Nasturtium

Nasturtium makes the same mistake many gardeners do — it responds to rich soil by putting on an impressive show of foliage while forgetting the point. In a heavily composted or fertilized bed, you may end up with a dense, lush mat of round green leaves and almost no flowers. The plant is not sick; it's just comfortable. Planted in a lean, average spot — the strip along a path, the edge of a gravel bed, the corner that never gets amended — it will flower generously all season.

The seeds are large and easy to handle, which makes nasturtiums one of the better plants for direct sowing. Sow them at your last frost date, about half an inch deep, and expect germination in 7 to 12 days once the soil is above 60°F. They don't like root disturbance, so if you're transplanting, keep the cells undisturbed and move them promptly. Trailing varieties like Empress of India can spread 2 to 3 feet; compact types like Jewel Mix and Alaska stay under 12 inches. Plan spacing accordingly.

The entire plant is edible. Leaves, flowers, and the unripe seed pods are all used in the kitchen. The flavor is peppery, similar to watercress — the flowers less so than the leaves, and the leaves less so than the seeds. Pickled nasturtium seeds are sometimes used as a caper substitute. The flowers are useful as a garnish or in salads, though the flavor is strong enough that a few go a long way. For harvest, pick flowers in the morning before heat sets in.

As a trap crop, nasturtiums have a genuine and observable function: black bean aphids in particular seem to prefer nasturtium foliage to cucumbers, squash, and brassicas planted nearby. This doesn't eliminate aphids from the garden, but it can concentrate them on the nasturtium, where you can deal with them in one place rather than chasing them across multiple crops. If the nasturtium becomes heavily infested, cut the affected stems off and dispose of them rather than leaving the aphid colonies to spread.

Nasturtiums are killed by frost but self-sow readily in most climates. The seeds are large and visible, so it's easy to collect them — harvest the round, wrinkled seeds as they form and dry on the plant, and store them in a paper envelope in a cool place. Or let some scatter on their own and see where they show up the following spring. In mild-winter zones, the plant can sometimes behave as a short-lived perennial.