How to Dry Medicinal Plants for Maximum Potency

Drying medicinal plants is the most common form of traditional preservation. There’s drying and then there’s drying: have you ever compared the difference in smell between chamomile dried by your herbalist and that of a commercial herbal tea bag? With this transformation sheet, you’ll have all the information and tips you need to make products that are far superior to those on the market, with little effort and simple tools.

Why dry medicinal plants?

Economical, drying preserves most of a plant’s medicinal properties over a period of around 1 year. As each part of the plant has its own cycles, they only have the maximum amount of active ingredients at one time of the year; drying your plants means having access to the best your garden has to offer all year round.

Plants are mainly made up of water (generally between 65 and 85%). Since water is the source of life, as long as there is so much of it, micro-organisms will thrive in it, and the plant won’t survive.

Tips for selecting and preparing plants for drying

Reduce water in plants to be prepared for drying

If possible, pick the plants to be dehydrated during a dry period (there will be less water in the plant);
Clean plants only when necessary; avoid soaking.

Mulching plants in the garden reduces the presence of soil on aerial parts

Reduced cutting slows down the degradation of the dried plant (by oxidation).

Keep the plant in the largest possible pieces;
Except for the roots. They are separated from the plant and cut into strips (to reduce drying time and avoid cutting a dried root, which can be laborious);
The main vein of the leaves or the stem of the plant can be removed if it is very large like for Great Mullein (Verbascum thapus). The aim is to optimize drying time at the major part of the leaf and avoid storing plants that still have too much water and won’t keep;
Remove all non-useful parts before drying.

Drying methods for medicinal plants

dried flowers by hanging bouquet — Suspension drying of plants by Roger Ward

By suspension (traditional method):

This method is particularly suitable for small plants where the leaves and flowers are picked from the stem and the leaves are small, for example: oats, thyme, yarrow, rosemary, savory… For this method, keep the stem, leaves and flower together.

Select and ensure plant cleanliness (see Selecting and preparing plants for drying);
Take a few whole stems and make a bouquet;
Wrap string or raffia around the bouquet and keep some string to secure it in place;
Hang the leaves by the stem (upside down) and hang them to dry… if the area is well lit, you can put a paper bag around the bouquet.

On trellises or horizontal trays

Drying plants on trellises by Audray Pepin

Make sure the plant is healthy and clean;
Cut off the medicinal part to be preserved
Arrange the parts to be dried on the tray to prevent them from touching
Switch on the ventilation (note: the ventilation should blow the hot air upwards; if you have horizontal ventilation, try fitting deflectors to prevent dried plants from moving all over the dryer).

Drying temperature: 30°C

In general, for a dryer with several types of plants, we set the temperature at 30°C. If we’re afraid of drying too long at this temperature, we generally increase ventilation rather than heat… This temperature is especially critical for plants with many volatile active ingredients (recognizable by their fragrant bouquet), such as essential oils.

Avoid drying medicinal plants in the oven with the door ajar. The oven is too hot and promotes evaporation of volatile compounds. If you have an aromatic plant, you may prefer (failing the suggestions given) simply to spread it out on paper and leave it in an airy, dry place.

For your own good …

Plants originating from the wild must be dried at 40°C.

This is an important exception! If it’s possible that these plants have been soiled by the droppings of a fox, coyote, wolf or domestic dog, then to avoid any risk of echinococcosis transmission, dry your harvest at 40°C. It’s extremely rare, but since the consequences are far-reaching, it’s best not to take any chances.

Tips

Optimize your drying

Protect from light (dark place, or use a paper bag);
Avoid drying at temperatures above 30°C or 35°C, to preserve volatile components such as essential oils;
Ensure good ventilation to evacuate humidity (rapid drying at low temperature is ideal);
Make sure plants are completely dehydrated before storing them in an airtight container. They should be light and crisp. If in doubt, leave them a little longer. A partially dehydrated plant will rot and destroy all plants stored in the same container.

If available, prefer using a dehumidifier instead of heat, in order to speed up the drying process of your plants.

Optimize storage

Drying increases the preservation of active ingredients in plants. That said, you only have to compare a freshly dried plant with one that has been dried for several years to see that the process only slows down the degradation process… As the months go by, the plant loses its brightness (tannins), its smell and its taste (essential oils). It will become increasingly bland and less rich in active ingredients.

As most plants have a 1-year cycle, if you grow your plants in the garden, renew your supplies every year… then you’ll always have the best quality for your uses.

That said, there are a few tips for optimizing preservation during storage:

Protect them from crushing (dried plants are fragile; the more whole they are, the less oxidation and the longer they will keep);
Protect them from light (opaque container, storage in a cupboard…);
Limit access to air. Use airtight containers;
Avoid exposure to excessive heat.

Always observe and smell a plant before eating it. A good smell and crunchy bits indicate the quality of the plant.

The right tools for drying medicinal plants

Commercial dryer

A dehydrator with the hot air pushed upwards

wind dehydrator pushed upwards — Vertical dehydrator

Most models allow you to add trays (to expand your capacity later).

They can also be used as a heat source under your mesh shelf or horizontal tray device.

If you choose this option, check :

That the thermometer can be set to a low temperature (30°C);
That the capacity is right for you;
Trays are easy to clean: they often can’t go in the dishwasher and are fragile.

A horizontal hot air dehydrator

Horizontal wind dehydrator for drying medicinal plants — Dehydrator
horizontal hot air dehydrator

These models often offer more control over drying temperature (especially low temperatures). Trays can be removed to increase the spacing between them, which can be handy if you’re drying large flowers head-down.

With these models, get into the habit of closing the ventilation before opening the panel.

Build your own dryer:

Séchoir d'herboriste — View of a handmade dryer with door opened

We want horizontal, well-ventilated nets at around 30°C, arranged in a column in a dry, dark place. To create these conditions, all you need is a dark space, a fan and a small heat source. The most sophisticated dryers also have a dehumidifier and temperature sensors connected to the heat source, but these are not necessary.

drying tray, with muslin by Audray Pepin — Plant drying tray, with muslin

The images show an herbalist’s dryer and horizontal trays to produce a large volume of dried herbs… if you have the space and are a handyman… it’s perfect.

Alternatively, a mesh shelf (see photo), in a dry, warm, well-ventilated place out of the sun (an attic, an upstairs room…) can work with a smaller investment of time and space.

If necessary, add ventilation, a dehumidifier or a small heat source (e.g. a commercial dehydrator).

Container for storing dried plants

Drying plants - traditional storage photo by Bob — Drying plants
– traditional storage photo by Bob

In an ideal world, we store our plants in non-toxic, hermetically sealed, opaque and reusable jars.

These solutions often take up a lot of space and are expensive.

One way to achieve this is to paint the outside of the masson pots opaque black.

Personally, I place my plants in airtight plastic bags that I keep in cardboard crates, arranged in alphabetical order, and I reuse the bags as long as they’re airtight.

Photo credit

Title page photo credit:Jerzy Durczak

Photo Plant drying – traditional storage : Bob