Indoor gardening offers some amazing opportunities when it comes to growing exotic, expensive and flavorful herbs and spices. We can create a tropical oasis where spices such as ginger, lemongrass, lime leaf, turmeric, chillies, curry leaf and even vanilla can thrive while delicate saffron is harvested from flowering corms and dried for year-round use. There are many exciting species of spices to experiment with. Some of the lesser-known herbs such as epazote, used in Mexican cuisine, and Japanese perilla, also known as the sushi herb, produce well in hydroponic systems and add that extra special exotic touch to many dishes.
Best Hydroponic Systems for Growing Spices
Hydroponic systems for exotic herbs and spices don't need to be complicated and fall into two main categories. For longer-term plants and those that produce rhizomes such as ginger, galangal, turmeric and kaffir lime, use deep media beds or shallow, free-draining beds for saffron corms. For shorter-lived, smaller plants such as perilla, epazote and many other herbs and spices such as dwarf chillies, use other systems ranging from nutrient film technique and pond or raft system to drip, ebb and flow or aeroponics.
Since most of the exotic spices and herb plants that can be grown hydroponically originate in tropical and subtropical climates, they are generally not fussy about day length, but they do like heat. Most ginger species, vanilla orchids, cardamom, turmeric, curry leaf plant, lemongrass and chillies like year-round warmth with an optimal temperature range of 72 to 86o F. Many of these can be grown outdoors in summer and then brought inside to overwinter in containers.
For those who like Asian-inspired dishes, there are a good range of exotic herb and spice plants that mesh well together–-kaffir lime leaves and fruit, fresh ginger, sliced galangal and lemongrass can all be grown hydroponically in a relatively small space provided they are kept trimmed and compact. For those who like hot, spicy curries, chillies, curry leaf and turmeric can also be grown in containers, although they need a little more space than the average herb garden. And for lovers of delicate dishes, saffron, produced by the crocus bulb, is one of the easiest spices to grow in a small hydroponic garden, with the advantage of also providing the grower with beautiful purple blooms.
The Ginger Family
Traditional ginger rhizome (Zingiber officinale) is the most well-known crop in this category; there is also Myoga or Japanese ginger (Zingiber mioga), of which the young flower buds and leaves are used to flavor dishes. Another member is galangal or Thai ginger, which is similar in appearance to ginger but has a milder flavor. Galangal (Alpinia galangal) is a little more forgiving and seems to grow particularly well in hydroponics, being more cold tolerant in winter.
Ginger is an easy plant to start in hydroponics–-fresh, healthy rhizomes can be purchased from stores or Asian supermarkets and sown into a moist hydroponic medium such as coconut fiber at 77 to 86oF. The knobbly buds on the rhizome will grow into fresh, new shoots with roots developing from the rhizome. If conditions are warm enough, ginger plants will then produce a large number of shoots and an expanding root system of thick fleshy rhizomes, taking anywhere from 12 to 18 months before the first harvest of large rhizomes can occur.
The plants are best mounded up as the rhizomes develop—adding more growing medium around the base of the plant helps increase yields and quality of the harvested product. General purpose nutrient solutions at an EC of 2.2 to 2.6 can be applied, but using a fruiting or bloom formulation at a higher EC seems to assist with intensifying the flavor profile of the rhizomes.
Another member of the Zingiberaceae family is turmeric (Curcuma longa), which, like ginger, grows from a rhizome that can often be purchased fresh in Asian specialty stores. Turmeric can be grown hydroponically in much the same way as ginger and used fresh or dried and ground to create the distinctive yellow, powdered spice.
Saffron (Crocus sativus) has long been sought after as an expensive, delicate spice that adds both color and distinctive flavor to many dishes. Saffron is produced commercially as an outdoor field crop in countries such as Spain, India and Iran, where the climate is suitable and cheap labor is available for the time-consuming harvesting and processing of the flowers. However, saffron is an easy, small-scale crop for hydroponics and these days saffron bulbs are readily obtainable for those who want to grow it.
Saffron is the world's highest-priced spice and is composed of the bright yellow, dried stigma of the saffron flower. The saffron crocus grows from a small, rounded corm (similar to a bulb), which after flowering and vegetative growth, multiplies by the production of many small daughter corms. Each flower produces on average three strands of saffron, weighing in at much less than a gram, hence a huge number of flowers must be grown, picked, processed and dried to make just 100 grams of this spice. For the hobby hydroponic grower or household chef, a small plot of saffron should give sufficient spice to last for many months as only a few strands are used in most dishes.
While it is fairly easy to grow, saffron does need some specific requirements if the objective is to propagate and multiply the plants. There are two ways of running a saffron system. The dormant corms can be purchased, usually towards the end of summer or in early autumn, then planted, flowered, harvested and the corms discarded, all over a six-week period. Or after the short flowering period, the bulbs can be grown on, producing vegetation and new daughter cormlets over a period of many months until they become dormant in mid summer. The first system means the corms are planted at a high density since they won't be grown on and multiplied.
The second system needs more space for the plants to fully develop and many months of caring for the corms after they flower, although the reward is a supply of new corms that can be sold or given away to others and a higher yield of flowers in the next year. Tying up your hydroponic system with vegetative saffron for nine to 10 months may not be attractive to those with limited space, although trays of saffron plants are cold hardy and can be put outside for winter and spring if necessary.
Corms can be stored in a dry place and planted out when the hydroponic system is ready. The spacing should be approximately 4 to 5 in. apart and 1.5 to 2 in. deep, in a tray of free-
draining, sterile growing media such as coconut fiber with some perlite mixed in. The media needs to support the plants, but at the same time be friable enough for the young corms to form without deformities, so any substrate used for baby root crops would be suitable.
The flowers will have already been initiated in the corms during the summer dormancy period and flowering will occur when moisture is provided and temperatures start to drop in fall. Flowering is triggered by environmental conditions such as temperate and moisture, which is easily manipulated in a hydroponic growroom. The ideal conditions during flowering are: a 16-hour day length with day temperatures of 63oF and night temperatures of 54o F. An indoor growroom or greenhouse situation means the flowers are protected from rain, moisture and wind, and the lack of weeds makes harvesting high-quality flowers much easier.
Flowering will typically occur quite quickly after planting and within a few weeks the first emerging flower buds should be seen. The flowers will fully open in three to five days and be ready for harvest. As each flower blooms, it should be plucked or snipped from the plant and taken away for processing. The easiest way to remove the saffron stigmas from the center of the flower is to pull back and remove all the petals and then snip the golden strands at the base. The strands will need to be dried before storage.
Citrusy, aromatic kaffir lime leaves (Citrus hystrix) and fragrant lemongrass (Cymbopogen citratus) are distinctive and popular flavors associated with many Asian and ethnic dishes and also easy to grow hydroponically. Kaffir lime (also called Makrut lime) is a small, compact tree grown mostly for its distinctly flavored leaves, but the peel of the small knobbly fruit is also ground into a paste and used in many Asian dishes and curries.
Kaffir lime trees can handle cooler conditions than fruiting lime types and will produce for many years. In an indoor garden they are best kept regularly trimmed by harvesting foliage for culinary use so the tree remains compact and productive. Ideal temperatures for growth are 72 to 90oF, and the plant should be grown in a large pot or grow bed of media such as perlite, coco fiber or rockwool with a drip irrigation system. Warmth, high light, increased EC (2.2 to 3.0) and slight moisture stress will concentrate flavor and aromatic compounds in the plant, resulting in higher-quality harvested spices.
Lemongrass is a popular hydroponic herb, grown commercially for fresh harvests. Lemongrass seeds germinate rapidly within three to five days at 77 to 86oF, making this an easy plant to establish. Mature plants can become as large as 4 ft. in diameter with leaves 3-ft. long, but small plants can be grown if kept well trimmed.
Even the foliage of young seedlings contains the fresh pungent flavor of lemongrass, so harvesting can take place as soon as there is sufficient foliage to cut for use. Use of small rooting volumes such as nutrient film technique is not recommended due to the large and fibrous root system that rapidly develops and can cause system blockages and slow the flow of nutrients.
Lemongrass requires warm temperatures to produce well and develop a strong and distinctive flavor, although it will survive cool conditions in a dormant state. Optimal temperatures are 72 to 95oF, with a high humidity level (more than 80%) and full sunlight or high levels of artificial light. Full spectrum grow lamps are recommended for many spices such as lemongrass as there is evidence to suggest certain parts of the light spectrum such as UV assist with the development of flavor compounds in plants.
Epazote and Perilla
International cuisine has introduced us to some exciting exotic herbs, many of which have now become hydroponic crops.Two of these are epazote, often considered to be an essential ingredient in many traditional Mexican chilli sauces and bean dishes, and Japanese perilla or shiso, also known as the sushi herb. Both are small annual plants, easy to propagate from seed (perilla seed should be sown while still fresh) and grow well in nutrient film technique or media-based systems under similar conditions to those used for basil and cilantro.
Perilla (Perilla frutescens) is an attractive herb that is available in both deep purple and green forms with a flavour similar to mild basil. Perilla grows best under warm conditions of 64 to 79oF with full light and takes around 35 to 40 days to mature. It is also grown as a micro green species harvested after the development of the first seedling leaves.
Epazote (Chenopodium ambrosioides) is a small annual plant with a distinctive flavor often described as camphor or turpentine-like with a strong aroma. Easily grown from seed, epazote is a rapid growing herb requiring temperatures of 64 to 79oF, full light and with similar nutritional requires as other hydroponic herbs such as basil.
A hydroponic garden full of exotic herbs and spices originating from far away lands, ready to pluck and serve in fresh, fragrant dishes is a real possibility with a climate-controlled indoor garden. Many of these species are hardy plants, easy to grow and thrive under the advanced nutrition hydroponic systems provide. Even the smallest growing area can accommodate a saffron corm or two, making for eye-catching displays as well as impressive harvests.