Growing Watermelon

Best Planting Times for Watermelons in Washington

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

Washington’s climate varies widely, from maritime on the coast to continental in the east. This means careful consideration of local conditions for successful watermelon cultivation, particularly regarding soil warmth and frost dates.

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Useful Tools for Starting Watermelons Indoors

Utilizing the right tools can improve your success when starting watermelons.

Seeds

High-quality seeds are vital for good germination rates. Starting with premium watermelon seeds gives your plants a great head start.
5 pack of Watermelon Seeds
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Planting Trays

Starting in planting trays can help manage your seedlings effectively, allowing them to establish before transplantation outdoors, ensuring strong, healthy plants.
Planting Trays Image
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Grow Lights

Grow lights are essential for seedling growth, particularly when natural light is insufficient. They ensure your seedlings receive adequate light during the initial stages of growth.
Grow Lights Image
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Seed Starting Soil

Using light, fine soil designed for seed starting fosters rapid root development and healthy growth, giving your seedlings the best possible start.
Seed Starting Soil Image
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Greenhouse Growing

In Washington, especially in cooler regions, using a greenhouse can significantly enhance watermelon production by providing a controlled climate. Greenhouses help protect young plants from unexpected frost and extend the growing season, allowing for better fruit maturity and yield.

Consider investing in a 10×12 FT Greenhouse priced at $1,199 to create an ideal environment for your watermelons.
Greenhouse Image 1
Greenhouse Image 2
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Fertilizer

Using fertilizer in Washington can greatly benefit watermelon plants by supplementing essential nutrients deficient in the soil. It supports abundant fruit production and healthy growth.
Fertilizer Image
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Plant watermelons outdoors in Washington approximately 1-2 weeks after the last spring frost date, ensuring the soil is warm enough for optimal growth.

Average Last Frost Dates for Washington’s Major Cities

CityAverage Last Frost Date
SeattleApril 30
SpokaneMay 10
TacomaApril 25
VancouverApril 15
OlympiaApril 20

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

Other planting guides for Washington:

Broccoli Planting in Washington

Pumpkin Planting in Washington

Tomato Planting in Washington

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

Starting Watermelon Indoors

In cities like Seattle (Zone 8b), begin indoor watermelon seed starting between March 15 and April 15. This timeline ensures healthy seedlings ready for outdoor transplantation starting from late May to early June once the risk of frost has passed.

Transplanting Watermelon Seedlings

Transplant watermelon seedlings outdoors from June 1 to June 15, ensuring the soil has warmed above 70°F consistently. Space the seedlings 36-48 inches apart in rows with at least 5-6 feet between rows for optimal growth.

General Care and Maintenance

Watering

  • Provide consistent and deep watering to maintain evenly moist soil. Washington’s coastal climate generally supports moisture retention, but regular checks are essential to prevent dryness.
  • Water at the base of plants to avoid leaf wetness, reducing the risk of fungal diseases.

Fertilizing

  • Apply a balanced fertilizer during planting and when the first fruits start forming. Incorporating compost before planting can enhance soil fertility and structure.

Pest and Disease Management

  • Regularly monitor for common pests like aphids, striped cucumber beetles, and powdery mildew. Being vigilant is essential, especially in Washington’s humid environment.
  • Implement organic or integrated pest management methods to protect watermelon plants from pests and diseases.

Harvesting

  • Harvest watermelons when they reach their full size and the tendril next to the fruit becomes brown. Regular harvesting promotes optimal fruit quality and encourages further ripening.

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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