Why are tomatoes cracking?

Credit: Goldlocki

Q: My tomatoes are splitting at the top. I have them in very large pots in a sunny location and I water them everyday. I put compost and sea soil mixed with soil in the pots and gave them water soluble 20-20-20 twice.

There are two types of cracking that occurs:
(a) Concentric cracking, which is a splitting of the epidermis in circular patterns around the stem scar.
(b) Radial cracking which is a splitting of the epidermis from the stem scar towards the blossom end.

Cracking occurs as the tomato nears maturity. More susceptible varieties crack in the mature green stage and more tolerant varieties at later stages. The earlier the cracking then the deeper and longer the crack becomes. The problem is usually more severe on the lower trusses. Circular cracking often occurs on ripe tomatoes that are on the vine too long.

Causes of cracking

1. Alterations in the growth rate. Plants have periods where they might have very fast growth followed by slow growth and then fast again. These changes can cause fruit nearing maturation to crack. If the cells have “hardened” during the last slow growth then in the next fast growth period they may not be able to stretch enough and the epidermis cracks.

2. Fast growth. Some varieties have periods of very fast fruit growth with high temperatures and moisture levels.

3. Fruit temperature fluctuations and leaf removal. Wide fluctuations in temperature can also induce cracking. This is true especially when plants have been de-leafed too early leaving fruit without protection. The exposed fruit heats up dramatically in the sun. At night it cools relatively quickly and the differential is bigger than it would have been had the leaves covered the fruit. The expansion and contraction of the epidermis and its cells can result in cracking.

4. Succulent plants. Succulent plants that are high in nitrogen and low in potassium are more susceptible to cracking.

5. Rain and irrigation. Rain and excess irrigation will often cause cracking and if the fruit lacks leaf cover then the effect is even more dramatic. Tomato crops that do not receive water at regular intervals but rather receive it periodically at large intervals are likely to have cracking. This problem is related to the Conductivity Factor (CF) of the soil solution.

Control of Cracking

1. A good fertilizer programme that will avoid overly succulent plants.

2. Proper pruning and leaf removal. Excess removal will result in fruit being exposed too much to the sun.

3. Proper water management: do not over irrigate; water at fixed intervals and increase or decrease quantities as needed.