ALOHA, are you growing the superfoods ginger or turmeric or maybe both, or are interested in honing your gardening and horticulture skills, then check out this article and let us help you to nurture your plants and make them as happy and healthy as they can be. Whether you live here in Hawai’i or elsewhere in the world, ginger and turmeric are beneficial and beautiful plants to grow in your home garden, mixed media grow boxes, greenhouse, or on your farm or plant nursery. It not only benefits our human health as it is rich in beta-carotene, calcium, flavonoids, fiber, iron, niacin, potassium, zinc, vitamin C, vitamin B6, and other antioxidants, anticarcinogen, and antiinflammatory phytocompounds, but it is also great as a staple commodity crop because it is sustainable and has a relatively low carbon footprint and water requirements under optimal horticulture care.
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A Little About Ginger and Turmeric
Ginger, or ‘Awapuhi (in Ōlelo Hawai’i or the Hawaiian language), (Zingiber officinale) and turmeric, or ʻŌlena, (Curcuma longa) are native to tropical parts of Asia, but it is able to be grown in most, if not all, tropical and subtropical climates of humid and warm weather with adequate rainfall and loamy soil or indoors. They are both members of the ginger family, Zingiberaceae, and are grown for their rhizomes, which are edible and known for their flavor and nutritional and health benefits.
Rhizomes are a type of root structure, thus the part we are most interested in eating grows underground in the soil or media. Though other parts of rhizome plants, like flowers, are also beneficial, this interest or demand is based on culture, region, or preference. The ginger rhizome is light brown to almost a light gold in color on the outside skin while the flesh is a creamy, light yellow to a mild yellow (even in some ginger, there may appear to be a blue streak found in the interior flesh). Ginger has a sharp, warming flavor and is popular in teas, desserts, and many other dishes. The turmeric rhizome has a light-to-mid brown skin and the interior flesh is bright orange-yellow or a deep-yellow in color, and it is used both in cooking, beverages, supplements, and dyes.
Cultivation
Ginger and turmeric are cultivated in tropical and subtropical areas, including India, China, Nigeria, Indonesia, Bangladesh, Australia, and the United States. In these tropical climates, ginger and turmeric are perennial plants, meaning that they can live up to multiple years under proper care and optimal environmental conditions.
Ginger grows in warm, humid climates and is cultivated from sea level to an altitude of 5,000 feet, while turmeric grows from 1,300 to 3,000 feet. Optimum growing temperatures are 68 ºF to 77 ºF, with low temperatures leading to the plant’s dormancy and inactive growth. In warm areas, plants may require shade during the summer to avoid heat stress and foliar damage from direct sunlight. In Hawai’i and other similar regions, ginger and turmeric can be grown year-round and produce a steady supply of rhizomes. In non-tropical regions, ginger and turmeric will not be viable during periods of lower temperatures below 68 ºF, but these regions can also produce viable plants and rhizomes if propagation and cultivation occur during frost-free periods between mid-to-late April through mid-October.
Ginger and turmeric do well in sites with airy and loose, well-drained soil that has ample and consistent water. They also do well in soils high in organic matter. An ideal planting media would be peat, coconut fiber (or coco coir), or compost-based soil mix and straw mulch covering the rhizomes to maintain moisture.
Cultivar Selection
Selecting high-quality, disease-free rhizome-stock is important for growing ginger and turmeric. Horticulturists in the continental U.S. usually purchase rhizomes from Hawai’i or Asia (China, Indonesia, India, etc.). Rhizome pieces can usually be purchased pre-cut for a nominal fee, or as a whole rhizome (larger, intact rhizomes), or “hands”, that the producer will need to divide into smaller rhizome-sections of “fingers” (1-2 oz) or smaller “seed-sections” (less than 1 oz or 1.5 inches) also called seed-pieces.
Follow recommended rhizome-stock handling and sanitation procedures. Turmeric cultivars, which take longer to mature than ginger, are less widely available; sourcing and seed handling procedures are similar to ginger.
Propagation
To plant ginger and turmeric, the rhizomes must undergo sprout initiation, where the above-ground leafy part of the plant starts growing from the below-ground rhizome.
Ginger and turmeric are planted in stages, with seed-pieces prepared for pre-sprouting before planting. In non-tropical regions, ginger and turmeric should be pre-sprouted indoors or in a greenhouse environment in February or early March. Place the seed-pieces flat on top of planting media or coco coir, maintaining a temperature of 72- 85 ºF for 4- 8 weeks. The seed-pieces should be covered and kept at a depth of 1- 2 inches.
Warmer temperatures, nearer 85 ºF, result in faster germination. More rapid germination tends to occur with bottom heat, and trials in New Hampshire found that sprouting with heat mats resulted in substantially higher yields of baby ginger. Steady moisture and humidity (about 80%) should be maintained while avoiding heavy watering, and this can be done by propagating in a container wit
h a lid, humidity dome, or other coverable structure. Light is not necessary at this stage of propagation until the vegetative plant is visible. Maintain the sprouting ginger and turmeric until the green tops have emerged at least 1- 2 inches above the planting media.
Planting or Transplanting
Once the plants have sprouted, gradually harden them off before transplanting. Take the plants outside to acclimate about 1- 2 hours per day. Gradually increase that time for approximately 2 weeks before transplanting outside. After acclimation, the rhizome-seed with sprout can be directly planted into planting media or soil, leaving space on top of the rhizome for hilling or mounding.
Fertilization
Ginger and turmeric are moderate to heavy feeders, and they will require a good amount of nitrogen (N) and calcium (Ca) for optimal growth and development and larger rhizome production. The downside to this is that they are poor nutrient scavengers, and essential nutrients must be applied near the plant.
Ginger and turmeric prefer a neutral or slightly acidic pH and media temperatures of 40- 55°F. Amend the soil with an organic pH down (lower pH) or dolomite lime (increase pH) as needed and a balanced all-natural plant food, organic compost tea, NKF ferments, or slow-release fertilizer before planting. The best way to capture any nutrient and pH deficiencies in your soil is to take a soil test, and if you’re using planting media, check the guaranteed analysis for available macronutrients (N-P-K, Ca) and micronutrients. If your planting media or soil has any deficiencies, ensure that it is corrected before planting.
If soil or media pH is corrected using lime, then there will be a sufficient amount of calcium available for plant uptake. 
And, if lime is not used, then choose a fertilizer with available calcium and apply it before planting. Nitrogen, necessary for vegetative growth and other developmental stages, should be applied several times during cultivation at a rate up to 150 lbs per acre. The first nitrogen fertilization should occur prior to planting at a rate of 75- 100 lbs per acre, then again 2- 3 more times, or once every 5- 8 months at a rate of 25 lbs per acre. Towards the end of the growing season, potassium ratios are increased to promote optimal rhizome development and glossiness.
Hilling or Mounding
When planting in planting media or soil ensure to leave ample empty space at the top of the initial rhizome layer to allow for hilling or mounding of the plants twice. At about 45 and 90 days after planting, mounding should be done to help increase the rhizome size. However, turmeric does not require mounding. Leaves can show tip burn if the substrate is not kept sufficiently moist, or if the fertilizer levels are either too low or too high.
If ginger and turmeric are grown in rows, rows should be a minimum of 42 inches apart to ensure ample space for mounding. Ginger and turmeric can be planted 5- 6 inches apart in a row. Ensure to plant seed-pieces at a depth of up to 1 foot and that the media covering the rhizome-piece is airy and loose and well-drained. A single drip line should be established before planting, and after the first mounding event, an additional drip-line will be necessary to ensure proper soil moisture retention.
Ginger will need to be mounded 2- 3 times during the active growing season. The first mounding should occur once the base of the stem turns from a white to pink color; this may also be observed slightly beneath the soil layer towards the rhizome, so media may need to be slightly brushed away to confirm maturation. The second mounding should occur about 4-6 weeks after the first mounding; if a third and final mounding is necessary, it should occur 2 weeks after the second. Mounding should be performed with care to not damage underground rhizomes. Hand-weeding is recommended for weed control as this will be the best practice for rhizome care too.
Photoperiod
Ginger and turmeric can handle both long and short-day lighting in optimal environmental conditions. They require long day photoperiods (≥ 12 hours) for continuous growth without entering dormancy, then reduced day length (or daylight hours), or short days (≤ 11 hours), for flowering and rhizome production and swelling. Once the daylight hours have been reduced, similar to fall or rainy seasons, plants will exhibit yellowing leaves and other foliage, signaling the initiation of dormancy. At this stage, irrigation systems or direct watering can be stopped and the plants will begin to wilt. After wilting, the vegetative plants may be cut and removed up to 3 weeks before harvesting, and harvest preparation can begin.
Pest Management
Soil-borne and seed-borne diseases can devastate ginger and turmeric production. The crops are susceptible to bacterial wilt (Rolstonia solanacearum), bacterial soft rot (Erwinia sp.), and Pythium. Fusarium rot (Fusarium spp.) can affect the roots postharvest. Avoid planting ginger alongside or in rotation with solanaceous crops as tomatoes, peppers, and eggplant. Nematodes are also a potential pest of ginger and turmeric, and areas with a history of nematode infestation should be avoided. It is also good to avoid planting cover crops that may host nematodes.
Harvesting
Ginger and turmeric can be harvested at varying maturities during the growing season and the harvest time after planting depends on the end-use of the rhizome. Baby ginger and turmeric lack the tough outer skin of mature rhizomes; baby ginger is easier to cut. Rhizomes harvested 5 months after sprouting or planting (with or without green leaves attached) can be used and sold as fresh vegetables (low fiber, aromas, and flavors). Rhizomes harvested between 5- 7 months after sprouting or planting are suitable for curing and selling in retail and producing preserves and other products. Rhizomes with longer growing periods (> 7 months) are better suited to be dried or extracted for essential oils and other phytocompounds.
Ginger and turmeric rhizomes are best harvested by hand with a digging fork as younger rhizomes are more delicate. The tops (or vegetative plants) are trimmed and separated from the rhizomes and can be collected as green manure (or compost), and the rhizomes should be thoroughly washed to remove media or soil particles.
After washing, rhizomes storage should be at a low temperature and high relative humidity (55ºF and 70%) to prevent drying, and any diseased rhizomes should be discarded. It is best not to expose young rhizomes to sunlight as this will dehydrate, or dry, the rhizomes. Some horticulturists will utilize a 10% bleach rinse solution to treat the recently harvested rhizomes in the prevention of microbial and pest contamination.
