The timing depends on context. UMass reports constant or weekly liquid feeding in a commercial rosemary container crop, while Iowa allows periodic dilute feeding from early spring through summer. UMD withholds fertilizer for its described stressed indoor plant.
How to fertilize Rosmarinus officinalis
Feed established rosemary during active spring and summer growth, but do not add fertilizer to a stressed indoor plant. The right schedule depends on the setting.
Plant coveredRosmarinus officinalisRosemary · indoor and outdoor
Check for active growth
When to fertilize
Feeding is most defensible during active spring and summer growth. Do not continue a routine schedule through a low-light winter or while a newly moved indoor plant is stressed. The sources give no universal stop or restart date.
Follow the product label
Fertilizer type and dose
A dilute water-soluble or controlled-release fertilizer is suitable for an established container plant. UMass’s 20-10-20 rate belongs to commercial production, not a household dose.
Inspect a stressed plant before feeding
When not to fertilize
Before feeding a browning or declining indoor rosemary, inspect waterlogging, roots, light, and airflow. Browning or leaf loss is nonspecific and does not justify an extra feed.
Sources
- University of Massachusetts Amherst ExtensionFertilization; container production; liquid and controlled-release regimes
- University of Maryland Extension Ask ExtensionExpert response; indoor rosemary care
- Iowa State University Extension and OutreachBest herbs for indoors; growing conditions; fertilizer