Q. I live in one of the most northern zones, only get moderate to light sun and would appreciate a segment about growing herbs for cooking, including exactly which herbs are perennial. On a recent show you mentioned that Lemon Thyme was an annual in the north, but the plant tags I've seen say that Thyme is a perennial. (I know that Basil is annual and Mint and Oregano are perennial.) Thank You,
- ---Rodney in Traverse City, MI
But the 'annual vs. perennial' issue can be really tricky. Many herb families have members that are perennial even in the most Northern regions, but others that can only survive winter in the absolute warmest zones. In these cases, the genus—the plant family—is much less important than the specific species (family member) under discussion. With that in mind, let's try and sort out some of the mysteries of the most common/favorite culinary herbs.
Basil (Mostly Ocimum basilicum): There are an enormous number of different varieties, shapes, sizes and colors of this herb. All are extremely frost sensitive and need to be pinched back and/or harvested frequently to keep them from flowering. Like most herbs, the flavor changes for the worse when flowers appear—so pinch off anything that looks like it'll bud. And maybe start new plants or sow fresh seed every month or so to insure a good-tasting supply. Holy Basil (Ocimum sanctum) is perennial if taken indoors for the winter.
Dill: (Anethum graveolens) Only the annual form is grown in the U.S. Dill doesn't like to be transplanted; you get your best results when you sow the seed directly in the ground or pot. If you mostly want the aromatic leaves, harvest and pinch back frequently to prevent flowering. If you just want the seeds, don't remove leaves, enjoy the flowers (great attractors of beneficial insects) and then wait until the seedpods are dry to harvest. Another good candidate for the planting of successive runs.
Mint: (Mentha is the genus name; and although lemon balm (Melissa officinalis) has a different genus name, it's considered a mint family member.) A huge and diverse family, almost every member of which is an aggressive grower that can easily become invasive. Grow in containers, surround with deep edging, watch for escaping runners and don't allow the plants to flower unless you want a mint farm. Peppermint and spearmint are perennial in the harshest climates, while most of the 'fruit flavored' mints are grown as annuals North of Zone 6. (Pineapple, lime, orange and chocolate mint are much less aggressive growers, while apple mint is one of the worst.) The crushed leaves of mint family members catnip and lemon balm make excellent natural mosquito repellants; and lemon balm is felt to be a more effective anti-depressant than St. John's wort. Harvest mints early in the morning to get the highest essential oil content in the leaves.
Oregano and marjoram: Both of these herbs share the same genus name (Origanum), are sold interchangeably and cross-pollinate readily—making totally accurate identification of any specific plant almost an impossibility, even to experts. Winter survival is a better test: True 'Greek' oregano (species name heracleoticum) is a Mediterranean native that won't survive winter North of Zone 7; neither will the highly aromatic Sweet Marjoram (species majorana or hortensis) or French Marjoram. The hardy family members are common oregano and wild marjoram (both are known as the species vulgare)—they're a little less tasty but still nicely edible, and perennial to Zone 5 and maybe Zone 4 if they feel like it. No matter what the type, harvest and pinch frequently to prevent flowering.
Parsley (Petroselinum crispum): Doesn't like transplanting and the seeds are real drama queens. Best method: put the seeds in a little cloth bag, dip them in and out of a bowl of lukewarm water for two hours and then immediately plant them in the pot or ground. You MUST dip; if you just soak them, they'll die. (Told you they were drama queens.) Once it's up, just let it grow—parsley is a biennial that won't flower until its second year, so you can let the leaves get nice and big. Good choice for growing indoors on a super-sunny windowsill in winter.
Rosemary (genus name Rosmarinus): Perennial only in excellent-draining soil in Zone 7 or warmer climes (or in sheltered locations and/or in the heart of a city in somewhat iffy zones). Unlike most herbs, flowering doesn't affect the flavor.
Sage: There are close to a thousand different herbal members in the Salvia genus. Common garden sage, the essential 'stuffing herb' (Salvia officinalis), is perennial in the North. But like most of the rest of the salvias, delicious Pineapple sage (species name elegans) is an annual in all but the warmest zones; its bright red tubular flowers are a favorite of hummingbirds, and the flowers are an edible human treat as well. True white sage (species apiana) is also perennial only in warm climes; it's grown for bees and to clear evil spirits out of a room, and like many sages, has a foul taste.
Thyme (genus name Thymus): This family also runs the gamut of winter hardiness. Common thyme (species name vulgaris) has the best smell and flavor, but is perennial only in Zone 7 and warmer (same for the excellent mosquito-repelling lemon-scented thyme (species name citriodorus). The species (serpyllum) with a million aliases—Creeping thyme, Mother of Thyme, Wild Thyme—is the one that's perennial everywhere in the U.S.