Learn About Rosemary

Posted in: Rosemary
Learn About Rosemary

How To Sow    How To Grow    Tips    Common Pests    FAQ

How to Sow

Rosemary may be grown from seed sown early indoors and transplanted outside after frost, or planted as a potted plant.

Sowing Seed Indoors:

  • Sow rosemary seeds indoors 10 weeks before outdoor planting date in spring using a seed starting kit
  • Sow seeds ¼  inch deep in seed starting formula
  • Keep the soil moist at 70 degrees F
  • Seedlings will emerge in 14-21 days
  • As soon as the seedlings emerge, provide plenty of light on a sunny windowsill, or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
  • Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
  • If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 2 pairs of true leaves before transplanting to the garden so they have enough room to develop strong roots
  • Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.

Planting in the Garden:

  • Select a location in full sun where water drains quickly after a rainfall.
  • Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
  • Dig a hole for each plant large enough to amply accommodate the root ball. 
  • Carefully remove the plant from its pot and gently loosen the root ball with your hands to encourage good root development. 
  • Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand leaving a slight depression around the plant to hold water. 
  • Use the plant tag as a location marker. 
  • Water thoroughly, so that a puddle forms in the saucer you have created. This settles the plants in, drives out air pockets and results in good root-to-soil contact.
  • Rosemary may also be grown in containers. Make sure the potting mix is light and well drained. Use a mix for succulent plants, or add perlite to improve drainage. 
  • Do not allow plants to dry out, but never let the soil stay wet. A clay pot is recommended as it drains well.

How to Grow

  • Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. 
  • Mulches also help retain soil moisture and maintain even soil temperatures. For herbs, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time.  Always keep mulches off a plant's stems to prevent possible rot.
  • Keep plants well-watered during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. It's best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated. Rosemary is particularly susceptible to root rot, avoid overwatering, and make sure the soil drains well. Rosemary does benefit from misting in dry conditions.
  • Rosemary requires little care, but can benefit from occasional pruning. Pinch the stems to encourage bushiness or remove the branches to attain a desired shape.
  • Silver foliaged herbs prefer poor, well-drained soils and little fertilization.
  • Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
  • Rosemary is marginally hardy in zone 7 and many gardeners bring their plants inside during the winter.


Growing Tips

  • Clip leaves or stem tips as needed. Rosemary may be used dry or fresh.
  • If you are using rosemary fresh, pick it early in the morning for highest oil content. 
  • For drying or freezing, harvest leaves that have their maximum oil content, just before flowering.
  • Harvest leaves, tips and flowers. Chop or crumble leaves before using.
  • To dry, cut whole stems on a dry morning. Tie stems loosely together in small bunches and hang in a dry, airy location out of the sun. Rosemary may also be dried on a cheesecloth or a window screen in a dry, shady location. Do not use heat to dry rosemary as the fragrant oils can be volatile. When thoroughly dry, store in a tightly sealed glass jar in a dry, dark location.
  • Rosemary may also be frozen dry or in an ice cube tray in water or olive oil.


Common Disease Problems

Botrytis Blight: This causes the older leaves and the center of the plant to rot. It can start with a yellowish brown irregular spots on the leaves or water soaked spots on the stems. The fungus turns a fuzzy gray and emits a cloud of spores when touched. Burpee Recommends: Remove infected plants and plant debris to avoid the spread of the disease and make sure plants have good air circulation. Keep organic mulches away from the plants as spores can live in the organic matter. Use pea gravel as mulches they will help decrease humidity around the plants.

Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.

Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.

Powdery Mildew: This is a fungus disease that causes a white powdery look on the foliage and is often a problem when growing rosemary indoors. This disease weakens plants as it inhibits their ability to make carbohydrates for themselves using sunlight. Burpee Recommends: You can remove infected plant areas, increase air circulation, and try to reduce the humidity in the room. Check with your Cooperative Extension Service for fungicide recommendations.

Root and Crown Rot: A number of diseases can cause root and stem rots in rosemary. Symptoms include yellowing of the leaves, drying of the leaves and leaf tips, and whole branches may become brown and die. Burpee Recommends: Make sure the soil is very well drained and that the plant does not sit in water. Replace the soil with fresh potting mix for potted plants, after thoroughly cleaning the pot with a 10% bleach solution. Check with your Cooperative Extension Service for fungicide recommendations.

Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Leaves turn yellow or brown and may drop off: When the lower leaves turn yellow and the growth slows down this can indicate that the plant needs to be fertilized, or that it is rootbound. Burpee Recommends: If the roots are circling around in the pot (rootbound), clip them and repot the plant. For a nutrient deficiency, use Garden-tone as directed on the packaging.

Mealybugs: Flat wingless insects with a white waxy shell that form cottony looking masses on stems, branches and leaves. They suck the juices from leaves and stems and cause weak growth. They also attract ants with the honeydew they excrete, and the honeydew can grow a black sooty mold on it as well. Burpee Recommends: Wash infected plant parts under the faucet and try to rub the bugs off. They may also be controlled by predator insects such as lacewings, ladybugs and parasitic wasps. Check with your Cooperative Extension Service for pesticide recommendations.

Scale: Insects similar to mealybugs, they feature a waxy outer shell and suck the juices from plant stems and leaves. They weaken the plants and make them more susceptible to other pests and diseases and environmental stress. Burpee Recommends: If they are in the crawler stage (moving insects) they may be controlled with a cotton swab dipped in rubbing alcohol, or you may be able to scraping them off with your fingernail. Young plant parts that are infested may be removed. Check with your Cooperative Extension Service for pesticide recommendations such as horticultural oils.

Spider mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recomends: They may be able to be controlled with a forceful spray every other day. Check with your Cooperative Extension Service for miticide recommendations.


Every year I bring a rosemary plant inside in the fall and every year it dies in a few weeks. What am I doing wrong?  Rosemary often has a tough time adapting to indoor growing conditions after being outside. It is often much drier indoors than people realize when they start heating their homes in fall, and the plants also require full sun. Rosemary can benefit from a light misting when grown in doors, and be sure that the pot has excellent drainage. Also, do not allow the plant to dry out, but also do not allow it to sit in water. Place the pot on a tray of moistened pebbles.

I harvested rosemary leaves and tried cooking with them but they were all woody. What did I do wrong?  Always chop up your rosemary leaves before using them as flavoring or they will taste woody.

Are rosemary flowers edible? Yes they are! Remove the flower and you can scatter the petals on salads or appetizers.

When should I add rosemary to my cooking? Rosemary can be added early in the cooking process, at least twenty minutes before the food is ready.

How can I turn my rosemary into a topiary plant? Prune the side shoots to encourage vertical growth. Stake the plant and hold it to the stake with soft ties. Let it grow in full sun with plenty of water and when the plant is about 2 feet tall, snip the tops to encourage side shoots. Strip the bottom two thirds of the stem of the branches and leave the top third for shaping. Continue to pinch off the growing tips to maintain a full dense top.

May 10, 2021
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