This is a brief guide to growing lettuce in Hawaii

Arakaki, Alton

Hamasaki, Randall T.

Sakuoka, R.

Shimabuku, Robin

ScholarSpace at University of Hawai'i at Manoa

Cooperative Extension Service Home Garden VegetableApril 2000(slightly revised, May 2000)HGV-2Lettuce grows best during cool weather. Head typesare particularly sensitive to warm weather and rarelygrow well when the temperature gets higher than 75°F.Some types of lettuce grow satisfactorily at lower,warmer elevations in Hawaii, but even for those variet-ies, growth is generally better during cooler seasons.When the temperature is too high for the variety, lettuceplants will have symptoms including leaf tip-burn, earlybolting (flowering), and bitterness, and head types willalso have loose heads.VarietiesThe most common type of lettuce grown in Hawaii’slow-elevation areas is ‘Green Mignonette’, locally called“Manoa lettuce.” A selection of ‘Green Mignonette’made by CTAHR horticulturist Richard Hartmann wasnamed ‘UH Manoa’ and is available through the seedprogram of the CTAHR Agricultural Diagnostic ServiceCenter.Manoa lettuce is classified as a semi-head variety,but the size and firmness of the head varies consider-ably with the temperature under which it is grown. ‘UHManoa’ has medium-green to dark green “buttery”leaves. Its heads weigh up to 1 pound but are usuallysmaller.  It is heat-tolerant, slow to bolt, and resistant totip-burn, and it can be grown year-round in Hawaii, evenat low elevations, although it will form larger heads, takelonger to bolt, and have less tip-burn during coolerweather or at higher elevations. It should be protectedfrom heavy rains, which will bruise the soft leaves.CTAHR horticulturists consider seedlots of ‘UH Manoa’to be more uniform than ‘Green Mignonette’.The variety ‘Anuenue’, also developed by CTAHRand available from the seed program, is also sometimesgrown at at low elevations. It has a smoother leaf than‘UH Manoa’ and will form a larger head when condi-tions are suitable.Lettuce for the Home GardenTrue head lettuces can be grown with reliable suc-cess only at higher elevations, such as in Kula on Mauior Volcano and Kamuela on the island of Hawaii, wherethe variety grown is usually one of the ‘Great Lakes’strains. Some success has been obtained growing headlettuces at low elevations on Molokai between Septem-ber and March; cultivars such as ‘Mesa 659’, ‘Salinas’,and ‘Classic’ have headed well.In addition to the ‘Green Mignonette’ types, manyother varieties of leaf lettuce are available that garden-ers could test for their particular locations. Three thatwere slow to develop bitterness in trials at low eleva-tions were ‘Buttercrunch’, ‘Bibb’, and ‘Parris Island Cos’(a romaine type). ‘Summertime’ is a crisp head lettucethat has grown well at the CTAHR Urban Garden Cen-ter on Oahu and may be suitable for other low-elevationareas. Many lettuce varieties not suitable for commer-cial purposes may be useful in home gardens if they areharvested when young or if the weather is slightly coolerthan normal.Soil management and fertilizersLettuce does best in well drained soil with high organicmatter content and soil pH from slightly acid to neutral(pH 6–7). On more acidic soils, lettuce will show a goodresponse to applications of lime and compost mixed withthe soil to a depth of 6–8 inches. A general garden fertil-izer (such as 14-14-14) applied at a rate of 750–1000 lb/acre (about 13⁄4–21⁄4 lb per 100 ft2) should be sufficienton most soils for a crop of lettuce. Apply half the fertil-izer at sowing and the other half 3–4 weeks later.PlantingLettuce is generally seeded directly into the garden soil,but it is often transplanted. For direct sowing of leaf orsemi-head types, plant the seeds 1⁄4– 1⁄2 inch deep in rows8–10 inches apart; for head types, make the rows 12–15Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June30, 1914, in cooperation with the U.S. Department of Agriculture. H. Michael Harrington, Interim Director/Dean, Cooperative Extension Service/CTAHR, Universityof Hawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii withoutregard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status.CTAHR publications can be found on the Web site <http://www2.ctahr.hawaii.edu> or ordered by calling 808-956-7046 or sending e-mail to ctahrpub@hawaii.edu.HGV-2 Lettuce for the Home Garden CTAHR — Feb. 20002inches apart. As the plants grow, they may be harvestedfor use of the leaves until they have been thinned to 8–10 inches apart in the row. Some lettuces are suited togrowing in soil in containers and in hydroponic systems.IrrigationLettuce is very sensitive to inadequate moisture supply,and the soil should never be allowed to dry out. Hightemperature and low moisture supply cause tip-burn(drying and browning of the tips of the leaves). Irrigatein the morning before the heat of the day to avoid dis-ease establishment and excessive evaporation of water.Insect and mollusc pestsSlugs and snails can damage lettuce in home gardens.These mollusc pests can be controlled through sanita-tion, hand-picking, and baits labelled for use in lettuce.Insects such such as aphids, cutworms, fleahoppers,garden loopers (caterpillars), leafhoppers, thrips, andleafminers are occasional pests but rarely require insec-ticidal treatment in the home garden. Insecticidal soapscan be used to control soft-bodied insects such as aphids,fleahoppers, and immature thrips, should the need arise.(Caution: pesticide use is governed by state and federalregulations. Read the pesticide label to ensure that theintended use is included on it, and follow all label direc-tions.)Plant disease problemsThe most common diseases of lettuce are tip-burn, drop,bottom rot, downy mildew, and spotted wilt virus. Tip-burn is a physiological disorder that can be controlledby using resistant varieties and avoiding cultural prac-tices that cause rapid and excessive growth, such as over-application of fertilizers. Increasing the calcium supplyin strongly acidic soils by liming, slowing growth bylighter fertilizer applications, and keeping soil moistureat an ample and uniform level help reduce tip-burn.Drop and bottom rot are caused by soil fungi. Thesymptoms are slimy rotting of the lower leaves, thenthe stem, and then the entire plant. Control is difficult,but it helps to keep the foliage dry and to control soilfertility so that growth is not overly succulent. Irrigat-ing in the morning or using furrow or drip irrigation ispreferable to overhead irrigation if fungus is a problem.Soil fertility levels can be controlled by moderating pre-plant applications of manures or composts and by ap-plying fertilizers cautiously so as not to overapply.Cool and moist weather conditions favor the devel-opment of downy mildew. The fungus attacks the olderleaves first and causes light green or yellow spots. Awhite powdery growth may be visible on the undersideof the leaf. Good air circulation and keeping the foliagedry will help to reduce the disease.The symptoms of spotted wilt virus are many tinyspots on the younger leaves and stunted plants that failto develop and then rot. The virus is transmitted by thrips.Control measures are to prevent build-up of thrips andremove infected plants.Lettuce is also very susceptible to damage by root-knot nematodes. Symptoms appear as poor growth, stunt-ing, wilting during the heat of the day, and bumpy, knot-like growths in the roots. For more information on nema-todes, see CTAHR publication PD-15, Plant-parasiticnematodes and their management.HarvestingLettuce can be continuously harvested as soon as it islarge enough by picking individual leaves or by thin-ning whole plants. “Manoa” types and ‘Anuenue’ ma-ture in 50–60 days; head lettuces and romaine take about65–85 days. All types will mature faster when theweather is warm and slower when it is cool. Harvest theentire plant before bolting starts or bitterness develops.Seed availabilityManoa lettuce seed is available from garden stores andsometimes from U.S. mainland seed companies underthe name ‘Green Mignonette’. Seeds of ‘UH Manoa’and ‘Anuenue’ are sold by the CTAHR Agricultural Di-agnostic Service Center and are also sometimes avail-able at local garden stores. Seeds of many head and leafvarieties can be ordered from catalogs.Additional informationCommercial growers may wish to purchase CTAHRpublication RES-164, Lettuce production guidelines forHawaii, a 20-page guide published in 1996 that includescolor photographs of lettuce diseases.Revised, with assistance from Richard Sakuoka, Randall T.Hamasaki, Robin Shimabuku, and Alton Arakaki, fromCTAHR’s Home Garden Vegetable Series No. 2, 1978, by Ri-chard Hartmann, Yukio Nakagawa, and Richard Sakuoka.

Lettuce for the Home Garden

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Lettuce for the Home Garden

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