How to Grow Nasturtiums

Bush or trailing

Nasturtiums come in two growth habits. Bush types (Tropaeolum minus and compact varieties) form mounds about 12 inches tall that suit edging, beds and containers. Trailing types (T. majus) ramble up to 3 feet or more and look good spilling from hanging baskets and window boxes, covering banks or tied to a trellis. They are sometimes sold as “climbing” nasturtiums, but Wisconsin points out they have no tendrils and won’t climb on their own, so you have to tie them in.

Wisconsin lists several readily available compact varieties, including ‘Empress of India’ (crimson, good in containers), ‘Tom Thumb’ (6 to 9 inches) and the variegated ‘Alaska’ and ‘Tip Top Alaska’ series. Its dwarf ‘Baby’ series includes All-America Selections regional winners for the Northeast, Mountain/Southwest and Heartland regions. Illinois suggests ‘Moonlight’ as a trailing type for trellises.

Site and soil

Full sun gives the most flowers. Wisconsin notes that plants grow in partial shade but don’t bloom well there. In hot climates, some shade helps. The University of Maryland finds nasturtiums seem to do better in semi-shade, and UF/IFAS says the foliage stays fresher in Florida with some afternoon shade. Pick full sun in cool summers and morning sun with afternoon shade where summers are hot.

Soil should drain well and be no better than average. Cornell says they like sandy, dry ground. This is one of the few flowers that does worse in rich soil, so don’t add compost or fertilizer unless the ground is very poor.

Sowing

Nasturtiums are frost-tender and don’t like being transplanted, so sow them where they will grow after the danger of frost has passed and the soil has warmed. The dates for your zone above show when. The large seeds are easy to handle:

1. Soak seed in water for a few hours or overnight to speed germination.
2. Plant it 1/2 inch deep. Wisconsin notes the seed needs darkness to germinate, so cover it fully.
3. Space seeds 10 to 12 inches apart. Cornell allows 6 to 12 inches and UF/IFAS 12 to 18, so go closer for compact varieties and wider for trailers.
4. Keep the bed moist. Seedlings usually appear in 7 to 10 days and grow quickly in warm weather.

For a head start in short-season areas, sow indoors in peat pots 4 to 6 weeks before your last frost and plant the whole pot so the roots aren’t disturbed.

Care through the season

Water regularly, especially in hot, dry spells. Nasturtiums tolerate drought, but steady moisture keeps them blooming and keeps the leaves from turning harsh and peppery.

Picking flowers or removing spent ones prolongs bloom. If plants get leggy or tired in midsummer, Illinois recommends cutting them back lightly, and they will put out fresh growth for the rest of the season. In mixed containers, trailing types can smother their neighbors, so trim them back as needed.

The University of Maryland notes that nasturtiums grow best in early summer and fall weather. In hot-summer areas, expect plants to slow down in midsummer, and keep them watered through it.

Mild-winter regions

Nasturtium is a tender perennial, hardy to about zone 9a, and is grown as an annual elsewhere. Where frost is rare it behaves as a cool-season flower. The University of Arizona chart has seed sown from October through January in the Phoenix area, with bloom from February to May. UF/IFAS lists March-April and October-November for zone 9 and November through March for zones 10 and 11. A freeze knocks the plants back to the ground. Wisconsin warns that in warm, mild climates nasturtiums can bloom and seed year-round and may become invasive, though reseeding isn’t a problem in cold climates.

Pests and problems

• Aphids: the most common insect pest. Check new growth often, and skip pesticides on any plant you plan to eat.
• Imported cabbageworm: green caterpillars that chew holes in the leaves.
• Leafminers: winding trails inside the leaves look bad but don’t harm the plant.
• Few flowers, many leaves: too much fertilizer or soil that is too rich.
• Sudden collapse in fall: frost. The plants are tender and die at the first freeze.

Harvesting to eat

Leaves, flowers, flower buds and green seed pods are all edible. Young leaves are the most tender and flavorful, while older leaves can turn bitter. Flowers are milder than leaves, and Wisconsin notes both taste spicier in sunny, hot weather. Pick flower buds and green seed pods while they are still soft. Pickled, the pods stand in for capers. UF/IFAS says pods form about four months after sowing.

Store picked leaves and flowers in a plastic bag in the refrigerator and use them soon. If you plan to eat the plants, don’t use pesticides on or near them.