Oxalis tuberosa (Oca (New Zealand Yam))
Oxalis tuberosa (Oca (New Zealand Yam))
Contents
- Introduction & History
- Botanical Description
- Varieties & Selection
- Planting & Sowing
- Climate & Hardiness
- Growing & Training
- Watering & Feeding
- Propagation & Seed Saving
- Diseases & Pests
- Companion Planting & Crop Rotation
- Container Growing
- Harvesting & Storage
- Culinary Uses & Nutrition
- Preserving & Fun Facts
- Seasonal Care Calendar
- Frequently Asked Questions
Introduction & History
Oca (New Zealand Yam) (Oxalis tuberosa) is a perennial tubers vegetable in the Oxalidaceae family, growing to 30 cm tall with a 20 cm spread. It develops red/yellow/pink tubers ready for harvest in approximately 180 days from sowing. Hardy in USDA zones 3-10, it thrives in full sun with moderate watering and prefers soil pH 5.8-6.5.
Harvested part: tuber • USDA zones: 3-10 • Sowing: tuber/slip
History & Origin
Tubers sustained entire civilizations — potatoes fed the Inca Empire, sweet potatoes crossed the Pacific to Polynesia, and yams anchored West African agriculture. Their underground growth habit provides resilience against storms, grazing, and some pests. Oca has been cultivated as a valued garden variety, selected for its red/yellow/pink tubers and reliable performance across a range of growing conditions.
Botanical Description
Oxalis tuberosa is a perennial member of Oxalidaceae, forming a bushy/compact plant reaching 30 cm tall. It develops underground tubers with red/yellow/pink skin. Stems grow to 30 cm with green foliage. The root system is deep and taproot-based.
| Height | 30 cm |
| Spread | 20 cm |
| Growth habit | Perennial |
| Foliage | green |
| Flowers | yellow |
| Fruit colour | red/yellow/pink |
| Fruit shape | small finger-shaped tuber |
| Harvested part | tuber |
Varieties & Selection
Within the Oxalis genus, numerous varieties have been developed for different climates, uses, and growing conditions. Select varieties suited to your growing conditions, space, and culinary preferences. Disease-resistant varieties reduce the need for chemical intervention.
Planting & Sowing
Grow in full sun (6-8+ hours direct) in well-drained, fertile soil with pH 5.8-6.5. Plant tuber/slip when soil reaches 10°C. Space plants 20 cm apart in rows 75 cm apart.
| Sun requirement | Full Sun |
| Soil pH | 5.8-6.5 |
| Sowing method | Tuber/Slip |
| Sowing depth | 5 cm |
| In-row spacing | 20 cm |
| Row spacing | 75 cm |
| Germination temp | 20-28°C (optimum) |
| Days to germination | 0 days |
| Min soil temperature | 10°C |
| Water needs | Moderate |
Climate & Hardiness
Oca grows in USDA zones 3-10 and tolerates temperatures down to -2°C. Protect from hard frosts with fleece or cloches. In mild climates, autumn sowings can overwinter for early spring harvests.
🌍 Origin Map
Origin: South America
Growing & Training
Oca grows as a self-supporting plant and requires no special training or staking.
Group-Specific Growing Guide
Tubers are modified underground stems (potatoes, Jerusalem artichokes) or roots (sweet potatoes, yams) that store starch as energy reserves. Potato tubers form on stolons in response to short day lengths and cool soil temperatures (15–18°C). Hilling — mounding soil around stems — increases tuber-bearing stolon length and prevents greening (solanine accumulation from light exposure, which is toxic). Cut seed potatoes should be cured for 2–3 days before planting to form a protective callus layer. Sweet potatoes, despite the similar name, are Convolvulaceae (morning glory family) and are propagated from vine cuttings (slips), not tuber pieces.
Watering & Feeding
Watering
Water deeply once or twice per week, allowing the top 2-3 cm of soil to dry between waterings. Increase frequency during heatwaves and fruiting. Consistent moisture prevents cracking and blossom end rot.
Feeding
Moderate feeder. Avoid high-nitrogen fertilizer which promotes leaf growth at the expense of roots. Apply balanced or high-potash feed. Do not use fresh manure — it causes forking in root crops.
Propagation & Seed Saving
Seed saving difficulty: tuber (vegetative). Follow standard seed saving protocols for Oxalidaceae. Ensure proper isolation distances for cross-pollinating species.
Diseases & Pests
Common Diseases
Potato Blight (Phytophthora infestans): Brown patches on leaves spreading rapidly in wet weather. Caused the Irish Famine. Spray copper preventively, grow early varieties. Scab (Streptomyces scabies): Rough corky patches on tuber skin. Cosmetic — avoid lime before planting, water during tuber formation. Blackleg (Pectobacterium): Black slimy stem base, plants topple. Use certified seed, plant in warm soil, remove affected plants. Eelworm / Potato Cyst Nematode: Stunted growth, yellow lower leaves. Rotate 6+ years, use resistant varieties, grow trap crops (Solanum sisymbriifolium). Wireworm: Larvae bore neat holes through tubers. Most common in newly-converted grassland. Mustard green manure helps reduce populations.1. Cultural controls — crop rotation, resistant varieties, proper spacing, good hygiene (remove debris, sterilise tools)
2. Physical controls — insect mesh, fleece barriers, slug traps, hand-picking, companion planting
3. Biological controls — encourage natural predators (ladybirds, lacewings, hoverflies, ground beetles); use parasitic wasps, nematodes, or Bt spray
4. Chemical controls — last resort only; organic options (neem oil, pyrethrum, copper fungicide, insecticidal soap) before synthetic products
Companion Planting & Crop Rotation
Companion planting works through multiple mechanisms: aromatic plants repel pests (basil deters whitefly on tomatoes), deep-rooted plants break compaction for shallow-rooted neighbours, and nitrogen-fixing legumes enrich soil for heavy-feeding brassicas.
Antagonistic relationships include allelopathy (chemical growth inhibition), shared pest/disease vulnerability, and direct competition for the same soil nutrients or root zone space.
Crop Rotation
Oca belongs to no specific rotation group. It can be fitted into most rotation schemes flexibly. Avoid planting in the same spot annually to prevent soil-borne disease buildup.
Container Growing
Oca can be grown in containers. Use a pot at least 20 cm diameter and 20 cm deep. Ensure excellent drainage and feed every 2 weeks with liquid fertilizer once fruiting/growing begins.
• Drainage: Ensure generous drainage holes; use crocks or mesh at the base to prevent compost washout
• Feeding: Container compost nutrients deplete in 6–8 weeks; begin liquid feeding fortnightly from this point
• Watering: Check moisture daily; the 'finger test' (dry to 2 cm depth = water needed) prevents both over- and under-watering
• Position: Most vegetables need 6+ hours of direct sunlight; rotate containers weekly for even growth
• Insulation: In hot weather, double-pot (pot inside a larger pot with insulating gap) to prevent root overheating
Harvesting & Storage
Harvest Oca when tubers reach full size but before over-maturity. Roots are typically ready 180 days after sowing. Test-dig one root to check size before harvesting the row. Use a fork rather than a spade to avoid damage.
Storage
Store Oca in cool dry conditions. Expected storage life: 8 weeks under optimal conditions. Cure in warm, humid conditions for 1-2 weeks before long-term cool storage (2-4°C, 90-95% humidity). Don't wash before storing.
Preservation Methods
Root cellar: Store unwashed in sand/sawdust at 2-4°C, 90-95% humidity. Freezing: Blanch cubed/sliced pieces 3 minutes, cool rapidly, freeze. Canning: Pressure can only (low-acid). Dehydrating: Slice thin, dehydrate at 52°C for 6-10 hours.
Culinary Uses & Nutrition
Potato texture depends on starch content: floury/mealy (high starch) for baking/mashing, waxy (low starch) for salads/boiling. Never eat green potatoes — the green color indicates solanine, a toxic glycoalkaloid. Oca is a versatile ingredient used across multiple cuisines.
Preserving, Succession & Planning
Root cellar: Store unwashed in sand/sawdust at 2-4°C, 90-95% humidity. Freezing: Blanch cubed/sliced pieces 3 minutes, cool rapidly, freeze. Canning: Pressure can only (low-acid). Dehydrating: Slice thin, dehydrate at 52°C for 6-10 hours.
Year-Round Growing Calendar
Maximise your productivity with Oxalis tuberosa by planning across the full year:
- Late winter (Feb–Mar): Order seeds, clean and repair equipment, plan crop rotations, start indoor sowings for warm-season crops
- Spring (Apr–May): Direct sow hardy crops, transplant indoor-started seedlings after hardening off, apply compost and mulch
- Summer (Jun–Aug): Main growing and harvesting season; succession sow for autumn; water consistently; monitor for pests
- Autumn (Sep–Nov): Harvest storage crops, sow overwintering varieties, clear spent plants, incorporate green manures
- Winter (Dec–Jan): Process and store harvests, plan next season, maintain tools, order seed catalogues
Frequently Asked Questions
How long does it take to grow Oca (New Zealand Yam)?
Oca (New Zealand Yam) typically takes approximately 180 days from planting to harvest, depending on variety, climate, and growing conditions.
What are the best growing zones for Oca (New Zealand Yam)?
Oca (New Zealand Yam) grows well in USDA hardiness zones 3-10. In colder zones, start seeds indoors and transplant after the last frost.
Can I grow Oca (New Zealand Yam) in containers?
Yes, Oca (New Zealand Yam) is well-suited to container growing. Use a pot at least 20 cm in diameter with good drainage.
When should I plant Oca (New Zealand Yam)?
Direct sow outdoors after all frost risk has passed and soil temperature reaches 10°C.
What pests affect Oca (New Zealand Yam)?
Colorado potato beetle, wireworm, aphids, slugs, cutworms, leatherjackets, potato tuber moth, flea beetles
Seasonal Care Calendar
🌱 Spring (Mar–May)
Water: Regular as growth resumes
Feeding: Apply compost and balanced feed
Direct sow or transplant. Protect from late frosts with fleece. Begin succession sowing.
☀️ Summer (Jun–Aug)
Water: Consistent deep watering
Feeding: Regular liquid feed
Peak harvest. Continue succession sowing for autumn crops. Monitor for pests and diseases.
🍂 Autumn (Sep–Nov)
Water: Reduce gradually
Feeding: Final feed early autumn
Late harvest. Protect with cloches for extended season. Sow overwintering varieties.
❄️ Winter (Dec–Feb)
Water: Minimal
Feeding: None
Harvest overwintered crops. Maintain cold frames. Plan rotations and order seeds.