How to Grow Rosemary Seeds
Grow Guide #2314
Binomial name: Salvia rosmarinus
Life Cycle: Perennial
This 'How to Grow' guide details everything a home gardener needs to know to plant, grow and care for Rosemary (Salvia rosmarinus).
When to Sow Rosemary Seeds
Rosemary can be grown year-round in most climates. Avoid planting in extremely hot or cold weather which can affect germination and growth. Use the table below to identify the best time of year to sow rosemary in your climate.
Rosemary plants are perennial, meaning they live for several years. Choose a permanent position where plants can grow undisturbed by regular digging or other disturbance.
Rosemary plants are best grown in full sun. Choose a location that will receive at least 6 hours of full sun each day.
Rosemary plants need a very well drained soil. In most cases there is no need to enrich soil with manure or other fertilisers. Prepare soil by weeding it thoroughly and digging it over to loosen it. Keep the area free of weeds until planting. Learn more about preparing soil for planting here.
Rosemary plants can be grown in containers. If possible choose a variety that’s recommended for container growing. Use a good quality potting mix and make sure your container is large enough for mature plants; a minimum of 20 litres is recommended for rosemary. During the growing season, keep in mind that container grown plants may need additional fertiliser to encourage healthy growth.
How to Sow Rosemary Seeds
Rosemary seeds do not require any treatment (eg soaking, stratification) before sowing.
Rosemary seeds grow best when they are raised in trays or other containers and transplanted to the garden once established.
- Fill trays, punnets or jiffy pots with a good quality seed-raising mix, or use soil starter pellets.
- Sow seeds 3mm deep.
- Keep soil moist but never wet or dry.
- Seeds should germinate in around 15-25 days at a soil temperature of 21-17°C.
- Transplant seedlings to the garden once they have their first true leaves and are large enough to handle (usually 5-10cm tall).
- Plant out, spacing plants 150cm apart.
Tip: Seeds of this variety can be slow to germinate. Take note of the expected germination time, be patient and follow the recommended depth and temperature guidelines closely for the best chance of success.
How to Grow Rosemary
Rosemary plants are drought tolerant once established and grow best in soil that is dry and very well drained. Let the soil dry out between watering, and only water when the soil is dry about 10cm below the surface (test this by scratching away a little soil with your finger), even in summer. Water deeply in the early morning or late afternoon. Avoid watering the leaves of plants to avoid fungal diseases. Learn more about watering here.
If soil was well prepared no extra fertiliser should be necessary. In poor soil or to give your plants an extra boost, application of a balanced fertiliser or one formulated for fruit and vegetables can be beneficial:
- Apply slow release fertiliser at the recommended rate when transplanting or when seedlings are 5-10cm tall.
- Apply liquid fertiliser at the recommended rate and frequency while plants are fruiting or flowering.
When plants have finished flowering prune them back to neaten them and encourage strong new growth. Using sharp secateurs or snips, cut individual stems just above a set of lower leaves.
How to Harvest Rosemary
Rosemary should be ready to harvest in approximately 100-150 days.
Rosemary is ready to harvest when the stems have grown long enough to pick, and can be harvested as needed. Harvest by pinching off the outer stems and leaves, leaving some on the plant for future growth. Rosemary stems can be stored short term in a perforated plastic bag in the fridge. For longer term storage rosemary can be dried or preserved in oil.
Common Problems when Growing Rosemary
Like all plants, rosemary is susceptible to some pests, diseases and other problems. Below is a list of the most common problems gardeners encounter when growing rosemary plants:
- Aphids are small (2-4mm long) sap-sucking insects that congregate on the new shoots or the undersides of leaves. They can cause leaves to wilt or become discoloured, and also excrete honeydew which can attract ants and other insect pests. To manage aphids, remove them by spraying with a garden hose, apply a soap or alcohol spray, or encourage predatory insects to your garden. Read more about aphids here.
- Damping off is caused by a fungal growth that transfers from the soil to seeds or tender seedlings. Seeds may appear not to germinate, or young plants start to rot when they emerge from the soil and become soft and mushy at the base before dying. Use new potting mix if raising seedlings, do not water foliage and avoid waterlogged soil. Read more about damping off here.
- Powdery mildew is caused by fungal spores reproducing on the leaves of plants. First showing as white spots on leaves, affected areas can spread quickly to cover the entire leaf surface. While rarely fatal, powdery mildew can reduce yields. Water plants at soil level (not on leaves) to prevent spreading spores, allow good air flow between plants, remove affected leaves and if necessary spray with an appropriate fungicide or homemade spray. Read more here about powdery mildew here.
- Spider mites (Tetranychus urticae), also known as two spotted mites, are sap-sucking arachnids that cause dry, wilted or discoloured leaves. The undersides of leaves may feel dry and a little like fine sandpaper. Prune plants to allow good air flow or spray with eco-oil or wettable sulphur. Learn more about managing spider mites here.