Growing arugula in USDA Zone 9 means gardening in one of the warmest zones in the country: average winter lows of 20 to 30°F, an average last spring frost of Jan 30–Feb 15 and an average first autumn frost of Dec 1–15, giving a frost-free window of roughly 290–320 days. Frost dates vary by microclimate, elevation and year — check your local extension service.
Arugula is one of the fastest salad crops you can grow in Zone 9 — ready in as little as 30–45 days — and the cool months here give it a season that lasts for half the year. Sown from September to March it produces peppery, tender leaves almost continuously, but sown in summer it bolts in days and turns unpleasantly hot and bitter, so in Zone 9 arugula is firmly an autumn, winter and spring crop.
When to plant arugula in Zone 9
In Zone 9, September to March, in the cool months; succession-sow every two to three weeks.
The table below puts the whole season on one page, worked back from the Zone 9 frost averages and the crop's published days to maturity (30–45 days). Use the frost date calculator to check the averages for your own area.
| Stage | Zone 9 window | Notes |
|---|---|---|
| Start indoors | Not needed — direct sow | Germination takes 7–10 days |
| Direct sow outdoors | September to March, in the cool months; succession-sow every two to three weeks | — |
| Transplant outdoors | Not applicable — direct-sown | — |
| Days to maturity | 30–45 days | — |
| Cold tolerance | hardy | — |
Starting and planting
Arugula is direct-sown in Zone 9 in the cool months. Scatter seed thinly in rows or in a bed, cover very lightly — the seed is small — and keep the seedbed evenly moist until germination, which takes only 7–10 days. Thin seedlings to the final spacing once they are up. Because the crop is so fast, sow a small patch every two to three weeks from September to March for a continuous supply, and sow a little extra in autumn, when the mild weather gives the longest, easiest season.
Spacing, sun and soil
Space plants 6–8 inches apart. Crowded plants compete for light, water and nutrients, stay small, and invite disease through poor airflow, so thin seedlings to the final spacing once they are established. Use the plant spacing calculator to work out how many plants fit in your bed at that spacing before you sow.
This crop needs full sun — at least six hours of direct sun a day where possible. In Zone 9, a south-facing bed or an open spot away from trees and fences gives the strongest growth; part-shade types do better with morning sun and afternoon shade.
Soil should be deep, fertile and free-draining, with a pH of 6.0–7.0. Test your soil through your local extension service before amending it, and dig in plenty of compost, which improves drainage in heavy soil and holds moisture in light soil.
Watering
Water needs are moderate: aim for steady, even moisture rather than feast-and-famine watering. Keep the soil evenly moist — arugula that dries out grows slowly, turns tough and bolts early, and its flavour turns harsh. Water gently at the base in the morning and mulch lightly to hold moisture and keep the soil cool. In a dry spell, water deeply rather than sprinkling a little each day.
Companion planting
Good companions for arugula include marigolds, basil, onions and lettuce. The companion planting finder can suggest combinations for your whole bed. Avoid planting arugula where others of the same family (Brassicaceae) grew last year: rotate crops each season to reduce soil-borne disease and pest build-up.
Common pests and problems
Watch for cabbage worms, aphids, flea beetles and slugs. Inspect plants weekly — look under leaves, where small pests hide, and at the base of stems. Hand-pick larger pests, wash aphids off with a strong jet of water, and remove badly affected leaves rather than leaving them to spread a problem. Beyond pests, the main problems are weather-related: bolting in a hot spell, slow growth in cold soil, and damping off in seedlings kept too wet.
Harvest and storage
Start picking young leaves when they are a few inches long, and harvest regularly at 30–45 days from sowing. Pick the outer leaves and let the centre keep growing for a cut-and-come-again harvest, or cut the whole plant at the base. Pick in the morning when leaves are crisp, and use them the same day — arugula wilts fast.
Succession sowing is the whole secret with arugula in Zone 9: a fresh patch every couple of weeks from September to March means you always have young, mild leaves.
Frequently asked questions
When should I plant arugula in Zone 9?
Sow or transplant according to the table above, working from the average last frost of Jan 30–Feb 15 and the average first frost of Dec 1–15. These are zone averages — check your local extension service before planting out.
Can arugula survive a frost in Zone 9?
Cold tolerance for this crop is listed as hardy. Hardy crops can take a light frost, frost-tolerant crops can take a light frost once established, and tender crops are killed or badly damaged by frost, so use row cover on cold nights.
How long do arugula take to grow in Zone 9?
Germination takes 7–10 days and maturity takes 30–45 days from sowing or transplanting, according to standard published ranges.
Why does my arugula taste so bitter and hot?
Usually heat, age or drought. Arugula leaves turn hotter and more bitter as the plant ages, when the soil dries out, and once warm weather pushes it towards bolting. Pick young leaves, keep the soil evenly moist, and grow arugula in the cool months from September to March — summer-grown arugula in Zone 9 is almost always harsh.
See the November planting guide for Zone 9 for what else to sow that month, and when to plant bok choy in Zone 9 for a related crop.