Herb Drying Calculator

When to harvest herbs for drying

Harvest in the morning, after the dew has dried but before the sun gets hot — that is when the essential oils that carry flavour are at their strongest. Pick before the plant flowers if you can, since flavour often fades once flowering starts, and never take more than about a third of the plant at once so it can regrow. For leafy herbs such as basil, mint and parsley, cut the stems; for woody herbs such as rosemary, thyme and oregano, cut whole sprigs. Give the harvest a gentle shake outdoors to dislodge insects, and only wash it if it is visibly dirty — washing adds moisture and slows drying, which is the enemy of a good result. If you do wash, pat the leaves dry with a towel first. Harvest on a dry day: herbs picked wet take much longer to dry and are more likely to go mouldy.

Air drying, dehydrator or oven?

Air drying is the cheapest and gentlest method, and it suits most herbs: tie small bunches with string, hang them upside down in a warm, dark, well-ventilated place, and wait a week or two. Darkness matters because light bleaches the leaves and fades the flavour. Small, loose bunches dry faster than fat ones — if the middle of the bunch stays damp, it will mould. A dehydrator is faster and more reliable, especially in humid weather: spread the leaves in a single layer, use the lowest heat setting (around 95°F / 35°C for leafy herbs, up to 115°F / 46°C for woody ones), and check often. An oven on its lowest setting works in a pinch, but it is the riskiest method — temperatures creep up, the door needs to stay slightly open, and herbs can go from dry to burnt in minutes, so check every 15 minutes. Whichever method you use, the test is the same: the leaves are ready when they crumble easily, not when they bend.

Why fresh weight shrinks so much

Fresh herbs are roughly two-thirds water by weight, so drying removes most of the mass and leaves the flavour compounds behind. That is why the calculator’s ratio is about 3:1 for leafy herbs — 100 grams of fresh basil becomes roughly 30 grams dried — and about 4:1 for woody herbs such as rosemary and thyme, which hold less water in their tougher leaves. The flavour concentrates too, which is why the standard kitchen conversion is 1 tablespoon of fresh herb to 1 teaspoon of dried. Some herbs dry better than others: oregano, thyme, rosemary and sage keep — or even improve — their flavour dried, while basil, cilantro and parsley lose a noticeable amount and are often better frozen in oil or made into pesto. Chives and dill sit in the middle: acceptable dried, better frozen. If an herb tastes disappointing dried, try freezing the next harvest instead.

Storing dried herbs so they keep

Strip the dried leaves from the stems and store them whole — not ground — in airtight glass jars in a dark cupboard, because whole leaves keep their flavour longer than powder. Label each jar with the herb and the date: dried herbs are best within six months to a year, and after that they fade even if they still look fine. Keep jars away from the stove and the sink, since heat and steam are the enemies of stored herbs. If you open a jar and smell little, the herb has passed its best — use more of it, or replace it. One practical note: a single vigorous plant of mint or oregano can fill several jars in a season, so dry in small batches rather than letting a mountain of herbs wilt on the counter. For how much to plant and when to harvest, see the planting calendar, and for watering and feeding the plants themselves, the watering calculator and fertiliser calculator. Browse all the garden tools for more.