Blackheart

Blackheart is a disorder caused by environmental conditions. It occurs in a diverse collection of garden crops.


Celery, potatoes, sweet potatoes, and tomatoes are all susceptible to blackheart. Wherever it occurs, the causes of blackheart are the same. Unless it is seen in almonds. Then it’s a fungal disease called Verticillium wilt.


Causes of blackheart

Blackheart is caused by a lack of 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 miniature flood pushes oxygen out of the soil’s macropores and micropores. Blackheart takes hold.


Blackheart is also caused by extended periods of cold temperatures, like those in your refrigerator. You may be surprised to learn, as I was, that blossom end rot and blackheart result from similar conditions and may appear in tandem. Before adding calcium to your soil, be sure to have it tested first. Too much of a good thing can be a bad thing.


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 directly related to calcium uptake problems. That doesn’t mean your soil needs calcium. It means they can’t access enough of it. The only way to know how much calcium is in your soil is with a lab-based soil test. In many cases, the problem is irregular watering, soil salinity, and excessive fertilizer, specifically magnesium, nitrogen, or potassium.

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. [Unfortunately, I was unable to find licensable photos.] Fruit suffering from blackheart looks perfectly normal on the outside. Like hollow heart, which creates cavities within tubers, blackheart is seen as dark areas with distinct edges inside the fruit. These darkened areas start out 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:

• Plant 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.