USDA Zone 10 covers the warmest parts of the United States — South Florida, the southern tip of Texas, coastal Southern California and Hawaii — with average winter lows of 30 to 40°F. Frost is rare here: the average last spring frost falls between January 15 and 30, and the average first autumn frost between December 15 and 31. Frost dates are averages and ranges, not exact dates — they vary by microclimate, elevation and year, so check your local extension service before you plant.
This guide covers when to plant nasturtiums zone 10, and what soil, spacing, sun, water and care it needs in Zone 10.
Zone 10 at a glance
| Detail | Zone 10 guidance |
|---|---|
| Average last spring frost | Jan 15–30 (average/range; frost rare) |
| Average first autumn frost | Dec 15–31 (average/range; frost rare) |
| Winter low | 30 to 40°F |
| Days to germination | 7–14 days |
| Days to maturity | 50–60 |
| Sowing | direct sow |
| Sun | full sun |
| Soil pH | 6.0–7.5 |
| Spacing | 8–12 inches |
| Water needs | moderate |
When to plant nasturtiums in Zone 10
Nasturtiums are an easy, cheerful Zone 10 flower — they love heat, flower for months, and the leaves and flowers are edible, which makes them a favourite with kitchen gardeners. Sow seed outdoors from March through late summer, and sow a fresh batch every few weeks for continuous flowers and leaves. Because the average last frost falls between January 15 and 30 and frost is rare, there is no need to wait for a late-spring date. Work back from the frost dates rather than from a calendar date: the planting calendar hub gives the Zone 10 picture month by month. In the mildest parts of Zone 10, nasturtiums sown in autumn will flower through the winter.
Starting nasturtiums in Zone 10
Sow seed directly where the plants will grow — nasturtiums resent transplanting. Soak the seed overnight to speed germination, then sow about half an inch deep in warm soil; seeds germinate in 7–14 days. Thin seedlings to their final spacing once they have a few true leaves. Trailing types will scramble over the ground or climb a trellis, while compact types suit pots, window boxes and edging. Like cosmos, nasturtiums flower best in poor soil — rich soil gives leaves instead of flowers.
Soil, spacing, sun and water
Give nasturtiums full sun — at least 6 hours a day, with some afternoon shade in the hottest spots — in ordinary, well-drained soil with a pH of 6.0–7.5. They thrive in poor soil and need no fertiliser; too much nitrogen produces lush leaves and few flowers. Space plants 8–12 inches apart. Water deeply and less often rather than lightly every day, water at the base in the morning, and mulch lightly to keep the soil evenly moist while plants are young.
Nasturtiums need moderate water. Keep the soil moist while plants are young, then water only during dry spells — established plants are fairly drought-tolerant, and overwatering makes them leggy. In pots, check daily in summer, since containers dry out fast in Zone 10 heat.
Companion planting
Good companions for nasturtiums include lavender, marigolds, garlic, chives. The companion planting finder can suggest combinations for your whole bed. Rotate crops each year and avoid planting where the same family (Tropaeolaceae) grew last year, to reduce soil-borne disease.
Pests and problems
The common pests and problems to watch for with nasturtiums are aphids, slugs, cutworms. Inspect plants regularly, especially leaf undersides, and act early: hand-pick larger pests and wash aphids off with water. Healthy plants in the right soil and spacing resist pests better than stressed ones. In Zone 10's warm, humid weather, fungal problems spread fast on wet leaves, so water at the base and give plants room for air to circulate. Keep row cover or frost cloth handy for a rare cold snap, which can damage soft growth even though frost is rare here.
Harvest and storage
Nasturtiums take 50–60 days from sowing to first flowers. Pick the flowers and young leaves for salads — they have a peppery, watercress-like flavour — and pick them in the morning when they are fresh. Deadhead spent flowers every few days to keep plants blooming, or let some set seed: the green seed pods can be pickled as a caper substitute. Nasturtiums also work as a trap crop, luring aphids away from vegetables — check them regularly and remove badly infested leaves.
Nasturtiums are best eaten fresh, the day they are picked — the flowers wilt quickly and do not store well. The seeds keep well: let them dry fully on the plant, collect them, and store them in a paper envelope in a cool, dry place for next season. Green seed pods can be pickled in vinegar and kept for months.
Frequently asked questions
When should I plant nasturtiums in Zone 10?
From March through late summer, sowing a fresh batch every few weeks. In the mildest parts of Zone 10, an autumn sowing will flower through the winter, since frost is rare.
Are nasturtiums edible?
Yes — the flowers and young leaves have a peppery flavour and are good in salads, but only eat flowers you grew yourself without sprays. The green seed pods can be pickled as a caper substitute.
How long does nasturtiums take to grow in Zone 10?
Seeds germinate in 7–14 days and the crop takes 50–60 days to maturity; allow the longer end of the range in Zone 10's heat, and remember that frost dates are averages — check your local extension service for advice for your exact spot.
What soil and spacing does nasturtiums need in Zone 10?
Nasturtiums needs full sun and soil pH 6.0–7.5, spaced 8–12 inches apart. Dig in compost, water deeply, mulch, and test your soil through your local extension service.
For month-by-month guidance, see the March planting guide, and compare with Cosmos and Marigolds — two more Zone 10 planting guides. The companion planting finder can help you plan dates and spacing for your own garden.