3 Principles of Safe Drying: What to Do to Prevent Your Harvest from Moulding After Harvesting

After harvest, you are not done yet. It is during drying that it is decided whether your crop will turn into fragrant, high-quality dried material – or end up in the bin because of mould. It can appear quickly and ruin the entire harvest within a few days. How can you recognise mould, why does it develop, and how can you prevent it? Follow these three principles.

Mould is among the most common and at the same time most dangerous threats during drying herbs. At first glance, it may appear as a subtle white coating or small grey spots, but in reality it is microscopic fungi that spread quickly and can ruin the entire harvest. It most often appears inside dense flowers, where moisture accumulates and there is not enough air movement. Its development is mainly encouraged by high humidity, insufficient ventilation, and poor hygiene when handling harvested plants.

Choose a suitable drying method

If you want your herbs to retain as many aromatic terpenes as possible and not lose active compounds, make sure they dry slowly. Fast drying does reduce the risk of mould, but at the expense of the quality of the dried material. Herbs dried too quickly have an unpleasant odour and taste bitter.

The optimal drying time is roughly 7 to 21 days and will depend on the temperature, humidity, and movement of the surrounding air, as well as the size of the plants and their flowers. If you dry plants whole (hung upside down by the crown), they will dry the slowest. Drying will be slightly faster if you divide the plants into individual branches. The fastest method is then drying on drying nets, where you can dry individual flowers divided into smaller parts. A newer method is drying in drying bags made of breathable plastic. These protect the flowers from mould spores while also sealing in valuable terpenes.

The drying speed is also affected by how you clean the plants before drying. If you remove only the large leaves and trim the small “petal” leaves on the flowers only after drying (dry trim), they will dry slightly more slowly. If you clean the flowers thoroughly before drying (wet trim), they will dry faster.

You may also be interested in: Guide to perfect drying

Do not underestimate the right climate

Mould thrives best in a humid environment. During the drying process, relative humidity should not exceed 65%. Ideally, you should keep the humidity between 50% and 55%. You can easily reduce the air humidity in the drying area with a dehumidifier, but be careful that the warm air from the device does not blow directly onto the flowers. They would dry out too quickly.

The ideal temperature for drying medicinal herbs is roughly 18 °C - 20 °C. At higher temperatures, valuable monoterpenes evaporate quickly. If you want to slow the drying down a little, you can lower the temperature to 16 °C. Remember, however, that slower drying increases the risk of the crop being affected by mould.

To prevent moisture condensation, it is necessary to ensure constant air circulation in the drying room. If you are drying in a grow tent, leave the extract fan running at least at low power – it will help remove humid air and bring fresh air in. In the room where the tent is located, open a window or at least the door to the next room so that the air can move freely and does not build up in a closed space. If conditions allow, you can also use a small fan to gently move the air between the drying flowers. However, be careful that the airflow does not point directly at them.

Care pays off

Be as careful as possible during harvesting, drying, and subsequent processing. It would be a shame to throw away months of hard work in the final stage. When harvesting, inspect the plants thoroughly for signs of mould. Pay particular attention to the largest flowers, which may look healthy on the outside but already be mouldy inside. If you come across a mouldy part of the plant, separate it from the rest of the crop immediately and be even more cautious during drying. In such cases, it is often better to divide large flowers into smaller parts and dry them on drying nets.

Also pay attention to hygiene. Disinfect scissors and other tools before use and wear disposable gloves. This will protect not only the plants, but also your hands from resin, which can be irritating. If you have come across parts affected by mould, disinfect the tools again after removing them and replace the gloves with new ones.

Monitor the humidity and temperature in the drying area with a thermometer with hygrometer and check every day that everything is proceeding without problems. Mould can appear on the flowers even during the drying process. In such a case, remove the affected parts immediately, lower the humidity, and increase the temperature in the drying room.

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