An information system of crops in Hawaii
Department of Tropical Plant & Soil Sciences
University of Hawaii at Manoa



Other Links

Watermelon insects, pests, and plant disease pathogens, Knowledge Master, CTAHR
Ask the Experts--Watermelon


Adapted Cultivars

Red flesh type- Crimson Sweet (open pollinated)

- Glory (hybrid)

Seed Sources

Crimson Sweet- a, b, c, d, e, f, h

Glory- g

a. Abbott & Cobb, Inc.
P. O. Box F307
Feasterville, PA 19047
b. Asgrow Seed Co.
P. O. Box 1087
Tracy, CA 95376
c. W. Atlee Burpee & Co.
300 Park Avenue
Warminster, PA 18974
d. Harris Seeds
961 Lyell Avenue
Rochester, NY 14606
e. Siegers Seed Co 8265 Felch St. Zeeland, MI 49464
f. Stokes Seeds Inc.
Box 548
Buffalo, NY 14240
g. American Takii, Inc.
301 Natividad Road
Salinis, CA 93906
h. Otis S. Twilley
P. O. Box 65
Trevose, PA 19047


Soil Preparation

Watermelons prefer well drained sandy soils. The soil should be well plowed down to about 12 inches. Animal manure have appeared beneficial for early plant establishment leading to higher quality melons.

Manures may be applied in a furrow and covered 3 - 4 inches just below the planting row at the rate of about 4 tons per acre.

It is encouraged that stubble mulch or something similar be provided to ensure rapid vine extension and establishment and to minimize effects of the winds which could roll the vines from side to side interfering with fruit set and development.

Planting Layout and Irrigation

Usually, watermelon planting rows are laid out perpendicular to the prevailing tradewind. One line of trickle irrigation tubing is layed in this planting row. This layout permits the vines to grow down-wind (leeward direction) from where the seeds are p lanted and the up-wind side (windward side) should be free of vines. Two to three weeks after planting another trickle irrigation line should be laid on the leeward side about 20 inches away from the planted row. This is where the first and possibly sec ond sidedressing of fertilizer could be applied. Three to four weeks after planting still another trickle line should be layed on the windward side about 20 inches from the planted row. This is where most of the fertilizer sidedressings would be applied .

In areas where root rots could be a problem, one could consider planting in the middle of a raised bed 48 to 60 inches wide and 4 to 6 inches high.

The frequency and duration of irrigation depends largely on the weather, soil type and to some extent soil borne diseases particularly after the 12th week. In general, melons are irrigated via trickle two to three times a week, four to six hours per irri gation. For heavy soils and if plastic mulch is used one to two irrigations per week may be enough. The fruit set and early fruit development periods are particularly critical in that the growers should avoid water stressing the plants. The crop should not be irrigated heavily just before and during harvesting, for it usually inhibits sugar development in the fruit.

Diseases on Watermelons

Citrullus vulgaris Cucurbitaceae

Papaya Ring Spot Virus

Oidium sp., powdery mildew

Colletotrichum lagenarium, anthracnose

Melaidogyne sp., root-knot nematode

Mycosphaerella citrullina, gumming stem blight


Optimum pH: 5.5 - 6.8

Amount of N, P, K Taken up by Average Crop (lbs./acre)

N = 170P = 25 K = 150

Soil Amendment and Fertilization

Fertilizer and lime rates should be based on soil test results. For most Hawaiian soils with pH less than 5.0 and a calcium content below 2,000 lbs./acre, apply one ton (2,000 lbs.) per acre (4.5 lbs./100 square feet) of agricultural lime or its equivale nt 8 - 12 weeks before planting and broadcast incorporate at least 12 inches. One may consider incorporating just in the planting row (about a four feet swath).

For soils with less than 25 lbs./acre available phosphate, apply 1,000 lbs./acre (2.25 lbs./100 square feet) of treble superphosphate or its equivalent and incorporate at least 12 inches. Both lime and the phosphate could be incorporated together.

For soils low in magnesium, apply 150 - 200 lbs./acre magnesium sulfate (epsom salt) just before planting.

After adjusting deficiencies for pH and phosphorus or for soils within the acceptable pH range and moderate levels of available phosphorus, potassium, magnesium and calcium incorporate in the planting row 600 lbs./acre (1-1/3 lbs./100 square feet) of 10-2 0-20 fertilizer or its equivalent before planting (or transplanting). If magnesium is low, epsom salt could be applied with the 10-20-20. Three to four, six to eight, 10 - 12 and 14 - 16 weeks after planting, sidedress with 300 - 400 lbs./acre (2/3 to 1 lb. per 100 square feet) of 15-15-15 or its equivalent plus 100 lbs./acre sulfate of ammonia (21-0-0) or its equivalent on the windward side of the planted row (assuming vines are extending out to the leeward direction). It is suggested that the sidedre ssing be lightly covered with soil. Additional applications of fertilizers may depend on the progress of the crop.

For fields that have been heavily manured, the early nitrogen applications should be reduced or omitted. Additional nitrogen may be applied 10 - 12 weeks after planting.

Post-Harvest Handling

Watermelons are not adapted for long storage. At 40 degrees to 50 degrees F and 80 - 85 percent relative humidity, watermelons should keep two to three weeks. Watermelons lose red color at low storage temperatures, even at 50 degrees F; while color at 70 degrees F is intensified. Flavor is improved by holding for a week at room temperature.

Seeding to Harvest

Varies according to varieties, location, weather, culture, etc. Generally Crimson Sweet takes about 90 days from seeding and Glory takes about 80 days.

Length of Harvest

Varies, depending on pest incidence, culture, weather, etc.

Generally, between two to four weeks. It may be appropriate to remember that under favorable conditions growers have been able to harvest for as long as three months.

Estimated Yield

Varies, depending primarily on length of harvest. The average yield in the state (last 20 years) is 13,600 lbs./acre and (last five years) 19,800 lbs./acre.

Pruning of Fruits, Determining Maturity and Harvesting of Watermelons

In Hawaii, pruning or thinning of fruits is essentially the removal of deformed and melonfly-stung fruits. Deformed fruits results primarily from water stress and/or insufficient pollination. These fruits are removed at an early stage in order to obtain uniformly well-shaped fruits. In some instances growers remove well-formed fruits if there are more than two or three melons already developing on the plant, usually when there are more than three fruits on a plant, the younger fruits self aborts.

The theory involved in pruning is that when the number of melons per plant is reduced, the plant's producing power will be concentrated in a smaller number of fruits, thereby increasing size and perhaps quality.

Watermelons must be harvested at the right stage of maturity and should come from strong healthy vines. Fruits harvested too early, too late or from weak growing vines will be of poor eating quality. There are a number of ways to determine whether the w atermelon is ripe. The surest method is to stake and label each melon with the date when it reaches three inches in diameter, this melon should be ripe 30 days later. During the first week when Crimson Sweet or Glory melons are just developing, a growe r can accurately determine its age in days by the size of the melon therefore, the person staking (with dates) usually can back-date larger melons estimating when it was three inches in diameter.

Other means of determining the maturity of melons should employ as many as possible a combination of the following factors: (Experience may be necessary to employ the following characteristics.)

Melons should be cut from the vines rather than pulled off, leave the stems as long as possible. This is important for shipping as it helps prevent stem end rot of the melons. Furthermore to the consumer, a green stem is the most convincing evidence of a freshly harvested melon.


Pests on Watermelons

Aphis gossypii Glover, Melon Aphid

Dacus cucurbitae Coquillett, Melon Fly

Liriomyza sativae Blanchard, Vegetable Leafminer

Liriomyza trifolii (Burgess), Chrysanthemum Leafminer

Pycnoderes quadrimaculatus Guerin-Mene., Bean Caspid

Tetranychus neocalidonicus Andre, Vegetable Mite

Thrips palmi Karny, Melon Thrips

Trialeurodes vaporariorum (Westwood), Greenhouse Whitefly



Usually direct seeded, later thinned to one plant per three feet of row; i.e. two plants every six feet, etc.

Planting Schedule

Year round from sea level to 2,000 feet elevation. March - September, 2,000 feet to 3,000 feet elevation. Best market demand March through October; highest prices, March and April.


Assuming culture employing trickle irrigation and plastic mulch, space plants three feet apart between plants and 10 - 12 feet between rows. Allow 6 - 7 feet extra space between every two rows for spray and harvest equipment.

Amount of Seed

Direct seeding - 1 to 2 lbs./acre

Transplanting - 1/3 to 1/2 lb./acre

Seeding Depth

3/4 - 1 inch


For sweeping winds across flat areas, a wiliwili, Erythrina spp., windbreak planting or something similar spaced every 200 feet perpendicular to the wind direction plus at least a row of triploid sudex or double row of corn planted for every two rows of w atermelon. The corn or sudex should be planted two to three weeks before the watermelons and shreaded at about 80 days (before corn seeds mature). For some melon farms it may be necessary to remove the sudex or corn in order to protect watermelons from some unwelcomed harvesters.


Black polyethylene mulch can provide benefits in watermelon production. They include: reducing the cost of early weed control, enhancing the early growth and establishment of the crop, may also enhance nematicide activity, minimize leaching of soluble n utrients during heavy rains and maintaining a more uniform soil moisture level between irrigations.