Short answer: September is when the cool/mountain sowing list roughly doubles — peas, spinach, lettuce, carrot, basil, brussels sprouts and mustard greens all open for the first time this year. Broccoli and kale raised in August are ready to transplant, while onion and shallot reach their final month before closing until next winter.

The cool/mountain September context

This is the temperate zone's August arriving a month late. Spring is genuinely starting, but it starts colder and later here than further north, and the calendar's optimism runs ahead of the ground. The zone's frost period runs to the end of November — the same as temperate — but it's also bookended tighter at the other end: autumn frost returns as early as March, so every warm-season crop you start now is aiming at a shorter runway than the same crop in a milder zone.

Two things follow. First, soil warms slowly, so direct-sown seed is slow up — don't be alarmed if a carrot or pea row sits a fortnight before showing. Second, "cool/mountain" spans a lot of country, from mild inland districts to high-country gardens still hard-frosted in September. The sowing windows below are broad national planting dates, not cold-zone-specific ones — match the list to your own frosts and altitude, not the calendar.

What to sow now

Start basil under cover

Basil's window opens this month (September–February), but it's the one frost-tender crop on the list, so it starts indoors regardless of how mild the day feels. Its harvest here runs January–March — a month shorter than the temperate zone's, because autumn frost arrives earlier — which makes an early, under-cover start worth more, not less: get plants ready to go out the moment the last frost passes, so they use every week of that compressed season. Transplant on the calendar's timing, not a lucky warm week.

Cultivar picks: Cinnamon (Kings Seeds NZ) suits a tray start; or Genovese (Koanga Institute) — prick seedlings out at 2.5cm, then plant at 30cm once the soil hits 15°C — well into spring in a cool zone.

Cool-season and hardy crops to direct sow

These handle cold soil and are sown where they'll grow. Peas are cool-season — fine in cool weather, but young plants want a cloche in the hardest-frost gardens:

  • Peas (sow September–February) — direct sow; they fix their own nitrogen, so there's no need to feed the bed heavily first. If earlier sowings flowered but set nothing, Why Are My Peas Not Flowering in NZ Cool/Mountain? covers the cold-set causes; Best Peas to Grow in NZ Temperate Spring covers variety choice, which applies here too.
  • Carrot (sow September–May) — direct sow only; the roots resent being moved. Keep the seedbed moist until germination, which is slow in cold soil.
  • Spinach (sow September–February) — direct sow or raise in trays. It bolts in heat rather than minding cold, so this cool end of its window is the easy one.
  • Lettuce (sow September–March) — succession sow a short row every 2–3 weeks rather than one big batch.
  • Brussels sprouts (sow September–October only) — a short window; raise in trays, transplant at four to six weeks, and net against white butterfly from the start. Flavour improves after frost, which this zone delivers.
  • Mustard greens (sow September–October) — raise in trays and transplant at 6–8cm, or direct sow for a quicker baby-leaf harvest.

Last call: onion and shallot

Both close their sowing windows at the end of September. Onion (harvest January–March) has been open since July; shallot (harvest January–February) since August. Both are long-season alliums — in now, or not at all until next year. Direct sow onion and keep it out of high-nitrogen ground, which drives leaf at the bulb's expense; push shallot bulbs in 5cm deep and 15cm apart.

Transplant now: broccoli and kale

August's tray-raised seedlings can move into the garden this month — broccoli has until December to go out, kale until November. In the coldest gardens, hold them longer if hard frosts are still coming through — a checked transplant recovers slowly in cold soil. Cover young plants with netting as soon as they're planted, or white butterfly caterpillars will shred them. Kale doesn't merely tolerate the cold — a frost or two sweetens the leaves.

Harvest now

  • Coriander — cropping from earlier sowings; pick before it bolts. A cool September start is exactly what keeps it from running to seed, the fix explained in Why Is My Coriander Bolting Immediately in NZ Cool/Mountain?.
  • Mizuna and pak choy — cut-and-come-again greens from earlier sowings; take outer leaves rather than pulling whole plants.
  • Turnip — pull roots as they size up. Turnip dislikes summer heat and turns woody once it arrives, so don't leave this cool-season crop sitting.

Silverbeet also keeps running through its long August–May window — Growing Silverbeet Year-Round in NZ has the detail.

Recommended cultivars

  • Peas: Alderman Tall Climbing (Kings Seeds NZ), direct sown; or Amish Snap (Koanga Institute), tray-raised to dodge slugs and birds, on a trellis at least 1.6m tall.
  • Carrot: Amsterdam Sprint (Kings Seeds NZ); or Akaroa Long Red (Koanga Institute), scatter-sown and kept covered while it germinates.
  • Spinach: Bloomsdale (Kings Seeds NZ), direct sown; or Japanese/Land's End (Koanga Institute), tray-raised and transplanted at 25cm.
  • Lettuce: Buttercrunch or Coral Red (both Kings Seeds NZ), both direct sown.
  • Broccoli: Belstar F1 (Kings Seeds NZ); or de Cicco (Koanga Institute), transplanted at 30cm.
  • Kale: Blue Ridge F1 (Kings Seeds NZ); or Borecole (Koanga Institute), transplanted at 40cm or broadcast for baby leaves.
  • Coriander: Picante (Kings Seeds NZ), direct sown; or NZH (Koanga Institute) for tray-raising.
  • Brussels sprouts, mustard greens, onion, shallot: no specific cultivars catalogued yet — choose an NZ-suited variety from your usual supplier.

Know your zone? Explore the full NZ Cool/Mountain Planting Calendar for month-by-month sowing and harvest timing.