With unusual, dark colors in their skin and flesh, so-called black tomatoes (Solanum lycopersicum) give different ripeness indicators than more familiar varieties of tomatoes. Rather than being truly black, these tomatoes have green, brown or purplish tinges that give a blackish appearance, with each variety having different colorations. Most black tomatoes have a Russian origin. Reputed to have a rich, complex flavor with a balance between acidic and sweet, black tomatoes make a striking addition to salads and sliced tomato dishes. Consider several ripeness indicators, but personal taste and experience are your best guides.
Dark color occurs in varieties with different shapes and sizes. Both determinate and indeterminate varieties exist. Determinate plants stop growing when fruits begin to form, forming bushy plants with fruits that ripen at the same time. Indeterminate plants continue growing throughout their lifetimes. Tomatoes are perennials that originated in subtropical and tropical areas of Central and South America, hardy to U.S. Department of Agriculture plant hardiness zones 10 through 11. They're grown as annuals.
Ripe Fruit Color
The amount of black color varies from variety to variety and also with growing conditions. Black color develops more fully in higher temperatures, with blackish tones stronger in areas with hot summers. The colors are also enhanced where soils have higher acidity and mineral content. Generally, ripe black tomatoes have a good blend of greenish coloration combined with red, purplish or chocolate colors.
Small to Medium Black Tomatoes
Look for distinct varietal colorations to help choose ripe tomatoes. "Black Prince," an indeterminate heirloom Russian variety from Siberia, has 2- to 3-ounce, round tomatoes that mature in 70 days. Ripe fruits have dark shoulders that still show some green coloration on the top half and deep garnet red on the bottom half.
Indeterminate "Black from Tula" has green shoulders and a rosy-black color. "Black Sea Man" displays mahogany-colored tomatoes with olive-green shoulders on determinate plants. Fruits mature in 75 days.
Pear and Plum Black Tomatoes
Although it's named "Japanese Black Trifele," this variety originated in Russia. The pear-shaped fruits are mahogany when ripe, with interesting greenish-black patterns in the flesh when you slice it open. Indeterminate plants have ripe fruit in 81 days.
Also Russian but named for an African country, "Black Ethiopian" has plum-shaped, 5-ounce fruit colored a medley of mahogany, bronze and red when ripe. Indeterminate plants bear in 81 days.
Beefsteak Black Tomatoes
A taste-test winner, "Paul Robeson" bears large, mahogany-colored fruits in 80 days on indeterminate plants. Also winning awards for taste, "Carbon" ripens in 76 days on indeterminate plants. One of the darkest blacks, the tomatoes are purple-black when ripe.
The aptly named "Black Cherry" is an early producer, with blackish-red fruits ripening in 65 days on indeterminate plants. Ripening a little later at 70 days, "Chocolate Cherry" produces red 1-inch tomatoes tinged purplish-brown. These indeterminate plants are highly productive. If you mistakenly pick them a little early, fruits will ripen off the plant.
Other Ripeness Indicators
Other indications of ripeness are aroma and texture. A ripe tomato has a distinct fragrance that is hard to characterize but familiar once experienced. Black tomatoes become soft rather than firm as they ripen. This is one reason they're not more available commercially. The ripe fruit is easily damaged in shipment and has a short shelf life compared to commercial tomato varieties. The very best indication is taste. If you're not sure of ripeness, pick a tomato and eat it.
Tomatoes, including black tomatoes, need at least six hours of sun each day. They benefit from well-draining, fertile soil rich in organic material. Fast-growing plants need regular watering, about 1 inch of rain or irrigation weekly in warm summer areas and up to 2 inches weekly in hot summer climates. Soak the root zone thoroughly so water penetrates 6 to 8 inches of soil. Tomatoes can't withstand temperatures 32 degrees Fahrenheit or below, so cover them if late frosts threaten.
You'll get better growth and fruit production if you fertilize black tomatoes regularly with a low-nitrogen fertilizer such as 5-10-10. Apply about 1 1/2 tablespoons to each plant when tomatoes are beginning to form. Evenly spread the fertilizer in a ring around the drip line, which is where the branches end. Dig it into the top 1 to 2 inches of soil and water the plant thoroughly. Repeat the application every three weeks.