March is the month the light changes. Days are noticeably longer, and for the first time since autumn it feels possible that the garden will happen. In a zone this cold, though, March is still an indoor month for almost everything. The ground may thaw at the surface on mild days and freeze again at night, and tender crops would not survive a night outside. March's real work is starting the crops that will fill the short summer, and getting beds ready for the moment the soil can finally be worked.
The crops that earn a March sowing are the ones with a long road ahead: tomatoes, which take 60–85 days to maturity and need six to eight weeks indoors, and the brassicas — broccoli, cabbage and cauliflower — which are frost-tolerant and can go out earlier than tender crops once they are sturdy.
Zone 1 in March: the frost window
Zone 1 is the coldest USDA zone in this guide, with winter lows below -50°F. The average last spring frost falls around June 15 and the average first autumn frost falls around August 1, which leaves roughly six to seven weeks between the average last spring frost and the average first autumn frost. Everything here runs on the latest timetable in the United States: sow tender crops indoors late, transplant only after mid-June, and harvest fast. Those dates are USDA zone averages from the USDA Plant Hardiness Zone Map and NOAA frost records — they are ranges, not exact dates for any one garden, and they vary by microclimate, elevation and year, so check your local extension service before you plant tender crops outside. Our garden planner gives you the averages for your zone, and the planting calendar hub lists every zone and month.
Your March task list
- Start tomatoes and brassicas indoors; keep them under strong light close above the leaves.
- Prepare beds as the ground thaws: clear debris, fork in compost, and avoid walking on wet soil, which compacts it.
- Check and repair cold frames, cloches and row cover — you will need them soon.
- Order seed potatoes and onion sets for planting when the soil is workable.
- Plan crop rotation and companion planting so tomatoes do not follow potatoes or other tomato-family crops.
- Begin hardening off nothing yet — but get trays and pots ready for the hardening-off weeks ahead.
What to start indoors in March
- Tomatoes — Start tomatoes now, about six to eight weeks before your average last frost. They germinate in 7–14 days and take 60–85 days to maturity, so a March start gives them time to become stocky transplants.
- Broccoli, cabbage and cauliflower — These brassicas are frost-tolerant and take 55–90 days to maturity. Start them indoors now so they can go out early in cool weather.
- Kale and Swiss chard — Kale takes 50–65 days and chard 55–65 days; both are hardy. Start them indoors now for an early transplant, or plan to direct-sow them later.
- Basil (late March) — Basil is tender and takes 60–70 days, so a late-March sowing under warmth is early enough — it will still be indoors for weeks before it can go out.
Give seedlings strong light close above them, keep the soil moist but not soggy, and label every tray with the crop and sowing date.
What to direct-sow outdoors in March
Direct sowing outdoors is still risky in March, and in most of this zone the soil is too cold and wet to work. If a mild spell leaves a sheltered bed workable, peas are the one crop worth trying under cover. Otherwise, keep sowing indoors and use March to prepare beds — clear debris, add compost, and let the soil warm and dry.
What to transplant and harvest in March
Nothing tender is transplanted outside in March. Hardy seedlings started in January and February — onions and leeks — are still indoors, and will only go out when the soil can be worked and frost is no longer a nightly event. The transplanting to do now is potting on: move tomato and brassica seedlings into larger pots when they have true leaves.
No outdoor harvest yet. March eating is still stored food, indoor herbs, and microgreens. It is also the month to check stored seed potatoes if you keep them: look for sprouting and rot, and plan your potato order for planting once the soil warms.
Frost protection in March
March frost is a nightly reality, and a mild afternoon is not a promise. Row cover and cold frames can protect hardy seedlings by a few degrees, but they will not save a tender tomato from a hard freeze. Keep all tender plants indoors, and if you do try peas under cover, accept that a cold snap may take them — sow a little extra as insurance. Your frost dates are averages, so check your local extension service and the forecast before any outdoor planting.
March planting data — Zone 1
| Crop | Germination | Days to maturity | Spacing | Soil pH | Cold tolerance |
|---|---|---|---|---|---|
| Tomatoes | 7–14 days | 60–85 days | 24–36 in | 6.0–6.8 | tender |
| Broccoli | 7–14 days | 60–85 days | 18–24 in | 6.0–7.0 | frost-tolerant |
| Cabbage | 7–14 days | 60–90 days | 12–24 in | 6.0–7.0 | frost-tolerant |
| Kale | 7–10 days | 50–65 days | 12–18 in | 6.0–7.5 | hardy |
| Peas | 7–14 days | 60–70 days | 2–3 in | 6.0–7.5 | hardy |
Frequently asked questions
What can I plant in March?
Indoors: tomatoes, broccoli, cabbage, cauliflower, kale and chard. Outdoors: almost nothing yet in a zone this cold — the soil is too cold and frost is nightly.
When should I start tomato seeds indoors?
About six to eight weeks before your average last frost. Tomatoes germinate in 7–14 days and take 60–85 days to maturity, so a March start suits a late-spring or early-summer last frost.
Can I work the soil in March?
Only when it is no longer frozen and not soaking wet. Squeeze a handful: if it stays in a wet ball, wait.
When is the last frost in my zone?
In Zone 1, the average last spring frost falls around June 15 and the average first autumn frost falls around August 1. Frost dates here are zone averages, not exact dates for any one place, and they vary by microclimate, elevation and year — check your local extension service before planting tender crops outside.
March is the hinge of the year in a cold zone: the light returns, tomatoes and brassicas go into trays, and beds get ready. The garden is still mostly a promise — but it is a promise you are now actively keeping. Browse the planting calendar hub for every month in your zone, see last month, or look ahead to next month, and see how the same month looks in a milder zone in the Zone 7 January guide.