Tomatoes hollow inside? That is puffiness, and it starts at pollination

A tomato that looks fine outside but is hollow inside, with empty seed cavities and little gel, has puffiness. It is a pollination and seed-set problem, not a disease, and the fruit was set up that way around flowering and fruit set. You cannot refill a cavity, so the useful work is confirming the diagnosis and helping the flowers that are still coming.

Cut one open: what puffiness looks like

Iowa State University Extension describes the disorder as fruit where the outer wall is normal but the tomato is hollow inside, with one of the seed cavities usually empty. The University of Kentucky adds the outside clue: the fruit looks flattened on one or more sides. University of Wisconsin Extension describes fruit that appear somewhat bloated and angular, with cavities that may lack the normal gel and a fruit that is less dense.

Cut one open. A sound tomato is packed with seeds in gel. A puffy one has open space between the wall and what is inside. An Ohio State paper defines it as open cavities between the outer walls and the contents that would normally be filled with gel, seeds or placental tissue, and notes that puffy fruit tend to be soft, ribbed, spongy and gel-free.

Wisconsin’s description of a less dense fruit gives you a quick check: a fruit that feels light and angular next to its neighbours is worth cutting open.

What goes wrong inside

The Ohio State authors write that any factor that impairs pollination, fertilization or seed set promotes puffiness, and that it arises from either an overgrowth of the outer wall or poor development of the tissue inside the cavities. Either way the problem is set early, during flowering and fruit set, long before the fruit ripens, which is why changing your feeding today will not rescue the fruit already hanging there.

What pushes a tomato toward puffiness

Iowa State Extension lists extreme high or low temperatures, excessive nitrogen fertilization and heavy rains, which may interfere with normal pollination. The sources add a few more:

• Cool weather during bloom. University of Wisconsin Extension says puffiness is often due to cool temperatures during bloom that reduce insect activity and pollination. A cold, damp spring on a balcony fits.
• Heat and cold both count. Iowa State names extreme temperatures at either end, and the Ohio State paper lists high and low temperatures. For the temperatures at which flowers stop setting, see tomato flowers falling off.
• Low light. The University of Kentucky links puffiness to winter and early spring conditions that combine low light levels, high fertility and poor pollen viability.
• Nitrogen without potassium. University of Wisconsin Extension says high nitrogen and low potassium can also lead to puffiness. If feeding has also left the plant leafy and slow to flower, see tomato plant not flowering.
• Heavy rain. Iowa State lists it, and the Ohio State paper includes excessive rain among the associated conditions.
• Genetics. Wisconsin says some cultivars are more susceptible than others, and the Ohio State authors report a genetic component.

Cornell’s diagnostic key also lists puffiness among symptoms of potato leafroll virus, associated with systemic infection. If the whole plant looks sick as well as the fruit, think virus; if the plant is healthy and only the early fruit is hollow, think weather and pollination.

Puffiness or a variety that is meant to be hollow?

Stuffing tomatoes are bred to be roomy. Reimer Seeds describes Burgess Stuffing as looking like hollow bell peppers with very few seeds, and Charlie Chaplin as almost hollow when mature and resembling a bell pepper. These are seed-seller descriptions, so check what your own packet says.

Sign	Puffiness	Stuffing variety
Shape	Bloated, angular or flattened on one or more sides	Bell-pepper shape
Inside	Open space between wall and contents, little or no gel	Almost hollow, very few seeds
Which fruit	Most frequent on early fruit	Described as the variety’s normal fruit
Variety	Any type, some more prone than others	Sold as a stuffer

If your plant is a normal slicer or cherry and only some fruit are hollow, it is puffiness.

Hollow, or just scarred or cracked?

Puffiness is an inside problem on a fruit that is otherwise normal. If the damage is on the outside, a different page applies.

• Lumpy, puckered fruit with scarred bottoms is catfacing, another cold-flower problem.
• Rings or splits in the skin are covered in why tomatoes crack.
• Yellow shoulders or blotchy colour on a solid fruit are covered in blotchy ripening.

No cure for this fruit; what helps the next truss

Do not expect a rescue. Iowa State Extension says there are no effective controls and that puffiness should decline later in the summer.

For the flowers still to come:

1. Help the pollination. On a balcony there may be little wind or insect traffic. The technique is in hand-pollinating tomatoes and peppers.
2. Hold back on nitrogen. Iowa State and Wisconsin both name excess nitrogen, and the University of Kentucky says proper nutrient management is critical. Skip high-nitrogen feed; keep feeding balanced rather than stopping altogether.
3. Give it light. Kentucky calls maximizing light penetration critical. In a pot, that means the sunniest spot you have.
4. Pick varieties that are not prone. Kentucky and Wisconsin both point to variety choice. If early fruit keeps coming out hollow, try a different type next year.

Sources

• Iowa State University Extension: Managing Tomato Diseases, Disorders, and Pests
• University of Wisconsin-Madison Extension: Tomato disorder: Physiological fruit problems (A3798)
• University of Kentucky: Puffiness, Scouting Guides for Problems of Vegetables
• Ohio State University (Dariva et al., 2024): Fruit puffiness in a processing tomato population
• Cornell Vegetable Program: Tomato diagnostic key, entire fruit
• Reimer Seeds: Stuffer tomato varieties