Doing~ what comes unnaturally
How to hand-pollinate pawpaws
By Neal Peterson
Some people find that Pawpaw trees just donât produce fruit. âWhy?â
they ask. The answer usually is, âThey need a pollinator.â Sometimes
this means they need a helping hand in their pollination. Literally.
Hand-pollination. The question then be-comes, âHow do you do it if
youâve never done it? When is the pollen ripe? When is a flower in the
female stage and most receptive? How do you do the act itself â transfer
the pollen to its appointed spot?â Itâs all very easy, but â like
human sex â it ~ isnât necessarily obvious how to do It.âhe first
time. Here are some simple pointers to guide you if you aspire to pollinate
pawpaws by hand.
Pawpaw blossoms begin life as females and later become males. They are
designed this way to discourage
self-pollination. In the female stage the petals are held rather tightly
together, forcing the small flies and beetles that visit the flowers,
searching for nectar, to brush past the stigmas where the pollen they carry
on their backs can be deposited. In this stage, the petals will have turned
color, from green to maroon (although some green may still show) but the
anthers will be tightly pressed together as a solid green ball, and the
stigmas will appear green and shiny.
In the later male stage, the petals darken more, the fetid flower odor
intensifies, the ball of anthers loosens (no longer solid) and the anthers
turn from green to brown, shedding the yellow dust-like pollen. In this
stage, the petals flare back, allowing the visiting insects to brush easily
past the anthers, thereby collecting pollen on their backs.
The first trick for the hand pollinator is collecting the pollen. There are
many ways to do this, but my own
Preference is to use large empty gelatin capsules (size XXX) that you may
buy at health food stores. I open
the capsule and use one end as a cup to scrap the ripe-with-pollen anthers,
causing them to fall into the capsule. I then close the capsule and label
the contents with an indelible pen. These capsules, being made of gelatin,
absorb moisture, promote the anthers to release their pollen, which then
adheres to the sides of the capsule. I then use a very small camelâs hair
brush to collect the pollen from the sides of the capsule, and apply the
pollen to the stigmas of the female flower. For the sake of thoroughness,
and to learn the results of my efforts, I also tag the flowers I have
pollinated. The final pointer has to do with picking the right time of day
and the right type of day for pollinating. I find that I get the best
results on a perfect spring day, when the sun is bright, the air is warm,
the breezes gentle or not at all. I donât do it in early morning or late
in the day. When in doubt about how to do it, think like a flower, think
like a beetle.
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My Botanical Rendezvous
By Colleen Anderson
Iâm an infamously bad gardener, but six years ago I planted a Pawpaw seed
in my yard, and it grew. I nursed the little sprout along and, about the
second year, transplanted it to the sunny side of Arlington Court, where I
live. It thrived. Last year, the first blossoms appeared â only four of
them, but there was no denying it â my tree was at least a teenager. This
year, itâs an adult. The tree is tall and straight, and the lovely,
blood-brown, bell-shaped flowers are everywhere â there must be two
hundred. My tree could be fruitful â but, like people, paw-paws need
intimate company in order to reproduce â and there isnât another Pawpaw
within shouting distance.
So I have been assisting nature. My treeâs mate came from a fine stand of
pawpaws in Kentucky. I carried the precious pollen back in small capsules.
On a beautiful, warm day last week â the perfect sort of day for romance
â1 had a go at hand pollinating. It didnât take long, and it wasnât
very exciting â dipping a small brush into the pollen capsules and
delivering it to the waiting blossoms â but still, I tried to
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accomplish it without attracting attention. Plants may not care about who
watches their sexual encounters, but I couldnât get over the feeling that
there was something illicit about this endeavor.
Nevertheless, word got around. By that evening, my neighbors were teasing me
about my midaftemoon botanical rendezvous. All over the block, theyâre
calling me âMadame Pawpaw.â
I feel more like a grandmother-in-waiting. Iâm looking forward to the
story this summer will tell. Will my lovely young tree be compatible with
her Kentucky gentleman? Will the blossoms swell into clusters of fruit? Will
we have Arlington Court paw-paws this fall? Stay tuned. With luck, Iâll be
making a birth announcement.
This essay was originally broadcast as a commentary on West Virginia Public
Radio in April 1996. The
harvest was bountiful.
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Pawpaws in the Garden
SITE, SOILS, AND HABITAT. Although the Pawpaw is capable of fruiting in the
shade, optimum yields are obtained in open exposure, with some protection
from wind (on account of the large leaves). Germinating seedlings, however,
will not survive under those conditions because they are extremely sensitive
to full sunlight, which can kill them. Shading for the first year, and
sometimes the second, is normally required, and it is for this reason that
pawpaws are almost always found in nature as an understory tree. The soil
should be slightly acid (pH 5.5-7), deep, fertile, and well-drained. Good
drainage is essential to success. Pawpaws will not thrive in heavy soil or
water-logged soil. In habit it is a small tree, seldom taller than 25 feet.
Grown in full sun, the Pawpaw tree develops a narrowly pyramidal shape with
dense, drooping foliage down to the ground level. In the shade it has a more
open branching habit with few lower limbs and horizontally held leaves.
PROPAGATION BY GERMINATION. Pawpaw seed is slow to germinate but not
difficult if certain procedures are followed. Do not allow the seed to dry
for long periods (ie., months) because this can destroy the immature,
dormant embryo. To break dormancy, the seed must receive a period of
stratification (exposure to cold temperatures) for 90-120 days. this may be
accomplished by sowing the seed late in the fall and letting it overwinter;
the seed will germinate the following year in late July to late August.
Another way is to stratify the seed in the refrigerator (32-40F/0-5C). In
this case the seed should be stored in a plastic ziplock bag with a little
moist sphagnum moss to keep the seed moist and suppress fungal/bacterial
growth. After stratification the seed should be sown in a well-aerated soil
mix, pH 5.5-7, with an optimum temperature of 75-85F (25-30C). The root will
normally emerge from the seed coat on the 18th day, develop into a taproot
about 10 inches deep, and then send up a shoot on day number 64. Germination
is hypogeal: the shoot emerges without any cotyledons. For the first two
years growth is slow as the root system establishes itself, but thereafter
it accelerates. Fruitbearing normally begins when the sapling reaches 6
feet, which usually requires six to eight years.
PROPAGATION BY VEGETATIVE MEANS. Pawpaw clones are easily propagated by a
number of grafting and budding techniques, such as whip-and-tongue, cleft,
bark inlay, and chip budding. The only method that does not produce good
results is T-budding. Shoot cuttings have proved virtually impossible to
root, while root cuttings are usually successful. Although it is common for
a Pawpaw to sucker from the roots, and would therefore seem a natural way to
propagate a clone through transplanting root suckers, in practice this is
extremely difficult. Pawpaws are ordinarily quite difficult to transplant.
They have fleshy, brittle roots with very few fine hairs. Experimentation
has shown that, to be successful, transplantation should be done in the
spring at the time that new growth commences, or soon after. (This is
basically the same as for magnolia.) If many roots are lost, it may be
desirable to prune the top to bring it into balance with the remaining
roots.
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POLLINATION, NATURAL AND ARTIFICIAL.
Pollination is the major limitation to Pawpaw fruit set. The flowers are
protogynous, meaning that the stigma (the female receptive organ) ripens
before the pollen, and is no longer receptive when the pollen is shed. Thus
the flower is designed not to be self-pollinated. In addition, Pawpaw trees
are self-incompatible, requiring pollen from a genetically different tree in
order to be fertilized. Finally, the natural pollinators of the
Pawpawâvarious species of flies and beetlesâare not efficient or
dependable. Although it requires a little extra labor, hand pollination can
be well worth the effort and can be done as follows: Using a small, flexible
artistâs brush, transfer a quantity of fresh pollen from the anthers of
the flower of one clone to the ripe stigma of the flower of another clone.
Pollen is ripe when the little ball of anthers is brown in color, loose and
friable; pollen grains appear as yellow dust on the brush hairs. The stigma
is ripe when the tips of the pistils are green and glossy, and the anther
ball is still hard and green. Do not overburden the tree with fruit, as this
will stress the tree, resulting in smaller than normal fruit, and may cause
limbs to break under excessive weight.
PESTS. In its native habitat the Pawpaw has few pests of any importance. The
worst pest is Talponia plummeriana, the Pawpaw peduncle borer, a small moth
larva (about 5 mm long) that burrows in the fleshy tissues of the flower,
causing the flower to wither and drop. In some years this borer is capable
of destroying the majority of blossoms. Another pest is Eurytides
marcellus, whose larvae feed exclusively on young Pawpaw foliage, but never
in great numbers. The adult butterfly is of such great beauty that this
should be thought more a blessing than a curse. Sometimes the fruit surface
may be covered with patches that are hard and black; this is a fungus
infection, but it seldom has any effect on flavor or edibility. Deer will
not eat the leaves, twigs, or fruit. Outside its native region, the Pawpaw
is sometimes reported to be plagued by pests, but this may be because of
poor health resulting from improper soils and an unsuitable climate.
The Pawpaw Foundation, August 1990
Bees show no interest in Pawpaw flowers. The task of pollination is left to
unenthustic species of flies and beetles. A better solution for the home
gardener is to hand pollinate. Using a small soft artistâs brush to
transfer pollen to the Stigma (Female part of the blossom) Pollen is ripe
for gathering when the ball of anthers is brownish in color loose and
friable. (Male part of blossom, up to top inside flower above the female
part) Pollen grains should appear as small beige colored particles on the
brush hairs. The stigma (female part) is receptive when the tips of the
pistils are green, glossy, and sticky, and the anther (male part) is firm
and greenish to light yellow in color.
So the female part is ready when the male part is not in the same
blossom.
Gordon C. Nofs
6422 E. Pierson Rd.
Flint, Michigan 48506-2258