Nasturtium

Nasturtium (Tropaeolum majus) is a warm-weather annual with long stems, round, parasol-like leaves and spurred, five-petaled flowers in cream, yellow, orange, red and burgundy. It comes from Central and South America and is an easy-to-grow tender perennial that’s grown as an annual in cold climates.

Bushy or trailing. Depending on the variety, plants either form low mounds or trail up to 3 feet (90 cm); compact types stay about 12 inches (30 cm) tall, which makes them good for edging. Trailing or “climbing” types can grow up to 10 feet (3 m) and quickly cover fences and trellises, but they need support to climb.

Good to eat. The leaves, flowers and seed pods are edible, with a slightly peppery taste like watercress.

Sow outdoors after frost. Nasturtiums don’t transplant well, so it’s best to sow the seeds straight into the garden once the danger of frost has passed. In the UK, gardening experts give March to May as the time to sow outdoors.

Sow ½–1 inch deep and cover the seeds. Sow ½ to 1 inch (1.3–2.5 cm) deep and cover the seeds, because they need darkness to germinate. Soaking them in water for a few hours or overnight before sowing can improve germination. Keep the seedbed moist, and expect seedlings in 7 to 14 days at 60–65 °F (16–18 °C).

Or start them indoors. For earlier flowers, sow in peat pots indoors 4 to 6 weeks before your last expected spring frost.

Spacing. Space plants 8 to 12 inches (20–30 cm) apart. In a hanging basket or a 10-inch (25 cm) container, thin to 3 to 5 plants.

Sun and soil. Plant nasturtiums in well-drained soil in full sun. They’ll grow in partial shade but won’t bloom well there. Poor to average soil is best, and some afternoon shade helps in hot summers. Rich soil isn’t a good idea: too much nitrogen gives you more leaves than flowers.

Pots and baskets. Trailing types are useful in hanging baskets and window boxes or tumbling down walls, and nasturtiums do very well in containers.

Watering. Nasturtiums like dry soil and tolerate drought, but water them regularly through the season to keep them flowering strongly. Well-watered plants also have milder-tasting leaves and flowers.

Feeding. Don’t fertilize unless your soil is extremely poor: high rates of fertilizer give more leaves and fewer flowers.

Deadheading and trimming. Deadheading or picking the flowers keeps the plants blooming. If plants get leggy or tired in summer, cut them back lightly and they’ll regrow for the rest of the season. In mixed containers, trim them now and then so they don’t crowd out their neighbors.

Support. Climbing and trailing varieties need a trellis or other support to climb.

The most common pests are aphids and the caterpillars of the imported cabbageworm. Watch for whiteflies and mealybugs too; gardening experts also lists glasshouse whitefly and glasshouse red spider mite. Leafminers may leave winding trails in the leaves, but these don’t harm the plant.

Nasturtiums can be affected by virus diseases. They also self-seed, which can make them spread.

Pick flowers when they’re fully open; leaves can be picked at any time. Young leaves are the most tender and flavorful, while older leaves can turn bitter. The flower buds and unripe seed pods are edible too, and have been compared to capers when pickled.

Keep picked leaves and flowers in plastic bags in the refrigerator.

Eating. Nasturtium leaves, buds, flowers, pods and seeds are edible, with a spicy, peppery taste. Plants stressed by heat can produce leaves and flowers that taste stronger than most people like.

Skin. Gardening experts list garden nasturtium as a skin allergen and recommends wearing gloves when handling it.

Pets. Pet poison experts list Tropaeolum majus as non-toxic to dogs, cats and horses, with no records of toxic ingestion. Gardening experts’s plant database, however, flags it as a problem for cats, dogs and horses without giving details. Don’t confuse garden nasturtium with watercress, whose botanical name is Nasturtium officinale: it’s a different plant, and pet poison experts list it as toxic to dogs, cats and horses.