Duck Potato (Wapato)

If you can control the level of your pond or basin, drop it over winter and expose the mud, then bring it back up in spring. Leave it flooded year round and the stand will simply regrow from tubers instead. A winter draw-down exposes the seedbed that fallen achenes need, and a plant can drop up to 20,000 viable achenes. Seedlings are the only way new genetics enter a patch that otherwise just clones itself.

Give cleaned achenes three months of moist cold stratification, then broadcast them in spring onto well worked, saturated soil and leave them uncovered on the surface. Germination wants direct sun and 80 to 90F. Expect this to work in a nursery flat or greenhouse, not scattered across open water. The seed needs sunlight striking the soil surface to germinate, so burying it defeats the sowing. Seed is worth the trouble because it keeps genetic diversity in a patch that otherwise clones itself from tubers forever.

Test or judge your water first. If it is oligotrophic, low in nutrients, a fertilizer application or a richer water source will speed biomass production and revegetation. If the pond or ditch already runs green and nutrient-rich (eutrophic), fertilization is not necessary — skip it entirely. Many surface waters are already rich in nutrients, so feeding adds nothing the plant cannot get and simply drives algae. Wapato only responds to fertility that is actually missing.

Through the growing season keep fresh water roughly 6 to 12 inches deep over the root zone in full sun, on soil that stays saturated. Right after planting, back the water off to about half an inch over the soil surface until plants take hold. Slightly acid water, pH 6.0 to 6.5, suits it best, though it tolerates worse. Hydrology is the single factor that decides whether a wetland planting takes. Wapato is an obligate wetland plant with no drought strategy, and a patch that dries out mid-season quits building the tubers you are growing it for.

Wait until the stems and leaves yellow and collapse and the water level drops, then work the mud with a hoe, rake, or pitchfork, or loosen it with your feet the way it has traditionally been done. The tubers float free and can be skimmed off the surface. They sit on rhizome tips out from the parent plant, not directly under it, so search wide. Boil, roast, or bake them in embers like a potato. Before the top dies back each fall the plant translocates its nutrients and carbohydrates down into the subterranean tubers. Dig early and you get small, starchless tubers and you rob the crown of the reserve it regrows from.

Plant tubers while the plant is dormant, any time from fall through winter into early spring. Press them into saturated, finely textured mud where permanent standing water is less than a foot deep, and never let the leaves of potted or bare-root stock sit submerged. Space 1 to 2 feet apart on poor or disturbed sites, up to 6 feet apart on good ones. Until you plant, keep collected tubers moist and cool in damp peat moss. Tubers are the plant's overwintering starch store, so moving them while the top has died back costs the plant nothing, and transplanting tubers takes better than bare-root stock. A single plant makes up to 40 tubers and each one can throw 3 to 5 shoots, so even 6-foot spacing closes into a solid stand in one season.

While the plants are dormant, dig through the stand with a rake, hoe, or shovel, take the best tubers for the kitchen or for replanting, and pull the rest. Digging plugs about 6 inches deep is enough. Collect no more than a quarter of the plants in any area: if you take no more than a square foot out of every 4 square feet, the patch closes the gap back up in one good growing season, leaving enough plants and rhizomes to regrow. This is a highly rhizomatous perennial that can become weedy, and a stand left alone crowds itself and everything near it. Harvesting is the thinning, so digging your food and controlling the patch are the same job.