Slice the cucumber lengthwise. A hollow cucumber has a gap or en cavity down the center where the seeds should sit, sometimes running the length of the fruit and sometimes only in one section. Often the fruit is also a little misshapen — or pinched at one end — and the seeds near the gap are small or missing. The flesh around it is usually normal in color and flavor. If the inside is soft, discolored or smells off, that is rot rather than hollowness, and the fruit belongs in the trash, not the kitchen.
Poor pollination is the most common cause. University of Delaware Extension notes that hollowness and open cavities in cucumbers and summer squash can come from inadequate pollination and reduced seed set. University of Maryland Extension shows the same thing in cross-section: an underdeveloped seed cavity, often toward one end of a deformed fruit. Cucumbers depend on bees to carry pollen from male to female flowers, so rainy or cool weather that keeps bees from flying, insecticides that kill them, and left on after bloom all reduce pollination.
Stress adds to the problem. University of Delaware notes that in hot spells, with days in the 90s and nights in the high 70s, cucumbers often abort fruit or set misshapen fruit, and it recommends irrigating so plants never come under water stress. Boron deficiency, or low boron and calcium together, can also increase hollowness. Don't add boron on a hunch, though: the gap between too little and too much is narrow, and a soil test through your extension office is the way to know.
Variety can play a part as well. Some cucumbers are more prone to hollow centers than others, so if one variety keeps producing hollow fruit while another beside it doesn't, try a different one next year. Parthenocarpic varieties, which set fruit without pollination, sidestep the pollination side of the problem, though heat and water stress still affect them. Keeping notes on which varieties came out solid in your garden is the most reliable guide for next spring's order.
Hollow cucumbers are safe to eat; use them sliced fresh rather than for whole pickles, where the gap shows. Going forward, remove row covers as soon as flowers open, plant flowers nearby for bees, and keep insecticides off open blooms. Water deeply at the base and about 3 inches deep to keep moisture even, especially through hot spells. Pick every other day, slicers at 6 to 10 inches and picklers at 2 to 6 inches, so the vine keeps flowering and setting fruit.
Before using any product, read the whole label. It must list the crop you’re treating, and its directions on amount, timing, protective gear, bees and days before harvest are legal requirements. If this page and the label disagree, follow the label.
- Blossom End RotDark, sunken, leathery patch on the blossom end of tomato or pepper fruit. The developing fruit is short of calcium, usually because of uneven watering rather than a lack of calcium in the soil.
- Fruit CrackingTomatoes crack at the stem end or shoulder, cabbage heads split, and carrots split lengthwise — usually after heavy rain follows dry weather.
- AnthracnoseSunken, dark circular lesions on ripening fruit, sometimes with salmon-colored spores in the center.
- Bird DamageBerries pecked or missing, seeds scratched from beds, and seedlings dislodged — birds feeding on ripe fruit, seeds, or soil grubs.
- Brown Marmorated Stink BugSunken, corky dimples on fruit and pods caused by a mottled brown shield bug feeding through the skin.
- Why are my zucchini and squash flowers falling off?The first zucchini and squash flowers are often all male, and male flowers fall off a day after opening — that's normal. If female flowers (tiny fruit at the base) drop, look at pollination and heat.
- Why are my cucumbers bitter?Bitter cucumbers are producing cucurbitacins — compounds the plant makes in response to stress, usually drought or uneven watering.
- Why are some of my potatoes hollow inside when I cut them?Hollow heart in potatoes is caused by rapid, uneven growth — usually after a period of drought followed by heavy watering or rain — and is not a disease.
- What does drought stress actually look like, and how do I know when to water versus when something else is wrong?Drought stress progresses from midday wilting to all-day wilting, leaf curl, and eventually aborted fruit and flowers — the key is catching it before the plant has been dry long enough to abort reproductive structures.