When to fertilize watermelons?

Fertilizing Watermelons: What Fertilizers To Use On Watermelon Plants

I could be eating a juicy wedge of watermelon when it’s 20 below, the wind is howling and there’s 3 feet of snow on the ground, and I would still be daydreaming about warm, lazy summer days and nights. There is no other food that is so synonymous with summer. Growing your own watermelon may take a bit of work but is definitely rewarding. In order to get the sweetest, juiciest melon, what kind of fertilizer do you need to use on watermelon plants?

Watermelon Fertilizer Schedule

There is no set watermelon fertilizer schedule. Fertilizing is determined by the current soil condition and, thereafter, by the stage at which the watermelon plant is growing. For example, is it an emergent seedling or is it in bloom? Both stages have different nutritional needs.

When fertilizing watermelon plants, use nitrogen based fertilizer at the onset. Once the plant begins flowering, however, switch to feeding the watermelon a phosphorus and potassium based fertilizer. Watermelons require ample potassium and phosphorus for optimal melon production.

What Fertilizers to Use on Watermelon

How you are going to fertilize watermelon plants and with what type of fertilizer are best determined by a soil test prior to sowing or transplanting. In the absence of a soil test, it’s a good idea to apply 5-10-10 at the rate of 15 pounds per 500 feet. To minimize possible nitrogen burn, mix the fertilizer thoroughly through the top 6 inches of soil.

Providing compost rich soil at the onset of planting will also ensure healthy vines and fruit. Compost aids in improving the soil structure, adds micronutrients and aids in water retention. Amend the soil with 4 inches of well-aged compost mixed into the top 6 inches of soil prior to setting watermelon seeds or transplanting.

Mulching around the watermelon plants will improve moisture retention, retard weed growth and slowly add nitrogen rich organic matter to the soil as it breaks down. Use straw, shredded newspaper or grass clippings in a 3- to 4-inch layer around the melon plants.

Once the seedlings have emerged or you are ready to transplant, top dress with either 5-5-5- or 10-10-10 general all-purpose fertilizer. Fertilize the watermelon plants in the amount of 1 1/2 pounds per 100 square feet of garden space. When fertilizing watermelons with granular food, do not let the fertilizer come into contact with the leaves. The leaves are sensitive and you could damage them. Water the fertilizer in well so the roots can easily absorb the nutrients.

You can also apply liquid seaweed fertilizer when the foliage first emerges and once the plants have flowered.

Just before or as soon as the vines begin to run, a second application of nitrogen is advisable. This is usually 30-60 days from planting. Use a 33-0-0 fertilizer at the rate of ½ pound per every 50 feet of the watermelon row. Water the fertilizer in well. Fertilize again once the fruit has just emerged.

You may also side dress the vines prior to running with a 34-0-0 food at the rate of 1 pound per 100 feet of row or calcium nitrate at 2 pound per 100 feet of row. Side dress again once the fruit has just appeared on the vine.

Avoid using any nitrogen rich fertilizer once the fruit has set. Excess nitrogen will just result in superfluous foliage and the growth of the vine, and will not nourish the fruit. An application of fertilizer that is higher in phosphorous and potassium can be applied while the fruit is maturing.

Most importantly, give the watermelon plants water. There’s a reason the word “water” is in their name. Plentiful water will allow for the largest, sweetest, and juiciest fruit. Don’t overwater, however. Allow the top 1-2 inches to dry out between watering.

How to Grow Watermelon: Watermelon demands warm temperatures—both soil and air.

Luscious, liquid sweetness: since watermelon is nearly always eaten on its own either sliced or quartered, growing it juicy and sweet is always the objective.

To grow sweet and tasty watermelon, follow these steps:

Temperature. Watermelon demands warm temperatures—both soil and air. Transplant or direct seed watermelon only when the average soil and daytime air temperatures are at least 70°F (21°C). Do not grow watermelon unprotected where nighttime air temperatures fall below 60°F (16°C). If the air temperature dips, protect watermelons with floating row covers.

More growing tips at How to Grow Watermelon.

Soil. Grow watermelon in rich, well-drained soil. Planting watermelon on hills or mounds ensures that roots stay warm and that the soil is well drained. Amend the planting area with compost and well-rotted manure. Where you plan to sow seed or set transplants, dig a hole 1 foot (30 cm) deep and 1 foot wide; fill the hole with rich aged compost and manure mixed with several handfuls of sand—the growing spot will be both moisture retentive and well-draining. Add a handful each of rock phosphate (rich in phosphorus), earthworm castings (all-round nutrient rich), and Epsom salts (rich in magnesium). Use the soil removed from the hole to build a mound on top and rake it flat. Sow seed or set a transplant there. Watermelon roots commonly grow 8 to 10 or more inches deep; the hole and mound become a reservoir of moisture and nutrients. More tips: Watermelon Seed Starting Tips.

Care. Space watermelons 6 to 12 feet (1.8-3.6 m) apart; don’t let plants compete for soil moisture or nutrients. (Keep weeds down until vines spread and shade the soil.) If watermelons are stressed for water or nutrients when they start to set fruit, they will be small and less flavorful. Feed watermelons with a dilute solution of fish emulsion fertilizer—1 tablespoon per gallon of water—weekly from the time the plant is a seedling until the first female flower appears. (Mark the calendar on the day the female flowers fully open—the fruit will be ready for harvest 35 days later.)

Water. Give watermelons even moisture from planting through fruit set. During the first 3 to 4 weeks of growth a watermelon develops its root system. The root system supplies the growing plant with both moisture and nutrients. An extensive and strong root system allows the watermelon to take up nearly 95 percent of its weight in water and develop its large cells which are easily seen with the naked eye—these large, water-filled cells give watermelon its crunchy, crisp, yet tender consistency. Never allow a developing watermelon to dry out completely or it may split. Water whenever the top 3 to 4 inches (8-10 cm) of soil become dry; simply stick your finger into the soil to test the soil moisture. Apply a heavy mulch to keep the soil moist after the sun begins to warm the garden in summer.

When to water. Do not overwater a watermelon once it has begun to set fruit or its developing natural sugars will be diluted. The leaves of a watermelon commonly wilt in the hot afternoon sun. Water immediately if the watermelon’s leaves wilt before noon or if they appeared stressed by heat or drought. Never allow the vine itself to become dry. A soaker hose or drip irrigation is the best way to deliver water to watermelon roots; overhead watering may encourage the development of fungal diseases which commonly attack leaves.

No water. Stop watering a watermelon about 2 weeks before the fruits are ready to harvest. Holding back water at this point will concentrate the plant’s sugars and the fruits will become sweeter tasting. More tips:

Harvest. A watermelon is ready for harvest when the curly tendrils on the stem nearest the fruit dry up and turn brown and the spot on bottom of the fruit turns from white or green to yellow or creamy yellow and the top of the fruit turns a dull color. Mark Twain observed that a green melon says “pink” or “pank” when thumped with the knuckles. A ripe watermelon says “punk.” “Punk” is best described as a solid dull sound. More tips: How to Harvest and Store Watermelon.

Two flavorful watermelon favorites:

Watermelon varieties to grow: Watermelons: Top 10 Varieties.

Watermelon profits, farming information and growth stages

Today, we discuss the topic of growth stages of watermelon, watermelon profits and yield. Watermelon (Citrullus lanatus) is a fruit, belongs to family Cucurbitaceae is a flowering plant originally from South Africa. It is a fruit, which is a special type referred by botanists as a pepo, a berry that has a thick rind and flesh mesocarp and endocarp.

Watermelon fruit contains about 6% sugar and 92% water by weight. As with many other fruits, Watermelon is a source of vitamin C. Watermelon rinds, generally a light green or pale green color, are also edible and have many hidden nutrients, but most people avoid eating them due to their unappealing flavor. Watermelons are sometimes used as a vegetable.

Watermelon fruit of standard size grows into long, rambling vines. There are smaller, hybrid vines, which spread to a diameter of 5 or 6 feet. Watermelon vines are clothed with large leaves and light yellow color flowers, which are followed by the juicy fruit.

Watermelon Plant.

Some facts about Watermelon farming:

  • The watermelon is a flowering plant that originated in northeast Africa, where it is originate growing wild. Citrullus colocynthis has sometimes been considered to be a wild ancestor of the watermelon; its native range extends from North Africa and West Africa to west India.
  • Botanically, watermelon is known Citrullus lanatus and it belongs to Cucurbitaceae family.
  • Watermelons need a long growing season with a hot summer, humid atmosphere and a lot of space. These melons are very easy to grow when planting in fertile, well-drained soil with full sun.
  • Watermelons grow in sandy loam soil that drains easily. It grows well in black soil and sandy soil. However, they should have a good amount of organic content and must not withhold water. Water must easily drain off from the soil else the vines are probable to develop fungal infections.
  • According to the Food and Agriculture Organization of the United Nations (FAO), China is the top producer, with 75 million produced in 2014.
  • Watermelons require a long growing season (at least 80 days) and warm ground for seeds to germinate and grow. The soil must be 70 degrees F or warmer at planting time.
  • Watermelon bed in a sunny location with well-drained, loose, rich soil that has a pH level between 6.0 and 7.5. Acidic soil could result in withering away of the seeds. While soil with a neutral pH is preferred, it can grow well even if the soil is slightly alkaline.
  • Give watermelons at least six to eight feet of space between plants because planting them too close discourages the growth of large melons and encourages vegetation growth. For growing watermelons, the best temperatures are between 70 and 90 degrees Fahrenheit, but above this temperature range, the plants can drop their flowers and bland melons effect from consistent temperatures below 50 degrees Fahrenheit during the growing period.
  • The time it takes for a watermelon to mature could be anywhere from 65 to 90 days after planting. Once the fruit sets to tiny marble-sized melons, it takes up to 45 days for those tiny melons to develop into watermelons 10 pounds in size or more.
  • Watermelon is a dry season crop and it should be planted with irrigation. The watermelon beds are irrigated 2 days prior to sowing and then again 5 days after sowing the seeds. As the plant grows, irrigation is finished on a weekly basis. Attention should be paid to water stress at the time of irrigation since it can lead to fruit cracking. While irrigating, water should be restricted to the root zone of the plant.
  • The watermelon sowing time is mid-January to March month and under protection in November to December.
  • In India, since the climate is mostly tropical, all seasons are appropriate for watermelon cultivation. However, watermelon is sensitive to cold and frost. Hence, in parts of the country where winter is severe, watermelons are cultivated after the frost has passed. In places like Tamil Nadu, Maharashtra, Andhra Pradesh, and etc. watermelon cultivation is feasible almost any time of the year.

Read: Okra Farming Cost and Profits per Acre.

Growing stages of Watermelon plant

Seedling: The first stage is also called germination of watermelon growth occurs when seeds are placed in the soil. When soil temperatures exceed 65 degrees Fahrenheit, bury the seed depth of 4 times its width. Once planted and then watered, the seed sends out a stem, or hypocotyl, and root, or radicle. In 3 to 12 days, the hypocotyl pushes the first two leaves, or embryonic leaves, above the surface of the soil.

Vining: 5 to 10 days after germination, the first set of true leaves emerge from the stem. These leaves are capable of photosynthesis, which is the system plants use sunlight to convert carbon dioxide and water to food. A vine of about one foot long grows out and large lobed leaves begin to form. This runner will continue to develop until it reaches about 12 feet in length. About one month after a watermelon plant sends out its first vine, several more vines will start to grow. Leaves form on all the vines and start to grow larger. At this time, top dress plants with 1/2 cup bone meal and gently works it into the soil, being careful not to damage shallow roots. Present watermelon seedlings with one to two inches of water per week.

Growing Stages of Watermelon.

Growth: Watermelon is a space hog; vines can attain 20 feet in length. Thus plant where there is plenty of open ground. Add a balanced fertilizer that is very high in nitrogen. Sow 8 to 10 watermelon seeds in a hill, and push seeds one inch into the soil. Space hills 3 to 4 feet apart, with at least eight feet between rows. Thin plants to the three best in each hill. Maintain soil free of weeds by shallow hoeing or with a layer of mulch.

Watermelon plants have moderately deep roots and watering is seldom essential unless the weather turns dry for a prolonged period. When vines initiate to ramble, side dress plants with half a cup of balanced fertilizer (5-10-5). The third application of fertilizer must be made when melons are set. Withhold water as melons create to mature to intensify sweetness.

Flowering: About 2 weeks after a plant sends out most of its runners, watermelon produces male and female flowers. The male watermelon flowers develop first. They give pollen, but do not produce fruit. The watermelon female flowers form shortly after the male flowers. Watermelon flowers last for one day so there must be an adequate number of bees and other pollinators in the area when the flowers are viable.

Fruiting: Once pollinated, the miniature fruits swell up to form speedily growing watermelons. They are considered viable after they attain the size of a golf ball. This generally takes a day or two. Watermelons will continue to develop for 30 to 35 days as long as they remain undisturbed.

Fruits may be harvested 80 to 100 days after planting. Harvest the fruit when fully mature because once picked they stop ripening and will not develop in any way. Fruits are ripe when the tendrils at the point where the fruit stalk is attached to the major stem become dry and when the color of the rind in contact with mulch turn from green to yellow. Pick fruits with the watermelon fruit stalk attached using a sharp knife. The cut surface of the stalk can be treated with Bordeaux paste.

Depending on the watermelon variety, the fruit takes up to 1 month to fully mature. It can be difficult to know when the melons are fully ripe, particularly at the beginning of the season. Some signs are the tendrils on the vine varying from green to brown, the spot on the ground where the melon laid changes from white to yellow and the sound made when thumping the watermelon changes to a hollow sound.

Read: Garlic Cultivation Project Report.

The yield of Watermelon and profits of Watermelon:

Yield of Fruits

The average yield of 25-30 tonnes/hectare (4.5kg – 11kg/fruit) can be obtained depending on watermelon variety and adherence to good agricultural practices.

When it comes to watermelon profits, it is very much profitable crop due to growing demand and income per acre. A watermelon farmer gets a profit of 2 lakhs to 3 lakhs per acre in India in 2 to 3 months period. However, Japanese watermelon gives good profits for farmers.

In western countries, The yield of watermelon is about 10,000 to 75,000lbs/acre and expected profits are $1000 to $25,000 per acre.

Read: Growing Tomatoes from Seeds.

Watering and Fertilizing Watermelon

You should think about fertilizing watermelon after the vines begin to spread out and again when the blossoms appear and the fruit is set. You should think about watering your watermelon patch for the first few weeks after planting the seeds.

Watering Watermelon
Watermelon plants have somewhat deep roots that are good at extracting moisture from the soil. Until these roots are developed, you should water the plants regularly with slow, deep soaks. For the first 3 weeks after planting, water your watermelon patch once or twice a week if no rain falls in your area. After the seeds have sprouted, scale back the watering to once every 10 days or so. When the vines begin to spread out, you can stop watering all together, as long as rain falls every 10-14 days. If you’re not sure if the plants are getting enough water, dig down about 4 inches into the soil with your fingers. You want the dirt at this depth to be moist, but not wet. If it is dry, water the plants. If it’s wet, let it dry out for a few days and check again. Stop watering the plants altogether about 10 days before you harvest the melons. This will allow the sugars in the fruit to concentrate and the flesh to stay crisp. This makes for much better tasting watermelon.

Fertilizing Watermelon

Wait until the vines begin to spread out before fertilizing your watermelon plants. If you’re using a granular fertilizer, choose a balanced one like a 10-10-10 or 5-5-5. These three numbers mean that there are balanced amounts of nitrogen, potassium and phosphate in the fertilizer. Follow the manufacturer’s directions for the correct dosage. Most granular fertilizers are applied at a rate of 1 1/2 pounds per 100 square feet. Scatter the fertilizer around the plants and water it in well. Make sure that the fertilizer does not come in contact with the plant, as this may cause the plant to burn.

A water-soluble type fertilizer also works well. This is our method of choice, and we typically use a 1 gallon jug to mix the fertilizer and then pour it right at the base of the main stem. A second application of fertilizer can be used after the blossoms appear and the fruit begins to set. This will ensure that the plants are getting the energy they need to produce high quality fruit.

In our own garden, we add fertilizer to the soil a few days before we even plant. We scatter a balanced granule fertilizer in our watermelon patch, along with some lime, and water it all in. Then a few days later, we till one last time and plant the seeds. After that, we switch to a water soluble fertilizer for the rest of the season.

Now that you know about fertilizing and watering watermelons, it’s time to think about harvesting them.

Watermelon (Citrullus lanatus​) ​is grown in all parts of the country, but the warmer temperatures and longer ​summers ​of ​the ​​south ​are​​ ​especially favorable for​ ​this juicy treat. In ​northern states select short-season varieties​, start seeds early indoors​, and do whatever it takes to protect ​this ​​cold-sensitive crop from frost.​

​Grow watermelon ​– available in many shapes and ​sizes — ​in well-worked soil under full sun after all danger of frost has passed. Give them plenty of room ​to roam ​and keep the patch well-watered. When the melon responds to a rap from your knuckles with a good resonant thunk, it’s ready!

Watermelon is not only low in calories it’s packed full with nutrients and valuable health benefits. Thirst-quenching fruits are an excellent source of potassium, vitamins A and C, dietary fiber and beta-carotene. They also include super-sized amounts of lycopene, a powerful anti-cancer compound. So go ahead and eat it up!

Fun Fact: Early explorers used this flavorful fruit to store water, similar to a canteen.


Watermelon Seeds

This great summer treat is even better when you grow it yourself.

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Choose from a large selection of heirloom watermelon seeds available at Planet Natural. Planting instructions are included with each ​packet and shipping is FREE!

Quick Guide: Planting, Growing & Harvesting Watermelon

  1. Choose a watermelon based on your climate — short-season varieties exist!
  2. Start seeds indoors or choose nutrient-rich soil outdoors in full sun
  3. Warm the soil and provide additional coverage for cooler weather
  4. Water and fertilize regularly for optimal results
  5. Provide plenty of space for vines and fruit
  6. Consult a clairvoyant to determine when to harvest — it’s an art form
  7. Pests and diseases include cucumber beetles, aphids, mites, squash bugs, fusarium wilt, anthracnose, alternaria leaf spot, and curly top

Site Preparation

Select a site where your plants will get full sun and good air circulation. A gentle, south-facing slope is ideal. Watermelons grow in many kinds of soil, but prefer a light, sandy, fertile loam that drains easily. Add generous amounts of manure, compost and leaves to your garden and work the soil well prior to planting. Melons like lots of water, so keep the soil moist at all times.

How to Plant

In cooler climates, start watermelon seeds indoors 3-4 weeks before the last frost date and watch the weather carefully before planting outdoors.

For direct seeding, soak seeds in compost tea for 15 minutes prior to planting. Plant in hills 1/2 to 1 inch deep. For most varieties, sow two to three seeds per hill, spacing the hills 8 to 10 feet apart. Thin seedlings in the hill to two seedlings one week after they have germinated. Small bush varieties may be spaced 3 feet apart.

If black or clear plastic was used to pre-warm the bed, cut holes in the plastic and set the plants 1/2 to 1 inch deeper than they were planted in their containers. Water thoroughly after transplanting.

Watermelons are heavy feeders. Apply an organic fertilizer during planting. Spray plants with liquid fertilizer and seaweed extract throughout the garden season. Cut back on nitrogen levels after flowers form. Continue with phosphorous and potassium applications until just before harvest.

Tip: Use Harvest Guard® row cover to warm the air and soil around heat-loving crops. It can also be used as a barrier to protect plants from invading pests.


Determining when to harvest watermelons can be difficult and requires some experience. For the most part when ripe, the curled tendril at the stem end dries to brown, the underside of the fruit turns yellow or cream colored, and the melon will yield a deep, resonant sound when thumped.

Allow 80-90 days for bush varieties to reach maturity and 90-100 days or more for the larger varieties.

Insect & Disease Problems

Cucumber beetles, aphids, mites, squash bugs, fusarium wilt, anthracnose, alternaria leaf spot, and curly top are some of the problems home gardeners should be on the lookout for. Visit our Pest Problem Solver for pictures, descriptions and a complete list of safe, effective remedies.

Seed Saving Instructions

Watermelons will cross-pollinate, so isolate 1/2 mile from other varieties to maintain purity. When fruit is ready to eat, the seeds are also mature. Collect seeds and wash gently with a mild dishwashing soap. Rinse thoroughly and allow to dry.


Recommended Varieties

Standard Seeded Varieties:

  • Crimson Sweet
  • Royal Sweet
  • Top Gun
  • Sentinel
  • Sangria

Seedless Varieties:

  • Liberty
  • 7197
  • 7187
  • Majestic
  • Obsession
  • Fascination


It is best to base fertilizer application on the results of a soil test. If a soil test has not been taken, apply 5-10-10 at 30 pounds per 1,000 square feet before planting. Melons should be side-dressed before the vines start to “run.” Side-dress with 34-0-0 at 1 pound per 100 feet of row or calcium nitrate

(15.5-0-0) at 2 pounds per 100 feet of row. Sidedress a second time after bloom when fruit is developing on the vine. Too much nitrogen fertilizer can encourage excess vine growth and reduce fruit growth. For information on how to submit a soil sample, please see HGIC 1652, Soil Testing.


Watermelons need a lot of water. In fact, water comprises 92 percent of the watermelon fruit. Surprisingly, the bulk of watermelon roots are found in the top 12 inches of soil. Consequently when watering, try and apply only as much water as the root zone (top 12”) can hold. Going beyond this depth not only wastes water, but the nutrients in the soil solution as well. Proper watering may require several short duration water cycles during the day.

The use of drip irrigation is very beneficial in that no water is applied to the foliage but is applied to the plant root zone instead. An inexpensive timer attached to the water source and applying water to your drip system allows automation of multiple short irrigation cycles. Although watermelon plants should not suffer from lack of water during any growth stage, it is extremely important to maintain consistent irrigation cycles during fruit set and development. If using overhead irrigation, water in the morning so the foliage has time to dry before dark. Wet foliage encourages foliar diseases.


Watermelon plants have male and female flowers. For proper fruit development, sufficient pollen must be moved from the male flower to the female flower. The male flowers produce big sticky grains of pollen when compared to pollen from most other plants. Consequently, wind movement of pollen from male to female flowers is inadequate, and insects, such as honeybees, native bumblebees, and others, are necessary for proper pollination. For proper fruit development, a female blossom requires between 500-1000 grains of pollen, which is usually achieved by around eight bee visits for seeded and twenty-one bee visits for seedless watermelons. The greater number of bee visits necessary for seedless watermelons is due to the pollinators carrying infertile pollen from surrounding male seedless flowers as well as fertile pollen from the seeded varieties.

The seeded varieties listed in the “Recommended Varieties” section have viable pollen, and if sufficient numbers of pollinators are available, fruit set should not be a problem. The seedless varieties listed above do not have viable pollen and will need a seeded variety planted within 10 feet to provide adequate pollen for seedless watermelon fruit set.


Make sure to know the approximate number of days to maturity for the particular variety to be planted. For example, most of the varieties listed take between 85 to 90 days from transplant to first ripe fruit. From the time of fruit set, it takes approximately 35 days to fruit ripening. A few rules of thumb to use to help determine if the watermelon variety is ready for harvest:

  • the fruit looks to be expected size,
  • the tendril closest to the fruit turns brown,
  • the skin color loses its gloss and becomes dull in color, and
  • the bottom of the fruit has a large white to cream color oval spot.


Poor pollination is the most common cause of mis-shapened fruit. Honeybees and several species of native bees pollinate watermelons. If adequate pollen is not deposited, fruit may be mis-shapened. To promote proper pollination, consider establishing a honeybee colony on site. Honeybee information can be found at http://scstatebeekeepers.com/ and http://www.clemson.edu/extension/beekeepers/index.html. To protect pollinators, avoid spraying insecticides while bees are foraging, especially between 8:00 am and 4:00 pm.

Watermelon fruit may be mis-shapened because of poor pollination.
Justin Ballew, Commercial Horticulture Agent, Marion County, ©2016, Clemson Extension

Blossom end rot is caused by a calcium deficiency within the plant. However, the development of blossom end rot may not necessarily indicate a calcium deficiency in the soil. Calcium is highly mobile in the plants, and a consistent supply of calcium in the soil solution is necessary to prevent blossom end rot in developing fruit. If the water supply is interrupted, calcium is unable to move to the fruit and rot develops. To prevent blossom end rot, keep the soil uniformly moist, but not saturated. Do not allow the soil to dry out in between watering. Soil test before planting to ensure there is a sufficient level of calcium in the soil. See the “Watering” section for tips on proper watering.

Excessive vine growth and few fruit are usually the result of an over-application of nitrogen fertilizer or by planting too close. For more information, refer to the “Fertilizing” section.

Blossom end rot is caused by a calcium deficiency in the fruit.
Justin Ballew, Commercial Horticulture Agent, Marion County, ©2016, Clemson Extension

Insect problems are usually critical only in the seedling or early growth stage. Cucumber beetles, squash bugs, and aphids are the most harmful insect pests. For more information, please see HGIC 2207, Cucumber, Squash, Melon & Other Cucurbit Insect Pests.

One of the least expensive and most effective disease control measures is crop rotation. Do not plant after watermelon or similar crops, such as cantaloupe, cucumber, squash, and pumpkins, for at least three years. Overhead watering encourages many plant diseases. Diseases that may become a problem include anthracnose, gummy stem blight, powdery mildew, and nematodes. For more information, please see HGIC 2206, Cucumber, Squash, Melon & Other Cucurbit Diseases, and HGIC 2216, Root-Knot Nematodes in the Vegetable Garden.

Watermelon Nutrient Analysis


Analyzing plant tissues for nutrient levels is done for several reasons. Results can be used to determine rates of post-plant fertilizer applications, to test for nutrient deficiencies, and to determine rates of fertilizer needed for subsequent crops. Detecting nutrient deficiencies before the appearance of deficiency symptoms helps prevent or minimize reductions in yield and fruit quality. When fertilizers are applied through an irrigation system (fertigation) regular tissue analysis allows for adjustments in fertigation rates.5

The appropriate time to collect tissue samples will depend on the purpose of the analysis. For in-season corrections, detecting deficiencies early in the season is better, as any corrective applications will have time to be effective. Late season applications have little effect on yield and quality.5 Because watermelon plants have low rates of N uptake early in the season, tissue collection for analysis should begin when plants reach the 3- to 4-leaf stage.2

For many crops, the leaf is the standard reference tissue used to determine nutrient status, but it depends on where the samples will be sent for analysis and the tissue used to develop the reference information. For watermelons, petioles are commonly used for analysis.5 For most nutrient tests, tissue from the most recently matured leaf provides the best indication of a plants nutrient status. These are leaves that have changed from lighter-green to a mature dark-green color, and the leaves have reached the fully expanded size. For elements that are relatively immobile in the plant , tissues from younger leaves are better indicators of deficiencies.

Collect whole leaves or petioles without including any stem or root tissues. Collect tissues of the same physiological age and position (most recently matured). If sampling from very young plants, the whole above-ground part of the plant can be collected. Samples should consist of 25 to 100 leaves (or petioles), with larger samples providing more accurate estimates of the average plant nutrient status. Avoid collecting from plants damaged by disease, insects, chemicals, etc. Samples contaminated with soil, dust, or pesticide residue should be briefly washed and rinsed with distilled (not tap) water and blotted dry before sending to the lab for analysis.5

If test results will be used to diagnose nutrient deficiency symptoms, collect one sample (25 to 100 petioles) from the affected/symptomatic plants and another sample from healthy, normal looking plants. Keep the samples separate, and label them properly to avoid mixing up the results.5

Samples should be stored in a cool, dry place until they can be shipped to the testing laboratory and sent as soon as possible. Air dry samples for several hours before shipping. If not using shipping materials supplied by the lab, wrap samples in dry paper towel and place them in a large paper envelope. Do not put them in a plastic bag. It is best to collect and ship samples early in the week so that samples do not sit in a shipping facility over the weekend.5

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