Common name for Rosmarinus officinalis, a hardy evergreen sub-shrub grown chiefly for its aromatic leaves which are used in culinary seasoning and which yield an oil once used in medicine. Small light blue flowers are borne in April or May, in loose clusters that spring from the leaf axils. The foliage is white and woolly on the under side and dark and shiny above. Plants can grow to a height of 6 feet and last for years if given winter protection.
Growing the Herb Rosemary
Rosemary prefers dry, well-drained soil and in the South and Pacific Coast States, where soil is dry and rocky, they are planted as hedges. There is also a low-growing or prostrate variety.
Rosemary grows well with occasional watering, and does much better where the soil is alkaline. All varieties prefer full sun and most can tolerate slightly shady areas.
Rosemary propagates easily by taking six inch long stem cuttings that are stuck in a mixture of sand, loam, and leaf mold, ideally in a controlled environment such as a greenhouse or cold frame.
Outdoors, in containers, and hydroponic cultures.
Rosemary plants usually grow to a height of 3 to 4 feet (90 – 120cm).
Rosemary plants should be spaced between 18 and 24 inches (45 – 60 cm) apart.
Preferred pH Range
Rosemary will grow in a pH range between 6.0 (mildly acidic) and 8.5 (alkaline) with a preferred range between 6.0 and 7.5.
Sow indoors in sunny location or under plant grow lights eight weeks before last frost. Rosemary propagates well via stem cuttings.
Seed Germination Period
Rosemary seeds will germinate in approximately 15 to 25 days. Patience and consistent moisture levels are key.
Number of Seeds per Gram
There are approximately 1,000 rosemary seeds per gram, depending on variety.
Rosemary prefers a light and well-drained soil.
Alternative Growing Media
Soilless potting mixes (Pro-Mix, Sunshine Mix, etc.), perlite, vermiculite, coco peat, rockwool, or Oasis cubes.
Time From Seed to Saleable Plant
Sow in seed flats 22 weeks before sale in 4-inch (10cm) diameter pots. Seeds to finished plugs, 12 weeks; plugs to saleable plants, 10 weeks.
Sun & Lighting Requirements
Rosemary grown outdoors prefers full sun.
Rosemary will grow indoors satisfactorily under standard fluorescent lamps, and exceptionally well under high output T5 fluorescent plant lights, compact fluorescent, or high intensity discharge (metal halide or high pressure sodium) plant growing lights. Keep standard fluorescent lamps between 2 and 4 inches from the tops of the plants, high output and compact fluorescents approximately one foot above the plants, and HID lights between 2 and 4 feet above the plants, depending on wattage.
Have an oscillating fan gently stir seedlings for at least 2 hours per day to stimulate shorter, sturdier, and more natural plant habit.
Perennial. Zones 7a to 10b.
Average water needs. Water on a regular schedule, but do not overwater. Allow soil to go dry between waterings, then soak thoroughly.
Potential Plant Pests and Diseases
Rosemary can be susceptible to whitefly, scale, and mealybug and is susceptible to powdery mildew.
Rosemary is a great companion plant to sage, cabbage, beans, carrots and thyme. It repels or distracts the bean beetle, deters cabbage flies, and repels many bean parasites. Do not plant near basil.
Drought tolerant, suitable for xeriscaping. Rosemary is known to attract bees, butterflies and birds. Fragrant flowers. Suitable for containers.