Blackheart

Blackheart is a disorder caused by environmental conditions. It occurs in celery, potatoes, sweet potatoes, tomatoes, and other garden crops. The causes of blackheart are the same. If seen in almonds, it’s a fungal disease called Verticillium wilt.

Causes of blackheart

Blackheart is the result of insufficient oxygen or too much CO2. How can you control those levels, you might ask. It’s easy. Picture this: it’s a hot day. Your plants are wilting. You add water, a lot of water. Your intentions are good, but now the ground is saturated. This localized flood pushes oxygen out of the macropores and micropores of the soil, and blackheart takes hold. Blackheart is also caused by too many cold days, like in your refrigerator. 

Blackheart of celery

If young tissues in the middle of your celery plants turn black, it may be blackheart. Much like blossom end rot of tomatoes and tip burn of lettuce, this condition is a calcium uptake problem. It means plants cannot access enough of it. It may be a calcium soil deficiency or insufficient water. An inexpensive lab-based soil test is the only way to know what is in your soil. Irregular watering, soil salinity, and excessive fertilizer, specifically magnesium, nitrogen, or potassium, can interfere with calcium uptake.

Celery blackheart (PlantVillage) CC BY 3.0

Blackheart of tomatoes and potatoes (sweet and otherwise)

Commonly affecting potatoes and tomatoes, blackheart causes them to turn black in the middle. Fruit suffering from blackheart looks perfectly normal on the outside. Like hollow heart, which creates cavities within tubers, blackheart creates dark areas with distinct edges inside the fruit. 

These darkened areas start as random spots that can expand. There may be small cavities, but they are mostly absent. These symptoms are similar to soft rot and Phytophthora root and stem rot, except that the interior stays firm. Eventually, these darkened areas will rot. If your seed potatoes have blackheart, they will grow into weak plants, if they grow at all.

Potato infected with Phytophthora stem and root rot (I.Sáček, senior) Public Domain

Potato infected with soft rot (Scot Nelson) Public Domain

Preventing blackheart

To prevent blackheart from occurring, use these tips:

• Install resistant varieties.
• Provide good drainage.
• Avoid overwatering and over-fertilizing.
• Do not harvest potatoes in extreme heat (above 86°F) or cold (below 35°F).
• Store harvested potatoes loosely in a cabinet rather than tightly bagged or in the refrigerator.
• Store tomatoes in your pantry or on a countertop.

I hope the only blackhearts you have to deal with are the ones found in comic books.