Brittlestem Hempnettle prefers consistently moist soil but can tolerate short periods of dryness once established. Water deeply when the top 2-3 cm of soil feels dry. Avoid waterlogging, as this can lead to root rot.

Reduce watering frequency during cooler months or if the plant is dormant.

Pruning is typically not essential for Galeopsis tetrahit, as it is an annual.

However, to prevent self-seeding or to tidy up the plant, you can deadhead spent flowers or cut back the plant in late summer or early autumn before it goes to seed.

This will also encourage a bushier habit if done earlier in the season.

Brittlestem Hempnettle is easily propagated by seeds. Sow seeds directly outdoors in early spring, after the last frost, or in late autumn for germination the following spring.

Seeds require light for germination, so sow them on the soil surface. It can also self-seed readily in suitable conditions.

As an annual, Galeopsis tetrahit does not require repotting. If grown in containers and desired to overwinter or encourage larger growth, it can be moved to a larger pot in spring before active growth begins.

However, it is typically treated as a seasonal plant and allowed to complete its life cycle.