How to Grow Ocas USA | Care, Pests & Disease Control

Diseases

Wet rot / stem rot

moderate

Choanephora cucurbitarum

Water-soaked wet rot with white silky mycelium

Named by Cultivariable: lower stems blacken and soften.

Oca virus diseases (Papaya mosaic virus and unidentified potyviruses)

low

Named by Cultivariable in some varieties, typically mild in impact; RHS's UK conservatory-context page reports the crop as generally disease-free, a genuine difference in growing context kept honest rather than merged.

Oca decline (symptom complex: knobbly tubers, early sprouting, reduced yields, fasciation)

low

A named symptom complex from Cultivariable: knobbly tubers, early sprouting, reduced yields, and fasciation.

Bacterial soft rot (oca tubers, causal agent not yet confirmed)

moderate

Named by Cultivariable affecting tubers; no specific bacterium identified.

Pests

Tarnished plant bug

low

Lygus lineolaris

Named by Cultivariable as targeting flowers, mainly a concern for breeders rather than tuber yield.

Wireworms

low

Elateridae (click beetle larvae, various spp.)

Named by Cultivariable as causing mostly cosmetic tuber damage, rarely a serious problem.

Vine weevil

low

Otiorhynchus sulcatus

Named by RHS as the main UK risk for container/conservatory-grown plants.

Voles

high

Microtus spp. / Arvicola spp.

Named by Cultivariable as the most damaging pest, especially at harvest time when tubers are abundant underground.

Quick Facts

Factor	Value
Sunlight	4-8 hours direct sun
Minimum survivable temp	1C
Drainage	Loose, light, well-drained (Cultivariable); RHS: loam/sand, well-drained.
Lifecycle	Tuberous, short-day perennial grown as an annual crop. RHS rates it H2 (1-5C, tolerant of low temperatures but not surviving freezing). Cultivariable notes it survives to USDA zone 9a (20-25F minimum) but most of that zone runs too hot in summer for good tuber yields.
Edible parts	tubers

At a Glance

Growth Stages

Stage	BBCH	Notes
Planting	0	Cultivariable: plant whole tubers 2-3in deep, 18in spacing between plants, 24-48in between rows for good air circulation; plant after the final frost, through August in cool climates. RHS: separate and replant tubers in autumn or spring.
Vegetative growth	3	Cultivariable: performs best in full sun where summer highs stay below 85F with cool nights; give partial shade in hotter spells. Loose, light soil with added compost or organic fertiliser supports easy tuber harvest later.
Short-day tuber initiation	4	Cultivariable: tuber formation only begins once day length drops to 12 hours or less, starting after the autumn equinox (22-23 September) -- around six weeks of short days is needed before a reasonable harvest is possible.
Harvest	8	Cultivariable: harvest no earlier than early November, with the third week of November giving roughly 80% of potential yield; loose soil makes lifting the tubers easier and reduces damage.

Harvest & Storage

When to pick: Cultivariable: harvest no earlier than early November -- tuber formation only begins after the autumn equinox once days shorten to 12 hours or less, so a third-week-of-November harvest captures roughly 80% of potential yield.

Storage

40F/4C at 90%+ humidity gives storage life over a year (Cultivariable); flavour mellows and loses acidity over 4-6 weeks if stored at room temperature instead.

Oca, Seed to Harvest

Oca in flower

A well-established planting of oca (Oxalis tuberosa) -- flowering doesn't need to be encouraged or removed for a good tuber crop, unlike some root vegetables.

Clover-like trifoliate leaves

Oca's leaves are unmistakably clover-like, in three heart-shaped leaflets -- a useful identification feature, since oca is a distant relative of common wood sorrel and shares its leaf shape.

Foliage after rain

Cultivariable notes oca performs best where summer stays below 85F with cool nights -- conditions that also keep the foliage looking fresh like this through the growing season.

An establishing young plant

Cultivariable recommends loose, light soil for oca -- not just for growth, but because it makes lifting the tubers at harvest much easier.

The harvested crop

RHS describes the tubers as fleshy and red or yellow -- exactly the colours seen here, freshly lifted from the soil after the foliage has died back.

A good harvest

Cultivariable notes tuber formation only begins after the autumn equinox once days shorten to 12 hours or less -- a harvest like this depends on getting several weeks of that short-day period before the first hard frost.

Freshly dug, roots attached

Tubers still attached to their stems and roots -- Cultivariable recommends harvesting no earlier than early November for the best yield.

A dense foliage mat

Left to spread, oca's low, sprawling habit covers the ground densely -- Cultivariable gives a typical spread of 2-3ft per plant.

Low, sprawling growth

Oca plants typically grow only around 18 inches tall, but Cultivariable notes they frequently sprawl lower than that as they spread.

References

1. Cultivariable (specialist Andean roots and tubers breeder/grower resource) - Oca (Oxalis tuberosa) growing guide

   Light: full sun in cool climates, partial shade where temperatures often exceed 80F; requires short days (12h or less) to initiate tuber formation, beginning after the autumn equinox. Soil: loose, light soil for easy harvest, tolerates poor soil, benefits from compost/organic fertiliser, pH 5.5-7.5 (optimal 5.5-7.0). Size: ~18in tall (often sprawls lower), 2-3ft spread, tubers 4-8in long, 1.5in wide. Hardiness/climate: best where summer highs stay below 85F with cool nights (low 70s F or cooler); survives to USDA zone 9a (20-25F) but most of that zone is too hot in summer; well suited to Pacific Northwest and coastal California. Planting: whole tubers 2-3in deep, 18in spacing between plants, 24-48in between rows; plant after final frost through August. Propagation: tubers, or stem/stolon cuttings rooted before tuber formation; seed has no dormancy and a short viable lifespan. Pests: voles cause significant tuber damage especially at harvest; tarnished plant bugs target flowers; wireworms cause mostly cosmetic tuber damage. Diseases: stem rot (lower stems blacken/soften), bacterial soft rot on tubers, "oca decline" symptom complex (knobbly tubers, early sprouting, reduced yields, fasciation), mild viruses including Papaya mosaic virus and unidentified potyviruses. Harvest: no earlier than early November, third week of November gives ~80% potential yield. Storage: 40F/4C at 90%+ humidity gives over a year of storage life; oca loses acidity in storage, lowest after 4-6 weeks at 70F.

2. Royal Horticultural Society - Oxalis tuberosa (oca)

   Hardiness H2 (1-5C, tolerant of low temperatures but not surviving freezing). Soil: loam, sand, well-drained, acid/alkaline/neutral pH. Sun/aspect: full sun to partial shade, east/west-facing. Exposure: sheltered. Size: 0.1-0.5m height and spread, 2-5 years to maturity. Propagation: separate and replant tubers in autumn or spring. Pests: potentially vulnerable to vine weevil. Diseases: generally disease-free. Edible use: produces edible, fleshy, red or yellow tubers, grown as a food crop as well as ornamentally.

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.