Why are grocery store tomatoes hard as rocks?

A hard core in tomato centers is a disappointment when you were expecting delicious, juicy fruit. Fortunately, it is just a transient condition.

It takes a long time for these tomatoes to mature. When they do, the central core can be whitish-greenish, stringy and tough. Within, there is less flesh and much 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 circumstances, particularly an up-and-down temperature, disrupt the ripening process of a tomato. Tomatoes that have been exposed to low temperatures overnight are especially prone to developing hard center cores. That’s why hard core centers in tomatoes are more frequent earlier and later in the season when the weather is more volatile.

2. Tomatoes get too much fertilizer.
Excess fertilizer (particularly when combined with stressful conditions) adds to the tough central core of a tomato.

3. Tomato variety is juicy.
Older tomato varieties known for their juiciness are more likely to develop hard, white center cores. These types feature a five-cavity inner structure filled with a jelly-like substance (locular jelly). Fewer tough, white cores occur in newer hybrid kinds known to yield firmer fruit.

How can I prevent my tomatoes from developing hard centers?

  • Use frost protection, such as tunnel row covers, floating row covers, water barriers, or individual plant coverings, to maintain warm, constant temperatures during chilly nights.
  • Use fertilizer sparingly, especially 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. Planting juicier varieties should be avoided.

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