Growing geraniums in USDA Zone 10 means gardening with a mild winter and only a rare frost. Geraniums — the bedding geraniums grown for bright, long-lasting flowers — are tender plants that Zone 10 suits better than almost anywhere else, because frost is rare. Here they can be grown as perennials, flowering for most of the year. This guide covers when to plant geraniums in Zone 10, with the soil, spacing, sun, water and care it needs. Use the Zone 10 planting calendar to see what else to sow alongside it.
Zone 10 at a glance
USDA Zone 10 has average winter lows of 30 to 40°F, a last frost around Jan 15–30 and a first frost around Dec 15–31 — and frost is rare in much of the zone. Plan around those averages, not the calendar: a cold night or a warm spell can shift everything by a week or two, so check your local extension service for your area. Geraniums are cool-season flowers here, grown through autumn, winter and spring rather than through summer heat.
| 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) |
| Days to germination | 7–14 days |
| Days to maturity | 70–90 days |
| Sowing | Start indoors in December–January |
| Transplanting / planting out | After the average last frost (Jan 15–30), or autumn-sown plants flower from late winter |
| Harvest | Flowers 70–90 days after sowing; pick regularly to keep plants flowering |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 12–18 inches |
| Water needs | moderate |
When to plant geraniums in Zone 10
Start geraniums indoors in December or January and transplant after the average last frost of Jan 15–30, from February onwards. They take 70–90 days to maturity, so an early start gives flowers by late spring. In Zone 10, established plants often live through winter and flower again, but a cold snap in the Dec 15–31 to Jan 15–30 window can damage soft growth, so keep fleece or a pot you can move under cover handy. If you are unsure of your own dates, the seed-starting calculator will help you work the timing out. Frost dates are zone averages — check your local extension service before you commit to a date.
Starting geraniums in Zone 10
Geraniums are started indoors, since the seed needs warmth and light to get going. Sow thinly in trays, keep the compost moist but not wet, and give seedlings strong light — seeds germinate in 7–14 days. Grow them on until they are sturdy, then harden off for a week before planting out 12–18 inches apart. Many gardeners also grow geraniums from cuttings, which root easily.
Soil, spacing, sun and water
Geraniums want full sun and well-drained soil with a pH of 6.0–7.0, and they hate wet feet more than they hate dry soil. Dig in compost, but in heavy soil grow them in raised beds or containers where drainage is guaranteed. A little extra grit in the planting hole helps in Zone 10's wetter spells. Geraniums need moderate water. Water at the base when the top of the soil feels dry, and let the soil dry a little between waterings — constant wet soil causes root rot. Water in the morning so leaves dry before night, and water pots more often than beds in hot weather.
Companion planting
Good companions for geraniums include lavender, marigolds, garlic, chives. The companion planting finder can suggest combinations for your whole bed. Do not plant geraniums in shade or in soil that stays wet, and do not crowd them — still air and wet leaves invite disease. Good companions include lavender, marigolds, garlic and chives, and they sit well at the front of a sunny bed.
Pests and problems
The common pests and problems to watch for with geraniums are aphids, slugs, cutworms. Aphids cluster on shoot tips and buds, slugs take young plants, and cutworms can sever stems at soil level. Check plants when you deadhead, wash aphids off, and protect young plants until they are established. Geraniums are generally tougher than most bedding plants once they are growing strongly.
Harvest and storage
Geraniums are not harvested like a crop — the harvest is the flowers, and the way to get more is to deadhead spent blooms regularly. Pinch off faded flower heads and any yellowing leaves, and plants will keep flowering for months. Take cuttings in late summer to carry your best plants through winter. Take cuttings in late summer, root them in pots of compost, and keep them in a bright, frost-free spot over winter. In Zone 10 you can often leave plants in the ground with a mulch, and they will shoot again in spring.
Making the most of Zone 10
Zone 10 is one of the few places where geraniums can be treated as perennials rather than annuals, so it pays to grow them well and keep the best plants. The only real risk is a rare frost, so watch the forecast in December and January and cover plants on cold nights. Related reading: Snapdragons in Zone 10 and January in Zone 10. Also see November in Zone 10 for what else to sow alongside it.
Frequently asked questions
When should I plant geraniums in Zone 10?
Start geraniums indoors in December or January and transplant after the average last frost of Jan 15–30, from February onwards. Check your local extension service — these are zone averages, not exact dates for your garden.
How long do geraniums take to grow in Zone 10?
Seeds germinate in 7–14 days, and the crop takes 70–90 days to maturity. In Zone 10, allow the longer end of the range if conditions are cool or dry at sowing time.
Can geraniums survive winter in Zone 10?
Usually yes, because frost is rare in Zone 10, with an average last frost of Jan 15–30 and a first frost of Dec 15–31, but a hard cold snap can damage soft growth, so mulch the roots and cover plants on frosty nights.
What soil and spacing do geraniums need in Zone 10?
Geraniums need full sun and soil pH 6.0–7.0, spaced 12–18 inches apart. Dig in well-rotted compost, water deeply, mulch, and test your soil through your local extension service.