Singkamas (Pachyrhizus erosus)

About Singkamas

Singkamas (Pachyrhizus erosus) is the quintessential Filipino street snack root — the crisp, mildly sweet tuber that vendors peel, slice, and bag alongside green mango in market stalls and sidewalk stands across the Philippines. Dipped in bagoong (fermented shrimp paste) or sprinkled with salt and vinegar, singkamas offers a cooling, crunchy refreshment that Filipinos have enjoyed for centuries during the sweltering summer months.

The plant itself is a vigorous tropical legume — a climbing vine that can reach 3-6 meters in length, producing trifoliate leaves, purple or white pea-like flowers, and the prized underground tuber that gives singkamas its culinary identity. The tuber is turnip-shaped (round to slightly flattened), 10-20 cm in diameter, with papery tan-brown skin that peels easily to reveal crisp, white, juicy flesh. The texture resembles a cross between an apple and a water chestnut — simultaneously crunchy and moist, with a mild sweetness and clean, starchy flavor.

As a legume, singkamas fixes atmospheric nitrogen through root nodule bacteria, enriching the soil for subsequent crops — making it valuable in crop rotation systems practiced by Filipino smallholder farmers. The vine grows rapidly in the Philippine tropical lowlands, requiring minimal inputs once established, though the key to good tuber quality is consistent removal of flower buds to redirect the plant's energy from seed production to tuber development.

An important safety note: while the tuber is perfectly safe to eat raw or cooked, all other parts of the singkamas plant — leaves, stems, seeds, and seed pods — are toxic. The seeds contain rotenone and related compounds historically used as natural insecticide and fish poison in Southeast Asia. Only the peeled root should ever be consumed.

History & Discovery

Pachyrhizus erosus is native to Mexico and Central America, where it has been cultivated since pre-Columbian times. The Aztec name xīcamatl (from which "jicama" derives) appears in 16th-century Spanish colonial records, and archaeological evidence suggests domestication stretching back thousands of years in the Mesoamerican lowlands.

Singkamas reached the Philippines via the Manila-Acapulco galleon trade (1565-1815) — one of many New World crops that transformed Philippine agriculture during the Spanish colonial era, alongside kamote (sweet potato), kamatis (tomato), and mais (corn). The plant adapted rapidly to the Philippine tropical climate, and within a few generations, it had become deeply embedded in Filipino street food culture — so thoroughly that many Filipinos are surprised to learn of its Mexican origins.

The Tagalog name "singkamas" likely derives from a Hispanic-influenced adaptation of local naming conventions. Regional names include hikamas (Visayan), singkamas (Pampanga), and bangkuang (reflecting Malay connections). The plant spread from the Philippines throughout Southeast Asia, where it is now cultivated in Indonesia (bengkuang), Vietnam (cây đậu), Thailand (man kaeo), and Malaysia.

How to Plant Singkamas in the Philippines

Singkamas is grown exclusively from seed — direct-sown into prepared beds, as the taproot system does not tolerate transplanting well. Seeds are widely available from agricultural supply stores and local markets throughout the Philippines.

Propagation Steps

1. Prepare the planting bed: Choose a sunny location and work the soil to a depth of 30-40 cm. Singkamas tubers need loose, well-draining soil to expand — compacted soil produces small, misshapen roots. Sandy loam is ideal. Incorporate 2-3 kg of organic compost per square meter.
2. Pre-soak seeds: Soak singkamas seeds in room-temperature water for 12-24 hours before planting to soften the hard seed coat and accelerate germination from 14 days to 7-10 days.
3. Sow seeds directly: Plant seeds 3-5 cm deep, spaced 20-30 cm apart within rows, with rows 60-75 cm apart. Place 2 seeds per hole and thin to the stronger seedling after germination. Singkamas does not transplant well — always direct sow.
4. Water thoroughly: Water the bed immediately after planting and keep consistently moist until germination (7-14 days). Avoid waterlogging, which can rot seeds before they sprout.
5. Provide support (optional): Install a trellis, bamboo stakes, or string support for the climbing vine. While not strictly necessary (the vine can sprawl on the ground), trellising improves air circulation, reduces fungal disease, and makes de-flowering easier.
6. Remove flower buds religiously: Begin pinching off flower buds as soon as they appear — typically 60-75 days after planting. This is the most critical cultural practice for singkamas. Flowering and seed production divert energy from tuber growth, resulting in smaller, woodier roots. Check plants every 3-4 days and remove all buds.
7. Harvest carefully: At 4-5 months, when the vine begins yellowing, loosen soil around each tuber with a garden fork before pulling. Handle tubers gently — damaged skin reduces shelf life.

Best Planting Season

Plant singkamas at the start of the wet season (June-July) for harvest during the cooler dry months (October-December). The vine benefits from rainfall during vegetative growth, while the tuber matures and concentrates sweetness during the drier final weeks. A second planting in November is possible in irrigated areas, with harvest in March-April.

Care Guide

Sunlight

Singkamas requires full sun — at least 6-8 hours of direct sunlight daily for vigorous vine growth and tuber development. The vine grows toward available light, so trellised plants in sunny locations produce the most biomass and largest tubers. Partial shade results in spindly vines and undersized roots.

Water

Water singkamas consistently during the first 2 months of growth — every 2-3 days during dry spells, adjusting for rainfall. During tuber bulking (months 3-5), maintain moderate moisture but allow soil to dry slightly between waterings. Overwatering during the final month before harvest produces watery, less sweet tubers. Reduce watering as the vine begins to yellow to concentrate flavors in the tuber.

Soil

Loose, well-draining sandy loam is ideal — the most important factor is soil texture, not fertility. Compacted or heavy clay soil restricts tuber expansion and produces deformed, fibrous roots. If your garden has clay soil, amend with sand and organic matter, or plant in raised beds filled with loose mix. Optimal pH is 5.5-7.0. As a legume, singkamas fixes its own nitrogen, so heavy nitrogen fertilization is unnecessary and can actually reduce tuber quality by promoting excessive vine growth.

Humidity & Temperature

Singkamas thrives in the Philippine tropical lowlands — 25-35°C with moderate to high humidity. The plant is frost-sensitive and cannot tolerate temperatures below 15°C. In the Philippine climate, temperature is never a limiting factor. Singkamas performs best in areas with a distinct wet-dry seasonal pattern, which synchronizes vine growth (wet) with tuber maturation (dry).

Fertilizer

As a nitrogen-fixing legume, singkamas has modest fertilizer needs. Apply complete fertilizer (14-14-14) at 50-75 g per linear meter as a side-dressing at 30-45 days after planting. A second application at 60-75 days supports tuber bulking. Avoid excess nitrogen — it stimulates vine growth at the expense of tuber development. Potassium (from muriate of potash) during tuber bulking improves root quality and sweetness.

Pruning & De-flowering

The most critical management practice for singkamas is systematic removal of flower buds. Begin inspecting vines at 60 days and pinch off all flower clusters every 3-4 days until harvest. This single practice can double tuber weight compared to vines allowed to flower freely. Vine tip pruning (topping) at 2-3 meters can also redirect energy to the root, though this is less critical than de-flowering.

Growing Medium Options

Edible Uses & Nutrition

Singkamas occupies a unique niche in Filipino food culture — it is one of the few root vegetables consumed almost exclusively raw. Its crisp texture, mild sweetness, and high water content make it a natural refreshment food, eaten as a snack rather than a cooked vegetable in most Filipino contexts.

Edible Parts

• Tuberous root (peeled): The only edible part — crisp, white, juicy flesh eaten raw or cooked
• All other parts are TOXIC: Leaves, stems, seeds, seed pods, and flowers contain rotenone and must never be eaten

Culinary Uses in Filipino Cooking

• Raw with bagoong: The classic — peeled, sliced into sticks or wedges, and dipped in bagoong (shrimp paste). The most common way Filipinos eat singkamas.
• Street snack: Peeled and sold in plastic bags by ambulant vendors, often alongside green mango — sprinkled with salt, vinegar, or chili-salt
• Lumpiang sariwa filling: Diced singkamas provides the signature crunch in fresh spring rolls (lumpiang sariwa) — julienned and sautéed with other vegetables
• Lumpiang shanghai: Finely diced singkamas added to the pork filling for texture and moisture
• Filipino salad: Julienned raw singkamas tossed with green mango, tomato, onion, and bagoong dressing
• Atsara-style pickle: Singkamas pickled in vinegar, sugar, and pepper — a crunchy accompaniment to grilled meats
• Stir-fry ingredient: Added to ginisang gulay (sautéed vegetables) for crunch, retaining its texture even after cooking

Nutritional Information

Per 100 g of raw singkamas tuber (USDA FoodData Central):

Singkamas is extremely low in calories, high in dietary fiber (including prebiotic inulin), and about 90% water — making it one of the most hydrating and diet-friendly snack foods available. Its low glycemic index makes it suitable for diabetic diets. The inulin content supports beneficial gut bacteria, contributing to digestive health.

Air Quality & Oxygen

As an annual vine crop, singkamas provides modest but meaningful seasonal contributions to air quality. The vigorous vine's trifoliate leaves generate oxygen through photosynthesis during its 4-5 month growing season. As a legume, singkamas also fixes atmospheric nitrogen — enriching the soil and reducing the need for synthetic nitrogen fertilizers in subsequent crops.

In urban garden settings, singkamas vines grown on trellises can serve as a temporary green screen, providing partial shade and contributing to microclimate cooling during the growing season. The plant's air quality contribution is seasonal and modest compared to perennial trees, but meaningful in the context of vegetable gardens and urban growing spaces.

Toxicity & Safety

Humans — Root (SAFE): The peeled singkamas tuber is entirely safe to eat raw or cooked. No toxic compounds are present in the root flesh.

Humans — All Other Parts (TOXIC): The seeds, seed pods, leaves, stems, and flowers contain rotenone, pachyrhizin, and related rotenoid compounds that are toxic to humans and animals. Ingestion of seeds can cause severe gastrointestinal distress, convulsions, and potentially death. Historically, singkamas seeds were used as fish poison (tubli fishing) and as insecticide powder in the Philippines and throughout Southeast Asia. Never consume any part of the plant except the peeled root.

Pets: The ASPCA does not have a specific listing for singkamas/jicama. The root is generally considered safe for dogs in small amounts (raw, peeled, cut into pieces). The seeds, leaves, and vine are toxic to pets due to rotenone content and must be kept away from animals. If you grow singkamas in a garden accessible to pets, ensure they cannot reach fallen seed pods or chew on the vine.

Common Pests & Diseases in the Philippines

• Bean fly (Ophiomyia phaseoli): Larvae mine through stems near the base, causing wilting and plant death in young seedlings. Apply systemic insecticide at planting or use seed treatment. Most critical during the first 3 weeks after emergence.
• Aphids: Colonize young shoots and leaf undersides, causing curling, stunting, and honeydew production. Control with neem oil spray or insecticidal soap. Aphids also vector viral diseases.
• Pod borers: If flowers are not removed, developing pods attract borer insects. Since seed production should be prevented anyway (for tuber quality), consistent de-flowering eliminates this pest pathway.
• Root-knot nematodes (Meloidogyne spp.): Microscopic worms that cause galls on roots, reducing tuber quality and yield. Rotate crops — don't plant singkamas in the same bed consecutively. Incorporate organic matter to promote nematode-suppressing soil biology.
• Powdery mildew: White fungal coating on leaves during cool, humid periods. Improve air circulation through trellising and reduce overhead watering. Severe cases respond to sulfur or potassium bicarbonate sprays.
• Tuber rot (Rhizoctonia, Sclerotinia): Fungal decay of the tuber in waterlogged soil. Ensure good drainage and avoid overwatering, especially during the final month before harvest.

Frequently Asked Questions

Sources

• Plants of the World Online — Pachyrhizus erosus (L.) Urb. Royal Botanic Gardens, Kew.
• PROSEA (Plant Resources of South-East Asia) — Pachyrhizus erosus species profile.
• USDA FoodData Central — Jicama (yambean), raw. FDC ID: 170073.
• FNRI-DOST — Philippine Food Composition Tables: Singkamas nutritional data.
• Sørensen, M. (1996). Yam Bean — Pachyrhizus DC. Promoting the conservation and use of underutilized crops. IPGRI.
• Philippine Statistics Authority — Root crop production statistics.

This guide is for informational purposes. Only eat the peeled root — all other plant parts are toxic. Consult local agricultural extension offices (ATI, DA-RFO) for region-specific growing recommendations.