Zenmai
Osmunda japonica
Family: Osmundaceae
What it is like
Osmunda japonica is a FERN growing to 1 m (3ft 3in). See above for USDA hardiness. It is hardy to UK zone 6. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils and can grow in very acid soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist or wet soil.
Height (m): 1
Where it is found
Moist places all over Japan.
E. Asia - China, Japan.
Conservation Status:
Countries/locations it is found in
How it is used
Food
Rating: 2
Young fronds - cooked. An edible starch is obtained from the rhizome.
Root: includes bulbs, corms, tubers, rhizomes etc.
Medicine
Rating: 0
Other
Rating:
How it is grown
Likes a soil of swamp mud and loamy or fibrous peat, sand and loam. Succeeds in most moist soils, preferring acid conditions. Requires a constant supply of water, doing well by ponds, streams etc. Plants thrive in full sun so long as there is no shortage of moisture in the soil and also in shady situations beneath shrubs etc. Plants are hardy to at least -20°c, they are evergreen in warm winter areas but deciduous elsewhere. Members of this genus are rarely if ever troubled by browsing deer. Closely related to O. regalis.
Propagating it: Spores - they very quickly lose their viability (within 3 days) and are best sown as soon as they are ripe on the surface of a humus-rich sterilized soil in a lightly shaded place in a greenhouse. Keep the compost moist, preferably by putting a plastic bag over the pot. Plants develop very rapidly, pot on small clumps of plantlets as soon as they are large enough to handle and keep humid until they are well established. Do not plant outside until the ferns are at least 2 years old. Cultivars usually come true to type. Division of the rootstock in the dormant season. This is a very strenuous exercise due to the mass of wiry roots.
Best place to grow: Woodland Garden Dappled Shade; Shady Edge; Bog Garden;
Habit: Fern
Hardiness: 5-9
Growth:
Soil: Light (sandy), medium, heavy (clay)
Shade: Semi-shade, no shade
Moisture: Moist, wet
Things to keep in mind
Although we have found no reports of toxicity for this species, a number of ferns contain carcinogens so some caution is advisable. Many ferns also contain thiaminase, an enzyme that robs the body of its vitamin B complex. In small quantities this enzyme will do no harm to people eating an adequate diet that is rich in vitamin B, though large quantities can cause severe health problems. The enzyme is destroyed by heat or thorough drying, so cooking the plant will remove the thiaminase.