Sweet peas in the coastal subtropics can be a bit hit and miss…

Question: Hi Jerry, We always appreciate your work. We live at Bray Park, Brisbane. For years we have tried to grow sweet peas but have never been very successful.

I was wondering if you would be willing to give us some guidance for this autumn such as soil preparation, time to sow, and the best position.

Best Regards
Noel

Reply

Sweet peas, Lathyrus odoratus, in the coastal subtropics can be a bit hit and miss – especially if you rigidly adhere to the gardening tradition of sowing them on 17th March.

Sixty five years ago, Harry Oakman wrote ‘Gardening in Queensland’ which included the cultural requirements of sweet pea, then commonly grown as a winter cut flower.

Forty years ago in London I observed how the heat island effect influenced the gardening year. Observing the changes, including the reduced risk of hard frost, I learned that flexibility in a sowing timetable can reap rewards.

Relatively easy to grow, sweet peas like cool weather, fertile soil, all day sunshine, excellent drainage, watering at the base, and weekly feeding. Fresh seed doesn’t need chitting (sorry, Grandad), but do pre-soak seed in water overnight.

Good flowers (pictured) are more reliably achieved in the Central Desert Uplands of far Western Queensland than here in coastal SE Queensland because our humidity, dewfall and more frequent showers really assist mildew, the arch enemy of sweet peas. And because our minimum overnight winter temperatures in SE QLD are rising, like everywhere. I’m sure you don’t need reminding that nowhere on Earth has had a single month of ‘traditional’ weather – the kind of weather that Oakman took for granted – since 1985.

On Saint Patrick’s Day 2023 (17.3.23) formerly the traditional day to sow sweet peas in Australia, it was 37C in Tamworth (NSW), 37C in Blackall (QLD), 33C in Brisbane (QLD), 30C in Sydney (NSW), and 37C in Melbourne (VIC).

Sweet peas require a soil temperature of between 12.5C to 18.5C and about 50 days with temperatures falling below 16C to bloom well.

While sweet peas traditionally prefer all day sunshine, it’s now wise to position them where they get shade to avoid the western sun. Why? Their flower colour starts fading when temperatures exceed 18.5C.

21st century sweet peas grown in a warm climate will look their best when picked early in the day and used as a cut flower indoors.

Separately, I’ve prepared a seed bed for my winter crops. My garden has had six useful showers of rain since October 2022 – La Ninas aren’t what they used to be. Sowing will wait until we get a week below 30C.

Jerry Coleby-Williams
Director, Seed Savers Network
19th March 2023