September · USDA Zone 4
autumnWhat to plant in September in USDA zone 4
Autumn planting guide for zone 4 (Northern Maine, northern Wisconsin, Montana, parts of New England) — a 125-day growing season with last frost around mid-May and first frost around mid-September.
Sow outdoors in September — zone 4
Direct-sow these seeds into prepared garden beds or large containers. Soil temperature matters more than the calendar date — wait for a sustained warm-up before sowing tender crops.
- Garlic (late September to early October)
- Spinach, mache, lettuce (overwintering)
- Cover crops on empty beds
Harvest in September — zone 4
These crops should be ready or in active harvest in September for zone 4 gardens. Pick fruiting crops every 2-3 days to keep production going.
- Tomatoes (final), winter squash, pumpkins, apples, onions, potatoes
Universal September tasks
These apply across most US and UK gardens in September, regardless of zone.
- Plant garlic (zones 3-5 — start of the window).
- Sow autumn salad, spinach, lettuce, radishes, and mache.
- Transplant fall brassicas if not done in August.
- Sow cover crops (winter rye, vetch, clover) on empty beds.
- Harvest and cure winter squash, pumpkins, and onions.
- Start collecting and saving heirloom seed from open-pollinated favorites.
Why this works for zone 4
Zone 4 has average annual minimum temperatures of -30 to -20°F (-34 to -29°C) and a frost-free window from mid-May to mid-September — about 125 growing days. Tomatoes and peppers benefit from row covers in early season. Mulch heavily over winter for perennials and garlic.
Dates are zone-wide averages. Local microclimates (south-facing slopes, urban heat, lakeside warmth, elevation) can shift the window by 1-2 weeks within the same zone.
UK gardeners — September
September starts the UK's autumn garden. Sow winter salad, spring cabbage, mustard, mizuna, and overwintering onions. Plant garlic and overwintering broad beans late month. Harvest apples, pears, plums, sweetcorn, and main-crop potatoes.
Source and methodology
Frost-date averages from NOAA Climate Data Online within USDA zone 4. Hardiness boundaries from the USDA Plant Hardiness Zone Map (2023). Crop timing curated against US Cooperative Extension Service publications (UNL, UMN, NC State, Texas A&M, UF/IFAS, Oregon State) and cross-referenced against the RHS sowing calendar. Curated by the Growli editorial team.
Keep going
- ← August in zone 4
- October in zone 4 →
- All zones — what to plant in September
- USDA Zone 4 — frost dates and crop list
- Full 12-month planting calendar