May in Sydney is the wrong time of year to be starting chilli seeds outdoors. The day length is short, the soil is cooling, and even our mild winters punish young chilli plants. But for the more demanding varieties — the slow-growing super-hots, the longer-season heirloom varieties, and anything that needs a long pre-transplant period — May is exactly when the heated propagator earns its keep.

Why start in May

Most fast-growing varieties — jalapeños, cayenne types, most paprika varieties — can be started in August or September and still have time to fruit before the autumn weather closes in. They do not need a May start.

The varieties that benefit from a May start are the slow ones. Carolina Reapers, Trinidad Scorpions, Ghost Peppers, 7 Pots. Some of the larger heirloom Capsicum baccatum varieties (the South American types). Some of the Capsicum pubescens (rocoto) varieties, which are slow to germinate and slow to mature. These benefit from three to five months of growing time before the spring transplant.

A May-started super-hot plant transplanted in September is a much stronger plant than an August-started equivalent. It fruits earlier, fruits more, and survives the first autumn cool snap better.

The propagator setup

The setup is not complicated. A heated propagator base, a clear lid, a thermostat if possible, and a grow light. I run my propagator at 26-28 degrees Celsius for germination, drop it to 22-24 degrees once the seedlings are up, and run the grow light for 14-16 hours a day.

The heat is essential for chilli seed germination — particularly for the super-hots, which can take three or four weeks to germinate and which germinate poorly below about 24 degrees. The light is essential once the seedlings are up — a Sydney bay window in May does not give enough light, and leggy seedlings struggle later.

The germination time honesty

The germination times in the seed catalogue assume good conditions. In a heated propagator at 27 degrees, my actual germination times look like this. Jalapeños: 7-10 days. Cayenne types: 8-12 days. Habaneros: 14-21 days. Super-hots (Reapers, Scorpions, Ghosts): 21-35 days, with stragglers taking longer. Rocotos: 14-30 days, very variable.

If a super-hot batch has not germinated in three weeks, do not throw it out. Some seeds germinate at five weeks.

The transplant timing

Once a seedling has two or three sets of true leaves and a developing root system, it can move out of the propagator. In Sydney in winter, this usually means moving into a small pot under a grow light, not outside. The plants stay in pots under lights until late August, when the night temperatures are reliably above about 10 degrees and the plants can move outside.

The risk in May-started chillis is overgrowth in the pot phase. A super-hot in a 100mm pot can outgrow the pot before transplant time. I move my super-hots up to 200mm pots around July to give them root room.

The variety mix for autumn starts

My May propagator usually has three to four super-hot varieties, one or two rocoto varieties, and one or two slow heirloom varieties. The fast varieties wait until August. The September transplant moves about 30 plants into the garden, which is more than my household actually needs but the surplus goes to mates.

If you have not done a May start before, pick one or two slow varieties and a heated propagator and see how it goes. The patience pays back when the September plants go into the ground already a foot tall.