Why is there a hard core in tomato centers?

A hard core in tomato centers is a disappointment when you were expecting delicious, juicy fruit. Thankfully, it’s a temporary condition.

These tomatoes take a long time to ripen. When they do, the central core can be whitish-greenish, stringy and tough. There is little flesh inside, but rather a fibrous tissue. Why do some tomatoes grow a white, tough center while others are flavorful, moist, and ripe?

Three reasons why tomato centers may be hard

1. Temperatures fluctuate.
Stressful weather conditions, especially an up-and-down thermometer, disturb a tomato’s ripening process. Tomatoes exposed to low temperatures overnight are particularly susceptible to developing hard central cores. That’s one reason hard core centers in tomatoes are common earlier and later in the season while the weather is more changeable.

2. Tomatoes get too much fertilizer.
Excessive fertilizer (especially accompanied by stressful weather) contributes to a tomato’s tough center core.

3. Tomato variety is juicy.
Older types of tomatoes with reputation for juiciness are more apt to develop hard, white central cores. These varieties have an interior structure made up of five cavities, filled with a jelly-like material (locular jelly). Newer hybrid varieties known to produce firmer fruit develop fewer tough, white centers.

How can I prevent my tomatoes from developing hard centers?

  • Provide warm, consistent temperatures during cool evenings by using frost protection, such as tunnel row covers, floating row covers, water barriers, or individual plant covers.
  • Apply fertilizer in moderation, particularly during the first month that plants are in the ground.
  • Plant newer tomato varieties that have been known to resist hard core, such as Carnival, Celebrity, Daybreak, Mountain Fresh, Mountain Spring, Sun Leaper, and Sunmaster. Avoid planting juicier varieties. 

Get more tips on our Tomato Problems Pinterest board.

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Return from Hard Core in Tomato Centers to Tomato Dirt home

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