Growing Watermelon

Best Planting Times for Watermelons in Iowa

Planting MethodActivityRecommended Dates
Outdoor PlantingIndoor Seed StartingApril 15 – May 15
Transplant OutdoorsJune 1 – June 15
Greenhouse PlantingYear-roundAdjust planting based on temperature control in the greenhouse

Planting Conditions

Watermelon Planting Conditions

Iowa’s climate can be humid in the summer, which is suitable for watermelon growth. However, growers should be mindful of the potential for late spring frosts and ensure soil temperatures are warm enough to support healthy plant development.

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Greenhouse Growing

In Iowa, using a greenhouse for watermelon cultivation can be highly beneficial, especially to avoid frost damage during late spring and to provide a controlled environment that minimizes pest issues and diseases. It allows for earlier planting and can extend the growing season into fall.

Consider investing in a 10×12 FT Greenhouse (Right now priced at $899) to ensure your watermelons thrive in a controlled environment.
Greenhouse Image 1
Greenhouse Image 2
Check the latest price on Amazon.

Fertilizer

Supplementing with fertilizer is crucial for maximizing watermelon yields in Iowa. High-quality fertilizers replenish essential nutrients in the soil and promote vigorous plant growth for a bountiful harvest.
Fertilizer Image
Check out Fertilizer on Amazon

Other planting guides for Iowa:

Broccoli Planting in Iowa

Pumpkin Planting in Iowa

Tomato Planting in Iowa

Any questions on growing cucumbers? Visit our forum to discuss: Growing Cucumbers.

For successful watermelon planting in Iowa, sow seeds outdoors after the last frost date and ensure soil temperatures are at least 70°F for optimum germination.

Average Last Frost Dates for Iowa’s Major Cities

CityAverage Last Frost Date
Des MoinesMay 6
Cedar RapidsMay 9
DavenportMay 8
Sioux CityMay 15
WaterlooMay 7
AmesMay 10
Iowa CityMay 4

Disclaimer: Frost dates are average estimates, and actual conditions may vary. It is recommended to monitor local forecasts and adapt planting decisions accordingly.

Starting Watermelon Indoors

In Iowa, begin indoor watermelon seed starting between April 15 and May 15. This timeline ensures healthy seedlings ready for outdoor transplantation by late May or early June when the risk of frost has passed.

Transplanting Watermelon Seedlings

Transplant watermelon seedlings outdoors from May 25 to June 10, ensuring the soil has warmed above 65°F consistently. Space the seedlings 24-36 inches apart in rows with at least 36-48 inches between rows for optimal growth.

General Care and Maintenance

Watering

  • Provide consistent deep watering to maintain evenly moist soil. Iowa’s varying climate conditions require regular watering, particularly during dry spells.
  • Water at the base of plants to avoid leaf wetness, which can lead to fungal diseases.

Fertilizing

  • Apply a balanced fertilizer during planting and again when the plants begin to set fruit. Incorporating compost before planting can enhance soil health and fertility.

Pest and Disease Management

  • Regularly monitor for pests like aphids, cucumber beetles, and signs of diseases such as powdery mildew. Although Iowa is humid, being vigilant against pests is crucial for a healthy crop.
  • Utilize organic or integrated pest management strategies to safeguard watermelon plants from pests and diseases.

Harvesting

  • Harvest watermelons when they exhibit a uniform color, tapping them to check for a hollow sound, indicating ripeness. Regular harvesting ensures peak quality and flavor.

The importance of good soil

Before starting to grow it is important to take a step back and find the condition of the soil in your garden,The optimal soil is a blend that includes the mineral-rich dirt along with organicrich organic matter that plants need to thrive.


In my garden I try to compost as mutch as possible, so I can mix in the nutrient ritch compost in my soil. I use both hot composting of food scraps and cold composting of all organic garden “waste”..
If you dont have the time or space for composting, it is possible to get compost ready to use in garden centers and Community Composting.
You can read more on Community Composting here: https://www.epa.gov/sustainable-management-food/community-composting

If you are uncertain of the quality of your soil, you can get easy to use soil tests at amazon for 17 dollars. Check latest prices here: Soil testing kit.

Also remember to check out how much sunlight your growing area gets, and that the rain drains well. If you treat your soil well and plan you crops according to your climate you will succeed with any plant you want.

The satisfaction when you harvest your own produce is well worth the time you put in 🙂

BeeJay
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