Hollow Heart

Sometimes things look fine on the outside when the inside is damaged.

If you cut a beet, potato, seed, or watermelon in half and find a hole in the center, it has hollow heart. Also known as hallowheart, this condition indicates that the plant faced more stress than it could handle.

Watermelon with early-stage hollow heart (utroja0) Pixabay

Hallowheart of watermelons

Hollow heart in watermelons is a pollination problem. Poor pollination occurs when temperatures are low or when there are not enough pollinators in the area. Somehow, poor pollination causes the interior of watermelon to develop triangular, often symmetrical gaps in the fruit. Seedless watermelons are more susceptible to hollow heart than seeded varieties, and orange and yellow-fleshed watermelons are the most likely to develop this condition. Improve pollination rates in your garden by attracting pollinators with flowers that appeal to honey bees and bumblebees. You can offset low temperatures with row covers.

Hollow heart in watermelons can also occur when they get too much fertilizer and insufficient water. The cells responsible for producing fruit cannot keep up with the cells producing rind under those conditions.
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Hollow heart of beets

If you cut into a beet and find an empty center, it’s time to send a soil sample to a lab for testing. Hollow heart in beets is commonly a symptom of a boron deficiency. Look closely at the petioles (leaf stems) for signs of cracking, abnormalities, or stunting. If the cavity is rotting, it may be blackheart.

Hollow heart of potatoes

Hollow heart in potatoes can be a weather problem or a water problem. Potatoes are greedy plants. They need a lot of water and nutrients to produce those fat tubers. Hollow heart occurs when a developing potato is hit with cold weather, followed by hot weather. Or when a sudden dry spell ends with an extended wet period. Like that one time you forgot to water them and then gave them extra water to make up the difference.

​Where the cavity occurs will tell you its cause. Water or nutrient stresses that occur later in the growing season create holes at the bud end of the tuber. These cavities do not have a brown center. When hollow heart appears at the stem end of a tuber, cold weather followed by hot weather is the culprit. Brown centers are a common symptom of stem end hollow heart.

Hollow heart in potatoes is one of many problems related to irregular irrigation. Splitting and spraing (brown lines) are also water-related. This condition is a lot like blossom end rot in tomatoes. The lack of water causes deficiencies in immobile nutrients. [Did you know tomatoes and potatoes are so closely related that you can graft the two together to get potatoes from underground and tomatoes above ground? It’s called a pomato.]

​Small potato varieties are less likely to develop hollow heart than larger ones. Russet Burbank and Yukon Gold are highly susceptible to hollow heart.

A pomato (sold as TomTato) in a store display. (Jonas Ingold) CC BY-SA 2.0

Hollow heart in seeds

Garden peas and other seeds can also develop hollow heart when unusually high temperatures occur right after germination begins. Because this disorder happens so early in the plants’ development, it leaves them vulnerable to several fungal diseases. The best way to avoid hollow heart in peas and other seeds is to plant at the optimal time of year for each species.

​Bottom line: regular irrigation, planting at the appropriate time, and the right amount of nutrients can help prevent hollow heart in your garden.