Ripening green tomatoes in the Seattle area

August 30, 2012 / Ecoyards
Close-up of unripe green tomatoes growing on a vine with leaves and stems visible in the background.

Tips for Ripening Tomatoes in Puget Sound

Puget Sound gardeners are a patient bunch—especially when it comes to tomatoes. We dream of juicy red fruit in spring, plant in late May, then spend the summer nurturing our tomato plants. But by late August, many of us are still staring at stubborn green tomatoes. Sound familiar?

In our region, tomato ripening can be tricky. The key factors? Temperature and ethylene, a natural hormone. Surprisingly, when temperatures exceed 85°F, tomatoes may stop turning red and instead become yellowish-green or orange.

Here’s how to encourage ripening—before the first frost hits around November 17 in Seattle:

What You Can Do Now

  • Be patient. Cooler temps in September often help with ripening.
  • Triage your crop. Remove blossoms and small green fruit that won’t mature in time. This lets the plant focus on ripening larger tomatoes.
  • Prune wisely. Clip new shoots to redirect energy, but keep mature leaves for nutrients.
  • Stress the roots. The University of Washington Elizabeth C. Miller Library recommends cutting halfway around the root zone (8–12 inches from the stem) with a shovel to encourage ripening.
  • Use plastic covers or floating row covers to trap warmth and protect from chilly nights.
  • Pick and ripen indoors. Harvest tomatoes that are full-sized and glossy green. Leave a bit of stem to prevent decay. Wrap in newspaper and store in a cool, dark place; or place in a paper bag with a banana or apple to speed ripening with ethylene gas.

For Next Year

  • Start with healthy transplants, not seeds, and don’t plant until mid-May when soil is warm.
  • Choose early-ripening varieties like Early Girl, Sungold, Early Cascade, or cherry tomatoes.
  • Plant deep. Bury the stem at least 8 inches deep to encourage root growth—strip off lower leaves if needed. WSU suggests planting sideways in a trench for more surface roots in warm soil.
  • Warm the soil with black or red plastic mulch.

With a few of these tricks, you might just beat the odds and enjoy more red tomatoes, just as nature (and your taste buds) intended.

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