Organic Sweet Peas: Seed to Bloom Growing Guide
Sweet peas are one of the most enchanting flowers of the cool season, loved for their delicate ruffled blooms, unforgettable fragrance and generous flowering habit. Whether grown in an organic home garden or for cut-flower production, sweet peas are surprisingly easy to cultivate with the right timing, deep pots, good soil preparation and strong support. From sowing in autumn or winter through to harvesting long stems for the vase, this guide walks you through everything needed to grow beautiful, healthy sweet peas in Australian conditions.
Sowing Sweet Peas: Timing, Pots & Propagation Mix
When to Sow Sweet Peas
Sweet peas can be sown from late March to August—autumn through late winter. If you plan to transplant into a polytunnel, you can start even earlier. Some early-flowering varieties bloom under short day length (10 hours of daylight), making them ideal for autumn sowing.
However, consider your soil and climate:
- Sweet peas hate wet feet, so heavy winter soil can cause issues
- Flowers may need protection from late winter or early spring storms, wind and frost
- If heat arrives early in late spring, earlier sowing gives a longer bloom season
Sweet peas are cold hardy, but it’s best to transplant once nighttime temperatures stay above –5°C.
To work out timing:
- Start seeds indoors 4–5 weeks before transplanting
- Transplant 4–5 weeks before your last frost
- If you're unsure, transplant at the same time you plant garden peas
After three seasons of research, we’ve found the most reliable method is to:
- Work out when flowering will be triggered by day length,
- Then count 10–12 weeks backward to determine sowing time.
Where you sow depends on how wet your garden is, and whether frost might damage emerging flowers.
Which Pots Are Best?
We prefer transplanting sweet peas, so we always sow into pots.
Because sweet peas are deep-rooted, choose deep pots such as:
- Forestry tubes (50mm × 50mm × 120mm)
- 5" root trainers
If sowing in late winter, these are usually deep enough.
If sowing in late autumn, keep an eye on the base of the pots— If roots start poking out and the garden still isn’t ready, pot up to a 1L pot.
Once sweet peas become root bound, they never fully recover.
Propagation Mix
Use a peat moss, multi-purpose propagation mix that has been watered into the pot as opposed to packed tightly.
We use our seed raising mix (recipe found here) which includes a base fertiliser with great results.
Sowing Sweet Peas
Depending on the germination rate listed on the packet, sow 1–2 seeds per pot, 5mm deep, and lightly cover with propagation mix.
Optimal germination temperature: 10°C
Avoid using bottom heat, as sweet pea seeds can easily overheat, reducing germination success.
Our Germination Method
We often germinate seeds using the paper towel method in a cool room. As soon as the rootlet emerges, seeds are transferred carefully into prepared pots.
This approach:
- Ensures no potting space or soil is wasted
- Allows us to monitor germination closely
- Produces germination within 5–7 days for most seeds
If a seed has not germinated, we gently nick or file the seed coat and leave it a few extra days. This improves overall germination, especially for seeds with tougher outer coatings.
While many growers recommend soaking sweet pea seeds, we do not. Our trials have shown better results without soaking.
Growing Out a Seedling
Once sweet pea seeds have germinated, provide plenty of bright light to prevent seedlings from becoming leggy, weak, or stretched.
Sweet peas are naturally cold tolerant and benefit from being grown hard. Move seedlings outside on sunny winter days to strengthen them, reduce legginess, and acclimate them for transplanting.
Just be sure to protect from:
- Heavy frost (below –5°C)
- Strong winds
- Extended periods of cold, wet soil
Pinching & Side Shoots
Pinching depends on when the seeds were sown:
- Do NOT pinch autumn-sown sweet peas.
- For later sowings, pinch the growing tip when plants reach around 10cm tall to encourage bushier growth and more flowering stems.
Roger Parsons, leading UK sweet pea specialist and author of Sweet Peas – The Essential Guide, explains:
“Autumn-sown plants grown cold will have reached 75mm high by winter and side shoots will form naturally at this time… Left unstopped, those side shoots that are starting to form in winter will be just the right length for planting out in early spring. It is the cold weather that encourages natural side shoot development.”
If a plant has not begun forming side shoots by winter, this is the stage when pinching becomes beneficial.
Support & Trellising
Unless you are growing a dwarf or knee-high variety, most sweet peas reach 180–200cm and need support. Home garden options include:
- Teepee structures
- Arches or tunnels
- Netting on stakes
- Metal fencing or mesh
For later sowings, tall 2m+ stakes spaced every 3m can support two layers of Hortonova netting placed one over the other, creating around 180cm of vertical growing space for tendrils to climb.
A windbreak is extremely helpful—strong winds can damage stems and reduce flower quality.
Plant Spacing
Space seedlings 15–30cm apart, depending on your support.
We plant two rows, one on either side of the trellis, at 15cm spacing.
Continue to tie or clip plants to the support as they grow. Securing stems encourages:
- Upward growth
- Straighter stems
- Longer cut-flower length
Protection
After transplanting, protect young plants from:
- Hard frost
- Slugs & snails
- Mice
- Magpies
Sweet peas are cold tolerant, but a severe frost can damage or kill young seedlings and ruin forming flower stems.
Harvesting & Vase Life
Sweet peas have a naturally short vase life—around 4–6 days. To make the most of your blooms:
- Harvest during the coolest part of the day
- Pick when 1–2 flowers on the stem are open
- Place stems into clean water with flower food or a small amount of sugar
The remaining buds will continue to open in the vase, helping extend their display.
Important Warning
All parts of the sweet pea plant are poisonous if ingested.
Please take care around children and pets.
Recommended Resources
If you’ve been caught by the sweet pea bug (it happens!), these expert growers and authors are well worth reading and learning from:
- Roger Parsons — Sweet Peas: An Essential Guide
- Dr Keith Hammett — world-renowned breeder and sweet pea specialist
- Erin Benzakein of Floret Flower Farm
- Marryn Mathis — Sweet Pea School: Growing & Arranging the Garden’s Most Romantic Blooms