How to Dry Rosemary: 4 Methods, Times and Temperatures

Rosemary is about as easy to dry as herbs get. It’s a sturdy herb that air-dries without special equipment, and America’s Test Kitchen found that dried rosemary holds up reasonably well in dishes that cook for a while in liquid.¹ The one thing to watch is heat. Studies on rosemary show that the hotter you dry it, the more of its aroma you lose.

At a glance

Method	Settings from named sources	Time	Notes
Air-drying	Bundles of 5–6 stems, hung at 70–80°F in a dry, ventilated spot out of direct sun²	Generally 2–4 weeks²	Cheapest; no added heat
Dehydrator	95–115°F, up to 125°F where humid³; Penn State says 95–110°F⁴	1–4 hours³	Use the low end
Oven	Lowest setting, not above 180°F, door open⁴	3–4 hours⁴	Or overnight with only the oven light on³
Microwave	On high, from 30 seconds to 3 minutes depending on the source (table below)	Minutes	Small batches only; paper towels can catch fire⁴
Sun	Not recommended³		Costs color and flavor

Before you start

Most herbs are best harvested for drying just before the flowers first open, picked early in the morning once the dew has dried. Cut herbs shouldn’t lie in the sun or sit around after harvest.⁵

Rinse the stems in cool water and shake off the excess, then pat off all the visible water with towels or paper towels. You’ll often read that rinsing rids herbs of pathogens. The extension guides call it cleaning and make no such claim.

Air-drying

Air-drying is the easiest and cheapest method, and it’s the one rosemary suits best. Here’s the Wisconsin method: tie washed branches into small bundles of 5–6 stems and hang them upside down somewhere warm (70–80°F), dry and well ventilated, out of direct sun, until the moisture is gone. That’s generally 2–4 weeks.² How long it takes depends on the humidity and airflow where you hang it. Keep the bundles small. Bundles that are too big will mold, the University of Tennessee warns.⁶

Keep drying herbs away from the sink, stove and dishwasher, where the air is moist. An attic, a kitchen or any warm spot with moving air works, and drying indoors usually gives better color and flavor than drying outdoors, though outdoors is often possible.³ A paper bag punched with holes keeps dust off, and it catches the needles as they drop.

Dehydrator

NCHFP says to preheat with the thermostat at 95–115°F, going as high as 125°F where it’s humid, and to expect 1–4 hours, checking now and then.³ Penn State’s range tops out lower, at 110°F.⁴ For rosemary, the studies below favor the low end of either range. Pat the sprigs dry first and lay them in a single layer.

Oven

Penn State’s method is the lowest temperature, not above 180°F, for 3 to 4 hours with the door open.⁴ The Wisconsin guide gives the same numbers, with the herbs in a single layer and stirred now and then.² Drying herbs too hot can cost you flavor, Oregon State warns.⁵ Two hours at 200°F gets passed around a lot, but it’s in none of the extension guides we checked, and it’s far hotter than the conditions that kept rosemary’s aroma in the studies below.

If your oven can’t hold 180°F or lower, use the cool-oven method. Strip the needles, lay them on a paper towel, cover with another towel and another layer, and repeat for up to five layers. Leave them overnight in an oven warmed only by the light of an electric oven or the pilot light of a gas one.³

Microwave

The microwave is fast, and it’s for small amounts only.³ The guides don’t agree on timing:

Source	Amount	Time on high	Method
Penn State⁴	Per cup	2–3 minutes	Start with 1 minute, mix every 30 seconds, keep checking
University of Tennessee⁶	Per cup	2–3 minutes	Start with 1 minute, mix every 30 seconds
Oregon State⁵	1 cup (never more than 1–2 cups)	1–2 minutes	Stir every 30 seconds after the first minute until almost dry, then finish at room temperature
University of Wisconsin²	4 or 5 branches between paper towels	2–3 minutes	Another 30 seconds if not brittle
America’s Test Kitchen⁷	Not stated, on a paper towel	30–40 seconds	Crumble and store

To start, give a few sprigs a minute, then 30-second rounds until the needles snap.

Two safety points apply whatever timing you use. If the load is too small, the paper towels can catch fire, Penn State warns.⁴ And Oregon State says not to use paper towels made from recycled paper, which can contain metal scraps that arc.⁵ The Wisconsin guidance calls the microwave a last resort that cooks the herbs and gives very poor quality. It notes that the heat drives off some of the oils along with the water, so microwaved herbs may taste less intense than herbs dried other ways.²

Where the guides disagree

Question	What named sources say
Dehydrator temperature	95–115°F, up to 125°F where humidity is high (NCHFP, Tennessee, Oregon State)³⁵⁶; 95–110°F (Penn State)⁴
Air-drying time	Generally 2–4 weeks for sturdy herbs hung in bundles (Wisconsin)²; usually 5–10 days for tender herbs hung in small bunches inside bags (Oregon State)⁵
Microwave time	From 30–40 seconds (America’s Test Kitchen) to 2–3 minutes per cup (Penn State, Tennessee); see the table above
Oven	Lowest setting up to 180°F with the door open for 3–4 hours (Penn State, Wisconsin)⁴²; or no heat but the oven light or pilot light, overnight (NCHFP, Tennessee)³⁶

Where you get a range, start low and check often.

What heat does to rosemary

Two Italian studies measured what drying heat does to rosemary’s aroma:

Study	What was tested	What happened
Di Cesare et al., 2001⁸	Leaves dried in ordinary air at 50°C (122°F), or in dried air at 30°C (86°F)	At 50°C, linalool disappeared from the leaves, and borneol, camphor, eucalyptol and α-pinene ended up below fresh levels. At 30°C, all the characteristic compounds stayed close to fresh.
Piga et al., 2007⁹	Sardinian rosemary and thyme, oven-dried at several temperatures and air speeds	Losses of volatile compounds depended directly on drying temperature and time. For rosemary, 38°C (100°F) with low air flow worked best and prevented the decrease.

We did the Fahrenheit conversions. Both studies measured what’s in the oil, not how a dish tastes. Put them next to the extension guides and they point the same way: air-drying at room temperature, or a dehydrator at the bottom of its range, is the gentlest choice. That’s our read of the sources, not a tested recommendation.

How to tell it’s done

Rosemary’s needle-like leaves snap instead of crumbling when they’re dry, so the stem test works better than the crumble test. The stems should be brittle and break when you bend them, and the leaves should fall off the stems. Strip the needles and toss the stems.

Check again after you pack them. Wisconsin’s advice is to watch the filled containers for a couple of days. If you see any moisture, take the herbs out and dry them longer.²

Air-dried herbs can carry bugs. The University of Tennessee says air-dried herbs and seeds need treating to kill insects and their eggs, either by heating at 160°F for 30 minutes or by freezing at 0°F or lower for at least 48 hours. It recommends freezing for better flavor.⁶

Storing dried rosemary

Keep the leaves whole and crumble them as you cook. Penn State says storing herbs whole is preferred.¹⁰ Use airtight containers somewhere cool, dry and dark, away from the stove and sink. Dried herbs can also go into airtight containers in the freezer.

How long dried rosemary keeps depends on who you ask, and none of these numbers was measured on rosemary:

Source	Scope	Figure
Penn State⁴	Most home-dried herbs	Keep well for up to a year
Oregon State⁵	Home-dried herbs	Up to one year; for best flavor, use within six months to a year
University of Wisconsin²	Home-dried herbs	Keep for years, but use within a year for best flavor
America’s Test Kitchen⁷	Herbs dried in the microwave by its method	Up to 3 months, airtight
McCormick¹¹	Leafy dried herbs, a spice company’s own guidance	1–3 years

They don’t agree, so we’ve left them side by side. McCormick defines shelf life as how long spices stay most aromatic,¹¹ and that’s the right way to read every number here: a quality window, not a safety date. The real test is your nose. Crush a pinch, and if the smell is faint, the rosemary has faded.

Herbs in oil are a separate food-safety question. A 2011 review of home-prepared vegetables and herbs stored in oil says to refrigerate them and use them within four days or throw them out, and calls freezing the safest option.¹²

Not yet measured

How home dehydrators and microwaves compare with the laboratory conditions in the two studies above.
How long home-dried rosemary keeps, measured on rosemary rather than herbs in general.
Microwave times by oven wattage for rosemary.

Science: Substituting Dried Herbs for Fresh, America’s Test Kitchen. americastestkitchen.com · Publication ↩
Drying Herbs, Wisconsin Master Gardener Program, University of Wisconsin-Madison. mastergardener.extension.wisc.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰
Herbs (drying), National Center for Home Food Preservation. nchfp.uga.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰
Let’s Preserve: Drying Herbs, Penn State Extension. extension.psu.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹
Drying herbs (SP 50-921), Oregon State University Extension Service. extension.oregonstate.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷
Drying Herbs, University of Tennessee Extension. lawrence.tennessee.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵
When You Should Actually Use Dried Herbs, America’s Test Kitchen. americastestkitchen.com · Publication ↩ ↩²
Di Cesare et al., Industrie Alimentari, 2001 (abstract, via FAO AGRIS). agris.fao.org · Peer-reviewed ↩
Piga et al., 3rd CIGR Section VI International Symposium, 2007. iris.uniss.it · Peer-reviewed ↩
Preserving Herbs by Drying, Penn State Extension. extension.psu.edu · Reference work ↩
How Long Do Spices Last?, McCormick. mccormick.com · Merchant ↩ ↩²
Nummer et al., Food Protection Trends, 2011. foodprotection.org · Peer-reviewed ↩

How to Dry Rosemary: Methods, Temperatures and What Heat Does to It