Slice open a hot pepper and you will see tiny blisterlike sacs on the inner wall of the pepper. These sacs contain capsaicinoids or organic chemicals. Capsaicinoids make peppers hot.
The more sacs you see on the inside of a pepper the hotter the pepper will be. When a pepper is cut or handled roughly the sacs break and splash onto the pepper’s seeds and inner walls. That’s when you taste the hotness of a pepper.
The best-known capsaicinoid is capsaicin. Capsaicin is so potent that the average person can detect its presence even when it is diluted in water to 10 parts per million.
The hotness or pungency of a pepper is measured in Scoville Heat Units (SHU). American pharmacologist Wilbur Scoville invented this scale in 1912; it is basically a taste test. Scoville asked five people to taste diluted capsaicinoids from peppers; if the tasters could still taste the hotness of a pepper when 1 part of the pepper was diluted with say 10,000 parts water, then that pepper would be rated 10,000 on the SHU. A habañero pepper is rated up to 500,000 SHU.
Here are hot peppers–also called chili peppers–you can grow in the garden:
Mildly Hot Peppers (from 100 to 2,500 SHU)
Anaheim. Mild to moderately hot. Long, tapered, pointed fruit; 7 to 8 inches long, 1 inch wide. Light green turning crimson red when ripe; medium to thick-walled. Use for stuffing when red. The plant grows to 30 inches.
Ancho (called Poblano when picked green). Mildly pungent to hot (1,000-1,500 SHU). Large, conical fruit to 5 inches long, to nearly 4 inches wide; dark green turning red when ripe. Use in chili rellenos. The plant grows to 36 inches tall.
Big Jim. Medium hot (500-1,000 SHU). Large to very large fruit to 9 inches long, 2 inches wide at should tapers to blunt end; medium-green turning red when ripe. Use fresh, dried, or canned.
Hungarian Yellow Wax (also called Hungarian Long Wax). Very pungent. Slightly tapered fruit to 7 inches long, 1½ inches in diameter. Waxy yellow turning red at maturity; medium thick-walled. For canning and pickling. Upright plant to 24 inches. 62 days. Open-pollinated.
Italian White Wax. Mild when young, very pungent at maturity. Tapered, point fruit to 3 inches long ½ inch in diameter; pale yellow turning red at maturity. Upright plant to 40 inches tall. Open-pollinated.
Caloro. Pungent. Similar to Santa Fe Grande. Compact plant to 24 inches tall. Prolific fruit. Widely adapted and grows in difficult climates. Good for containers. Pickle or use as a sandwich garnish or as an appetizer.
Mexi Belle. Mildly hot, pungent ribs (100-500 SHU). Bell pepper shape, medium-sized 3 to 4 lobes; medium green turning red when ripe; thick walls. Compact plant 14 to 30 inches high. Will produce 10 to 20 pods. Widely adapted. All America Selection. Matures in 70 days. Stuff or add to stir-fries.
Mulatto. Pungent. Pods are 4 to 6 inches long, and 3 inches wide tapering to a blunt end. The plant grows to 36 inches tall. Matures to dark chocolate brown. Set fruit best in cool temperatures. Stuff like ancho or used dry to make mole sauce.
New Mexico #6. Mildly hot and flavorful. Anaheim type. Tapered fruit to 6 inches long, 1½ inches in diameter; green turning red when ripe. Use for chili rellenos when green; popular for drying. The plant grows to 30 inches tall.
Medium Hot Peppers (from 2,500 to 5,000 SHU)
Ancho 101. Mildly pungent (1,000-1,500 SHU). Heart-shaped, pointed, from 3 to 6 inches long, thin-walled; dark green turning red at maturity. Grows best where the weather is in the 70°sF. This tall plant may require staking. Use for chiles rellenos.
Cascabel. Moderately pungent, spicy flavor (1,500-2,500). Cherry-type, spherical, shiny fruit to 1 inch in diameter; dark green turning deep red at maturity; medium thin walls. The plant grows to 36 inches tall. Grows well in moderate climates. Pods rattle when dry. Grind dry pods into powder to flavor fish and shrimp.
Guajillo. Biting hot. Large, tapered fruit to 5½ inches long to 1 inch in diameter; turns translucent red when ripe; thin-walled. The plant grows to 36 inches tall. Good for drying. 58 to 90 days to maturity. Has a fruity flavor; used in red enchilada sauce.
Hungarian Rainbow Wax. Semi-hot flavor. Blocky, thick-fleshed fruit with 3 to 4 lobes; light yellow to a rainbow of sunset colors to red when fully ripe. Use for relishes and salsas. 62 days to maturity.
Hungarian Wax. Medium hot. Pods are 6 to 8 inches long; bright red at maturity. The plant grows to 24 inches tall. 70 days to maturity.
NuMex Mirasol. (2,500-5,000 SHU). Pods are 3 to 4 inches long ½ to ¾ inches wide; grow to 24 inches tall with multiple stems and branches and clusters of fruit at the end of each branch. 90 days to maturity. Used in dry, red form as a chile powder.
Fiery Hot Peppers (from 5,000 to 500,000 SHU)
Aji. Very hot (5,000-15,000 SHU). Pods 3 to 5 inches long; orange-red at maturity. Use in sauces and stews.
Dr. Greenleaf Red Hot Tabasco. Very pungent (5,000-15,000 SHU). Heavy cropping, virus resistant. 120 days to maturity.
Fresno Grande. Very pungent. Improved Fresno type; small, conical fruit tapering to a point, to 3 inches long; medium green turning to bright red when ripe; medium thick-walled. The plant grows to 24 inches tall.
Habañero. Hottest pepper (100,000-500,000 SHU). Square to heart-shaped fruit, often wrinkled, to 2½ inches long, 1 inch wide; light-green turning orange or red at maturity. Requires a long, hot, humid growing season. Use fresh in salsas or fermented to make hot sauce.
Jalapeño. Very pungent (5,000-15,000). Sausage-shaped fruit tapering to a blunt end, about 3 inches long, 1½ inches in diameter; deep-green turning bright red when ripe; medium-thick walls. 75 days to maturity. Use as a spice and condiment, as an ingredient in salsa.
Large Red Thick (Charleston Cayenne). Spicy; hotter than Jalapeno. Pods are 5 to 10 inches long, ½ to 1 inch wide, and crescent, or irregular in shape. Large Red Thick is grown in the West; Charleston Cayenne is grown in the Southeast. Often ground into flakes for pizza.
Long Red Slim Cayenne. Very pungent. Long, slender fruit tapered to a point, to 7 inches long and ½ inch wide, often wrinkled; dark green ripening to bright red. The plant grows to 24 inches tall. High-yielding plant. 72 days to maturity.
Louisiana Hot. Very hot. Elongated, tapered fruit to 4 inches long; green turning red at maturity. Heirloom variety.
Peter Pepper. Very pungent. Fruit to 4 inches long, 1½ inches wide, named for its penis shape; turning red when ripe. Use for pickling when green; dries well. The plant grows to 24 inches tall; very prolific.
Pretty Purple Pepper. Extremely hot. Dark purple fruit turns red at maturity. The plant grows to 30 inches tall.
Scotch Bonnet. Very hot (100,000-500,000). Shaped like a tam-o’-shanter; pods mature to yellow, red, or orange. Plants grow to 40 or more inches tall. Requires warm to hot growing season. Late maturing.
Serrano. Very pungent (5,000-15,000 SHU). Slender, cylindrical fruit to 2 to 5 inches long, ½ inch in diameter, taper to blunt point; medium dark-green ripening to bright red; thin walls. The plant grows to 36 inches tall; highly productive. 80 days to maturity. Adapted to hot, humid climates. Use for salsa relish.
Super Cayenne. Fiery flavor (30,000-50,000). Slightly curved fruit to 4 inches long; red when ripe. Use fresh dried. Compact plant to 24 inches tall. Good container plant. All America Selection. 70 days to maturity.
Supper Chili. Very hot. Small, elongated, cylindrical fruit to 2½ inches long, ½ inch wide; pale-green turning red when ripe. Harvest from green to red stages. Upright plant. All-American selection. 70 days to maturity.
Tabasco. Extremely hot (5,000-15,000). Small, slender pods 1 to 2 inches long, ¼ inch wide; yellow-green turning scarlet when ripe. Easy to grow; grow in containers. Used to make the Louisiana hot sauce.
Thai Hot. Extremely pungent. Small, cone-shaped fruit 1 to 2½ inches long; very prolific. Compact plant. Reaches maturity in 40 days. Grows well in containers. Use pods in Asian dishes.
Tiny Samoa. Very hot. Very small fruit, ⅛ inch thick and ½ inch long; green turning to red when ripe. Prolific producer. Can be grown in the house.
Takanotsume Japanese. Sharply pungent. Pods to 2½ inches long, ¼ inch wide. Grow in most areas. 90 days to maturity. Dried and used in Asian soups.