Harvesting at the right moment

Harvest timing is the most reproducible finding in the whole cultivation literature: the content and composition of a plant's active compounds change with developmental stage, with season, and even with time of day. A supplier harvesting for biomass cuts late, at maximum bulk. You can cut at the stage that maximises what you actually want.

Timing is a stage, not a date. The useful instruction is not "harvest in July" but "harvest at full flower", "harvest after dieback", "harvest when the lower leaves brown". Those stages arrive on different dates in different years, and a rule tied to the calendar will be wrong in half of them.

The general rules, by plant part.

| Part | Harvest when | Why | |---|---|---| | Leaf | Before flowering | Flowering moves resources out of the leaf and aroma declines | | Flower | Fully open, at peak | Composition shifts across the flowering period | | Root | After top growth dies back | Root energy peaks at dormancy | | Seed | When mature and dry | Immature seed stores badly | | Bark | Spring or autumn sap flow | Bark separates cleanly then | | Whole aerial | At full flower | The traditional compromise for flowering-top herbs |

Time of day is real and it is not folklore. Volatile-oil content varies diurnally in aromatic plants. The practical convention is mid-morning, after the dew has dried but before the heat of the day, because damp material moulds and hot material has already begun to lose volatiles. The literature supports diurnal variation existing; the exact peak differs by species, so the convention is a sensible default rather than a law.

Cut, do not pull. Clean cuts with a sharp tool heal and let the plant regrow. Tearing damages the crown. For repeated leaf harvest this is the difference between a plant that gives four cuts and one that gives one.

Harvest in dry conditions. Wet plant material is the main cause of mouldy drying batches. After rain, wait. After dew, wait.

Take no more than the plant can give. The conventional limits — never more than a third of a perennial's top growth, never all of a stand, leave the strongest plants to seed — exist because over-harvesting kills stands, and because a stand that seeds itself is a stand you do not have to replant.

The specific windows, gathered.

• Mints, lemon balm, sage, thyme, oregano: leaf, before flowering, repeated
• Chamomile, calendula, lavender, rose: flowers fully open, repeatedly, daily at peak
• St John's wort, yarrow, mullein: flowering tops at full flower
• Echinacea, valerian, dandelion, comfrey: roots after dieback
• Milk thistle, fennel, dill: seed when mature and dry
• Elderberry: berries when fully ripe and dark, whole umbels
• Hawthorn: flowers in spring, berries in autumn
• Willow, hawthorn bark: spring or autumn, from pruned branches rather than the trunk