Watermelon seeds
I’m sure you’re familiar with where watermelon seeds come from. Just in case, here’s a fun illustration.
Collecting watermelon seeds is simple as washing off any remaining fruit with cool water and drying them off on a paper towel. These seeds need to be fully dried out before storing and germinating. Seeds that do not fully dry out beforehand will not grow well, if at all. For this reason, I do not recommend freezing watermelon seeds for storage.
I recommend storing watermelon seeds in a dry place that is hidden from direct sources of light to prevent premature germination while in storage.
How do you germinate watermelon seeds?
Germinate watermelon seeds after they’ve fully dried out. Sprouts should appear after 10 days using one of these reliable methods.
The paper towel method: Place seeds on a damp paper towel and seal the towel inside a plastic bag. store the bag in the refrigerator and check on it every few days. Once signs of sprouting appear, delicately transplant the seedlings into a permanent home.
Shallow starting trays: This is the best method for germinating seeds out of season or in colder climates. Fill starting trays with a mixture of 80% coconut coir and 20% compost. The coconut coir is a good growth medium and the compost supplies early nutrients to the seedlings. keep the soil moist but reduce watering once sprouts are visible to avoid fungal issues. Never let the trays completely dry out.
Direct sewing: When temperatures are reliably above 70 degrees Fahrenheit, you may sew seeds directly into the soil. Watermelons do best in sandy loam soil. For the best results, amend the area with compost before planting. Plant seeds no more than 2 inches into the ground, or up to the second knuckle on your finger. Keep the planted area well-watered and watch your seedlings break through the topsoil in a few weeks.
How do you transplant watermelon seedlings?
Watermelon seedlings do not transplant well because their juvenile roots are notoriously fragile. If you must transplant a watermelon seedling to another location, avoid damaging the roots at all costs.
The best way to relocate watermelon seedlings is to move them with their original soil and roots intact. Then transport the young plants to a permanent container or patch of soil.
How often should you water watermelons?
Watermelons need about an inch of water per week. Never let the soil completely dry out to keep the plants alive and thriving.
When watering, water the soil, never the fruit or the foliage. Watermelon plants enjoy wet soil but allowing water to pool on the leaves means putting them at risk of fungal/bacterial blights.
Just remember to keep the soil moist, not the plant itself.
Soil and nutrients
Watermelon seedlings are very hungry for nitrogen while mature plants require more potassium. Before planting, amend the soil with compost and worm castings for an initial boost of nitrogen. Then once the plant produces flowers, supplement the soil with dried banana peel powder or banana peel tea to support fruit development.
If you are growing hydroponically, start with a nitrogen-rich nutrient salt. Allow the plant to grow to its flowering stage, then switch to a potassium-based fertilizer to encourage fruit development.
Here is a more detailed list of nutrient requirements found in Wayne Schmidt’s EXTREME MELON GROWING project.
Watermelon Required Nutrient Levels | parts per million (ppm):
nitrogen: 215 ppm
Wayne Schmidt’s EXTREME MELON GROWING project.
phosphate: 86 ppm
potassium: 343 ppm
magnesium: 85 ppm
calcium: 175 ppm
sulfur: 113 ppm
iron: 7 ppm
manganese: 2 ppm
zinc: 0.25 ppm
boron: 0.70 ppm
copper: 0.07 ppm
molybdate: 0.05 ppm
Growing area
Most fully grown watermelon roots only grow about 8 to 10 inches deep.
Aboveground, watermelon plants grow outward in the form of thick vines. Some growers choose to tame these vines with trellis systems made of wood fences and chicken wire.
Depending on the variety, the leaves of a healthy watermelon plant are generally large and end in 3 points. Flowers from these plants are typically yellow and precede fruiting after pollination. This is your signal to fertilize with potassium.
Once flowers are pollinated, a baby watermelon bump will begin to swell directly beneath the flower. This is your signal to fertilize with potassium.
Pollination
Pollination may happen naturally outside depending on the abundance of local pollinating species. However, to ensure success, manual pollination is simple as rubbing pollen from several male flowers pollen over a female flower.
Manual pollination should happen as early in the morning as possible to collect as much pollen as possible.
To tell the difference between male and female flowers on a watermelon plant, look for a swollen bump between the flower petals and the stem. Female flowers will have this bump which will develop into a watermelon after pollination.
When should you harvest watermelon?
According to the USDA, Watermelons will take about 70 to 90 days to bear mature fruit. Indicators that let you know your watermelon is ripe and ready to disconnect from the vine will include:
- Cream-colored patch
- Browned and shriveled vine
- Dark rind
- Firmness
- Low internal pitch when flicked
- sweet smell
Watermelons will display a combination of these characteristics when completely ripe. Remember that a little patience today will yield sweet rewards for you in the future, so resist the temptation to prematurely pluck your crops.