How to Grow Sweet Peas

There's an old tradition that says you should sow your sweet pea seeds on the eve of St Patrick's Day or before sunrise on March 17th. Whether you're a believer or not, it's definitely a tradition many Australian gardeners follow.

Sweet peas are an easy-to-grow annual flower that makes a colourful addition to your garden during cooler months. From seed packet to soil, we've put together some handy information to teach you how to grow sweet peas from seed.

It is best to start preparing your soil about three weeks away from sowing, so aim to get started around the 24th of February. In hotter regions, sowing can be made later into the autumn months when the soil is cooler. Perennial sweet pea varieties such as our Sweet Pea Everlasting Mix can be sown both in spring and autumn.

Sweet peas enjoy more of an alkaline soil with a pH of around 7-8. If you’re unsure of your soil’s pH, at-home testing kits are readily available at garden centres. If your soil is not naturally this alkaline (not many of us are so lucky), you'll need to add some garden lime to the soil first to raise the pH.

Be sure to add a generous amount of good quality compost with a balanced, slow-release fertiliser to your garden beds and incorporate it well, breaking up any compaction with a garden fork as you go. Avoid high-nitrogen feeds or fresh manures if possible because too much nitrogen will promote a lot of leaf growth rather than flowers.

Your sweet peas will be happiest when their heads are in the sun and their roots are deep in cool, moist soil. If your garden gets a lot of sun, plant low-growing annuals, such as alyssum or pansies, in front of your sweet peas to shade their roots.

Apply mulch such as sugarcane over the beds to keep the soil from drying out quickly.

After roughly 2-4 weeks you should be ready to sow your seeds. Give your soil a good watering so it's nice and damp and dig a trench no deeper than 3cm. Roughly measure the depth using your finger or a dibber, place your seeds into the holes, and press down firmly.

Unless the weather is particularly hot and dry, additional watering won't be needed. Sweet peas hate having 'wet feet', and we don't recommend soaking the seeds prior to sowing as they’re prone to rot. Germination can take anywhere between 7-15 days depending on your soil temperature.

If your region is having a particularly rainy season and you are worried about the seeds rotting, try sowing the seeds into some Jiffy Peat Pellets and transplanting them as seedlings. All-in-one soil pellets eliminate the risk of transplant shock and root disturbance, so you’ll have happy seedlings with this method.

If starting seedlings in pots, transplant once they are roughly 5-8cm tall and large enough to handle. Using your hands form a shallow trench the same depth as the pots your seedlings are in. Space each seedling to the distance indicated on your packet seeds, usually 25-30 centimeters apart. Push back the soil to the base of each seedling, ensuring you keep the level the same as the original pot. Keep the seedlings moist once transplanted to avoid transplant shock.

To determine whether your plants require water, put your finger into the soil bed to roughly the first joint. If dry, water them at soil level in the morning.

It doesn't take long for your sweet peas to climb, so supports should be added at the planting stage and except for the bush types, it's a good idea to give at least 1.8m of good support.

Trellises are most commonly used but alternative options include chicken wire, bushy, stubbly twigs, and fishing line hung from above. It's really anything that your plant can climb.

Sweet pea flowers suffer from bud drop so be careful not to over water.

Pods will turn from a light green to a yellow-green to more of a brown colour. This is when your pods should be picked from flowers. Leave the roots in the ground as they have little nodules that add nitrogen to your soil. Just note that saved seeds may not produce true-to-type flowers due to cross-pollination. Sweet pea pods are not edible and are in fact toxic.