How to Grow Mashua
Mashua (Tropaeolum tuberosum – also commonly known as tuberous nasturtium, climbing nasturtium, añu, or cubio) is a root crop that was developed in the Andes mountains of South America.
Mashua is a member of the nasturtium family and has a form similar to the common garden Nasturtium. It has long twining stems on which three to five lobed leaves form. In the fall (or mid to late summer for the variety Ken Aslet), mashua forms trumpet-shaped orange or orange and yellow flowers.
Mashua is traditionally grown at elevations of 3000 to 3700 meters, where the average annual temperature is 52F or less (Grau 2003). It is poorly adapted to warm, dry conditions and so is best suited to cool, mild climates in North America. You can grow mashua without any great challenges in the maritime Pacific Northwest.
It is an attractive plant and is probably better known as an ornamental than an edible outside of its native range. Plants grow up to at least 8 and possibly up to 12 feet tall if given something to climb. They are fast growing in cool, wet weather and are generally able to outcompete and smother weeds.
Underground, the plant forms tubers that reach up to at least 13 inches in length, although more typically in the 3 to 8 inch range. The tubers have a shiny, waxy skin that cleans easily. Tubers cluster relatively closely under the base of the plant. Most mashua varieties have predominantly white tubers, although yellow, orange, red, and purple tubers are formed by some varieties. Given a long enough frost-free autumn, plenty of water, and an overall cool climate, mashua can produce very high yields. We average 5lb per plant, but have seen as much as 16lb from a single plant. Warm climate yields are smaller; perhaps 2-3lb per plant.
In addition to the domesticated mashua, there is a wild variety, Tropaeolum tuberosum ssp. silvestre. This northern limit of the subspecies is unknown, but it reaches from Peru south into Argentina (Bulacio 2012). Wild mashua’s thickened stolons can barely be categorized as tubers. The reach a maximum thickness of about half an inch. They are more pungent and contain more forms of glucosinolates than the domesticated mashua. Although not particularly useful as an edible (other than for its leaves), wild mashua may prove useful for breeding with the domesticated varieties.
Domesticated mashua is sometimes divided into two botanical varieties, var. lineamaculatum and var. piliferum (Hind 2010). The origin of these botanical varieties is unknown and they don’t appear to be particularly useful. The variety Ken Aslet is generally associated with var. lineamaculatum and the variety Blanca (offered as Sidney in the UK) with var. piliferum.
Genetically, mashua is generally considered to be tetraploid (Gibbs 1978) and displays a fair degree of phenotypic variability in progeny from self pollinated seeds, similar to that seen in tetraploid potatoes. There is some evidence also for diploid and triploid forms. It is probably an autopolyploid (Grau 2003).
Evidence exists for ancient use of mashua, as much as 8000 years ago, probably with later domestication. The first archaelogical evidence of mashua use dates to roughly 700 to 1400 years ago (Grau 2003).
Mashua appears to have originated in the Titicaca basin of Peru and Bolivia and that is where its greatest diversity is still found. Although mashua remains a fairly diverse crop, it may still be in danger in the Andean region, where it has been particularly vulnerable to replacement by other crops (Leon 1964). Unlike some of the other crops that were once quite vulnerable, such as yacon and maca, mashua has yet to find a niche in global markets, although it has recently been proposed as a possible new “superfood”.
The three common names for mashua in Peru, Bolivia, and Colombia, respectively mashua, isaño, and cubio, may indicate that the crop was widespread and well known prior to conquests by both the Incas and the Spanish (Grau 2003). Mashua is a name of Quechua origin and isaño of Aymara, both peoples of the central Andes. Cubio was the name used by the Muisca of the Colombian Andes (Torres 1992).
Information is not available over its entire range but, in Ecuador, loss of varieties amounting to 46.5% of its previously assessed genetic variability has occurred in recent decades (Tapia 2001).
Mashua was introduced to Europe as early as 1827 (Hind 2010) and appears to have been grown continuously since then, but primarily on small scale as an ornamental.
Mashua tubers are high in vitamin C and relatively high in protein for a root crop. The vitamin C content may vary significantly with variety and growing conditions. Some measurements of vitamin C content in mashua are as high as 120mg/100g (Torres 1992), which is more than twice as much as an orange and comparable to an equal weight of kale.
Mashua contains large amounts of glucosinolates (mustard oils) and, as a consequence, isothiocyanates. Isothiocyanates have antibiotic and insecticidal properties. They also appear to play a role in carcinogen detoxiification and/or promotion of apoptosis in pre-cancerous cells (Shapiro 1998). So, mashua consumption may be protective against some kinds of cancer.
On the other hand, those compounds may have effects on male hormones or sperm function. This has only been studied in rats, so effects on humans are a matter of speculation. Cardenas-Valencia reported in 2008 on rats were dosed with an extract prepared by first boiling and the freeze-drying the tubers. The dosage of the extract was corrected so that the amount of extract was equivalent to that found in a similar weight of raw tubers. Rats were dosed with 1g mashua per 1kg of body weight. In human terms, a 70kg man would consume 70g or 2.5 ounces of mashua. At the end of 42 days, they found slight reduction in sperm count and daily sperm production in the rats that ate mashua. The reduction was fairly consistent over the study period, not worsening with continued consumption. They found no difference in testosterone between the control and treatment groups. This would seem to refute the idea that mashua is an anaphrodesiac, but it may be best to limit conmsumption when trying to conceive since sperm production was slightly reduced.
Nobody really knows what the long term effects of mashua consumption are in humans when consumed as part of a normal diet. Mashua has long been consumed in the Andes and is still commonly eaten in Colombia, Ecuador, and Peru, so its effects are probably not significant with normal consumption of cooked mashua if, in fact, they occur in humans at all. I’m not worried about it, but by all means do your own research and consume mashua according to your appetite for risk. For what it’s worth, I have eaten a lot of mashua and have no complaints so far.
All parts of the plant can be eaten raw or cooked. The tubers are the most frequently consumed part. They can be eaten raw, although this doesn’t appear to have been a common practice in the Andes. The raw flavor of mashua is not appealing to most people, or at least to those with western palates. The strong flavor is the result of glucosinolate and, consequently, isothiocyanate content (Johns 1981). It is more common to eat mashua cooked, which produces a result similar to turnip. Apparently mashua is also sometimes consumed as a dessert, by boiling and then freezing the tubers. Having tried this, I only recommend it to the adventurous. Although not a traditional method of preparation, we’ve found that it makes a pretty tasty pickle. The flowers have large nectaries and are sweet with a bit of aniseed flavor. Leaves are tasty as a salad green and the larger leaves can be used as a wrap, like grape leaves but spicier.
We think that mashua has a greater gap between its potential and the current state of the crop than any of the other Andean tubers. You can’t just toss some mashua on a plate and expect it to be delicious, but it can be in the right dish. Undercooked, it can be horrible, although there are a few people who like it that way. Without special attention, fully cooked mashua tastes basically like turnip; not bad, but not terribly exciting. Still, its other attributes make it very appealing. Despite its current limitations, we’re really enthusiastic about mashua and think it has a bright future.
For cooks who like to explore in the kitchen, mashua is definitely worth some attention. While plain, boiled mashua is not the worlds most appealing dish, we keep stumbling over better ways to prepare it. As mentioned, mashua pickles are delicious and the adventurous fermenter could probably produce a very unique product. Also, we have found that mashua can replace potato in Indian dishes and is often an improvement. It works well in strongly spiced dishes where it can’t get the upper hand. Cumin seems to have an almost magical balancing effect against its less appealing flavors. Roasted in a slow-cooker with meat for 8 to 12 hours, all of the unpleasant flavors disappear and the tubers become soft and rich with just a hint of exotic aftertaste. The fattier the meat, the better the mashua pairs with it. These experiences make us optimistic that there are more delicious ways to cook with mashua just waiting to be discovered.
Culture is similar to the potato. The crop is generally propagated from seed tubers, which are planted in the spring. The plant requires short days in order to form tubers (with the exception of the day neutral variety Ken Aslet) and is optimally harvested around mid-November or possibly even later.
We get a lot of inquiries about the appropriate USDA zone for the plants that we offer. The best advice that we can offer is not to pay too much attention to USDA zones. All that they really tell you is how cold a winter the plant can survive. If you are going to dig your mashua before winter, as most people will, the USDA zone is not particularly relevant. It is much more important to look at your summer high temperatures and your average first frost date. All of that said, mashua best fits USDA zone 9a (low temperature of 20-25 degrees F). Approximately half of the tubers can be expected to survive a multiple day freeze at 25 degrees and approximately 20% at 20 degrees.
Mashua is typically hilled up at least once during the growing season. At a minimum, this provides some protection to the tubers, which often grow up and out of the soil. It may also improve yields, although we have not observed significant differences in yield between plants that are hilled and those that aren’t.
At minimum, you will receive enough material to start the number of plants stated in the product description. You may receive whole tubers or pieces of tubers since mashua tubers can be too large to easily fit in a packet. We’re usually pretty generous with mashua and you will probably find that you can start more plants than the minimum that we guarantee if you are willing to further cut up the tubers.
The picture shows the size of the tubers that you will typically receive.
Seed packets contain 10 seeds. Expect about 50% germination over three months for domesticated mashua seed and 80% germination over 3 months for wild mashua seed.
Although it likes to climb, mashua also grows just fine on the ground
Mashua tubers are particularly vulnerable to dehydration and will do better stored in soil than exposed to the air. Keep them in a dark, cool place. Check on them from time to time. If you find that they are becoming soft, either put them in some barely damp soil or in the crisper of your refrigerator. A storage life of six months is about the best that you can expect.
Tubers will begin to sprout in March. If you order in March or April, you will probably receive tubers that have already sprouted. Sprouted tubers can wait to be planted for a couple of weeks, so it is not an emergency. It is best to store the tubers where they can get some light, once they have sprouted; sprouts that grow in darkness will become spindly and fragile. We recommend potting the tubers in some barely damp soil with the tip of the sprout exposed and then transplanting after the last frost.
Mashua is very tolerant about transplanting and you will get a head start by potting them. You don’t have to put them individually; you can pot a bunch in a single container and then divide them when you transplant.
Mashua grows very quickly once it has sprouted. To keep potted plants manageable, you can trim the stems back to a few leaves. They will readily send up new stems from the remaining nodes, so you can be very aggressive in trimming them.
When to plant
Plant mashua in the spring after risk of frost has passed. You don’t need to hurry with most varieties, because mashua won’t begin to form tubers until after the autumn equinox (about September 21). The exception is the variety Ken Aslet, which can form tubers earlier and may consequently benefit from early planting.
Where to plant
Mashua likes water and prefers full sun in mild climates. Where temperatures frequently exceed 80 degrees F, mashua will grow best in an area that has afternoon shade. We don’t know what the upper temperature limit is for mashua; some customers grow it in climates that infrequently reach 100F in the summer and report daytime wilting, but recovery overnight. In dry climates, it requires frequent watering and will benefit from some wind protection. It likes to climb and will make more efficient use of space if it can. Interestingly, traditional Andean culture of mashua does not appear to have involved any trellising. Instead, the plants are just allowed to pile on top of the ground, forming a mound with about a two foot radius. Mashua can make a very good weed suppressing crop when grown in this fashion. Mashua is not fussy about soil, so long as it is not too dry; moderately acidic soil is ideal.
How to plant
You can cut tubers for more plants, much as you would seed potatoes. Make sure each piece has at least two eyes. It is best if the seed pieces are at least 1/2 ounce. If you cut tubers, let them heal for a few days in indirect sun before planting them.
Plant whole tubers and seed pieces about 2-3″ deep (shallower for smaller pieces and deeper for larger). Orientation of the tuber doesn’t seem to matter. We usually plant them horizontally, but tubers are found in a jumble at harvest, so there is probably no right or wrong way to plant them.
In-row spacing of 30 inches works very well. 84″ row spacing will leave a comfortable walkway. 72″ between rows will usually leave just a little walking space in between. 60″ between rows will form a dense, unbroken canopy.
Mashua thrives even in relatively poor soils, but loose, light soils benefit you at harvest time. A little complete organic fertilizer or compost should provide mashua sufficient nutrition. We have not done careful testing, but most of the Andean root crops respond poorly to rich fertilizers. Likewise, most Andean root crops prefer moderately acidic soils, although mashua appears to have a wide range of soil tolerance.
Mashua will definitely benefit from hilling up or mulching if you are at risk of frost before harvest. It has a habit of piling up tubers right at the surface and these will be ruined in a frost if they are not protected.
Mashua grows very well in half-barrel or larger containers.
Mashua seeds have slow and irregular germination. Start your seeds at least three months before you want to transplant. You may see germination within a month, but most will take longer. Scarification techniques, like chipping the seed with a nail clipper or filing improve germination time. Once they break the surface, mashua seedlings grow very quickly and are typically ready to plant out in 2-3 weeks.
With the exception of the variety Ken Aslet and several of the evaluation varieties from our breeding program, mashua varieties have a short day dependency for tuber formation; they don’t begin to form tubers until day length falls to 12.5 to 13 hours, which typically falls somewhere in the first half of September. About 10 weeks are required to form a good yield, which places harvest around mid-November. Mashua will continue to grow much longer than that, so harvest can be delayed until the plants are killed by frost. Where harvest can be delayed until late December, yields can be very large. We have had single plant yields as high as 16.6 pounds when mashua was given a very long growing season and grown on trellis.
In the Andes, mashua is sometimes exposed to the sun for several days following harvest to sweeten the tubers (Grau 2003). We have tried this for as long as two weeks, but have not been able to detect any obvious change in the flavor of the tubers. It is possible that more intense sunlight is required.
Mashua is one of the more difficult of the Andean root crops to store. It dehydrates relatively quickly once dug. Tubers will last 6 to 8 weeks at room temperature and moderate humidity before the reduction in quality makes them unappealing for eating. Storage conditions of 35-38F and 95% humidity can extend storage to 8 months, allowing for some deterioration. Tubers exposed to light will become green, but this does not affect edibility.
The only traditional method of preservation for mashua is a kind of low tech freeze-drying similar to the process used to make chuño from potatoes. Mashua can also be preserved by pickling or canning, using processing instructions for potatoes. Some varieties discolor when processed for canning.
There is no reason for you to buy the same tubers from us again next year. Reserve some of your crop for replanting and come buy a new variety from us instead!
We recommend saving the largest tubers for replanting. Larger tubers generally produce bigger plants faster, with more stems, which leads to greater yield.
Mashua, like most plants that are propagated vegetatively, is naturally a hybrid. It sets seed easily in a favorable climate, although not until late in the season (so, frost/freeze protection may be required to mature seed). The seed, since it is produced by hybrid plants, will not be true to type. Instead, it will produce new varieties of mashua, some of which may prove to be superior.
You can propagate mashua via cuttings. Take six to nine inch sections of stem and set the bottom about two inches deep in damp soil. Significant root formation takes four to six weeks, after which the new plant can be hardened off and moved outside. Do not pull the full stem free of the tuber. Unlike most of the other Andean tubers, mashua responds very poorly to this technique and will often fail to sprout from the remaining eyes once you have pulled the dominant sprout.
Mashua is often said to be totally resistant to pests and diseases and it almost lives up to that reputation. We have only seen one disease in mashua: a viral mosaic. We’ve been able to learn very little about it, but we think it turned up in our garden, rather than coming in with the tubers, which means that it probably is not a specialist pathogen of mashua. Mashua is probably vulnerable to at least some of the viruses that infect the garden nasturtium (T. majus).
Recognized viruses of mashua include Papaya mosaic virus, Potato virus T, Sowbane mosaic virus, and Tropaeolum mosaic virus (FAO 2007). None of these viruses are likely to occur in varieties that arrived in North America through agricultural quarantine.
The cercozoan Spongospora subterranea, which is responsible for the condition known as powdery scab in potatoes also affects mashua (Torres 1992). It does not reduce edibility significantly, but it does affect the appearance of the tubers.
Pests are another matter. Although mashua usualy grows fast enough to outpace them, there are a few pests that like to nibble on it. The most serious are probably the larvae of cabbage white butterflies, which can cause a lot of damage when they are present in large numbers. Flea beetles and aphids can also cause problems, although they tend to be more severe in greenhouses. The other problem is field mice (voles), which will dig and eat the shallow tubers. They typically ignore them until late in the season, when mashua is one of the few plants left in the ground. Deer can also become a problem. Although they tend to browse mashua lightly at first, they eventually develop a taste for it and then can do an incredible amount of damage in a short time.
Breeding objectives for North America are similar to those for oca and ulluco. As a plant that is both dependant on short days for tuber formation and vulnerable to frost, mashua cultivation is limited to climates with mild autumn weather. Varieties that form tubers in longer days will allow expansion into other regions with cool summers but early frosts. Several varieties with critical daylenths greater than 13 hours now exist and breeding this trait into new varieties appears to be relatively easily, with roughly 5% of the progeny of crosses between short day and intermediate daylength varieties having similar intermediate photoperiods.
Breeding for greater tolerance to heat and drought would further expand the possible range for mashua in North America. New varieties should be trialled in warmer climates.
No discussion of mashua breeding objectives would be complete without considerations of flavor. Mashua has two flavor components that people seem to find objectionable: the aniseed flavor and the pungent, mustard flavor. In fact, either one of these might be more acceptable given the absence of the other. Breeding to reduce the pungency, likely associated with isothiocyanate content, might also reduce the content of substances implicated as anaphrodesiacs, which could increase consumer acceptance whether or not these substances actually exist in biologically significant concentrations.