Help! Tomato White Heart Disorder!

The right soil and irrigation water pH is essential for good tomato production.

“I am growing in raised beds and hydroponically in EarthBoxes. Nothing does very well and tomatoes are horrid with hard white cores. I recently found the water from our community well tests at 8.6 pH. I am wondering if your peat formula would buffer the high water pH. Right now I am using the organic formula in the boxes. I would like to use all earth boxes to grow in as I am a senior with mobility limitations. Your suggestions please.” Question from Patricia of Eagle, Hawaii.

Answer: High pH is certainly causing your crops troubles. Tomato “white heart” or “white core” is very unpleasant, but this physiological disorder can be overcome. It is believed to be caused by nutrient deficiencies due to soil pH problems and/or extreme weather. Several studies point to potassium deficiency as being the primary cause. Tomato choice may also play a role. Many older/heirloom tomato varieties with large seed cavities appear to be more susceptible to tomato white heart disorder.

Tomatoes grow and produce best in soils with a slightly acid pH between 6.0 to 6.8. This is what you need to shoot for in your growing. We add dolomite lime to our peat mixes to naturally raise the pH to a more neutral range, but Black Gold Canadian Sphagnum Peat Moss contains pure peat moss, so we do recommend blending this with our compost blend and perlite (a ratio of 3:1:1, peat, compost, perlite would work well), if you want to blend your own mix. Adding a good fertilizer formulated for tomatoes is also essential.

I also recommend you adjust the pH of your irrigation water. Check out this free webinar about adjusting irrigation water pH: Free Webinar: Tools for Adjusting Water pH Alkalinity from Penn State Extension.

Finally, choose newer, high-performing tomato varieties with smaller seed cavities. The varieties ‘Delicious‘, ‘Pink Passion‘, or any new cherry tomato on the market would be good choices.

I hope this helps!!! Keep us posted on your progress.

Happy gardening, Jessie


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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