MG Volunteer: “OSU Extension Master Gardener volunteer. How may I help you?”

Caller: My tomatoes are rotting from the bottom up. It’s late August now, and there is a black, leathery area on the bottoms of my tomatoes.
MGV: How many plants do you have? Are they all affected?
Caller: I have four; all are affected except the one I have planted in a different location.
MGV: Do all the fruit have the problem?
Caller: Most of them do; it seems like a few of the smaller less developed fruits are OK.
MGV: How much and how often are you watering the plants?
Caller: : I water for an hour every other day using drip irrigation.
MGV: What about fertilizer?
Caller: I haven’t put any fertilizer on.
MGV:How is the drainage?
Caller: : Not very good. Clay soil.
MGV: Have you had a soil test done?
Caller: No.

Diagnosis:

Blossom End Rot: Physiologic disorder causes a sunken, black, leathery depression at bottom of fruit. It is caused when demand for calcium exceeds supply. Can be a simple lack of calcium or can be caused by excessive nitrogen fertilization that can impede movement of calcium into plant. High salt levels in the soil can also cause calcium uptake problems. Uneven watering may make the problem worse. To read more about this, visit this website.

Recommendations:

Cultural:

  1. Take a soil test to ensure soil has enough calcium. Tomato plants prefer pH between 6.8 and 7. Apply lime in the fall to ensure enough calcium is available for plants next year. Mix lime in 8 to 12 inches deep.
  2. Do not overwater. Water deeply every 7 to 10 days. Use mulch in conjunction with regular watering schedule to ensure soil stays evenly moist.
  3. Do not plant tomatoes where water stands. Maintain well-drained soil.

Biological & Chemical: None

(Thanks to the Benton County Master Gardeners for developing this scenario)