Short answer: September is the temperate zone's second big sowing month running, with peas, basil, spinach, lettuce, brussels sprouts and mustard greens all opening for the first time this year. At the same time, August's broccoli and kale seedlings are ready to go from trays into the garden, and onion and shallot are making their last call for the season.

The NZ Temperate September Growing Context

Spring is properly underway — soil is warming and frost risk is easing, though the zone's frost period technically runs to the end of November, so it isn't over yet. That combination (warming soil, lingering frost risk) is exactly why this month's new sowings split into two groups: hardy direct-sow crops that don't mind a late frost, and the first frost-tender ones (basil) that need an indoor start regardless.

Typical September conditions in temperate gardens:

  • Warming soil, but frost risk continues to late November
  • Seven new sowing windows open, on top of everything still running from August
  • Broccoli and kale ready to transplant from trays
  • Onion and shallot close their sowing windows this month
  • Coriander, mizuna, pak choy and turnip all cropping

What to Sow This Month

Peas

Peas' sowing window opens in September and runs through February. Direct sow — peas fix their own nitrogen, so there's no need to feed the bed heavily beforehand. For variety-by-variety detail on what actually performs here, see Best Peas to Grow in NZ Temperate Spring.

Cultivar picks: Alderman Tall Climbing (Kings Seeds NZ), direct sown; or Amish Snap (Koanga Institute), started in trays to dodge slugs, snails and birds, transplanted at 5cm high on a trellis at least 1.6m tall.

Basil

Basil's window opens this month too, running through February — but this is a frost-tender crop, so it starts indoors regardless of the warming soil outside. Transplant only after the last frost, not before.

Cultivar picks: Cinnamon (Kings Seeds NZ), raised as transplants; or Genovese (Koanga Institute), pricked out at 2.5cm spacing and transplanted at 30cm once ground temperature reaches 15°C.

Spinach

Spinach's window runs September through February. Direct sow or raise in trays — it bolts in heat rather than minding the cold, so this end of the window is easier than late summer.

Cultivar picks: Bloomsdale (Kings Seeds NZ), direct sown; or Japanese/Land's End (Koanga Institute), raised in trays and transplanted at 25cm spacing — sow after peas or beans in the same bed for the best-flavoured leaves, and use part-shade in hot weather to delay bolting.

Lettuce

Lettuce's window reopens this month after closing at the end of March, running through to March again. Succession sow every 2–3 weeks rather than one large batch, and start planning for shade cloth once summer heat arrives.

Cultivar picks: Buttercrunch or Coral Red (both Kings Seeds NZ), both direct sown.

Also new this month

  • Brussels Sprouts — sows September through October only, a short window; raise in trays and transplant at 4–6 weeks, netted against white butterfly from the start.
  • Mustard Greens — sows September through October; raise in trays and transplant at 6–8cm high, or direct sow instead for a quicker baby-leaf harvest.

Last call: Onion and Shallot

Both close their sowing windows at the end of September. Onion's been open since July; shallot since August. Miss this month and neither reopens until next year.

Transplant This Month: Broccoli and Kale

Both were sown into trays in August and are ready to go out now — broccoli's transplant window runs September through December, kale's September through November. Net both against white butterfly the moment they're in the ground; unprotected seedlings can be stripped within days of transplanting.

What to Harvest This Month

  • Coriander — cropping from July and August sowings; harvest before it bolts in the first warm spell.
  • Mizuna and Pak Choy — both cut-and-come-again greens from earlier sowings; pick outer leaves rather than pulling whole plants.
  • Turnip — from the August sowing, ready to pull as roots size up; don't leave them too long once summer heat arrives, since turnip bolts and toughens in the heat this variety dislikes.

Garden Jobs for September

Net broccoli and kale the moment they're transplanted

White butterfly pressure starts as soon as seedlings go into open ground, not later in the season. Net at transplanting rather than waiting for visible damage.

Get a trellis up before peas need it

Climbing peas need support in place early — putting a trellis in after plants are already scrambling means damaged stems and awkward training. Have it ready before sowing, not after.

Keep basil indoors until frost risk has genuinely passed

The frost period doesn't end until November. An early warm week is not the same as the last frost — transplant on the calendar's timing, not a lucky stretch of weather.

Common September Mistakes

Transplanting basil out too early

A mild September week can look like summer, but frost risk runs to November. Basil planted out now can be wiped out by a late frost that costs weeks of growth.

Missing the onion and shallot cutoff

Both close out this month. Sow late and you're waiting until next year rather than catching a late-season crop.

Leaving turnip too long once it's ready

Turnip dislikes summer heat and turns woody or bolts once it arrives. Pull roots as they size up rather than letting them sit and hoping for bigger.

Looking Ahead

October brings cucumber's sowing window, while broccoli and kale (transplanted this month) head toward their first harvests over summer. Basil and peas, sown this month, will still be establishing, and beetroot, carrot, pak choy, radish and silverbeet all keep running through their long August/September sowing windows regardless.

Ready for next month? See *What to Plant in NZ Temperate in October*, or explore the full NZ Temperate Planting Calendar →.