Nasturtium

Nasturtium (Tropaeolum majus) is the fastest edible flower you can grow from seed - 35-52 days to first bloom, with minimal inputs and enough uses in the kitchen that calling it a companion plant understates it. The entire plant is edible: flowers at $8-12/lb at specialty markets (USDA AMS Specialty Crop Market News, 2023), peppery young leaves that stand in for watercress in salads, and unripe seed pods pickled exactly like capers. One $1.99 packet covers all of that.

What it actually is

Nasturtium belongs to the family Tropaeolaceae - it is unrelated to watercress (Nasturtium officinale) despite sharing a common name based on similar peppery flavor compounds (glucosinolates, specifically glucotropaeolin). The round, shield-shaped leaves and the spurred flowers in orange, yellow, and red shades are distinctive and unmistakable.

Two main growth habits exist: compact bush types (‘Jewel Mix’, ‘Alaska’) that reach 12-15 inches and trailing/climbing types (‘Spitfire’, ‘Hermine Grashoff’) that sprawl or climb to 6-10 feet. Bush types suit bed edges and containers; trailing types work on trellises or as ground cover. ‘Alaska’ has variegated leaves and is worth growing for ornamental value alone if flowers are secondary.

Nasturtiums are half-hardy annuals - frost-sensitive but cool-weather tolerant. They actually produce better in cooler conditions (55-65°F). In hot weather, they tend to flower less and produce more foliage. In very hot climates (zones 9-10), grow them as fall and winter annuals.

The ROI case

Fresh edible nasturtium flowers retail at $8-12/lb at specialty grocers (USDA AMS Specialty Crop Market News, 2023) and often higher at farmers markets where direct-to-restaurant sales run $15-20/lb for cleaned, same-day-picked flowers. A $1.99 seed packet contains 20-30 large seeds - more than enough for a productive planting.

Beyond flowers, the culinary triple play adds value. Young leaves contain the same peppery glucosinolates as watercress and can substitute for it in salads, sandwiches, and as a garnish - watercress runs $8-12/lb at retail. Unripe green seed pods picked before they mature and pickled in brine are a convincing caper substitute; capers run $15-25/lb at grocery stores. None of these substitutions requires restaurant-quality precision - they just taste good.

Nasturtiums self-sow, though less aggressively than borage. In zones 6-9, dropped seed germinates reliably the following spring.

Growing requirements

Direct sow nasturtium seeds where they are to grow - they have a long taproot and resent transplanting. Sow after the last frost date, 0.5 inch deep, 6 inches apart. Germination in 7-14 days at soil temperatures of 55-65°F. Soaking seeds overnight speeds germination.

Soil pH of 6.0-7.5. Nasturtiums are most productive in poor to moderately fertile soil. Rich, heavily amended soil with high nitrogen drives leaf production at the expense of flowers - a common complaint from gardeners who amend everything heavily before planting. If your soil has been well-composted for other crops, plant nasturtiums in a less-amended corner or skip fertilizer entirely.

Water lightly once established - 0.5-1 inch per week. Overwatering and high humidity increase aphid pressure and reduce flowering. Drought stress is tolerated better than wet roots.

Partial shade works in hot climates to extend the season. In cool climates (zones 4-6), full sun maximizes flower production.

What goes wrong

Aphids - specifically the black bean aphid (Aphis fabae) and the nasturtium aphid (Aphis nasturtii) - colonize nasturtiums heavily, to the point that many gardeners intentionally grow nasturtiums as a trap crop to draw aphids away from nearby vegetables. This is one of the more reliable companion planting strategies because it exploits a real aphid preference rather than vague repellent claims. The trade-off: if you’re growing nasturtiums for harvest, monitor aphid pressure closely and knock them off with water or apply insecticidal soap before infestations establish.

Flea beetles (Phyllotreta spp.) create small round holes in leaves. Damage is mostly cosmetic. Row cover over young seedlings prevents flea beetle damage during the most vulnerable stage.

Cucumber mosaic virus (CMV) causes mosaic discoloration and leaf distortion. Aphids spread it. Controlling aphid populations is the primary prevention.

Powdery mildew (Erysiphe sp.) appears late in the season on crowded plantings. Thin plants for better airflow.

Harvest and storage

Harvest flowers in the morning just as they fully open. Pinch the flower off at the spur where it meets the stem. Regular harvesting encourages continued production - allowing flowers to go to seed signals the plant to wind down.

Flowers last 4-6 hours at room temperature, 24-48 hours refrigerated between barely-damp paper towels. They do not dry well.

Young leaves (first two to three sets) are most tender and least fibrous. Harvest these the same day you use them; they wilt quickly once cut.

Unripe seed pods for pickling: harvest when pods are green and still plump but before they begin to yellow or dry. The three-lobed pod clusters should feel firm. Bring to a quick boil, pack in 5% brine solution with garlic and herbs, and process using standard water-bath canning or refrigerate for immediate use. Processed pickled nasturtium seeds keep 6-12 months.

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Related crops: Cucumber, Zucchini

Related reading: Companion Planting Basics - what the evidence actually says about nasturtiums as a trap crop and aphid management