How to Grow Hopniss UK

Soil & Growing Conditions

Water: High; a plant of marshes, wet thickets and stream banks

Soil pH range

5 7.5

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Quick Facts

Factor	Value
Soil pH	5 - 7.5
Soil texture	High organic matter, loam, sand or shallow rocky ground
Drainage	Moist to occasionally wet
Lifecycle	Hardy herbaceous perennial climber, dying back each winter and regrowing from its tubers.

Harvest & Storage

When to pick: Tubers can be lifted in the first year but take 2-3 years to make a worthwhile crop. They form in strings along the runners, so lift carefully and replant the small ones.

Hopniss through the season

How the crop forms

Tubers are strung along the underground runners like beads. This is what makes hopniss productive, and also what makes it persistent.

A single tuber

Lifted with the runner still attached. Replant the small ones as you go and the bed keeps itself going.

A harvest

Tubers can be lifted in the first year but take two to three years to make a worthwhile crop.

Inside

NC State compares the cooked tuber to a potato but nuttier and finer in texture, with appreciably more protein.

The flower

Maroon and pink, and strongly scented. Hopniss is a legume, and fixes its own nitrogen.

Buds

Flowering comes in mid to late summer on established plants.

It climbs

A vine 8-16 feet long that will use whatever support it finds, including standing trees.

And it spreads

NC State records that it can become weedy and will spread to form colonies. Give it a contained bed rather than a mixed border.

Where it grows wild

A plant of tidal and non-tidal marshes, wet thickets and stream banks. A damp corner suits it.

In cultivation

Grown up a support in a botanical garden bed. Hardy to USDA zone 4, so most of Britain and Canada can grow it outdoors.

What the research guides add

Hopniss, also called groundnut, is a native vine grown for its tubers, and NC State flags one catch for gardeners.

• A native perennial twining vine of the bean family that grows 8 to 16 feet long; it is the tuber that is most desirable, and the only place it is cultivated as a food crop is Japan. (NC State Extension)
• It grows in sun to partial shade and needs moist conditions, preferring sandy or gravelly loams with some humus added. (NC State Extension)
• Plant tubers two to three inches deep in early spring and mulch to stop competition from weeds and grass. After one year several one-inch-thick tubers can be harvested from each plant. (NC State Extension)
• It spreads to form colonies and can become weedy. Cooked mature tubers are similar to a potato but with a nuttier flavour and finer texture. (NC State Extension)

Sources for this section

• NC State Extension: Apios americana (Plant Toolbox)

Section researched and checked on 25 October 2026 by the SoilCommander Editorial Team. How we check facts: editorial policy.

References

1. NC State Extension - Apios americana
2. Plants For A Future (PFAF) - Apios americana

2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.