Growing Seedless Watermelons

Seedless watermelons are less vigorous than normal watermelons. They require starting indoors under specific temperature and moisture ranges to ensure proper germination. Some seeds may develop under stressful conditions. Seedless watermelons require a pollinator watermelon or normal seeded watermelon to set fruits.
Seeds of Ace pollinator and complete growing instructions are included with each seedless watermelon order.
If you are reading this it is probably because you have purchased one of David\’s Garden Seeds and Products seven seedless watermelons and the envelope the seeds came in referred you to this page.


Triploid watermelons requires special cultural practices. Two of these practices are critical:1) For good seed germination you must keep the growing medium on the dry side and 85º.
You must inter-plant the field with a pollinator. We provide a pollinator called Ace.
While there is attractive profit potential in triploids, we strongly recommend that you gain experience in a small test planting before attempting full-scale production.

What are triploid watermelons?

triploid watermelons are commonly called “seedless” watermelons. Producing fruits without seeds is, of course, the idea, and triploids usually do produce a crop that doesn’t have seeds, but which has in their place pips – thin, whitish ovules which are edible.
You might find an occasional hard black seed, the presence and quantity of which is environmentally influenced.
A triploid (3 sets of chromosomes) is a hybrid resulting from a cross between a diploid (2 sets) and a tetraploid (4 sets). The triploid plant appears normal, but during meiosis, chromosome pairing—critical to the formation of ovules and pollen—cannot take place because of the odd number of chromosomes.Therefore, seeds will not form.

Germination Triploid Seeds

  1. You must be careful here. Triploid seeds germinate weakly, and if the soil is too moist or if there are temperature fluctuations, this can result in failure.

Direct seeding is asking for trouble. We recommend sowing indoors in a soilless peat mix that is maintained warm:

  1. Specifically, moisten a light, peat mix, but make it “on the dry side.” If you can squeeze a handful and get free water, themix is too wet and you should let it sit for 6-8 hours to drain before using.
  2. A wet mix will stress the germinating seeds and result in either failed or weak germination. Fill 2 – 2½” cell type containers (plug trays) with mix.
  3. Start seedlings 3 weeks before soil temperature is expected to be warm, at least 65º, after danger of frost has passed.
  4. Sow 2-3 seeds per cell, covering them 1/2 inch.
  5. Cover plug trays with thin poly sheeting to prevent drying. Keep poly-covered trays out of direct sunlight to avoid overheating. If the mix becomes too dry before seedlings emerge, mist with warm water, but keep “on the dry side.” Never make the mix wet!
  6. Use a heat mat to keep the temperature of the mix at 85ºF. Avoid fluctuations. This warm temperature is critical to good germination percentage and enough vigor in the early growth to make a good seedling.
  7. When seeds begin to emerge usually in two to three days, move the plug trays into full light, such as a warm greenhouse. If you delay at this point, seedlings are apt to be leggy(grow long and thin).

Germination Ace Seeds

You will also need to start the Ace pollinators at the same time you start the triploids.

Seedling Development

When emergence of seedlings begins move them to full sun in the greenhouse. If practicable, maintain greenhouse temperature at 85º until full emergence and 70º is minimum, even at night!
When most of the seedlings have emerged, carefully remove any seed coats which may be clinging to the seed leaves.
When all seedlings are up, thin to 1-2 plants per cell by using scissors to clip unwanted plants at their base, rather than bypulling them out. Reduce greenhouse air temperature to 75º daytime and 65º at night.


Seedlings are ready for transplanting to the field about three weeks after sowing, when they have 2-3 true leaves and rootshave sufficiently filled the cell to hold the soil mix when the plant is removed.
Younger plants may be too fragile for handling and planting. Older plants, particularly ones with 4 or more true leaves, are susceptible to shock when transplanting, which may delay plant growth in the field and can reduce the size of the fruits and the total yield.
Remove plants from the cell containers carefully to avoid tearing roots. Your removal of the plants must be gentle enough that the plug stays intact and roots are not damaged.
Do not tug plants out by the leaves until they are first loosened in some way. Transplant to the field only after frost danger has passed and soil is warm
The soil is warm when at 9:00 AM, the soil temperature at 4 inches is regularly at 65º for five days in a row.
When transplanting, water with a high phosphorous transplant fertilizer.

The Planting Pattern

You must interplant the Ace pollinator with the triploid to supply the necessary pollen. Plant one Ace plant with three triploids.
The plants are spaced 18 inches apart with rows being 36 inches apart.
Ace flowers for an extended period of time, so it will supply pollen the entire time triploids are making female flowers.
To ensure proper pollination there must be a steady source of pollen for the entire time the triploids are making female flowers.

Honeybees for Pollination

Pollination is essential for fruit growth. Honeybees are effective pollinating insects. It is critical that adequate numbers of bees are present when the crop blossoms. While the number of beehives necessary to provide thorough pollination varies with conditions, a ratio of 3 hives per 2 aces is usually adequate.


Nutritional requirements for triploids have to be managed to avoid excess nitrogen. Excess nitrogen, can result in hollow heart which triploids are susceptible to.


Southern exposure and sweet(pH of 67), light, well-drained soil is ideal. Good soil moisture is important in early stages of growth and during pollination when fruits are setting.
After this point do not water unless the soil is very dry and leaves begin to show signs of wilting in midday. Excess water will cause the watermelon to loose some of its sweetness.


There are 3 ways to tell when a watermelon is ripe:

  1. The tendril nearest the point on the vine where fruit stem attaches is browning/dead.
  2. The spot where the fruit rests on the ground is yellow.
  3. The classic mystery – you hear \”punk\”, as opposed to \”pink\” or \”pank\”, when you flick the melon with your fingers.


STORAGE: Hold at 45°F and 85% humidity 2-3 weeks.
Average Direct Seeding Rate:
One ounce of seeds will cover a row 340 feet long. One thousand seeds will cover five hundred feet.

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