Nasturtium

Direct sow after your last frost, soaking the seed first

Once all danger of frost has passed, soak the seeds in water for several hours or overnight, then sow them half an inch deep and 10 to 12 inches apart in well-drained soil in full sun. Keep the seedbed moist; expect germination in 7 to 10 days. Nasturtium is a frost-tender warm-weather annual, and its large hard-coated seed germinates faster once soaked. The half-inch depth matters because the seed needs darkness to germinate. Plants in partial shade bloom poorly.

Interplant with squash and brassicas as a companion

When you sow, put nasturtium alongside squash and pumpkins, and among broccoli and cabbage. This is one of the few companion pairings with research behind it rather than chart folklore. Trials have shown nasturtium reduces squash bug populations, and an Iowa study found that nasturtium and marigold each helped reduce squash bug and cucumber beetle damage. In brassicas, thyme, onion and nasturtium reduced cabbage looper and imported cabbageworm damage in broccoli.

⚠ Nasturtium is itself a favorite of aphids and imported cabbageworms, so site it where you can watch it rather than assume it repels everything.

If you start indoors, use peat or paper pots and plant the whole pot

In short-season gardens, start seed indoors 4 to 6 weeks before your last expected spring frost, but sow into peat or paper pots rather than plastic cells. Set the entire pot into the ground after frost danger passes without disturbing the roots. Nasturtium resents root disturbance and does not transplant well, so a pot that goes into the soil intact avoids the transplant shock that stalls or kills bare-rooted seedlings.

Water regularly to keep the leaves mild and the bloom coming

Although nasturtium tolerates drought, water it regularly through the growing season. Keep plants well watered if you are eating the leaves. Steady water moderates the spiciness of the leaves and flowers, while heat-stressed plants turn harshly pungent. Regular water also sustains strong blooming rather than merely keeping the plant alive.

Withhold fertilizer unless the soil is genuinely poor

Skip the feeding on average garden soil. Only fertilize if your soil is extremely poor, and then lightly. Nasturtium grows best in poor to average, well-drained ground and tolerates drought and neglect. High fertility pushes nasturtium into leaf at the expense of bloom, so a well-fed plant gives you a mound of foliage and few of the flowers you actually want. This is the single most common way growers ruin the crop.

Deadhead through bloom, and cut back plants that go leggy

Keep picking or deadheading the flowers once bloom begins. If plants decline or go leggy by midseason, cut them back lightly and they will push new growth for the rest of the season. Deadheading or picking the flowers prolongs blooming (UW-Madison Extension), so harvesting the crop and maintaining it are the same act. Illinois Extension adds that plants that decline or go leggy in summer can be cut back lightly and will regrow for the remainder of the season.

Scout for aphids, cabbageworms and whiteflies, and control them without spray

Check leaf undersides and growing tips for aphids, whiteflies and imported cabbageworms. Knock aphids off with a jet of water, pick caterpillars by hand, and pull out any plant that has become an aphid colony. Leafminers may make serpentine trails on the leaves, but this does not damage the plant and needs no action. These are the pests extension records on nasturtium, and because you eat the leaves, buds, flowers and pods, the plant is a food crop where physical removal is the appropriate control rather than a chemical one.

⚠ Every part of this plant is eaten, so do not treat it with pesticides. Systemic insecticides are taken up into the tissue and cannot be washed off. Do not eat nasturtium from a florist or a cut-flower source. Plants bought from a garden center or nursery may have been treated: flush the soil with water and grow the plant on yourself before eating any part of it.

Pick leaves, flowers and green pods the day you will eat them

Harvest young leaves and open flowers all season, taking the youngest leaves for the most tender flavor. Pick blossoms early or late in the day while they are cool, on the day you will use them and no more than a day early. Wash gently, dry, and refrigerate in plastic bags. Gather flower buds and immature green seed pods to pickle as a caper substitute. Blossoms are thin-tissued and collapse quickly once cut and warm, so freshness at harvest is what the eating quality depends on. Older leaves turn bitter, and the seed pods must be taken while still green and soft, before they harden into seed.

⚠ Introduce any new edible flower into your diet slowly, since some people react to plants considered safe to eat.