Download Watermelon - Ozaukee Master Gardeners

Africa is considered to be the native
home of the watermelon. It was found
growing wild by Livingstone in 1854. On
the American continent, watermelons
were grown as early as 1629 in Massachusetts, and prior to 1664 in Florida.
Watermelon leaves are heart-shaped
with three to seven lobes per leaf and
are produced on trailing vines. Plants
are monoecious with yellow flowers that
are approximately 1 ¾ inches in diameter.
Culture
mound and protect young plants until they
are established from wind and cold
weather with cloches or plastic tunnels.
Planting in raised beds covered with green
or black plastic mulch can produce ripe
melons 2 weeks earlier. Black plastic
mulch is very effective because it absorb
heat, warms the soil, and maintains good
soil moisture levels. The plastic can be installed when the soil is in good planting
condition, any time from a few days to 2-3
weeks before planting. This will speed the
harvest since the soil will be very warm
when the seeds and transplants are
planted.
Pinch out the growing points of the main
shoots when they are 6ft long and train
side shoots between other plants in the
row. Reduce sub lateral growths from the
side shoots to two or three leaves after
fruits start to develop, and place a pad or
block of wood beneath each fruit to protect
it from soil borne pests and disease (not
necessary if plastic mulch is used).
Watermelons are generally insectpollinated but in cold seasons, if fruits are
not setting, it may be necessary to hand
pollinate. The female flower has a tiny
bump (the embryonic fruit) behind the petals, which the male flower
lacks. This makes it easy to
distinguish between them.
To hand-pollinate, take a
male flower, remove all the
petals and press it against
the female flower. Alternatively, use a fine paintbrush
to transfer the pollen from the
stamens of the male flower to
the stigma of the female.
You can lengthen the growing season by protecting plants from late
spring frosts and early fall frosts. There
are a variety of ways to prolong the growing season, including planting on a southern slope, creating a warmer microclimate
using floating row covers, dark plastic
mulch to warm the soil, clear plastic tunnels, cold frames, or using windbreaks to
shield plants.
Master
Gardeners
Journal
MG 285
March 1, 2003
MASTER GARDENERS
Melons require a long growing season of
90 to 125 days with temperatures averaging between 70-80oF. Watermelons are
less tolerant of cool conditions than muskmelon. They are best adapted to the
warmer, longer-season areas of the US,
and have a difficult time maturing in
shorter-season areas like ours. Melons
can be direct sown but will yield a much
better crop if started indoors and transplanted into the garden after the soil has
warmed. Start the seeds indoor in late
April or early May. Sow 1 inch deep in 33 ½ inch peat pots using a sterile seedling
mix. You can buy or mix your own sterile
potting mix for starting transplants. The
mix should include peat, sphagnum or
compost to retain moisture; vermiculite or
perlite for aeration; and mineral and nutrient sources to encourage growth after the
first roots form. Germination is in 7-10
days when soil temperature is in the optimum range of 70-85oF. Like most vine
crops, melons require even moisture levels to keep from rotting. The soil should
be barely moist to the touch. Seedlings
should be hardened off before planting, by
reducing water slightly and gradually exposing them to outside temperatures and
sunlight. Vine crops cannot tolerate cool
temperatures, so be sure to bring them
inside the greenhouse
if the temperature
threatens to dip below
40-45oF. Transplant
the seedlings outdoors
in early June when
they are 4 to 6” tall.
Space transplants 4
feet apart in rows 6
foot apart for regular
size melons, and 2feet apart in rows 4feet apart for seedless and icebox varieties. Plant each seedling on a slight
Watermelon
Citrullus lanatus
Cultivar Selection
Recent breeding efforts in watermelon have focused on disease resistance, yield, earliness, and smaller more manageable sized
fruit. Flesh color ranges from pink to red to yellow. Icebox melons are a good choice for short-season gardeners. If you grow seedless melons, you must plant a row of a standard seed variety alongside for pollination.
Irrigation
Melons are shallow-rooted crops and require frequent watering. All vine crops require supplemental irrigation of 1 inch of
water every week in order to assure a constant supply of moisture, particularly during
bloom and fruit development. Soil moisture should not drop below 65%. A handful
of soil at 65% can be formed into a firm
ball. The ball will feel moist, but the soil will
not stick to your hand, and the ball will be
pliable. When broken, the ball will crumble
into medium-sized fragments. Moisture
stress can reduce crop yields. If leaves
begin to wilt midday, plants are moisture
MASTER GARDENERS
stressed. Plants that wilt intermittently may
produce smaller yields, while plants that
wilt frequently or that wilt too long die due
to irreversible cell damage.
Drip irrigation works particularly well with
black plastic mulch. When irrigating vine
crops, it is important to keep water away
from the crown of the plant as even a few
hours of crown wetness can damage the
root system. Water in the morning or early
afternoon so the foliage dries by evening.
This helps prevent the spread of leaf diseases.
Fertility
Melons prefer a soil pH between 6.0 and
6.8; adding lime in SE Wisconsin should
not be necessary. Vine crops require low
nitrogen and high potassium and phosphorous for good fruit development. At planting
time, apply 2 tablespoons per hill of a complete fertilizer such as 10-10-10 or similar
analysis. One week after blossoming begins, side-dress with a 1 tablespoon of 210-0 (ammonium sulfate) or 20-10-10 per
hill, or alternately feed every ten to 14 days
with a liquid feed such as ‘Miracle Grow’ as
the fruits begin to develop. Reduce watering and feeding as fruits ripen.
Harvest
It is difficult to know when to harvest watermelons. If your crop is large enough, you
can periodically sample fruit for flavor. Another method is to observe the part of the
fruit that touches the soil, called the ground
spot. When the ground spot changes from
white to creamy yellow, the melon is ripe
and ready for harvest. A deep-yellow
ground spot indicates overripe fruit. A third
method to determine watermelon ripeness
involves observing the tendril nearest the
melon. If the tendril is firm and green, the
melon is not yet ripe. If the tendril is wilting, the melon is ripe. If the tendril is completely wilted, the melon is overripe. Watermelons will keep for 1 week if stored at
55 to 60 oF. with a relative humidity of 85 to
95%.
Providing university researchbased horticulture information
and educational opportunities
Milwaukee County UW-Extension
932 South 60th Street
West Allis, WI 53214-3346
Phone: (414) 290-2400
Fax: (414) 290-2424
http://milwaukee.uwex.edu
Ozaukee County UW-Extension
Box 994
121 West Main Street
Port Washington, WI 53074
Phone: (262) 284-8288
http://www.co.ozaukee.wi.us
/MasterGardener
Compiled By
John T. Kovatch
.
Pests
Striped
cucumber beetle
Key pests include two species of cucumber beetles; striped and spotted. The striped
(top)
cucumber beetles are more serious in Wisconsin. Cucumber beetles are a problem
Spotted
on vine crops because they transmit the bacterial wilt organism. The striped cucumcucumber beetle
ber beetle is 1/5 inch long and yellow-green in color with three black stripes running
(bottom)
the length of its body. Spotted cucumber beetles are yellow-green with 12 black
spots on their backs. Non-chemical control can be achieved in small plantings by
covering the plants with floating row covers to keep the beetles out. Make sure you
uncover flowering plants to allow the bees to enter and pollinate the plants. If bacterial wilt infections have already occurred, remove the diseased plants immediately to prevent the spread of the disease while insects are present. For
more information, consult University of Wisconsin - Extension publication A2088, Managing Insects in the Home Vege-
Diseases
Watermelons are subject to several wilts, and fungal and viral diseases. Most can be controlled with good soil management, proper rotation, and garden sanitation. Many diseases can be eliminated or reduced by avoiding overhead watering. Where disease is a known problem, choose resistant varieties. Remove plant refuse and control insect pests.