How to Grow Tuberous Mint
I’ve done something here that I normally try pretty hard to avoid: introducing a new name for a well known plant. In this case, a name for a group of plants. There are several edible, tuberous species in the genus Stachys, which is part of the mint family, Lamiaceae. All have similar growth habits, cultivation details, and culinary uses, so we can lump them together for the most part. Tuberous mint is a name descriptive of this group of plants and perhaps more usefully so than calling them tuberous Stachys, a name which is probably less evocative for growers who do not often resort to Latin names.
The most well known of these plants is Stachys affinis, the Chinese artichoke, crosne, or chorogi. The tubers of Chinese artichoke are generally small, two to three inches (5 to 7.5 cm) in length, and no more than half an inch (1.2 cm) wide. They are white, with a segmented appearance that makes them tempting to compare to grubs. They are crisp and slightly nutty tasting and are often eaten raw, but also can be cooked or pickled. All parts of the plant are edible, but only the tubers are really worthwhile, in my opinion. Yields are fairly small; a quarter pound (114 g) from an individual plant is very good.
In most places, Chinese artichoke is one of those plants that you really have to grow yourself. It is rarely available in markets and it doesn’t store very well. In climates where the soil doesn’t freeze to significant depth, it is best harvested and used fresh through fall and winter. A fresh Chinese artichoke tuber has the texture of a radish, with a flavor that combines elements of radish, turnip, and walnut (in my opinion of course), while tubers that have been sitting in a box at the store for more than a day or two may have no flavor at all.
Two other species produce tubers that are nearly indistinguishable, although they are often larger and a little more earthy tasting. These plants are Stachys floridana, Florida betony, and Stachys palustris, marsh woundwort. These two species may actually be more interesting than the better known Chinese artichoke, because they generally have better yields and readily produce seed, which means that they can be more easily improved through breeding.
The tubers of Florida betony may reach up to twelve inches (30 cm) in length and about three quarters of an inch (2 cm) in diameter. Marsh woundwort tubers may grow as long as eighteen inches (46 cm) although most of that lenth is rather thin. It is still perfectly edible and may even be preferable for some dishes. I find that the thicker, more useful part of the tubers is typically about four to six inches (10 to 15 cm) in length.
If you have seen mint plants, the tuberous mints will look familiar. They have the signature small, serrated leaves and angular stems of the mint family. Chinese artichoke reaches about 18 inches (45 cm) in height, while Florida betony and marsh woundwort are generally shorter in cultivation but may occasionally grow up to 24 inches (60 cm). These plants are best grown where they can establish as a perennial population, because it is very hard to find all of the tubers when you harvest. Once you have grown mint tubers, you could be growing them forever.
Chinese artichoke and Florida betony are generally diploids. Marsh woundwort is found in diploid, tetraploid, and hexaploid forms. The diploids and tetraploids are mostly native to North America, while the hexaploids are mostly native to Europe (Luczaj 2011).
These plants are relatively recent to cultivation. Chinese artichoke cultivation began in northern China around the thirteenth century. Marsh woundwort may have been cultivated in eastern Europe in the nineteenth and twentieth centuries and in Britain prior to the introduction of the potato (Luczaj 2011). Marsh woundwort and Florida betony were both used by native Americans.
Marsh woundwort was used as a food in Poland and Ukraine, both raw and as a flour that was used as a thickener or to stretch bread dough (Luczaj 2011).
Relatively little information is available about the nutritional values of any of the mint tubers. All three species employ stachyose as their primary carbohydrate, although they also contain a smaller portion of starch. Stachyose is not digestible by humans, so these tubers are relatively low in calories. As with most vegetables that contain undigestible sugars, excessive consumption may cause gas. This is not usually a problem with tuberous mint since it is generally consumed in smaller portions than other roots with undigestible sugars, such as Jerusalem artichoke and yacon.
The tubers of Chinese artichoke are considered to be high in iron, although I couldn’t find an original source for this information.
Tubers can be eaten raw or cooked. All make a good addition to salads. Cooking is generally done for short periods of time. Stir frying works very well. Steaming or briefly boiling for two to four minutes also produces good results.
In China, Japan, and Korea, Chinese artichoke is often fermented. This both serves to preserve it and increases the fraction of digestible sugars. Ingredients are sometimes added to color the tubers; in Japan, perilla is added to color them red.
Tuberous mints need plenty of water. They are not drought tolerant plants, but they will succeed under a wide temperature range. Marsh woundwort is the most tolerant of chilly conditions, while Florida betony is the most heat tolerant, and Chinese artichoke falls somewhere in between. In our garden, Florida betony survives the coldest weather (into the mid 20s F (around -4 C), but Marsh woundwort grows better in cold conditions.
Tuberous mints need a consistent supply of water to produce good yields. If the soil is allowed to dry out too frequently, yields will suffer. Full sun is also required to produce good yields; although tuberous mints will happily grow in shade, they don’t receive the energy necessary to form lots of tubers.
All three plants should be hardy (as tubers) down to USDA zone 6. Chinese artichoke is typically hardy down to USDA zone 5 (zone 4 under mulch), Florida betony to USDA zone 6, and marsh woundwort is unknown, but probably suitable for zone 5/6. The foliage will die by the time temperatures reach the lower 20s F (less than -4 C) but the tubers are set fairly deep and survive shallow freezing pretty well. These ratings are for plants in the ground; in containers where they can’t form tubers as deeply, they may be less hardy.
None of these plants have any photoperiod dependencies. That’s a refreshing change!
Marsh woundwort prefers wet and probably acidic soil. The weight of tubers produced in pots was found to be roughly two to four times greater in wet soil than dry (Wilcock 1974). This is not particularly surprising, given that the native environment of marsh woundwort is, well, marshes.
Soil should drain well and be in the vicinity of neutral pH for Chinese artichoke.
Little information is available about optimum soil conditions for Florida betony, but it performs well in the same soil conditions as Chinese artichoke for us. The fact that it is a noxious weed of lawns throughout the Southeast suggests that it probably tolerates a wide range of soil conditions.
Mint 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, in slightly damp soil. Tubers will quickly become soft when exposed to air, but they can be rehydrated simply by potting them in some damp soil.
Seed of marsh woundwort and Florida betony has a storage life of at least 3 years at 50° F (10° C).
In mild climates, Chinese artichoke and marsh woundwort are best planted in the fall. They will sprout very quickly after the temperature rises into the 40s F (5 to 10 C). Florida betony is best planted in spring in cooler climates, once the soil temperature has risen into the 50s F (10 to 15 C). In the South, it can probably be planted at any time of year.
In row spacing of nine to fifteen inches (22.5 to 37.5 cm) works well. Tighter spacing should only be used where water is abundant. I plant on a fifteen inch spacing, which seems to increase the number of large tubers. Thirty inch (75 cm) row spacing will leave a comfortable walkway. Plants are best grown in raised beds so that they cannot spread out of control.
Starting from Tubers
Tubers can be planted in fall or spring in mild climates. Florida betony foliage grows fastest under warm temperatures (in the 70s F) and long day conditions (McElroy 2002). Presumably, increased growth in long day conditions is due simply to the increased amount of sunlight. This information appears to be true for Chinese artichoke and marsh woundwort as well, although I haven’t studied it carefully.
You can cut tubers for more plants, much as you would seed potatoes. Make sure each piece has at least three segments for best results. Plant two to three inches (5 to 7.5 cm) deep, preferring deeper planting for larger tubers. Orientation of the tuber doesn’t appear to matter, but I plant them horizontally, which is generally how they are found when dug.
Dormancy varies considerably among the three species here. Marsh woundwort emerges earliest, in late winter. Chinese artichoke emerges in early spring. Florida bettony doesn’t wake up until mid-spring.
Starting from Seeds
Florida betony seeds will germinate over several weeks at 70° F (21 C) and should be started four to six weeks before your last frost.
Marsh woundwort requires stratification, at least two months of cold, wet conditions, after which it will germinate over two to three months at 70° F. This requires some planning. I begin stratification in November and then sow the seeds indoors in pots in February.
No information is available about germinating Chinese artichoke seeds, due to their rarity. I would guess that their requirements are more similar to Florida betony than marsh woundwort.
Where you have grown tuberous mints previously, you must thin the new plants in the spring to your preferred spacing. Failure to thin will result in crowding and poor yields of small tubers.
Many sources recommend keeping the foliage of Chinese artichoke trimmed back to about six inches (15 cm) in order to maximize the size of the tubers. I haven’t found this to be necessary and it doesn’t make a lot of sense to me either. Our plants grow quite large, up to about two feet (60 cm) tall, and they produce large numbers of tubers. Ostensibly, the reason for trimming the plants is to prevent flowering and the loss of energy that the plant will divert into trying to form seed. I have had some plants flower and, as far as I could tell, it didn’t make much difference in yield. The closely related Florida betony, which flowers profusely, also provides very good tuber yields. So, you might experiment with keeping the plants trimmed to see how it works for you, but I don’t recommend that you adopt it as standard practice without some testing.
In parts of the southeast, Florida betony is considered a noxious weed. The same is true for marsh woundwort in parts of Europe, where it is a common weed in cereal, potato, and beet plots (Luczaj 2011). All three species can become difficult to control in almost any climate, since even tiny pieces of rhizome can generate a new plant. It is best to grow these plants in pots or in a hard sided bed. Although they are normally shallow rooted, they may set tubers as deep as 18 inches (45 cm) if they are stopped by an obstacle, which means that they can escape from under beds with short walls.
All three species can make good understory plants for shrubs or trees. The only problem is that they will probably escape your control in such an environment and become very weedy. As essentially wild plants, they are very good at taking care of themselves in a mixed planting. Maybe too good.
All three species are suitable for growing as perennials. In fact, it may be quite difficult to grow them in any other way. The large number of small tubers makes these plants nearly impossible to harvest completely and even small fragments of rhizome can easily produce new plants. Hard sided beds can be used for a perennial patch. You also might experiment with using animals for control. Our patch is located where ducks can reach three sides through a fence. This prevents escape to those sides because the ducks eat all of the tubers.
Marsh woundwort is particularly good at escape, but all three will easily find the gaps between cement blocks or wood slats and try to make their escape into the larger garden. Do not establish a patch where you plan to rototill in the future. Rototilling is a very efficient way of spreading tuberous mints.
Tuberous mint grows very well in containers of three gallons (11 l) or larger size.
In cool summer climates, tubers are generally harvested in fall. In frost free climates, they may be best harvested in spring.
Tubers are ready for harvest any time after the foliage dies back in the fall. The tubers can be rather deep. Florida betony tubers are typically formed 4 to 6 inches deep, but Chinese artichoke and marsh woundwort may form tubers anywhere from 8 to 18 inches deep and sometimes even deeper where they run into obstructions like the sides of a raised bed.
The tubers keep very poorly out of the ground. They dehydrate rapidly and must be stored under cool, high humidity conditions. They also tend to discolor. Because of this, they are best left in the ground and harvested as needed in climates where the ground doesn’t freeze.
They will last up to a week in the crisper drawer of a refrigerator without much decline in quality. Lightly wetted and sealed in a plastic bag, they can be stored through the winter for replanting in the spring, although this should be necessary only in very cold climates or where animals eat the tubers.
Tubers are traditionally pickled in Japan and that may be the only good way of preserving the tubers. They can potentially be dried and ground into flour.
All varieties of all three species are hybrids, so varieties can only be maintained through vegetative propagation.
You can propagate all of these plants with tubers, rhizome, or stem cuttings. For stem cuttings, take four to six inch (10 to 15 cm) sections of stem and set the bottom about two inches (5 cm) deep in damp soil. Significant root formation takes six to eight weeks, after which the new plant can be hardened off and moved outside.
Chinese artichoke rarely flowers or sets seed. Flowers are primarily formed in warm, dry weather. I had good flowering from the plants one year during a period of unusually warm weather. There have been some breeding programs that managed to get seed from Chinese artichoke, so it is possible. If you ever see your plants flowering, make sure to try to collect the seed!
Marsh woundwort and Florida betony set seed easily. It matures over a long period of time and can be difficult to collect. I tuck white plastic grocery bags around the base of the plant and collect the seeds that fall on them.
Hybrids of marsh woundwort exist in nature, so crosses with other wild relatives may be a way to increase genetic diversity in this crop (Wilcock 1974).
I have observed moderate pollinator interest in these plants, primarily from bumble bees, flies, and occasionally butterflies. If you are in an area where they migrate, monarch butterflies may visit Florida betony.
Spider mites and tarnished plant bug sometimes become serious pests.
Chinese artichoke, at least, is commonly infected with viruses. These eventually reduce yield. The only remedy is to abandon the current plot, killing off the volunteers by covering the soil with plastic and starting again with new tubers in new ground.
Marsh woundwort sometimes develops a condition where it no longer produces tubers, but only slightly thickened stolons. The condition is persistent and may be the result of a mutation or disease.
Two common development goals for these crops must be increasing the size of the individual tubers and the per plant yields. They would also benefit from a reduction in the depth of the eyes so that they would retain less soil.
In Chinese artichoke, restoring fertility by growing plants from seed or by crossing with other members of the genus Stachys could make further breeding possible.
We supply either whole or cut tubers. Chinese artichokes are typically provided whole. Florida bettony and marsh woundwort are typically provided in roughly three inch long segments.