How to Grow Yampah
The purpose of this guide is to provide information about growing, breeding, and using yampah in cultivation. While some of this information may be useful to foragers who are interested in collecting yampah, I am not providing any information about identifying species or differentiating them from poisonous species that are similar in appearance. Please consult a good foraging guide if you will be collecting yampah from the wild.
Yampah or yampa (Perideridia spp.) is a native North American root crop that is comprised of several species. Perideridia gairdneri (Gairdner’s yampah) is the largest and generally best known, with P. bolanderi (Bolander’s yampah) a close second in terms of yield, and P. oregana (Oregon yampah) a distant third. None of them are high yielding in the way that you would expect of domesticated plants; tubers of P. gairdneri and P. bolanderi may occasionally reach three inches in length, but more commonly about an inch. P. oregana is much smaller. There are other edible species in Perideridia, but I only have experience with these three.
Yampah belongs to the Apiaceae and so will have a very familiar architecture to anyone who has grown carrots, parsnips, skirret, root chervil, or many of the other edible and ornamental plants in that family. Underground, the plant forms usually two or three storage roots, but sometimes larger clusters. The roots are fascicled, which is a rather unusual feature in the Apiaceae. They are both edible and propagative, so you can eat the larger ones and replant the smaller ones. You can also cut off and replant the top of the storage root, eating only the lower part. This can be a useful technique when breeding. Cooked yampah has a flavor similar to parsnip but it is much less dense. It is also edible raw and has a crisp texture a bit like water chestnut, although the skin of the storage roots can be a bit woody. The grasslike leaves are also edible, although they are not very substantial and may become a little too tough to eat raw as the plants mature. The seeds can be used as a seasoning, similar to caraway.
The plant is perennial. It may flower as soon as the second year in good conditions, but it is not unusual for it to take longer, particularly in challenging conditions. Flowering may be intermittent, skipping one or more years before resuming (Baskin 1993). At flowering, the plants are usually two to three feet tall with umbels of white flowers. On occasion, plants grow significantly taller than that, reaching between four and five feet.
Yampah is primarily a meadow plant, growing in flat grassy areas with abundant spring moisture. Most species are found west of the Rocky Mountains, from southern British Columbia to northern Mexico.
Yampah was once a very important edible for native Americans, but the introduction of grazing animals to the west greatly reduced the amount of suitable habitat. Some sources also suggest that plants were overharvested by native Americans in some areas. Eating the raw roots in large quantities is said to have a laxative affect. I haven’t noticed this (and I’m not sure what a “large” quantity is) but you should probably take it easy when eating raw yampah. I think that they are much better tasting when cooked anyway. Luthur Burbank worked on this plant but, as with other minor edibles like rice root, none of his work seems to have survived. That may be an indication that breeding for improved yield is difficult, or merely that he couldn’t get people interested in eating yampah.
Yampah roots can be eaten raw or cooked. Raw, they are something like the texture of water chesnut with a little bit of parsnip flavor. Cooked, they take on a texture and flavor somewhere between potato and carrot. They can be boiled, roasted, or fried with good results. It is said that the raw root can act as a laxative in large amounts. I don’t know what is considered to be a large amount. I have never experienced any problems eating as much as a handful of raw yampah. That said, you might want to take it slow when snacking on the raw roots.
Roots should not be kept out of the ground long and should be planted as soon as you receive them in most areas where the plant can be grown. The exception is very wet areas. Yampah roots tend to rot it very wet soil, so you can attempt to store them in slightly damp sand or in pots. I wouldn’t say that this works really well, but it does work better than storing them in wet ground.
Like many plants in the family Apiaceae, yampah seeds do not have a particularly long storage life. I haven’t done germination tests to get percentages, but I have observed that germination is very sparse in the second year after seed is collected. Storing seeds in the freezer will probably extend their life.
I recommend direct sowing yampah seeds in fall. This is a difficult seed to germinate and seedlings grow poorly indoors. In contrast, it is easy to start yampah seeds outdoors, although they germinate over a very long period of time. Yampah has morphophysiological dormancy; in addition to requiring specific environmental conditions to germinate, the embryos are not fully developed at seed maturity and require several months at low temperatures to complete their development. If you can’t fall sow your yampah seeds, they will need 3 months of cold, moist stratification. A warm period is not required prior to cold stratification (Baskin 1993). You can mix them with a little moist soil in a plastic bag and put it in the refrigerator. Try to time the stratification so that it ends when temperatures are between 60 and 70 degrees F. Improved varieties are replanted from roots. Propagation is slow due to the small number of propagative roots produced, but once you reach the desired population size, you can simply harvest all but one from each plant to maintain the population.
Yampah spacing can be fairly dense under cultivation, as little as eight inches between plants. This requires regular watering. Yampah seems to do best with a drip system. You want the soil to be slightly moist at all times, but never soaking wet. Mulching helps. Avoid fertilizing or large amounts of organic matter in the soil. An annual amendment of compost or well rotted manure is sufficient. Under these conditions, you will be larger roots that you would typically find in the wild. If you are dry farming yampah, increase the spacing to 12 to 18 inches. Yampah should be grown in full sun. Root development is poor even in partial shade.
If sowing in pots, make sure the pots are at least eight inches deep. Yampah grows poorly in shallow pots. I’m not entirely sure of the reasons for this, since it generally does not produce a deep tap root. It may be because taller pots keep the yampah roots above the wettest soil. Germination appears to be best at temperatures of 15C during the day, with a nighttime temperature as low as 6C (Baskin 1993). First year plants may produce only cotyledons. In difficult climates, it may be preferable to grow yampah in pots for its first year, transplanting out the established, dormant roots in late fall or early winter. Do not transplant yampah when it is actively growing. The plants rarely survive the shock. Dormant plants transplant with a high rate of success in fall or early winter and an acceptable but slightly lower rate of success in spring.
Cool temperatures are required for bud growth on Perideridia roots. This undoubtedly varies between species, but the only available information suggests that winter temperatures below 15C are required. This limits yampah growing to temperate regions.
One compelling reason to grow yampah in pots is in order to compress the first two years of growth, producing reproductively mature plants much more quickly. It takes only about three months to go from seedling to a first year storage root. The first year roots can then be refrigerated for two months and then placed outdoors or in a greenhouse, at which point they will resume growth. After 3 or 4 months, water should be withheld and the plants will go dormant again. The roots can then be planted out in their final locations over winter and many will flower the following year.
Although it is a perennial, yampah completes its growth for the year by mid-summer, freeing up space for other plants. The only problem is that you don’t really want to disturb the roots. Shallow rooted plants like leafy greens might make a good secondary crop.
Unlike many perennial food plants that can be optionally grown as annuals, yampah is an obligate perennial. Even under ideal cirumstances, it will take two years to develop roots that are worth harvesting as food. Given the difficulties of establishing new plants, I recommend planting yampah in a site where it will persist for many years.
Most species of yampah grow in environments that are wet in spring, but dry out as summer approaches. This means that yampah does most of its growing and completes its reproductive cycle in a short growing season. By the beginning of summer, yampah begins to flower and most of the foliage other than the inflorescence dries up and falls away. It appears that the period of active growth can be extended by providing regular water, but even in that case the plants go into full reproductive mode by mid-summer. Unsurprisingly, the roots are in best condition in late spring, before the plant has put energy into flowering. It might be possible to improve the size and quality of yampah roots by carrying out reproductive pruning.
The yampah species that I have grown are all facultative outbreeders. They are capable of self-pollination, but seed set is poor. Seed set is much improved by crossing to other members of the same species and even to other members of the genus. I don’t know if this holds true for every plant in the genus.
As far as I can tell, P. gairderni, P. bolanderi, and P. oregana all hybridize easily. If you want to keep them pure, you will need to isolate them by typical distances for other Apiaceae like carrots (distance depends on climate and pollinator density). On the other hand, allowing them to cross pollinate appears to occasionally produce plants with larger roots, at least in the case of crosses between P. gairdneri and P. bolanderi. Large populations of crosses between Perideridia species are probably a good place to start with yampah breeding.
Chromosomal arrangements are surprisingly complex in Perideridia, with almost as many different chromosome complements as there are species in the genus. Both diploid and polyploid types are present. The diploids appear to cross easily with one another, forming a continuum of traits (Chuang 1969), while the polyploids are more distinct. Diploid chromosome numbers in Perideridia are n=8,9,10 and tetraploids are n=17,18,19,20,21,22. This at the very least suggests that allopolyploids exist at the tetraploid level, at least for the odd ploidies and probably others as well. Downie (2004) found some evidence for three different clades in North American Perideridia, with P. americana on its own (unsurprisingly), a second clade comprised of P. gairdneri, P. oregana, and P. leptocarpa, and the third containing all remaining species.
There are at least ten more species of yampah beyond those discussed in this guide. They are probably all edible, but there is not strong evidence of human use for all of them, so it is possible that they are not all safe.
Eastern yampah (P. americana), also known as wild dill, is the only yampah species found exclusively east of the Rocky Mountains, where it is found in greatest density in Missouri and Illinois (Chuang 1969). There is very little information to be found about edibility of this species. This may be because the roots are very small or it could be that the plant is not edible for other reasons. It may still be interesting for potential hybridization with other yampah species due to its different climate tolerance. Proceed carefully.
Red rooted yampah (P. erythrorhiza) is found in only a couple of locations in oregon. It differs from the other common yampah species in that its storage roots are sometimes a rusty red color and in having more and larger roots (Roberts 2003). One source indicates that it is edible, but it is not a primary source and I haven’t found any others. It may be an attractive candidate for hybridization given its larger size. I have not grown this species.
Kellogg’s yampah (P. kelloggii) has some history of use as an edible. Unlike most species of yampah, it produces long roots in clusters of 5 to 25 (Chuang 1970) that sometimes bear a tuberous swelling toward the end. This might well make it an attractive candidate for hybridization. I have not grown this species.
This species is now consider most likely to be a tetraploid variant of P. oregana. P. oregana contains all of the diploid numbers found in Perideridia, and P. leptocarpa is reported to have n=17, so it is most likely a hybrid of n=8 and n=9 variants of P. oregana.