Watermelons (Citrullus lanatus) thrive in U.S. Department of Agriculture plant hardiness zones 3 through 11. This quintessential summer plant, known for its juicy fruit that's high in vitamin C content, is primarily started via seed. If you are planting your first backyard watermelon garden, several tips and tricks can help ensure optimal seed germination success.
Only Use Fresh Seeds
Watermelon seeds rank as one of the easiest seeds to collect and save from ripe fruit. Simply scoop the seeds out of a watermelon, rinse them under water to remove any fruit pieces or fruit juices, and let them air-dry on a paper towel. In general, watermelon seeds stay viable for approximately four years. However, the longer you wait, the lower your chances of optimal germination. For the best results, plant watermelon seeds as soon as you harvest them. When buying commercial packets of seeds, check the expiration date to ensure the four-year limit hasn't passed.
Avoid Soaking the Seeds
Many types of plant seeds benefit from pre-planting soaking to soften the outer seed coating and hasten germination. However, watermelons are an exception to the rule. Soaking the seeds before planting increases the risks of various fungal diseases, such as anthracnose caused by the Colletotrichum lagenarium fungus.
Start the Seeds Indoors
Watermelon plants are very frost sensitive and exposure to cold temperatures can quickly kill them. Get a head start on the growing season by planting watermelon seeds in peat pots indoors approximately three to four weeks before the last frost date in your region. Once all risks of frost have passed, you can transplant the watermelon seedlings into the ground. This helps you to be able to enjoy the fruits of your harvest weeks earlier.
Fertilize Before Planting
Boosting the soil's fertility levels before planting watermelon seeds ensures quick germination and seedling establishment. For the best results with watermelons, use 3 pounds of 5-10-10 fertilizer for every 100 square feet of planting space.
The warmer the soil, the faster watermelon seeds germinate. For example, it takes approximately three days for a watermelon seed to germinate in 90 degree Fahrenheit conditions, and approximately 10 days when temperatures are at 70 degrees. If starting seeds indoors, consider using a space heater or heating pad to increase temperatures. If growing the seeds outdoors, try laying black plastic mulch over the planting site to help absorb the sun's heat and increase soil temperatures during the day, and in turn speed up watermelon germination.
Don't Plant Too Deep
Seeds that are planted too deep will fail to get established properly. For optimal germination, bury watermelon seeds at a depth between 1/2 and1 inch.
- University of Illinois Extension: Watermelon
- The Old Farmer's Almanac: Watermelon
- Clemson Cooperative Extension: Watermelons
- Cornell University Extension: Watermelon
- University of Arizona Extension: Melons
- North Carolina State University Extension: Watermelon Disease Handbook
- West Virginia University Extension Service: Seed Saving Tip
- Creatas Images/Creatas/Getty Images