How to Dry Rosemary: 4 Methods, Times and Temperatures

Rosemary (Salvia rosmarinus, mint family) is about as easy to dry as a herb gets.¹ NCHFP, Oregon State, the University of Tennessee and the University of Wisconsin all class it as a sturdy herb that air-dries without special equipment,²³⁴⁵ and America’s Test Kitchen found that dried rosemary holds up reasonably well in dishes that cook for a while in liquid.⁶ The one thing to manage is heat: studies on rosemary show that the hotter the drying, the more of its aroma is lost. The settings below come from university extension guides; where they disagree, the disagreement is shown rather than averaged.

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 sun⁴	Generally 2–4 weeks⁴	Cheapest; no added heat
Dehydrator	95–115°F, up to 125°F where humid²; Penn State says 95–110°F⁷	1–4 hours²	Use the low end
Oven	Lowest setting, not above 180°F, door open⁷	3–4 hours⁷	Or overnight with only the oven light on²
Microwave	On high, from 30 seconds to 3 minutes depending on the source (table below)	Minutes	Small batches only; paper towels can catch fire⁷
Sun	Not recommended⁷²³		Costs color and flavor²

Before you start

The extension guides agree on timing: the best point to harvest most herbs for drying is just before the flowers first open,²³ picked in the early morning once the dew has evaporated.³ Oregon State adds that cut herbs should not lie in the sun or sit unattended after harvest.³

Rinse the stems in cool water and shake off the excess,⁷² then remove all visible water with towels or paper towels.⁴ A widely repeated claim says rinsing rids herbs of pathogens; the extension guides present it as cleaning and make no such claim.

Air-drying

Air-drying is the easiest and cheapest method,⁴ and the one rosemary suits best. The Wisconsin method: tie washed branches into small bundles of 5–6 stems and hang them upside down in a warm (70–80°F), dry, well-ventilated place out of direct sunlight until the moisture has gone, generally 2–4 weeks.⁴ How long it takes depends on the humidity and air flow where you hang it (common practice). Keep the bundles small, because the University of Tennessee warns that herbs in bundles that are too large will mold.⁵

Penn State says to keep drying herbs away from the sink, stove and dishwasher, where the air is moist.⁷ Oregon State suggests an attic, a kitchen or any warm place with air circulation,³ and NCHFP says drying indoors usually gives better color and flavor than drying outdoors, though outdoors is often possible.² A paper bag punched with holes keeps dust off,⁷ and catches the needles as they drop (common practice).

Dehydrator

NCHFP’s instructions are to preheat with the thermostat at 95–115°F, going as high as 125°F where humidity is high, and to expect 1–4 hours, checking periodically.² Penn State’s range tops out lower, at 110°F.⁷ For rosemary, the studies below favor the low end of either range. Pat the sprigs free of surface water first (common practice) 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,⁷ and the Wisconsin guide gives the same figures, with the herbs in a single layer and stirred now and then.⁴ Oregon State warns that drying herbs at too high a temperature can cause flavor loss.³ Two hours at 200°F, a method that circulates widely, appears in none of the extension guides we checked, and it is 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.²⁵

Microwave

The microwave is fast and suits small amounts only.² The guides do not agree on the timing:

Source	Amount	Time on high	Method
Penn State⁷	Per cup	2–3 minutes	Start with 1 minute, mix every 30 seconds, keep checking
University of Tennessee⁵	Per cup	2–3 minutes	Start with 1 minute, mix every 30 seconds
Oregon State³	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 Wisconsin⁴	4 or 5 branches between paper towels	2–3 minutes	Another 30 seconds if not brittle
America’s Test Kitchen⁸	Not stated, on a paper towel	30–40 seconds	Crumble and store

As a starting point (Method), give a few sprigs a minute, then 30-second rounds until the needles snap.

Two safety points apply whatever the timing. Penn State warns that if the load is too small, the paper towels can catch fire,⁷ and Oregon State says not to use paper towels made from recycled paper, which can contain metal scraps that arc.³ The Wisconsin guidance calls the microwave a last resort that cooks the herbs and gives very poor quality, and 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.⁴

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)²³⁵; 95–110°F (Penn State)⁷
Air-drying time	Generally 2–4 weeks for sturdy herbs hung in bundles (Wisconsin)⁴; usually 5–10 days for tender herbs hung in small bunches inside bags (Oregon State)³
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)⁷⁴; or no heat but the oven light or pilot light, overnight (NCHFP, Tennessee)²⁵

None of these was tested side by side on the same herb, so we have not picked a winner. Where a range is given, starting low and checking often is the cautious reading (Method).

What heat does to rosemary

Rosemary’s smell comes from its essential oil, and two Italian studies measured what drying conditions do to it:

Study	What was tested	What happened
Di Cesare et al., 2001⁹	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., 2007¹⁰	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.

The Fahrenheit conversions are ours. Both studies report the makeup of the oil, not the taste of a dish. Read together with the extension guides, they point the same way: room-temperature air-drying, or a dehydrator at the bottom of its range, is the gentlest choice. That last sentence is our reading of the sources, not a tested recommendation.

How to tell it’s done

Rosemary’s needle-like leaves snap rather than crumble when dry (editorial), so the stem test is more useful than the crumble test. The guides say the stems should be brittle and break when bent,² and Oregon State adds that the leaves should fall from the stems.³ Strip the needles and discard the stems.⁴

Check your work after packing. The Wisconsin guidance is to watch the filled containers for a couple of days; if you see any moisture, take the herbs out and dry them longer.⁴

Air-dried herbs can carry insects. 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, and it recommends freezing for better flavor.⁵

Storing dried rosemary

Keep the leaves whole and crumble them as you cook; Penn State says storing herbs whole is preferred.¹¹ Use airtight containers in a cool, dry, dark place,² away from the stove and sink.⁷ Oregon State adds that dried herbs can also go into airtight containers in the freezer.³

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

Source	Scope	Figure
Penn State⁷	Most home-dried herbs	Keep well for up to a year
Oregon State³	Home-dried herbs	Up to one year; for best flavor, use within six months to a year
University of Wisconsin⁴	Home-dried herbs	Keep for years, but use within a year for best flavor
America’s Test Kitchen⁸	Herbs dried in the microwave by its method	Up to 3 months, airtight
McCormick¹²	Leafy dried herbs, a spice company’s own guidance	1–3 years

We have not averaged these. McCormick defines shelf life as how long spices stay most aromatic,¹² which is the right way to read every figure here: a quality window, not a safety date. The practical test is smell. Crush a pinch, and if the aroma 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 advises refrigerating them and using them within four days or discarding them, and calls freezing the safest option.¹³

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.

Salvia rosmarinus Spenn., Plants of the World Online, Royal Botanic Gardens, Kew. powo.science.kew.org · Reference work ↩
Herbs (drying), National Center for Home Food Preservation. nchfp.uga.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶
Drying herbs (SP 50-921), Oregon State University Extension Service. extension.oregonstate.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴
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 ↩¹¹ ↩¹² ↩¹³ ↩¹⁴
Drying Herbs, University of Tennessee Extension. lawrence.tennessee.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷
Science: Substituting Dried Herbs for Fresh, America’s Test Kitchen. americastestkitchen.com · Publication ↩
Let’s Preserve: Drying Herbs, Penn State Extension. extension.psu.edu · Reference work ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶
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