December in Zone 9 is a month when the quietest month in the garden, and one of the most useful: harvests continue, and next year gets planned. Zone 9 covers a warm band where average winter lows run 20 to 30°F, and that single fact shapes the whole month: what thrives, what struggles, and what is simply not worth trying yet. This guide answers the question behind "what to plant in december zone 9" directly — what to sow, what to start indoors, what to transplant, what to harvest, and which jobs are worth your time this month.
What December means in Zone 9
Zone 9 has a long, warm growing season with a short, mild winter. Frost is a real but brief visitor here: it usually arrives only in the coldest weeks, and it rarely lasts long. That makes Zone 9 one of the most forgiving zones in the country — you can garden in every month of the year, and the cool season is often the most productive part of it. In December, that means the garden is governed less by a single frost date and more by temperature, day length and soil warmth. Cool-season crops — lettuce, spinach, kale, peas, carrots and brassicas — are comfortable when nights are cool, while warm-season crops — tomatoes, peppers, beans, squash and basil — need warm soil and warm nights to grow well. Getting the timing right is mostly a matter of matching the crop to the month, rather than fighting the weather.
The frost averages still matter, even in a warm zone - the average last spring frost falls in the Jan 30–Feb 15 range and the first autumn frost in the Dec 1–15 range. Our frost date calculator gives you the averages for your zone, and the planting calendar by ZIP turns them into a plan for your own area.
Your December task list
- Harvest cool-season crops little and often, and use stored produce before it spoils.
- Direct-sow lettuce, spinach, peas and radishes in mild spells, under cloches or fleece where nights are cold.
- Start onions and leeks indoors for transplanting in the new year.
- Protect tender plants with frost cloth when a cold night is forecast, and bring containers under cover.
- Mulch beds, compost spent plants, and clean and sharpen tools while the garden is quiet.
- Plan next year's beds, order seeds early, and note what worked and what did not this year.
- Look after houseplants in the short days: give them maximum light, water sparingly, and keep them away from cold windows.
What to start indoors now
Onions, leeks and herbs can be started indoors now, and lettuce can be raised on a bright windowsill. Use clean pots and fresh seed compost, sow at the depth on the packet, and give seedlings strong light - a bright windowsill is the minimum, and a grow light hung close above them is better. Keep the soil moist but never waterlogged. Work out exact sowing dates with the seed-starting calculator, counting back from your average last frost.
What to direct-sow outdoors
Lettuce, spinach, peas, radishes and cilantro can still be sown in mild spells, especially under cover. Direct sowing suits crops that dislike transplanting, such as carrots, peas and beans. Prepare the bed first - fork it over, remove stones and weeds, and rake it level. Sow thinly, cover to the depth on the packet, and water gently. Check new sowings daily: the top layer of soil dries out fast. Thin seedlings to the spacing in the table below.
What to transplant now
Hardy brassicas and lettuce can go out in the mildest weather, but only where the soil is workable and no hard frost is imminent. Harden seedlings off first: set them outside in a sheltered spot for a few hours a day, building up over a week. Plant in the evening or on a cloudy day, water them in well, and mulch around - but not against - the stems. Do not crowd plants: close spacing invites disease.
What to harvest this month
Kale, chard, lettuce, spinach, carrots, beets, broccoli and cauliflower are all picked through the month. Harvest in the morning, when plants are cool and crisp, and pick little and often. Regular picking tells most vegetables to keep producing; left unpicked, beans, zucchini and peas slow down and stop. Use the harvest date calculator to work back from your sowing date and the crop's days to maturity.
Frost protection in Zone 9
Frost in Zone 9 is infrequent but real. The average last spring frost falls in the Jan 30-Feb 15 range and the average first autumn frost in the Dec 1-15 range, according to USDA zone averages and NOAA frost records. Those are averages, not promises: a cold snap can arrive a week or two either side of the range. When a cold night is forecast, water the soil in the afternoon - damp soil holds heat better than dry soil - cover tender plants with frost cloth or old sheets before sunset, and remove covers in the morning. Move containers against a warm wall, mulch around roots, and vent any cold frame on sunny days.
Soil, water and feeding in December
Feed beds with compost rather than guessing with fertiliser, and mulch after planting to hold moisture and suppress weeds. Water deeply and less often, aiming at the roots in the morning so foliage dries before night. If you have never tested your soil, send a sample to your local extension service. The watering calculator helps estimate what a bed needs, and the garden planner helps fit this month's sowings into your space.
Planting data for December in Zone 9
All figures below are broad published ranges from standard horticultural references, not exact figures for any variety or garden — they vary by variety, climate and soil. Use them to compare crops and to plan, not as promises.
| Crop | Days to germinate | Days to maturity | Spacing (inches) | Cold tolerance |
|---|---|---|---|---|
| Spinach | 7–14 | 40–50 | 4–6 | hardy |
| Tomatoes | 7–14 | 60–85 | 24–36 | tender |
| Lettuce | 7–10 | 45–60 | 8–12 | hardy |
| Carrots | 14–21 | 60–80 | 2–3 | hardy |
| Kale | 7–10 | 50–65 | 12–18 | hardy |
| Broccoli | 7–14 | 60–85 | 18–24 | frost-tolerant |
Browse the full planting calendar hub for every Zone 9 month, and see the neighbouring months in this zone:
Frequently asked questions
What should I plant in December in Zone 9?
Lettuce, spinach, peas, radishes and cilantro can still be sown in mild spells, especially under cover. Indoors, onions, leeks and herbs can be started indoors now, and lettuce can be raised on a bright windowsill. The exact mix depends on your soil and how much space you have, but those are the reliable starting points for this zone and month.
Is it too late — or too early — to plant in December in Zone 9?
It depends on the crop. Cool-season crops sown now still have time, because they mature in as little as 25–50 days for radishes and spinach, while warm-season crops need warm soil and a long frost-free run ahead of them. Check the days-to-maturity range in the table above against the time left before hot weather or frost, and sow accordingly.
When is the last frost in Zone 9?
The average last spring frost in Zone 9 falls in the Jan 30–Feb 15 range, and the average first autumn frost in the Dec 1–15 range, according to USDA zone averages and NOAA frost records. Those are averages, not exact dates — check your local extension service and the forecast before planting tender crops outside.
How do I protect plants from frost in Zone 9 in December?
Cover tender plants with frost cloth or old sheets before sunset, water the soil in the afternoon so it holds heat, move containers under cover, and mulch around roots. Remove covers in the morning so plants do not overheat. In Zone 9, a single cold night is usually the risk, not a long freeze, so a simple cover is often enough.