Why Tomatoes Split On The Vine

A tomato that was intact in the evening can be split open by morning, often after rain. Nothing has attacked it; the fruit has simply outgrown its own skin over a few hours.

The skin sets before the flesh finishes growing

A ripening tomato has a skin that has largely stopped expanding while the flesh inside continues to take up water through the plant's vascular system.

Under steady conditions the two stay in balance, because water arrives gradually and the fruit swells slowly enough for the skin to accommodate it.

When water arrives suddenly, the interior swells faster than the skin can stretch and the skin fails along its weakest line.

Irregular watering is the usual trigger

A plant that has been dry closes its stomata and slows uptake. When water becomes available again, roots absorb rapidly and push it into the fruit.

That is why splitting so often follows heavy rain at the end of a dry spell, and why container tomatoes that dry out between waterings split more than beds do.

Consistent moisture is the direct remedy, and mulch does more for it than watering more often, because it evens out the supply between waterings.

Two crack patterns with different causes

Concentric cracks form rings around the stem end and are typically associated with rapid growth in the final stage of ripening.

Radial cracks run from the stem down the side of the fruit and tend to be deeper and more damaging, often opening the flesh to insects and rot.

Varieties differ substantially in how prone they are to each, and thin-skinned heirloom types are generally more vulnerable than commercial hybrids bred for shipping.

Heat and sun exposure add to it

Fruit in direct afternoon sun heats well above air temperature, which stresses the skin and can also cause pale, papery sunscald patches on the exposed shoulder.

Foliage cover protects the fruit, which is one reason aggressive pruning of leaves late in the season can make splitting and scald worse rather than better.

What to do with fruit that has already cracked

A freshly split tomato is perfectly usable if picked promptly, since the flesh is undamaged and only the opening is a problem.

Left on the plant, the crack admits moisture, yeasts and insects, and the fruit sours quickly in warm weather. Time is the deciding factor.

Picking slightly under-ripe when heavy rain is forecast and finishing the ripening indoors is the standard defense, since a tomato past the color-break stage will ripen off the plant.