[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[nafex] Hand Pollenate Pawpaws.
Thought that there might be some interest for some out there.
Doing what comes unnaturally
How to hand-pollinate pawpaws
By Neal Peterson
Some people find that Pawpaw trees just don't produce fruit. "Why?" they
ask. The answer usually is, "They need a pollinator." Sometimes this
means they need a helping hand in their pollination. Literally.
Hand-pollination. The question then be-comes, "How do you do it if you've
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 - transfer the
pollen to its appointed spot?" It's all very easy, but - like human sex -
it ~ isn't necessarily obvious how to do It.'he 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
camel's 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 don't 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.
My Botanical Rendezvous
By Colleen Anderson
I'm 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 - only four of
them, but there was no denying it - my tree was at least a teenager.
This year, it's an adult. The tree is tall and straight, and the lovely,
blood-brown, bell-shaped flowers are everywhere - there must be two
hundred. My tree could be fruitful - but, like people, paw-paws need
intimate company in order to reproduce - and there isn't another Pawpaw
within shouting distance.
So I have been assisting nature. My tree's 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 - the perfect sort of day
for romance -1 had a go at hand pollinating. It didn't take long, and it
wasn't very exciting - dipping a small brush into the pollen capsules and
delivering it to the waiting blossoms - but still, I tried to
accomplish it without attracting attention. Plants may not care about who
watches their sexual encounters, but I couldn't 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, they're
calling me "Madame Pawpaw."
I feel more like a grandmother-in-waiting. I'm 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, I'll 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.
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.
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 Pawpaw-various species of flies and beetles-are 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 artist's 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 artist's 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
Gordon C. Nofs
Get your FREE download of MSN Explorer at http://explorer.msn.com