Disclaimer : The following is not intended to give instruction for large scale commercially grown cardamom, as exists in places such as India, Sri Lanka and Guatemala, though the basic principles of horticulture remain the same. If you are interested in growing it on a large or small scale in a suitably warm climate, please refer to the reference book I have given at the bottom of this article.
Having looked at a number of gardening blogs, websites, chatrooms, etc., I have come to the conclusion that it is nearly impossible for a novice gardener to wade through all the misinformation to find what they need to know about growing cardamom.
Having worked in horticulture for the past thirty years, I have had an interest in growing plants of the Ginger (Zingiberaceae) family, most of which are tropical and subtropical species. It didn’t take long to realize that almost all of the plants being sold as cardamom were not Elettaria and would never produce cardamom seed that we know as the spice. This brings me to the point “how do you know if the plant is a real or false cardamom?”
False cardamoms (many Alpinias such as Alpinia nutans and A. calcarata) have fragrant leaves when rubbed or crushed. The leaves of true cardamom ARE NOT FRAGRANT. As many species in the ginger family (Zingiberaceae) look much the same as young plants, this is perhaps the quickest way to separate out some of the imposters. So, if you happen to see “cardamom” for sale in a garden centre, rub the leaf and if it has spicy fragrance, it is definitely not Elettaria cardamomum.
Other differences only become apparent as the plants mature. True cardamom leaves are slightly pubescent (velvety) on the underside of the younger leaves of immature shoots. As the stems grow, the more mature leaves no longer have that velvety feel on the underside. The top side of the leaves are smooth and somewhat shiny (glabrous) at all stages of growth.
Some advice if you are sourcing plants or seed off the internet… ideally sourcing from India, Sri Lanka would suggest you should be getting the real deal, however there could be other issues due to unreliable shipping. Depending on the country of import, you may need a phytosanitary certificate as well, particularly if you are importing live plants. Inspection delays do not help. If you know someone travelling to those countries, you could make some arrangement with them.
I often see internet sellers showing a picture of a flower a different ginger species, usually some species of Alpinia. Clearly they do not know what they are selling and have never grown it themselves. Similarly, lots of sellers copy and paste images they’ve found elsewhere, or they may tell you the leaves are fragrant, don’t bother! Another giveaway is if a photo shows seed pods from the top of the leaf stem (from a terminal flower / inflorescence), do not buy! … true cardamom produces flowers/seeds at the base of the leafy stem (basal inflorescence) and are very close to the ground.
Temperatures, from my experience, should not fall below 12ºC to 14ºC at night. I give that range because other factors involved are humidity, soil moisture and soil porosity. If your plants experience several consecutive nights below 9ºC, your plants may suffer. Although you may not see it right away, your plants can easily get root rot in cold temperatures. If temperatures often drop below 6 ºC your plants will not survive. So, if a seller is telling you it can be grown outside in San Francisco, Auckland, or Berlin they are probably selling Alpinia nutans, which is much hardier but will never produce cardamom.
I also see a lot of advice to just go to your local spice shop and buy some cardamom pods. This could work for you but I suspect wouldn’t work for 90% of us. The issue is viability of the seed. Firstly, when cardamom seed is processed before shipping, the seed pods are dried and heat treated to prevent pathogens from getting established. If done properly, this would reduce the seeds’ viability to pretty much nothing. Secondly, how long has it been sitting in the shop, or how long since it was harvested? Unlike seeds of plants of temperate climates, tropical seeds generally have a relatively short life span (some exceptions being Cannas, for example, which have a very hard seed coat which can remain viable for decades). If a cardamom seed is fresh, it should germinate within 2 or 3 weeks. I have germinated “not so fresh” seed that was 6 months old that took 3 months to germinate. If your seed has been dried and is a year or more old, it could take 6 months or more, though I would think if it hasn’t germinated in 6 months, it will not germinate at all. It seems that for many species in the Zingiberaceae family, the seeds tend to go dormant after the first few months of being “fresh”, so that it becomes more difficult to break the dormancy the longer they have sat. Sowing fresh seed one might expect a germination rate of 80 – 90%. If the seed is a year old, the germination may be less than 10%.
The image below shows a sample of cardamom seed bought from my local spice shop. The seed was bought as dried pods and then separated out to show the variation in viability (as perceived by me). The seeds on the left are very dry, light brown in colour and would have no viability. In the middle, the group is medium to dark brown from which you may get a few to germinate, with luck, after several months. The seeds on the right are dark brown to black, plump, and still retain some moisture and clearly have the best chance of germinating… perhaps within 3 months. In this image, the seeds are clustered together as they are formed in the pods, so each group has 6-10 seeds (3 groups per pod). In the bought sample, about 40% had no viability, 45% marginal, and 15% seem promising.
To increase chance of germination, the seeds can be bathed in a nitric acid (HNO₃) solution of 50% for 15 minutes. When sowing seed, it is a good idea to also treat the seed and soil with both a fungicide and insecticide.
You will need a greenhouse or conservatory for the colder months. You can have plants in containers outside in the summer but they must be shaded 30-50% (same as inside the greenhouse). Your containers should not need to be deeper than 35cm. As the plant matures, a wider container is needed as the roots expand outward… they need that room to ensure adequate moisture as they are not drought tolerant. My mature plants are in shallow tubs up to 100cm diameter. Raised beds are perfectly fine but clearly can’t be moved around if needed, so would have to remain in place in the greenhouse. I would suggest avoid using native soil… instead use a sterilized potting soil or container mix, with a good balance of moisture retention and aeration. For my conditions I use a 50/50 mix of potting soil and coarse shredded coconut fibre (=coir; sometimes called coco peat… it is usually sold as dry compressed blocks). Avoid using peat moss based mixes as the peat is usually much too fine when you buy it and is difficult to wet. As well, fine peat breaks down much too quickly and you lose needed porosity.
As for pests, you may encounter thrip and mite problems particularly if you are growing in a greenhouse. Thrips are also a common problem where cardamom is commercially grown. Mites can easily get established if your humidity is low. There are lots of commercially available sprays that work well to get rid of these pests. If in doubt, please consult with a horticultural supplies dealer or garden centre. At the very least, frequent spraying the leaves (including the undersides) with just water can help keep pests in check (though you won’t make them disappear completely).
Pollinating flowers by hand
The flowers are normally pollinated by bees. Each flower lasts only one day. If your plants are in a closed greenhouse, you will need to pollinate by them hand with a tiny brush or toothpick. The flowers of true cardamom carry both male and female parts. In theory, they are self-compatible but in practice, cross pollination (xenogamy) is the rule. My observations are that flowers pollinated from other flowers on the same plant (geitonogamy) may start to form seed but abort seed capsule development within about a week of being pollinated. As for pollinating the stigma from pollen in the same flower (autogamy), there is almost no chance of success.
As mentioned, you will have the best success of pollination by using the pollen from one plant to pollinate a flower on a different plant. If your plants are genetically identical (by vegetative division) it may work but plants that were started from seed will automatically have some genetic variation, which is the best scenario. If you have only one flower, you can still give it a try but the chance of producing a seed pod is close to zero.
If you are over a certain age, you will need a strong pair of reading glasses to be able to see what you are doing. I use a toothpick to brush the underside of the anther to pick up pollen. If the pollen just falls away, try dampening the end of the toothpick so the pollen adheres. You can then transfer the pollen to the stigma of another flower. The receiving end of the stigma is cup or bowl shaped where the rim has tiny hairs (cilia) which help hold the pollen. Within the cup there is also a fluid, similar to nectar, which is called stigmatic fluid or exudate. This fluid also helps the pollen stick, but it also has the purpose of keeping the pollen hydrated.
It should be obvious if the pollen is available. If you are unable to get it, you are likely too early. Lots of flowers do their best to avoid autogamy by making the pollen available at a different time than the stigma is receptive. This is the problem with trying to pollinate within the same flower. If this leaves you frustrated, you can try preserving the pollen that you are able to gather by storing it in the fridge…. but you must store it with a desiccant such as silica gel (the little packets that one find in all kinds of bought goods) or calcium chloride (sold to absorb humidity in cupboards, closets, wardrobes, etc.). Fold a small piece of paper to fashion an envelope to keep the pollen in. Using a desiccant to store alongside the pollen in a sealed container reduces the chance of pathogens destroying the pollen. For long term storage in colder (freezer) conditions, this is a must… the pollen must be dried enough before it freezes, otherwise it will be destroyed by the freezing action (expansion) of water to ice. When you wish to use the pollen, it needs to return to room temperature and needs to rehydrate (just as many seeds need to hydrate before they will germinate). Rehydration can occur when the pollen is placed on the stigma.
While this post has dealt solely with one main species of cardamom, that being “green”, “small”, or “Malabar” cardamom (Elettaria cardamomum), which I have referred to as “true” cardamom━, there are other related plants that are called cardamom, such as “large”, “black” or “Nepal” cardamom (Amomum subulatum). This large cardamom grows in the sub-Himalayan regions of northeast India so could be classed as a “sub-tropical” rather than “tropical” plant. Its yellowish flowers also form at the base of the plant, but on a condensed spike rather than the spreading panicles of Elettaria. The large or black cardamom has a heavy smoky flavour due to how it is dried.
A number of other Amomum species from Asia are used in similar ways but have not found their way into mainstream western markets. Similarly, species of Aframomum as found in Africa (Grains of Paradise (Aframomum melegueta) being one example).
Unfortunately, many botanical names have changed over the past 150 years, such that there may still be some information on the internet that has been copied from outdated publications. A final note on botanical names; while there have been other named species of the genus Elettaria, those native to Malaysia and Indonesia have recently been reclassified as a new genus Sulettaria, leaving the genus Elettaria as monotypic… i.e. the genus contains only the one species.
Whatever climate you live in, if you wish to follow up with more detailed information I would recommend tracking down the textbook “Cardamom, the genus Elettaria” edited by P.N. Ravindran and K.J. Madhusoodanan.