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“Hollow” can describe two different problems on a tomato plant. Either a fruit has an empty cavity inside while its outer wall looks normal, or a stem has been bored or rotted out. The two need different diagnoses and different responses, so identify which structure is affected before changing anything in the garden.
In short: hollow fruit is usually a physiological disorder linked to weather extremes, heavy nitrogen, and uneven conditions during pollination, not an infectious disease. A hollow stem is more often a sign of an insect borer or the fungus white mold, and it calls for closer inspection of the plant.
Start by identifying which part is hollow
Cut a representative affected fruit in half, or look at the base of the affected stem, and note what you see:
- Fruit hollow inside: the skin and outer flesh look normal, but one seed cavity is empty or the fruit feels puffy and light. This is the condition Iowa State University Extension calls “Puffiness or Hollow Fruit.”
- Stem hollowed out: the stem is tunneled, rotted, or girdled, and the plant may be wilting above the damage. This is a plant-health problem that can kill the plant, not a fruit-quality issue.
If the fruit has deep scars, a dark sunken spot at the blossom end, or cracks, you are looking at a different disorder. Those lookalikes are covered below.
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Hollow fruit (puffiness)
Hollow fruit forms when the seed cavity does not fill properly and the fruit develops an empty pocket, while the outer wall remains smooth and apparently normal. Iowa State University Extension says the disorder occurs most often on early fruit and should decline later in the summer. Its guidance is clear that there are no effective controls for it, so the practical goal is to reduce the conditions that trigger it.
Conditions associated with hollow fruit
Two university sources list similar triggers. Both describe these as conditions that may interfere with pollination, not as a confirmed cause in any single garden.
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| Factor | Iowa State University Extension | UC ANR (UC Master Gardener Program of Contra Costa County) |
|---|---|---|
| Temperature | Extreme high or low temperatures | Above 90°F or below 55°F |
| Nitrogen | Excessive nitrogen fertilization | Excess nitrogen |
| Rainfall | Heavy rains | Heavy rainfall |
| Light | Not stated | Low light |
Because more than one factor is often present at the same time, a single bad week rarely explains the problem. Look at the pattern across the season: did the cavities appear during a heat spell, a cold snap, a wet stretch, or after a heavy feeding?
What to do now and next season
For fruit already affected, there is no treatment that will refill the cavity. Remove obviously damaged fruit if it bothers you, and leave the rest; the disorder is not a sign that the plant is infected.
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For the next season, focus on the variables you can control:
- Keep soil moisture even. Iowa State gives a general guideline of about 1 to 1½ inches of water per week during the growing season, applied during dry weather. That figure appears in the blossom-end-rot discussion on an undated page, so treat it as a starting point; needs vary with rainfall, soil type, containers, and heat.
- Mulch the bed. A mulch layer helps conserve soil moisture and moderate soil temperature, which supports the even-moisture goal above.
- Avoid heavy nitrogen. Excess nitrogen is on both sources’ lists. Use a balanced feeding plan rather than repeated high-nitrogen applications.
- Do not add calcium because fruit is hollow. The hollow-fruit guidance from these sources does not recommend calcium as a treatment.
Hollow stems
A hollow stem has a different set of causes. The University of Minnesota Extension diagnostic page for hollowed-out tomato stems identifies two main possibilities. Their signs are distinct, so inspect the plant before choosing a response.
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Stalk borer
- Timing: damage typically occurs from June to early August.
- Signs: leaves wilt, and an entrance hole may be visible near ground level. A caterpillar is sometimes found inside the stem.
- The caterpillar: ¾ to 2 inches long, with a reddish-brown head and a brownish-purple body marked with whitish stripes.
White mold (Sclerotinia sclerotiorum)
- Stem lesion: a dark, firm, water-soaked lesion on the stem.
- Girdling: girdled stems die and turn bone white.
- Inside the stem: black, mouse-dropping-shaped sclerotia, which are the fungus’s resting structures.
- Growth: cottony white growth may appear inside and outside infected stems when humidity is high. Fruit may be soft and rotted.
- Conditions: the page notes that cool, humid conditions favor it.
Checking a suspect stem
- Examine the stem at ground level for a small entrance hole. Note whether the stem above it is wilted.
- Split a section of the stem lengthwise. Look for a caterpillar or frass (insect droppings) inside a tunnel, which points toward a borer.
- Check for a water-soaked, dark, firm lesion, a girdled band around the stem, or cottony white growth, and look for black sclerotia. These signs point toward white mold.
- If the signs are unclear, or the plant is declining, take a clear photo and a sample to your local extension office for identification.
Do not assume a hollow stem is a pollination or fertilizer problem. Those factors are associated with hollow fruit, not with a tunneled or rotted stem.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Lookalikes that are not hollow fruit
Several tomato disorders can be mistaken for hollow fruit. They differ in where the damage sits and what it looks like from outside.
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| Disorder | Where it appears | Outside appearance | Inside the fruit | Source |
|---|---|---|---|---|
| Hollow fruit (puffiness) | Whole fruit | Outer wall looks normal | Empty seed cavity | Iowa State University Extension |
| Catfacing | Blossom end and surface | Malformed, flat or puckered, with a corky brown scar at the base | Cavities can extend deep into the flesh | University of Minnesota Extension |
| Blossom-end rot | Blossom end | Brown to black, sunken, shrunken, leathery lesion | Not stated | Iowa State University Extension; NC State Extension |
| Fruit cracking | Stem end or surface | Radial cracks from the stem, or concentric rings around it | Not stated | Iowa State University Extension |
Catfacing causes are not definitively known. The University of Minnesota Extension lists possible contributors such as disturbance to flowers or flower buds, cold temperatures, and contact with hormone-type herbicide sprays. Mildly affected fruit may still be safe to eat if it is not infected by secondary pathogens, according to that source.
Blossom-end rot is a calcium-related breakdown of tissue. NC State Extension explains that calcium deficiency in developing fruit can result from insufficient uptake or extreme fluctuations in water supply. Because the cause involves water as well as calcium, a soil test is the right first step before adding any amendment.
What to expect and when to get help
Hollow fruit that has already formed will not recover. Iowa State University Extension states, “There are no effective controls,” which is why the useful response is prevention in future seasons. The problem typically eases later in summer, so a plant with some hollow early fruit may still set good fruit afterward.
Get local help if a stem is hollow with wilting, lesions, or white growth, or if a plant is declining quickly. Hollow fruit alone, with normal stems and foliage, rarely needs intervention beyond consistent watering and balanced feeding.
The Bottom Line
Hollow fruit is usually a weather-and-nutrition disorder that you prevent next season through even watering, mulch, and moderate nitrogen. A hollow stem with wilting, an entry hole, lesions, or white growth needs inspection for a borer or white mold. Confirm which structure is hollow before acting.
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