Which Medicinal Herbs Can You Grow and Identify at Home?

Begin with sage, thyme and rosemary.

They are the strongest opening set for a reason that has nothing to do with reputation, which is that no two of them look alike. NC State describes sage leaves as grayish-green, hairy with white fuzz and about 4 inches long, thyme as a mound 6 to 12 inches high of tiny leaves only 1/4 to 1/2 inch long, and rosemary is woody with narrow needle leaves.

Somebody who has never grown a herb can separate those three across a bed at a glance. That is the property worth selecting for, because every other habit in the bed depends on it.

Mint and lavender come next. All five so far are in the mint family, and sage stems are square just as mint stems are, so the stem does not separate them. Mint gives itself away by its scent and by runners that spread through a bed, and lavender by its gray foliage and flower spike.

Yarrow is the sixth, identified by a flat flower head held over fern-fine leaves. It is also the one with a dangerous lookalike in the wild, covered in the lookalike section below.

Each plant above has its own profile carrying soil, spacing and seasonal care.

Less than their reputation suggests. NCCIH keeps fact sheets on three of the six, sage, lavender and peppermint oil, and has none for thyme, rosemary or yarrow among its herb fact sheets.

Two things follow from that table. The first is that the studies describe oils, extracts and capsules at measured doses, and a leaf picked from the bed is none of those, so a finding about lavender oil says little about a handful of lavender flowers.

The second is that risk depends on amount and form. NCCIH's warning about thujone in common sage applies to large amounts, which is why it calls sage likely safe at the amounts found in food and separately flags pregnancy.

Mint is the clearest case of the gap. The research NCCIH describes is mostly on peppermint oil, while the plant most gardeners grow is a pot of leaves, for which NCCIH says the evidence is not enough to judge.

The danger in a herb bed is usually a plant that shares a word or a look with another plant, because the word is what people trust and it is the part nobody checks.

Bay laurel is Laurus nobilis, in the family Lauraceae, and it is the leaf that goes into cooking. Skip laurel is a form of Prunus laurocerasus, cherry laurel, a hedging shrub in the rose family.

They are not close relatives, they are not interchangeable, and the only thing they share is the second half of a common name.

In the hand they separate on size and shine. NC State gives bay leaves as 1 to 3 inches long and leathery, and cherry laurel leaves as glossy and up to 10 inches long. Bay is not a pet-safe plant either, since the ASPCA lists it as toxic to dogs, cats and horses.

The second collision is quieter and costs nothing except a season.

Russian sage is Salvia yangii, an ornamental perennial with grayish, finely dissected leaves and purple flowers on tall branched stems, and it is not the culinary Salvia officinalis growing in the bed. Somebody who plants one expecting the other ends up with an attractive border plant and no sage.

Yarrow raises a different problem, because the risk sits outside the garden. University of Minnesota Extension lists yarrow among the plants that look similar to poison hemlock, a weed in which all parts are extremely toxic to people and livestock when eaten and small amounts can be deadly.

Poison hemlock stems are hollow, ridged and hairless, with purple spots or blotches, and its lacy white flowers sit in umbrella-shaped clusters 2 to 3 inches across on plants usually 4 to 6 feet tall. Minnesota's guidance is to wear gloves and eye protection to handle it and not to compost or burn it.

A yarrow bought in a pot under the name Achillea millefolium is not the danger. The danger is a white-flowered plant picked from a ditch or field edge because it looked like yarrow, which is why gathered wild material has no place in a bed kept for harvest.

All three cases come back to the same habit. A common name is a label somebody applied and the botanical name is what identifies the plant, so a nursery tag reading only laurel or only sage has not told you what you are buying.

Write the botanical name on the label rather than the common one. A label reading Salvia officinalis still answers the question in two years, where one reading sage does not.

Add the planting date while you are there, because it tells you the age of a woody herb, and age is what decides whether a bare-looking rosemary is worth cutting back or replacing.

The label in the bed is only half the job.

Once material has been cut and dried it has left the plant that identified it. UMN Extension labels drying bundles to prevent mix-ups, and Maryland Extension stores dried herbs in a labeled airtight container, so the label travels with the material from the moment it is cut.

One jar holds one plant. Dried leaves from two herbs put into the same jar cannot be separated again, and that is the moment an identification you were careful about is actually lost.

A harvested bed has a siting problem an ornamental border does not. Illinois Extension's harvesting advice starts with a check that the plants have not been sprayed with pesticides, since many products are not approved for herbs that are eaten.

So the boundary that matters is the one spray and drift can cross, and a harvested bed belongs apart from anything that gets treated, a lawn included.

The site then decides part of your list for you. UMN Extension says most herbs need at least six hours of direct sun and well-drained soil, and Illinois calls lavender demanding of full sun and extremely well-drained soil, so a damp shaded corner rules out sage, thyme, rosemary and lavender before you have bought anything.

Mint is a siting decision rather than a maintenance one. UMN Extension says hardy perennial mints can spread aggressively, and a free-standing pot of its own keeps it out of the thyme.

The bed is not harvested one way.

Leaf herbs and flower herbs each give a different part, and applying a leaf habit to a flower herb wastes the crop and the season with it.

Cut leaf herbs before they flower. Maryland and Illinois both say leaf production declines once flowering starts, and Illinois adds that removing flowers as they appear keeps new leaves coming.

How much you take decides whether the plant comes back. Illinois puts the limit for perennial herbs at about one-third of the growth at any one time, which on rosemary keeps the cut in green growth rather than old bare wood.

Time it for the morning once the plants have dried off and before the day gets hot, which is the window Illinois and Maryland both give. UMN Extension then hangs bundles of four or five stems upside down in a dark, dry, well-ventilated place for 7 to 14 days.

A garden gives you identified plant material.

That is the whole of what it gives you, and it is worth saying plainly, because what is in a leaf varies with the season, the site, the age of the plant and how it was dried.

Traditional use is a record that people have used a plant. It is not a dose, not a duration, and not evidence that the plant suits any particular person. NCCIH's own sage fact sheet describes traditional use and still concludes that definitive conclusions about its effects cannot be reached.

Some questions stop being gardening questions entirely. Anything involving prescribed medication, pregnancy, nursing, children or pets belongs with a qualified professional who knows the individual circumstances, and NCCIH flags pregnancy for sage and sedative drugs for lavender.

This is also why a plant can be worth growing without being worth taking. The two recommendations are separate, and this page only makes the first.

Apply the opening rule to every plant that arrives after the first six. A new herb earns a place when you could pick it out of the bed with every label removed, and it does not when the tag is the only thing separating it from its neighbor.

Buy from a nursery that sells under the botanical name.

It removes most of the problem at the counter rather than in the bed, and a supplier who will not tell you the species has answered a different question from the one you asked.

A plant that fails the test is not banned from the garden. It goes into a pot of its own, away from the harvested bed, until it is familiar enough that the label is a convenience rather than the only evidence.