Harvesting Plants: How, When, and Why Timing Matters

One of the most powerful aspects of working with herbs is understanding when to harvest. The chemistry of a plant is not static — it shifts with the seasons, with the time of day, and even with the stage of growth. If we pay attention to these rhythms, we can collect plants when they are at their most potent, vibrant, and medicinal. 

Leaves 

Leaves are typically best harvested in spring or early summer, when they are young and soft. At this stage, they contain higher levels of vitamins (such as A and C), minerals (like calcium, magnesium, and iron), while being low in fiber. At this stage the plant is investing heavily in photosynthesis.

As the leaves mature, their fiber content increases — with more cellulose and lignin — and the taste becomes more bitter. This is a natural part of the plant’s development: as it prepares to flower, it produces more defensive or structural compounds, such as tannins or bitter principles, which can still be useful medicinally but may be less desirable in certain preparations. 

Plants to harvest when they are young: blackcurrant leaf, stinging nettle, or raspberry leaf.

Flowers 

Flowers are rich in aromatic compounds, including essential oils. These are highly volatile and sensitive to both light and heat. For that reason, the optimal moment to harvest flowers is during their first bloom, in the early morning, once the dew has dried but before the day warms up. At this point, the plant has just opened its flowers and is at the peak of its reproductive energy — the chemistry is vibrant, the petals are full, and the scent is concentrated in the heart of the flower.

As the day progresses, sunlight and heat cause many of the aromatic compounds to evaporate. This is especially true for plants like roses or elderflowers. Some herbalists sometimes harvest roses just before they open, when the flower heads are formed but still closed. At this stage, the essential oils are enclosed within the petals and more concentrated, providing a stronger and more stable aromatic profile.

Roots

In early spring, just as the soil begins to unfreeze, and in autumn, once the aerial parts begin to die back, the plant redirects its nutrients and sugars toward the roots in preparation for regrowth or dormancy. This is when concentrations of inulin, starch, and other carbohydrates are at their highest.

Harvesting during these windows gives you roots that are sweeter, more nourishing, and less bitter. In contrast, roots harvested during the growing season may be depleted or overly fibrous, as the plant is directing energy into leaves, flowers, and fruits.

In Sweden, root harvesting typically takes place in March or April, when the first warm days arrive and the soil has begun to soften, or again in October, when the growing season ends. Plants like dandelion, burdock, or comfrey are excellent examples — their roots are most potent and flavorful during these transitional times.

Understanding these natural cycles allows us to work with the plant, not against it. Harvesting in rhythm with plant chemistry is not only more effective but also more respectful.