Oregano

Description

Oregano is the name given to many species of perennial herb belonging to the genus Origanum, including the major species Origanum vulgare which is grown for its leaves which are commonly used as a herb in cooking. Oregano plants can be woody or herbaceous and possess multiple branching stems. The leaves are oval or round and are arranged alternately on the stems. The plants produce small pink, purple or white flowers and small oval, brown fruits and can reach up to 1 m (3.3 ft) in height. Oregano is perennial and can be grown for 3–4 years but is commonly grown as an annual in northern climates. Oregano may also be referred to as European oregano or wild marjoram and originated from the Mediterranean.


Uses

The leaves of the oregano plant are used fresh or dried as a herb in cooking. They may also be dried and used to extract essential oil which is used in soaps or as flavorings in wines and liqueurs.


Propagation


Basic requirements
Oregano is a temperate or subtropical plant and will grow best in ample sunlight but can also be grown in partial shade. The plant grows best in light, well-draining soil with a pH of 4.5–8.7. Oregano will tolerate some cold but will grow best when the annual temperature does not fall below 15°C (59°F).

Propagation
Oregano can be grown from seeds, cuttings or by division or layering. Vegetative propagation is best for conserving desirable characteristics.

Seeds
Oregano seeds can be planted indoors to produce transplants or direct seeded. When direct seeding, seeds should be sown in rows spaced 50–60 cm (19–24 in) apart with seedlings thinned to allow 20 cm (8 in) between plants. Seeds will germinate in 4 days at a temperature of 21°C (70°F).

Cuttings
Root divisions and cuttings are best taken in late Spring when plant growth is at a maximum. Softwood cuttings taken from the new plant growth are quickest to root. Remove portions of stem 7.6–12.7 cm (3–5 in) in length using a sharp knife. Cut the stem at a 45° angle. Plant the cuttings in a light potting medium such as peat moss and vermiculite and keep moist until rooted.

General care and maintenance
Oregano grows very vigorously and requires little care. When the plant has reached approximately 15 cm (6 in) in height, pinching the growing tips will encourage the plant to branch. Oregano may be fertilized on a yearly basis with a balanced fertilizer. Once established, oregano requires little water. Supplemental irrigation may be applied during very dry spells. Divide established plants every few years to promote productivity and prevent the plant from becoming woody.

Harvesting
Organo is best harvested just before flowering. The entire plant can be harvested by clipping the branches to leave only the lowest set of leaves. The leaves can be used fresh or they can be dried for longer storage. The clipped plant will begin to set out new growth within 2 weeks of harvest.


References

Herb Society of America (2005). Oregano & marjoram. An Herb Society of America Fact Sheet. Available at: http://www.herbsociety.org/factsheets.... [Accessed 03 March 15]. Free to access.

Savio, Y. & Robinson, C. (1998). Oregano, winter marjoram, wild marjoram, pot marjoram. In: Speciality and Minor Crops Handbook. Chapter available at: http://www.ctahr.hawaii.edu/sustainag.... [Accessed 03 March 15]. Chapter free to access, entire publication available to purchase from Univ of California Agriculture & Natural Resources.


Common Pests and Diseases

Spider mites (Two-spotted spider mite)
Tetranychus urticae

Symptoms
Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant
Cause
Arachnid
Comments
Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack
Management
In the home garden, spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction

Mint rust
Puccinia menthae

Symptoms
Small, dusty, bright orange, yellow or brown pustules on undersides of leaves; new shoots may be pale and distorted; large areas of leaf tissue die and leaves may drop from plant
Cause
Fungus
Comments
Disease also affects mint and can spread from nearby mint plants
Management
Infected plants and rhizomes should be removed to prevent spread; heat treatment of roots may help to control the disease; roots should be immersed in hot water at 44°C (111°F) for 10 minutes, cooled using cool water and then planted as usual

Cutworms
Agrotis spp.

Symptoms
Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed
Cause
Insect
Comments
Cutworms have a wide host range and attack vegetables including asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato
Management
Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically

Thrips (Western flower thrips)
Frankliniella occidentalis

Symptoms
If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color
Cause
Insect
Comments
Transmit viruses such as Tomato spotted wilt virus; once acquired, the insect retains the ability to transmit the virus for the remainder of its life
Management
Avoid planting next to onions, garlic or cereals where very large numbers of thrips can build up; use reflective mulches early in growing season to deter thrips; apply appropriate insecticide if thrips become problematic

Aphids (Peach aphid)
Myzus persicae

Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants
Cause
Insects
Comments
Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use