Getting Oregano Right

By Conrad Richter

Oregano is one of the most popular herbs in the garden centre trade. In demand for its hot, spicy flavour, the “pizza herb” is a quick crop from seed, and an easy sale – provided you start with the right varieties.

The trouble is that the seed industry, out of ignorance, has for years sold the wrong seeds as oregano. Usually seeds of a plant that is more correctly called “common marjoram” – a hardy perennial with slightly hairy leaves and pinkish flowers – are offered as “oregano”. Common marjoram (not to be confused with sweet marjoram, Origanum majorana, an entirely different herb with its own distinct flavour and uses) has the right botanical name – Origanum vulgare – but none of the flavour and aroma typical of the imported dried product so loved in Greek and Italian cooking. Selling the common marjoram variety as oregano is a major disappointment for customers because the taste is totally insipid, hardly better than eating grass, and the leaves have little or no aroma. Sometimes, even, a completely different herb, summer savory (Satureja hortenis), masquerades as oregano in garden centres. When discerning customers find such mislabelled or inferior material sold as oregano, they go somewhere else.

 

Greek oregano
Although there are many varieties of aromatic oreganos, including types from Syria, Turkey, Mexico, and elsewhere, by far the variety most readily adapted for commercial pot and pack sales is the greek oregano (Origanum vulgare hirtum). The other regional and specialty varieties are rarely found in the horticultural trade because seed supplies are lacking, requiring more costly labour intensive propagation by cuttings. Of the truly aromatic oreganos, the greek variety is the only one for which seeds are available in commercial quantities.

The leaves of the greek oregano are somewhat hairy, and the flowers are white instead of pink. It is a perennial, surprisingly hardy to zone 4 which is much cooler than its native Greece. Because it yields a harvest of fresh or dried tops the first season, greek oregano can also be sold as in packs with spring annuals.

The spring season is the main market opportunity for oregano. Typically seeds would be started, grown and marketed in much the same way as annual bedding plants.

Oregano is also grown for the fresh-cut herbs market in greenhouses, usually equipped with hydroponic systems. This segment of the industry is still very small, but there is increasing interest. I am only going to discuss the production of pots and packs for spring sales in this article.

Propagation

Greek oregano can be sown in a variety of plug trays from a 128 tray to a 288 tray, or broadcast into seed flats. Larger growers are sowing direct in packs or in 3 or 3-1/2 inch pots to minimize labour cost. Plugs transplanted to a 4 inch pot will yield a superior product of consistent size, but the added cost of transplanting is an important consideration.

Sowing. The sowing medium should be a lightly fertilized peat with 20% perlite added to improve drainage. The pH should be between 5 to 7. Watering trays before seeding ensures even moisture profile down the trays and facilitates easy watering after owing without washing out seeds or seed cover. One gram of seeds contains 4500 seeds. Typical germination rates are between 60% and 75%. Each plug should get between 5 and 10 seeds, and direct seeded packs should get 10 to 15 seeds per cell, and direct seeded pots should get 15 to 20 seeds sown near the pot centres. After sowing, cover lightly with fine vermiculite.

Germination. Optimal temperature for germination is 22-25 degrees Celsius. After the initial watering under mist, trays should be kept evenly moist but not saturated with water, and humidity should be 85%. Germination occurs in 7-14 days. Light levels can be at ambient greenhouse levels throughout the germination and growing on stages. If a germination chamber is used, light is not required to promote germination, but enough light is needed to prevent seedlings from stretching until the trays are moved to the greenhouse.

Seedling establishment. As seedlings become established, reduce the temperature to 18-22 degrees Celsius, and humidity to 70-75%, and ensure ventilation is adequate to prevent damping off. Half strength feedings (50-75 ppm nitrogen) can be applied after seedlings are established. It takes 4-6 weeks for plugs to reach transplanting size.

Growing On

Greek oregano takes 10-12 weeks from seed to plug to finished 4 inch pots. Direct sowing in packs and in 3 or 3-1/2 inch pots takes 8-10 weeks to get marketable product from seed. The precise timing of the crop is not critical because flowering is not required or even desired. The objective is to produce plants with compact masses of well-formed leaves.

Transplanting. Plugs should be transplanted at the 4-6 week stage when seedlings have at least 4 pairs of true leaves. Avoid allowing plugs from getting root bound which would delay growth; however, if crop timing is off even root bound plugs will grow on well to produce a marketable crop.

Potting soil. Like most herbs of Mediterranean origin, greek oregano requires good drainage. Peat-based soils require perlite (20%) to ensure adequate drainage. Some growers are using custom compost-based mixes with sand and perlite for the “organically-grown” market.

Temperature, humidity and lighting. For active growth, the minimum nightime temperature is 8 degrees Celsius and 15 degrees during the daytime. Daytime temperatures over 30 degrees Celsius will slow growth. A regime of 18-22 C daytime and 15-18 C nightime will produce sturdy, compact plants. Humidity should not exceed 75%, and exposure should be full direct sun. Supplementary lighting is not required except in far northern areas where the day length is less than 10 hours.

Watering. Like many Mediterranean herbs, oreganos prefer conditions somewhat on the dry side. Overwatering will stunt growth and cause root rot.

Fertilization. In peat-based potting soils, regular feedings should build from 50 to 100 ppm with a complete fertilizer. Compost-based mixes usually do not require supplemental feeding before sale.

Pests and diseases. Whiteflies, spider mites, aphids and thrips attack oregano. Because herbs are edible plants there are few available controls when outbreaks of pests occur. The first line of defense is close monitoring of pest populations. Thorough examination of the crop weekly with the aid of yellow and blue sticky traps will identify outbreaks at the earliest stages when contact pesticides such as Safer’s insecticidal soap are most effective. Relatively little-known products suitable for application on edible plants have been introduced in the past 5-10 years such as neem-based sprays (e.g. NeemAzad), fungus-based (e.g. Naturalis-O) and others which may be useful on herbs such as oregano although they are usually slower acting than contact sprays and may not provide effective control on a fast crop like oregano. Beneficials such as whitefly parasites and mite predators are not effective on fast crops such as oregano. Thorough spot spraying with contact sprays at the earliest stages of pest infestation has given the best results. Mildew occurs when temperatures are low, air circulation is poor, and water is allowed to remain on leaves at night; but with care mildew is rarely a problem.

With the right variety, oregano can be a profitable crop that is fast and easy. Most experienced growers should be able to produce a nice crop of oregano plants in their first try.


Conrad Richter is Vice-President of Richters Herbs, Goodwood, Ontario, Canada.
 
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