have been variable to disappointing. Some success has been reported using softwood cuttings under intermittent mist with bottom heat (80° F) and supplemental light (14 hours). All grafting and budding techniques can be performed on the pawpaw, but T-budding is not recommended. Chip-budding has been reported to be successful. Scion wood should be gathered while the tree is dormant and kept refrigerated. Grafting can be done in the spring after vegetative growth begins.

Young pawpaw plants have fleshy, brittle roots with few fine root hairs, making them difficult to transplant. It is important to follow these helpful rules:

Use seedlings, not root suckers.
Move the tree with roots and soil intact. A container grown specimen is best.
Transplant the tree in the spring after bud break.
Give the plant good drainage and keep it well watered the first year.
Pests and diseases: Pawpaw trees are relatively disease free, including a resistance to Oak Root Fungus (Armillaria)

. A number of vertebrates such as foxes, opossums, squirrels and raccoons will eat the fruit, although deer, goats and rabbits will not eat the leaves or twigs. The attraction of pawpaw roots to gophers is a somewhat unknown factor, but it seems likely that they would not be the gopher's first choice. The Zebra Swallowtail butterfly's larvae feed exclusively on young, pawpaw foliage, but never in great numbers. On the West Coast, slugs, snails and earwigs can be easily controlled by the application of Tanglefoot to a band around the pawpaw tree trunk. It is important not to apply Tanglefoot directly to the bark, however.

Pollination: Poor pollination has always plagued the pawpaw in nature, and the problem has followed them into domestication. Pawpaw flowers are perfect, in that they have both male and female reproduction parts, but they are not self-pollinating. The flowers are also protogynaus, i.e., the female stigma matures and is no longer receptive when the male pollen is shed. In addition pawpaws are self-incompatible, requiring cross pollination from another unrelated pawpaw tree.

Bees show no interest in pawpaw flowers. The task of pollenization is left to unenthusiastic species of flies and beetles. A better solution for the home gardener is to hand pollinate, using a small, soft artist's brush to transfer pollen to the stigma. Pollen is ripe for gathering when the ball of anthers is brownish in color, loose and friable. Pollen grains should appear as small beige-colored particles on the brush hairs. The stigma is receptive when the tips of the pistils are green, glossy and sticky, and the anther ball is firm and greenish to light yellow in color.

Harvest: Pawpaw fruit ripens during a four-week period between mid August and into October, depending on various factors. When ripe, it is soft and yields easily to a gentle squeeze, and has a pronounced perfumed fragrance. The skin of the green fruit usually lightens in color as it ripens and often develops blackish splotches which do not affect the flavor or edibility. The yellow flesh is custard like and highly nutritious. The best fruit has a complex, tropical flavor unlike any other temperate zone fruit. At present, the primary use of pawpaws is for fresh eating out of hand. The ripe fruit is very perishable with a shelf life of 2 or 3 days, but will keep up to 3 weeks if it is refrigerated at 40° - 45° F.

Commercial potential: Although pawpaw fruit is not yet a commercially viable commodity, the domestication process is well underway. Several academic institutions are setting up seventeen Regional Variety Trial sites. Kentucky State University is the site of Pawpaw National Clonal Germ-plasm Repository. The pawpaw has also found its way to several overseas countries, and a few of these are actively engaged in research. Pawpaw leaves and twigs contain substances with promising anti-cancer and pesitcidal properties.

Plant selection: A number of mail-order sources of pawpaw plants now offer both grafted cultivars and seedlings. Most seedling plants have been propagated from mixed seeds and will eventually end up producing undesirable fruit. Purchasers are advised to graft such plants to a known cultivar or order grafted plants initially. Container grown plants are much more likely to survive transplanting.