Durable, Delectable Nasturtiums
I can't think of better annual flowers than nasturtiums. Not only are they fast and easy to grow--a bonus where the growing season is short -- but they look and taste good, too.
In fact, nasturtiums are so easy to grow that many home gardeners overlook them. To provide quick summer color, I plant nasturtiums at the ends of raised beds or along the edge of a flower border. The plants grow well in full sun or part shade, and bloom all season. And you can eat almost the whole plant. What more could a hurried, hungry gardener ask?
The nasturtiums home gardeners know and love are the two most common species: Tropaeolum majus, the trailing type or T. minus, the bush type. But note that some bush varieties trail a bit, and some trailers are less vigorous than others and almost bushlike. Although most often grown as annuals, nasturtiums are, botanically, herbaceous perennials; that is, they die to the ground in fall and grow again the next spring. In frost-free areas such as coastal California, they grow like weeds, with 6-inch diameter leaves atop 20-foot-long stems sprawling year-round. A few lesser-known species are perennial to USDA Hardiness Zone 7, and although they're a challenge to grow, they offer gardeners unique flower and foliage forms.
When you're choosing varieties to grow, first decide whether you want bush or trailing kinds. Consider the unusual double flowers of the camellia-like types, too. In addition, some varieties have variegated foliage that's attractive even when the plant is not flowering. The accompanying chart provides more details about the best varieties.
Trailing Nasturtiums. These nasturtiums have bigger flowers and leaves but don't produce as many flowers as the bush varieties do. They look great in hanging baskets, sprawling on a bed like a ground cover, or cascading over the edge of a raised bed. A vigorous trailing type, such as 'Tall Trailing Mix', can be trained on a fence as a climber. I plant this variety between tepees suorting pole and scarlet runner beans, and by midsummer I have a striking tepee of multicolored nasturtium flowers and delicious scarlet runner and pole beans to harvest and enjoy. 'Jewel of Africa Mix', another notable trailing type, features variegated leaves and a colorful combination of flowers.
Bush Nasturtiums. My favorite bush type is the variegated 'Tip Top Alaska Mix', an improved selection from the original 'Alaska' variety. Although it's not as floriferous and vigorous as other bush varieties, the vivid leaf markings more than make up for the meager flowering. Bush-type nasturtiums look great in window boxes and containers, or edging a path or border.
Flower Forms and Colors. Although several seed mixes, such as Whirlybird, offer a variety of flower colors, some of my favorites are the single-colored varieties. The scarlet flowers of 'Empress of India' contrast beautifully with its blue-green leaves. Although listed as a bush form, this one tends to trail to 1 to 2 feet long. 'Moonlight' (yellow and trailing) and 'Salmon Baby' (salmon with bush habit) offer more dramatic single-hued flower color.
The most unusual varieties have double flowers. These actually aren't new: They are rediscovered heirlooms dating back to the late nineteenth century. They look much like camellias or dahlias, so you'd be hard-pressed to recognize these flowers as nasturtiums. 'Apricot Twist' (apricot splashed with red) and 'Hermine Grashoff' (red) are two trailing types that don't form seeds and are available only as rooted cuttings. These nasturtiums aren't as vigorous as other trailing types and grow better in hanging baskets or containers.
How to Grow Nasturtiums
Not only are nasturtiums versatile and colorful, but they also are easy to grow and thrive on neglect. The large seeds germinate within a week and begin to flower about a month later, making them great choices for children or beginning gardeners. Sow in the garden about a week before the last frost date for your area. They can also be started indoors, but their taproots make them difficult to transplant. If you do grow them indoors, start them in peat pots, and when roots show through the pots' drainage holes, transplant the seedlings into the garden still in their pots.
Nasturtiums love cool, damp conditions and flower best in full sun. However, mine have also done well in part shade. In hot-summer areas, provide some afternoon shade, or cut them back in midsummer and allow the plants to regrow for a fall flower show.
For best flowering, grow nasturtiums in well-drained soil. They don't like excessive fertilization, especially nitrogen. If the soil is too rich, the plants will respond with large leaves and fewer flowers. Aphids are the main pests, but they seldom harm the plants unless it's a major infestation. Check the undersides of leaves for aphids, and eliminate them by spraying the plants with insecticidal soap.
Adding flowers to food has long been a custom in many cultures around the world. For centuries, Chinese cooks have used lotus, chrysanthemum, and lily flowers or buds in their recipes. American colonists added marigolds to mutton broth. Nasturtiums, among the best-known edible flowers, are popular with chefs. Not only do they dress up a plate, but they're high in vitamins A, C (10 times as much as in lettuce), and D. The leaves, flowers, buds, and seeds are all edible, with a peppery flavor that adds a zing to any dish.
Before harvesting a whole patch of nasturtiums, taste a few flowers first. Their flavor may vary depending on the plant, and on soil and weather conditions. Generally, the more stressed a plant is (by lack of water or nutrients, or exposure to adverse weather), the more pungent its flavor.
When harvesting the leaves, select young, tender ones. Harvest buds or fully opened flowers in midmorning, ideally on a cool day. The entire blossom is edible, but if you find the organs inside the petals to be bitter, you can remove them with scissors. Gently wash and dry the flowers and leaves, and store them in a plastic bag in the refrigerator.
In the kitchen, add the flowers to salads and stir-fry dishes. You can also stuff them and cook them with pasta. More ambitious cooks can try grinding the seeds for use as a pepper substitute, griding them for oil, or pickling the flower buds or immature seedpods and use as a substitute for capers.
Growing Unusual Perennial Nasturtiums
Several trailing and climbing species of Tropaeolum have unusual flower and leaf forms. However, they're hard to find and harder to grow (especially from seed) because they're adapted only to particular growing conditions. To grow best, these types require mild winters (hardy to zone 7) and cool, humid summers similar to those in England. Or grow them in a cool greenhouse. They like a location in part shade to full sun and prefer their roots be kept moist and cool. Most climbers twine around a support. The aggressive types grow well over trellises or pergolas.
The easiest of these nasturtiums to grow is T. tuberosum. Started from a tuber, it produces a vigorous 15-foot vine with 2-inch-diameter orange-and-yellow flowers. The flowers don't bloom until fall, but the three-lobed, partly divided foliage makes this vine attractive even when it's not blooming. In climates colder than zone 7, the edible tubers can be lifted in fall and stored in winter as you would dahlias. For an earlier-blooming variety, try 'Ken Aslet'.
Scotch flame flowers (T. speciosum). are relatively easy to grow and are available as plants. The 6-foot vines with ferny leaves produce 2-inch vivid scarlet lobelia-like flowers for several weeks in July. They aren't as aggressive as T. tuberosum, but they do spread by roots as deep as 2 feet, so they can become invasive.
Wreath nasturtium (T. polyphyllum) is available only from seed. The 3- to 4-foot vine grows from a rhizome (an underground stem) and produces beautiful gray-blue leaves and 1-inch golden yellow cup-shaped flowers. The plant blooms for only two to three weeks in early summer, then dies back until the next spring. Wreath nasturtium is best used as a low-growing rock garden plant because the leaves and flowers stand only about 3 inches tall.
T. tricolor is the most difficult to grow of the four. Furthermore, it's available only from seed. The fragile 3-foot-long vine produces spurlike yellow-centered, orange-red blooms fringed in purple.
Charlie Nardozzi is senior horticulturist at National Gardening Association.
Photography by Suzanne DeJohn/National Gardening Association