Many new varieties of watermelons have been developed in recent years.
Yellow and seedless types are finding an increasing share of the specialty watermelon market. It
is estimated that seedless red and yellow varieties that were virtually unknown ten years ago,
and represent about 5% of the market today will increase their market share substantially in the
near future. Small excellent quality "icebox" melons are also becoming increasingly popular.
Maturity is approximately 80 days for small ice box types to 95 days for
large-fruited melons from transplants in the Willamette Valley, or from seed in the lower Columbia River
and Snake River areas.
Red flesh, seeded:
Green-striped rind, 20-30 lb, nearly round: Crimson Jewel, Crimson Sweet (Fusarium
Oblong: Allsweet, Fiesta, Royal Sweet, Sangria (early), all are Fusarium 1
resistant; Klondike Striped Blue Ribbon. Note: Klondike melons are
listed as being susceptible to bacterial rind necrosis which can be problem in
Northwest production. For trial: Allsweet, Jubilee (Fusarium 1 resistant), Jubilee II (anthracnose resistant).
Dark green rind, 15-25 lb, oblong: Peacock Resistant, Calsweet,
Klondike R-7, Klondike 155 (deep pink flesh).
Light green rind, 15-25 lb, oblong: Royal Jubilee (has
darker green stripes).
Important Note: "Gray" watermelons of all types are believed to be more
susceptible to "Fruit Blotch", a disorder that has resulted in many seed companies discontinuing
sales of these types in the U.S.A. Some varieties of this type are: Charleston Gray, Baby Gray,
Prince Charles, Minilee, Mickylee, and Charlee.
Icebox or "Breakfast", 6-10 lb, red-flesh types: Sugar
Baby (dark green skin), Tiger Baby (oval with green stripes on light green background).
Yellow flesh, seeded: Yellow Doll, Petite Yellow.
King of Hearts, Nova, and Laurel (similar to Crimson Sweet); Scarlet Trio (Jubilee striping),
Farmers Wonderful, Tri-X-313 (main season, crisp, green-striped, oval, 15-18 lb).
For trial: Fummy and Jupiter (Sugar Baby types), Queen of Hearts,
Crimson Trio, Millionaire, Cotton Candy, Supersweet 5032, Novel One, Tri-X Triple Sweet (main season,
Crimson Sweet-type, 16-18 lb), Tri-X-626 (early, round, dark green, 14-16 lb), Tri-X Shadow (oval, dark green,
main season,14-16 lb), Tri-X Sunrise (oval, Jubilee-type, striped, 18-20 lb).
Seedless, yellow: Honey Heart, Orchid Sweet. For trial:
Tri-X Chiffon (round, green-striped, main season, bright yellow flesh, 10-12 lb).
Important "seedless" marketing note: "Seedless" varieties may have some
seeds, especially in the first fruits set if the plant is under moisture or temperature stress.
Varieties differ in the incidence of this (see also "pollination" section, below). Also, there are always
rudimentary seeds that are edible, but varieties differ in the color and texture of these, so this should
be pointed out to buyers.
Watermelons are best adapted to the warmer areas of Oregon, but may be
grown in western
Oregon if plastic ground mulches and row covers are used. They are grown
primarily in the Hermiston area, but may also be grown in the Ontario and
Air pollution (ozone, sulfur dioxide and sulfur trioxide) can seriously
injure watermelon vines.
Resistant varieties are Royal Jubilee, Charleston Gray and Prince Charles.
Susceptible ones are
Sugar Baby, Crimson Sweet, and Jubilee.
SEED AND SEED TREATMENT
Watermelon seed numbers approximately 8,000/lb. Use fungicide-treated seed.
Watermelons are subject to damping off and decay in cool wet soils. Seedless
varieties may germinate very poorly, depending on variety. Expect to require 30% extra
seed. Some seed companies offer primed seed, which can substantially improve germination.
The minimum soil temperature at the 2-inch depth required for
germination of these crops is 60 F,
with the optimum range between 70 to 95 F. Seedless varieties should not be
direct seeded (see "Transplant Production" section, below).
SEEDING AND TRANSPLANTING
Watermelons are normally direct seeded in eastern Oregon and
transplanted in western Oregon.
All seedless watermelons are transplanted (see "Transplant Production" and
"Flowering and Pollination" sections below). Use approximately 1.5-2.5 lb of seed/acre
depending on seed size and variety.
Under normal conditions, about 15-25 square feet per plant is optimal.
This would result in a
plant population of 1200-1700 per acre. Where wind damage may be a factor,
plant 6 seeds per foot and thin to an in-row spacing of 12-36 inches with 6-12 feet between
rows. The closer spacings help tie the vines together and reduce wind damage.
Begin seeding April 10 - May 5 in the Columbia Basin and mid-May in the
Willamette Valley. Minimum soil temperatures between 55 and 60 F at the 4-inch depth are
desirable for first 48 hours of planting. Plant the seed 1 inch deep.
Use windbreaks as necessary especially in eastern Oregon. Grain
windbreaks are effective when grain rows are used for each melon row. Establish windbreaks
in the fall, spacing windbreak rows at intervals the width of the melon rows. Winter wheat
varieties, rye, or oats can be used. Spring barley may be used for February plantings. Seed grain
thickly, 2-3 seeds/inch. This requires about 10 lb of barley, 9 lb of wheat, or 8 lb of rye to
seed grain rows 12 feet apart.
Windbreaks may be cultivated out after the melon plants are well established.
If they are not, windbreaks should not be allowed to touch the plants because abrasion of the
enlarging fruit can cause that fruit to be misshapen. Windbreaks may be
cut off or rototilled around mid June before melon vines develop long runners
that may be damaged by tractor tires.
Direct seeding is not recommended for seedless watermelons due to the
high cost of seed and its
slow and erratic germination under all but ideal conditions. To produce
transplants, seed in
modular trays in the greenhouse, allowing 3-4 square inches per plant.
Research in Florida and elsewhere has shown the following for seedless watermelon germination:
Note: As a general rule direct field seeding of the pollenizer variety should be done on the same day the triploid seed is planted in the greenhouse. Small-fruited,
icebox varieties usually flower earlier than standard watermelon varieties. If icebox varieties are to be used as the pollenizer, then direct seeding should be
delayed a week to ten days. The diploid icebox pollenizer variety will frequently set fruit and stop producing male blossoms while the triploid variety is still producing
female blossoms. Growers may make a second planting of a pollenizer 2 to 3 weeks after the initial planting to provide pollen for the late-developing
female blossoms on the triploid variety. No consistent differences among any standard and icebox types in effectiveness of pollination have been noted.
Icebox varieties used as pollenizers result in high early yields; standard varieties used as pollenizers result in high total yields.
- Seedless watermelon seed germination requires temperatures of 85-90 F.
- Excessive water during germination must be avoided. Water transplant growing medium well
and allow excess moisture to drain and moisture to stabilize for 24-48 hours. Bring medium temperature to 85-90 F before seeding.
- Seedcoat adherence to cotyledons may be virtually eliminated by orienting the seed in transplant trays with the pointed end up at a 45 to 90 degree angle.
- After seeding, place transplant trays in a germination room where temperature is held at 85-90 F and humidity is not limiting.
- When seedlings begin to emerge, move the trays to a greenhouse held at 80 F until emergence is complete.
- Water only if necessary during the first week. Do not overwater.
- After germination is complete, vary greenhouse temperature as needed to produce a sturdy transplant.
Depending on transplant container size,
seedlings should be
between 3 and 5 weeks old (with 3-4 leaves per plant) at transplanting. Older plants establish
very slowly in the field.
Transplant to the field after all danger of frost has passed and soil
temperatures are, and are likely to
remain, above 70 F. Once established, seedless varieties are quite vigorous,
and are resistant or tolerant to several soil-borne and foliar diseases.
FLOWERING AND POLLINATION
Watermelons bear separate male and female flowers on the same plant
(monoecious). Only the female flowers set fruit. Bees transfer pollen from male flowers to female
flowers, making fruit set possible.
It is recommended that at least one honey bee colony be introduced for
every acre during the
blooming period since native bee populations may not be adequate, or may not
with the blooming period. Research in California indicates that "a higher
quality marketable crop
results. Furthermore, "the harvest period was advanced a week or more and
shortened by one week, reducing the pickings necessary by 33%".
Placement of colonies in the field has an effect on the number of bee
visits per flower. Visits per
flower were more than doubled with colonies spaced no more than 175 yards
apart in comparison
with colonies placed at only one spot in a (40 acre) field. At no time should
any portion of a field
be more than 250 yards from a bee hive. Avoid using insecticides injurious to
bees and manage
application of pesticides in a manner to protect bees and apiaries from injury.
For successful seedless watermelon production, an adequate bee
population is especially
important to transfer the pollen from the pollenizer variety to the seedless
watermelons do not produce pollen). The pollenizer variety is normally
planted in alternate, or
every third row to insure adequate pollen movement by the bees. At least
eight visits to an
individual flower of the seedless variety are necessary for adequate hormonal
normal fruit development. For more information on beehive quality and pollination, see the
OSU Publication PNW-245 Evaluating Honey Bee Colonies for Pollination, A
Guide for Growers and Beekeepers.
When first flowers occur under periods of temperature or moisture
stress, first fruits are often
seedy, rough, small and of poor quality. To reduce this risk, growers often
remove first fruit by
hand when it is small or delay placement of bees for one or two weeks or until
the first female flowers have dropped off in the seedless variety.
Use a distinctly different variety for the normally seeded pollinator
in order to easily distinguish
the seedless fruit from the pollinator for marketing purposes.
Questions come up about cucumbers, melons, gourds, and summer and winter
squash, crossing and affecting the eating quality of one vine crop or another.
This is NOT a problem. Intercrossing is only a problem when seed is saved for
replanting, in which case squashes of the SAME species need to be isolated for
crop purity. Cucurbits of different species do not intercross sufficiently to create
problems for seed producers.
For information regarding cucurbit seed production, see the publication
"Cucurbit Seed Production in the Pacific Northwest," PNW 226, which can be
obtained from the Cooperative Extension Services of Oregon, Washington, and Idaho.
Gibberellic acid (GA) is labelled for stimulation of fruit set in watermelon (except in California) during periods of cool temperatures. The rate is 2 g
ai/acre in sufficient water to obtain thorough foliage coverage. The label calls for one application before bloom followed by
two more applications at intervals of 10-14 days. Caution: The efficacy of GA applications for stimulating fruit set in melons has not
been confirmed by research in the Pacific Northwest.
The following are general recommendations. A soil test is recommended
for each field to be
planted. The following are recommendations for eastern Oregon production.
Nitrogen: 90-120 (N) lb/acre. Apply l/2 to 3/4 of the N as a
side dressing as the vines
begin to send out runners. Account for residual N levels in the top 24
inches of soil, as you
plan your fertilizer requirements. Excess N is detrimental
to watermelon flavor.
Phosphorus: 50-80 (P2O5) lb/acre. Band all the phosphorus 2 inches to
the side and 2 inches
below the seed row.
Potassium: 60-120 (K2O) lb/acre. Broadcast before planting.
Sulfur: 30-50 (S) lb/acre. Broadcast before planting.
Micronutrients: Apply as determined by soil test. Micronutrients that
should be tested for are
zinc, manganese and boron.
Watermelon is known to be sensitive to manganese toxicity, a common problem
in low pH soils in western Oregon. Data from Mississippi indicates an
association between high leaf manganese concentration and poor growth and yield of
watermelon. Seedling watermelons react to manganese toxicity with stunted
growth and yellowish crinkled leaves. Older plants generally
exhibit brown spots on older leaves that may be mistaken for
symptoms of gummy stem blight.
Manganese toxicity is usually associated with soils having a pH
below 5.5. However, in wet seasons the condition may occur at
higher pH levels when the soil has been saturated for a period of
several days. This condition has been noted in several watermelon
fields with pH ranges at 5.8 or slightly higher when
the crop was planted flat. Planting watermelons and other
cucurbits on a bed is good insurance against manganese toxicity
during a wet season.
The best solution to manganese toxicity is to apply lime in the
fall at rates based on the results of a soil test. A pH of 6.0 should be maintained for maximum yields, according to the Mississippi study.
GROUND MULCHES AND ROW COVERS
The use of black plastic or clear plastic ground mulches is recommended,
especially in western
Oregon, to enhance yield and earliness. Black plastic mulch controls weeds,
may increase soil temperature, conserves moisture, and protects fruit from
ground rots. For black plastic mulch to increase soil temperature, it is
critical that the soil surface be smooth and that the plastic be in close
contact with the soil. This can only be achieved by laying the plastic with a
machine designed and properly adjusted for this task. Clear plastic mulch is
superior for heat transfer to the soil but does not control weeds.
A new generation of plastic mulch films allows
for good weed
control together with soil warming that is intermediate between black plastic
and clear film.
These films are called IRT (infrared-transmitting) or wavelength-selective and
are brown or green in color.
They are more expensive than black or clear films, but may be cost effective where soil
warming is important.
Plastic, spunbonded, and non-woven materials have been developed as crop covers for use as
windbreaks, for frost protection, and to enhance yield and earliness. They complement the use of
plastic mulch and drip irrigation in many crops. Some sources of these materials and information on their
American AgriFabrics, Alpharetta, GA. Phone 770-663-700, fax: 770-663-7690, email: firstname.lastname@example.org.
Ken-Bar, Inc., Reading, MA. Phone: 800-336-8882, fax: 781-944-1055, email: email@example.com.
Non-woven or spunbonded polyester and perforated polyethylene row covers
may be used for 4 to 8 weeks immediately after seeding or transplanting. Covers should be removed when
plants begin to
flower to allow proper pollination. Row covers increase heat unit
accumulation by 2 to 3 times
over ambient. Two to four degrees of frost protection may also be obtained at
night. Soil temperatures and root growth are also increased under row covers as are early
yields, and in some cases total yields.
Watermelons are deep rooted in sandy soils when growth is vigorous.
They require uniform irrigation for optimum growth and yield. Reduce irrigations as fruit reach
harvest stage. A total of 12-15 inches of water may be needed in western Oregon and 20-25 inches in
eastern Oregon, depending on seasonal variation, area, irrigation method (drip or sprinklers)
and variety. Approximate summer irrigation needs for the Hermiston area have been found to
be: 3.5 inches in May, 5.0 in June, 7.5 in July, and 7.0 in August. Research has shown that the
use of drip irrigation under black plastic
mulch is superior to sprinkler irrigation with black plastic mulch. Yields usually increase
dramatically. Drip irrigation under plastic mulch is an effective way of
applying water efficiently and may
reduce total water requirements by as much as 30%.
Soil type does not affect the amount of total water needed, but does
dictate frequency of water
application. Lighter soils need more frequent water applications, but less
water applied per application.
Watermelon is often grown with furrow irrigation in eastern Oregon. Water soluble polyacrylamide (PAM) is
useful for flocculating soil particles in irrigation furrows and
reducing erosion of soil from the furrow.
HARVESTING, HANDLING, AND STORAGE
Yields have ranged from 2,000-3,000 fruit per acre for standard
varieties and ground culture (more
for icebox types). This equals about 15 to 30 tons/acre. With the adoption
of new production
practices, yields of 45 to 70 tons/acre have been produced when plastic mulch,
row covers and
drip irrigation are used in conjunction with disease-resistant hybrids. Under
harvest in the Hermiston area begins around August 1.
Watermelons are hand harvested into bins or trucks for shed packing.
Use every sixth or eighth
row as a heap row. Shortly before the harvesting season begins, the vines are
turned out of the
alleys. Harvest only melons that are ripe. Ripeness is indicated by a
creamish to slight
yellowing of the white background color of the part of the melon that rests
on the ground.
Drying of the stem tendril nearest the attachment point of the watermelon and
green color tone of
the rind are also indicators of ripeness but these vary with cultivar. Melons
should be cut from
the vine rather than pulled, twisted, or broken off.
Never stand melons on end, and handle the melons carefully at all times.
For highest sugar levels,
vines must be maintained in a healthy state throughout harvest.
Seedless varieties have thicker, more durable rinds than standard
varieties, and hold better (do not
become overripe as quickly) in the field, and in storage.
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Hold watermelon at 50 to 60 F and a relative humidity of 90 %.
Watermelons are not adapted to
long storage. At low temperatures the are subject to various symptoms of
chilling injury and loss
of quality, and at high temperatures they are subject to decay. Between 50
and 60 F is a good
compromise. Watermelons should keep at this temperature range for 2 to 3
weeks; some will
keep longer. Melons held 6 weeks at room temperature will have poor
Watermelons should be consumed within 2 to 3 weeks after harvest,
primarily because of the
gradual loss of crispness. Quality in watermelons is determined largely by
high sugar content, a
deep red fresh color, and a pleasant crisp texture of the edible flesh. These
factors are dependent
on maturity, cultivar, and handling methods. Commercial melons for distant
market are usually
harvested when mature, but before full ripeness, to minimize handling damage
breakdown. They are at their best for eating when mature . Immature melons
have a pink flesh,
mature melons are red to dark red, and over-mature ones have orange flesh.
Actually, the red
color and flavor of watermelons improve during storage for 7 days at or above
while at 50 F or below color fades. The decrease in redness may be due to
chilling, since these
melons develop other symptoms of chilling, such as pitting and loss of flavor,
In tests with Florida watermelons stored at 43, 50, and 60 F for 2
weeks, chilling injury was
observed during and after storage at 43 and 50 F but not at 60 F. Decay,
mainly black rot, was
always higher on melons previously stored at 43 or 50 F than on those held at
60 F, and it
developed mainly after storage. Although decay is usually not a major form
extended storage at warm temperature 75 F will result in more decay than at
Seedless watermelons retain their quality for 2-3 weeks at temperatures of
50-60 F and 90%
Watermelons are sensitive to high levels of ethylene gas during storage,
as it hastens loss of
firmness. Melons exposed to 30 or 60 ppm ethylene for 7 days at 65 F were
eating. Even at the relatively low concentrations of 5 ppm ethylene,
watermelons will become
less firm and less acceptable. Watermelons should not be stored or shipped
with fruits that emit
substantial amounts of ethylene.
Rough handling will result in serious losses. Watermelons should not be
dropped, thrown, or
walked on, as internal bruising and flesh breakdown will occur. Cartons
holding three to five
melons and bulk bins with pallets, if used, can speed handling and minimize
Storage and marketing diseases are black rot, phytophthora rot, rhizopus
rot, and stem-end rot.
Watermelons are packaged in 55 to 80-lb cartons holding 3-5 melons;
80-lb 2WGA crates; 800 to
1000-lb small bins; 1400 to1800-lb medium bins; or, shipped in bulk truck
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