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 some New Zealanders 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.

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.