Horticulture Information Leaflet 509New 7/2000

Success with Container Productionof Twelve Herb Species

James L. Gibson1, Brian E. Whipker1, and Raymond Cloyd21 NCSU, 2 University of Illinois

Distributed in furtheranceof the Acts of Congress

of May 8 and June 30, 1914.Employment and program

opportunities are offered toall people regardless of

race, color, national origin,sex, age, or handicap.

North Carolina State University,North Carolina A&T State

University, U.S. Departmentof Agriculture, and local

governments cooperating.

College of Agriculture & Life SciencesDepartment of HorticulturalScience

NC STATE UNIVERSITY

Interest in growing herbs for the retail andwholesale market has increased greatlyover the past few years. Growers whohave had success in the production ofbedding plants have found anotherprofitable avenue in herb production. Herbshave cultural requirements similar tobedding plants and it should be easy forgreenhouse growers to add herbs to theirproduction schedule. The majority of herbsdiscussed in this article can be sown,transplanted, and finished by the grower.This publication will focus on theproduction of the top twelve herbs andprovides general guidelines for seedpropagation. Certain species likepeppermint or oregano can be propagatedvegetatively and would require growingstock plants.

Herb SpeciesGrowing an assortment of herbs for thewholesale or retail market will increasethe diversity of the growers productionlist. Herbs can be classified into threegroups: annual herbs, perennial herbs, andperennial shrub-type herbs (Table 1).Classifying herbs by when they aremarketable in a 4-inch pot is an idealmanner in which to strategize their spacerequirements, fertility requirements, andmarketing or shipping times. Table 1

contains summary information onproduction time, germination, growingtemperatures, and fertility.

The two herb species which are the mostdifficult to produce are lavender androsemary. Lavender seed requiresextensive care during germination.Because the length of time required forgermination is greater than other herbcrops, lavender may be frustrating toestablish in plug trays. Purchasing plugsmay be the best option for growers. The

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2same can be said for rosemary, as seed propagationof rosemary is not suggested because of thepossibility of infection by seed borne pathogens.Many herb growers grow rosemary stock plantsand achieve good success with rooted cuttings.Besides lavender and rosemary, all other herbspecies discussed in this article have similarcultural requirements.

Seeding and ContainersGermination takes from 4 to 14 days at 70-75F(Table 1). Seeds should be sown in a plug cellsize, which will enable the plant to betransplantable within two to three weeks aftersowing. The plugs should not become root boundin the plug tray before transplanting, as restrictionof the roots may result in stunting and stalling ofthe crop. Recommended tray sizes, for theattainment of a well-defined root ball, range froma 72 to a 512-cell tray. The larger cell will requireadditional production time to reach the transplantstage, but a larger herb plug is easier to establishin the final container. Cover the trays at nightwith plastic sheeting to increase the germinationrate, while preventing mice and other pests fromdisrupting the germination process. Most herbseeds are small and are multiple sown, thereforecare should be taken when extracting seedlingsfrom the plug tray to avoid root damage.Disturbing the root system will delay the cropsestablishment in the final flat.

The most common flat used for finishing the cropis an 1801, but some growers also use flats whichcontain 12 to 24 cells. Deep celled pots aresuggested for herb crops because of their abilityto support a larger root mass and their high waterholding capacity.

Root Substrate (Medium)Herbs are fast growing herbaceous plants,especially when grown in a good quality soillesssubstrate. An ideal mix for herbs should allow forrapid root development, while maintaining goodwater holding capacity. Mixes that stay too moist

may cause shoot growth to become weak andchlorotic due to the lack of oxygen in the substrate.The chances for root rots to occur are greater insubstrates that are saturated repeatedly.

IrrigationCareful irrigation is important in the establishmentof herb seedlings. Using a misting nozzle untilthe first true leaves appear is recommended.Growers need to be extremely careful incontrolling the amount of water pressure used toavoid washing out the seedlings. The operationsbest waterer should do the initial irrigation ofherbs in the finishing flats. Preventing plugsfrom being covered by substrate during the earlystages of plug establishment is crucial for theoverall uniformity and health of the crop. Thedifference in the plug size makes the task morechallenging when the root ball is small and shootgrowth is leggy. Sometimes making a series ofquick and uniform applications of water is bestfor the initial irrigation. Once the root systemshave fully developed in the finishing flat growersneed to pay closer attention to the chances ofsubstrate drying and subsequent wilting of theplants. Most herbs are very forgiving of occasionalwater stress, but repeated water stress can lead tolower leaf loss and a poor quality crop. Irrigationshould be conducted in the mornings to allow thefoliage to dry during the day to avoid theoccurrence of Botrytis or root rot.

NutritionOnce the cotyledons protrude from thegermination substrate, the first fertilization to theplug tray can be made. For the seedling stage,fertilize at a rate of 50 to 75 ppm of N with aconstant liquid feed. Rotating weekly between a15-0-15 and 20-10-20 is recommended for themajority of herbs at N rates between 150 and 200ppm (constant liquid feed). A clear wateringinstead of a fertilization is recommended for allherbs if the substrateis severely dry. By rotatingthese two soluble fertilizers, growers can providecalcium and low phosphorus amounts with the

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4Dark Weather Feed (15-0-15) and adequatemicronutrients and ammoniacal-nitrogen withthe 20-10-20. High levels of NH4-N (> 40% oftotal N) and/ or urea in a fertilizer mix should beavoided to prevent excessive stem elongation.Herbs will become soft and leggy with excessivefertilizer. To supply Mg, monthly applications ofepsom salts (MgSO4 . 4H20) should be made atthe rate of 1 to 2 lbs. per 100 gallons of water. Theroot substrate pH and electrical conductivity (EC)should be monitored on a weekly basis becauseof the potential of salt accumulation and/ or thedevelopment of high or low pH values. An idealpH range for herbs should be between 5.8 and 6.2and EC levels should be maintained between0.38 to 1.0 mS/cm for the 2:1 extraction method,0.76 to 2.0 mS/cm for the saturated pasteextraction method, or 1.0 to 2.6 mS/cm for thePourThru extraction method. (See HIL #590,Monitoring and Managing pH and EC Using thePourThru Extraction Method for additionalinformation.)

TemperatureProducing herbs in a cold frame-type structure orcool greenhouse provides an ideal environmentfor growing compact plants. Night temperaturesfor most herbs should be held between 55 to 60F, with warmer temperatures of 65 to 70 F beingrequired for basil and rosemary. Avoid daytemperatures above 85 F.

SchedulingScheduling herb crops can be challenging becauseof the variation in finishing times. With the use ofa computer spreadsheet, one can establish a springproduction schedule for herbs. Annual herbs likebasil should be sown a week later than theperennial type herbs, and purchased rosemaryand lavender plugs must be planted one or twoweeks before the sowing of annual herb seeds.The most important thing to follow when growingherbs is to stay on schedule. When crops arebecoming disproportionately large relative to thepot, one should separate the trays by a space of

about an inch to allow for improved airflowwhich will help prevent stretch and outbreaks ofBotrytis. Table 1 contains the timing informationneeded for setting up a schedule for springtimesales.

Major Insect/Mite Pests of HerbsInsecticides and miticides that can be used tomanage herb pests are listed in Table 2. Specificinformation about the most common insects andmites are discussed below.

AphidsAphids are soft-bodied insects with piercing-sucking mouthparts, which they use to removeplant fluids. They can cause leaf distortion, plantstunting and wilting. Aphids are also able totransmit viruses. In addition, aphids produce aclear, sticky liquid called honeydew, which is anexcellent growing medium for black sooty moldfungi. Aphids tend to congregate on vegetativeterminals and on leaf undersides. The two mostcommon aphid species are green peach aphid(Myzus persicae) and melon/cotton aphid (Aphisgossypii). Aphids dont need to mate to reproduce(parthenogenesis). Females can give birth toapproximately 100 to 200 live young. These liveyoung, which are pregnant females, can then givebirth to their own offspring in 7 to 10 days. Mostaphids found in greenhouses are non-winged;winged aphids develop when populations arehigh and/or when plant nutritional qualitydeclines. Aphids attack a wide-variety of herbsincluding watercress, arugula, nasturtium,oregano, dill, basil, mint, and tarragon.

WhitefliesWhiteflies are soft-bodied insects that attackrosemary, marjoram, mint, basil, oregano, sage,thyme, and lavender. The young (immature)stages use their piercing-sucking mouthparts toextract plant fluids. Whiteflies can cause plantstunting and wilting, and leaf distortion. Similarto aphids, whiteflies also produce honeydew.The most common whitefly species are the

5greenhouse whitefly (Trialeurodesvaporariorum) and the silverleaf whitefly(Bemisia argentifolii). Adult females lay eggs onleaf undersides. Eggs hatch into crawlers, whichmove around on plants, before settling down tofeed. Larvae enter a pupae stage, in which adultseventually emerge. The life cycle from egg toadult is temperature dependent, normally taking2 to 3 weeks. Immature stage of whiteflies aregenerally located on leaf undersides.

Spider MitesSpider mites, which are not insects, use theirstylet-like mouthparts to remove the green portionof plants (chlorophyll) resulting in thecharacteristic symptom known as stippling.They generally feed on the underside of leaves.Spider mites thrive under warm, dry conditions.The two-spotted spider mite (Tetranychus urticae)is the common mite pest of herbs. To correctlyidentify two-spotted spider mite look for the twoblack spots on the sides of the body. Female

spider mites dont need to mate to produceoffspring. As a result, populations can build-upvery rapidly. The life cycle from egg to adult canbe completed in 7 to 10 days at 85F. All stages(egg, nymphs, and adult) are normally located onleaf undersides. Although spider mites cannotfly, they can easily spread when herb foliage istouching (leaf-to-leaf contact). Herbs that aresusceptible to spider mites are mint, oregano,tarragon, hyssop, thyme, and lemon balm.

ThripsThrips are small (1/8 inch long) insects thatdamage plants by removing plant fluids withtheir piercing-sucking mouthparts. Thrips feedingcan cause leaf distortion, necrotic-spotting, andplant stunting. In addition, thrips can transmitviruses. Several thrips species may attack herbsin greenhouses; however, western flower thrips(Frankliniella occidentalis) is the most commonspecies. Female thrips lay eggs into plant tissue(leaves). Eggs hatch into wingless larvae that

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6feed on plant foliage. Thrips then undergo apupae stage, which generally occurs in thegrowing substrate. Later, winged adults emergefrom the pupae. The life cycle from egg to adultgenerally takes 2 to 3 weeks; however, at 85Fthe life cycle can be completed in 7 to 10 days.Thrips populations can build-up rapidly duringthe spring and summer months. Adult thrips arehighly attracted to yellow and blue flowers. Thripscan be easily distributed throughout a greenhouseon air currents from open doors or horizontal airflow (HAF) fans. Thrips may attack a variety ofherbs including mint, oregano, and sage.

Fungus GnatsFungus gnats (Bradysia spp.) are insects, whichresemble mosquitoes as adults. Large populationsof adults flying around impair a plantsappearance. Larva located in the growing substratefeed on roots, which can lead to plant stunting,wilting, and even death. Both adults and larvaeare capable of disseminating and transmittingplant diseases. Moist conditions may lead toincreased fungus gnat problems, especially duringpropagation and before herbs develop well-established root systems. Fungus gnats also breedin algae. Females lay eggs into the cracks andcrevices of growing substrate. Eggs hatch intolarvae, which are approximately 1/4 inch longwith a black head capsule. Larvae undergo apupae stage from which adults eventually emerge.The life cycle takes 21 to 28 days, depending ontemperature. Since adults dont fly very well,they are generally found near the growingsubstrate beneath the crop canopy. Many herbsare susceptible to fungus gnats under moistconditions.

CaterpillarsCaterpillars are the young (immature) stage ofmoths and butterflies. Many different caterpillarscan attack herbs; these include cabbage looper,imported cabbageworm, beet armyworm, blackcutworm, and swallowtail. Caterpillars damageherbs by using their chewing mouthparts to

remove foliage. Winged females, which mayenter greenhouses through openings such as doors,vents, or sidewalls, lay eggs on leaves. Eggshatch into caterpillars (larvae) which feed onplant parts. Larvae will eventually produce apupa (cocoon) and then emerge as adults. Adultsdo not feed on herbs. Adults may be captured onyellow sticky cards. Many herbs are susceptibleto caterpillars.

Major Diseases of HerbsThe most common diseases of herbs are listed inTable 3. In general, because few fungicides arelabeled for use on herbs and production times areshort, most growers will rogue infected plants.

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7Crop SpecificsBelow are a few crop specific pointers to considerfor growing herbs.

BasilOf the herb crops sown, basil is usually the firstto transplant. Plant the plugs immediately after awell developed rootball has formed in the plugtray. Stem rot diseases such as Fusarium mayappear in the plug tray when finished plants beginto stretch and crowd. Thin basil if there are morethan 2 seedlings per cell. Planting 3 or 4 seedlingsper pot will cause the finished product to lookuneven and unsightly. Basil will be ready to ship2 to 3 weeks after transplanting. If shipping isdelayed then pinch the plants to 3 to 4 nodes,which will require an additional 2.5 weeks for theplants to recover to saleable size. Growers shouldmonitor thrips, caterpillars, and slugs weekly.

ChivesChive seedlings can be transplanted into 4-inchpots two weeks after sowing if sown at the rate of12 or more seeds per cell. Chives, with 12 to 16seedlings per pot gives the plant adequate size forsales after 4 weeks of growth from the transplantdate. Chives require a slightly lower nutritionallevel of 125 ppm N than other herbs. Leaf tipswill brown if dried down.

CilantroCilantro, coriander, or Chinese parsley are allnames given to the same plant, with use in thekitchen determining which name is used. Cilantrois prized for its leaves in Mexican and Moroccancooking and coriander seeds are used in spicemixtures and pickling solutions. The seeds arelarge and seedlings should be ready to transplantin two weeks. Germination percentages areusually low in the plug tray; growers must becareful in monitoring the substrate temperatureand managing irrigation. Sometimes growerswill direct sow into 4-inch pots. Cilantro shouldbe sold early in the springtime. In the southeasternclimate, cilantro plants do poorly in the summer

heat. Because cilantro is a long day plant, boltingwill occur during the summer months.

LavenderLavender requires 5 to 6 weeks of growing for thefoliage to cover the pot. Fertilize plants once aweek with 150 to 200 ppm N during periods ofactive growth. During the winter months, fertilizeevery other week with 150 ppm N. The substrateshould be kept dry, but the plants should never bewater stressed. If lavender plants become leggy,and airflow is reduced to the foliage, the chancesfor infection by crown rotting fungi may occur.Watering in the morning hours is suggested.

PeppermintPeppermint has a long germination time and ishighly sensitive to saturated soil in the germinationplug tray. Peppermint seedlings initially growslowly and will take 3 weeks to becomeestablished, but will then grow rapidly. Becauseseedlings are slow growing, some growers maychoose to purchase vegetative cuttings. Loweringthe night temperatures to 55F once roots reachthe side of the pot is suggested. Transplantingpeppermint one week before the other perennialtype herbs and fertilizing with 200 ppm N willhelp in equaling out the shipping times with theother herb species. Whiteflies and thrips areattracted to peppermint.

OreganoOregano requires night temperatures around 55to 58F to remain compact. Fertilize oreganowith 125 ppm N. Oregano is ready to ship a fewdays after thyme, while oregano and sweetmarjoram are equal in growing time. If the plugsbecome stretched they can be pinched 1.5 inchesin length which will promote lateral branching.Oregano attracts whiteflies.

ParsleyParsley is very sensitive to excessive water,especially in the plug tray. Keep the substratesemi-moist during the germination process. Seed

8will rot under saturated conditions. Parsley willbe ready to ship 4 weeks after transplanting.Fertilize parsley on a constant liquid feed programat 125 ppm N or once weekly at 200 ppm N.Parsley is very sensitive to high EC. Lowerleaves will brown if dried down. Watch for spidermites on parsley. Weekly sprays of Azatin andBotaniguard are suggested for parsley.

RosemaryRosemary is susceptible to Rhizoctonia and thisfungus will cause unsightly scarring of the stems.Sometimes the presence of woody tissue on thestem is mistaken for the stem rot. The fungus hasa deep brown appearance and the woody tissue isgray and light brown in color. Discard the plantsif the symptoms are present. Rosemary plugsshould be planted immediately upon arrival fromthe plug producer. Using two plugs in the 4-inchpot will increase water uptake. Be careful interms of water management after transplanting.The substrate should remain dry, but the plantsshould never be water stressed. Plants can belightly pinched to 5 or 6 nodes after roots havereached the bottom of the pot. This will create afuller plant, but will add 1 or 2 more weeks to theproduction time.

SageGrowing sage requires that the substrate besomewhat dry between irrigations. Light wateringuntil root development reaches the outer edges ofthe pot is suggested. Fertilize sage at 200 ppm Nonce weekly. Flats are ready to ship in 4 weeks.Sage requires night temperatures around 60F.Avoid cooler temperatures which create favorableenvironmental conditions for stem, root, and leafrotting fungal pathogens.

Sweet MarjoramSweet marjoram requires night temperaturesaround 55 to 58F to remain compact. The feedingschedule for sweet marjoram is 125 ppm N,constant liquid feed. If the plugs becomesstretched, they can be pinched to 1.5 inches in

length, which will promote lateral branching.This will cause the plugs to become morevigorous. Sweet marjoram can become leggy atthe 6th week of growth from the transplant date.

TarragonFrench Tarragon should be purchased as rootedcuttings from a reputable propagator. The plantsare best grown at 55 to 60F. Growers shouldpinch the plants to 1.5 to 2 inches of growth if theplants are leggy. Cuttings should be soft and non-woody for best establishment in the finalcontainer. Tarragon should be fertilized with 150to 200 ppm N.

ThymeThyme plugs may become stretched during thepre-transplant stage if temperatures are above70F. Pinching the plugs to 1.5 to 2 inches ofgrowth before transplanting will result in bushierplants, but only cut them back if they are stretched.Plugs have to be watered in gently, otherwise, theplugs will be covered with substrate. The seedlingsare not strong enough to recover from beingblasted with the initial watering. They do bestwith a constant feeding at 150 ppm N. Thymeprefers a drier substrate.

For further reading:Laskey, M., 1991. Herbs, p. 577-581. In Vic Ball. Ball Red

Book. 15th Edition. Geo J. Ball Publishing, WestChicago, Illinois.

Long, J., 1998. Herbs, p. 253-271. In Vic Ball. Ball RedBook. 16th Edition. Ball Publishing, Batavia, Illinois.

Nau, J. 1993. The encyclopedia of seed germination. BallPublishing, Batavia, Illinois.