Sweet peas

Sweet peas (Lathyrus odoratus) are among the easiest, prettiest and most fragrant annuals to grow. Most need nothing more than a sunny spot and a support to grow on as they are tall climbers. Grow sweet peas in the garden with wire, a trellis or a tripod. They often do well grown against a fence. Sweet peas can even grow in a container such as a trough. There are also dwarf forms to use to edge garden beds or grow in a hanging basket. Check with your hardware or garden centre for varieties that do well in your area.

These colourful plants are particularly loved for their prolific and scented flowers. Sweet peas are grown from seed or planted as seedlings. In warm climates they are generally sown or planted in autumn as soil temperatures cool but in cool zones they can be grown from plantings in either autumn or spring. Spring sowings or plantings give summer flowers.

Sow seeds into moist soil (or moist seed raising mix such as Seasol Seed Raising & Cutting Potting Mix if growing in punnets) and if possible, avoid watering until shoots appear. Once the seedlings emerge and begin to grow in their permanent position, they may need assistance to reach the climbing support. This is easily done by poking some twigs into the soil beside the seedlings. The tiny tendrils will grasp the twigs and head upwards.

Growing conditions

Aspect Sweet peas need a bright, sunny location with sun all day (at least six to eight hours) to encourage strong and vigorous growth and plenty of flowers. Ideally position the climbing frame or trellis facing north (running east to west) to maximise winter sunshine especially for autumn plantings.

Soil Sweet peas grow in a wide range of soils but prefer slightly alkaline soil (pH 7 to 8) so add lime in autumn as part of soil preparation prior to sowing seed or planting seedlings where soils are acidic. Also dig in well-rotted compost or manure and/or Seasol Super Compost. For a no-dig option apply Seasol Liquid Compost. When planting seedings add a slow-release fertiliser such as Seasol plus Nutrient Roses & Flowers as part of soil preparation to help promote strong root development and healthy growth. In areas with poor drainage, grow sweet peas in raised garden beds (raised at least 30cm) or in large containers using a premium potting mix such as Seasol Advanced Potting Mix. Remember to keep them well-watered as sweet peas need moisture to flower.

Climate Sweet peas grow in all climates. The traditional planting time for sweet peas seeds in Australia is St Patrick’s Day (March 17) but where conditions are still too warm for successful sowing, use the traditional date as a reminder to buy seeds and start preparing for planting when air and soil temperatures begin to cool later in autumn. In cool zones, sweet peas can also be sown in late winter or early spring for summer flowers.

General care

Watering Maximise seed germination by not watering the soil or seed raising mix until the first sign of growth as this can help reduce root rot. Apply Seasol at the first sign of growth to help encourage strong root development, healthy growth and to boost resistance to heat, frost, and diseases.

Water regularly more frequently if plants are in hot, dry or exposed conditions or if they are growing in containers.

Feeding and mulching Sweet peas are heavy feeders. Apply a granular fertiliser such Seasol plus Nutrient Roses & Flowers for flowering every 6 to 8 weeks. Keep plants flowering by regularly feeding with a liquid fertiliser such as PowerFeed PRO SERIES for Roses & Flowers or PowerFeed All Purpose including Natives every 2 to 4 weeks. Once the plants have finished flowering and start to wither, dig them into the soil as green manure to boost soil health.

Spread mulch such as lucerne, sugar cane or straw around bulbs to deter weed competition.

Pruning Picking flowers regularly keeps plants blooming as it discourages seed formation.

Watch out Sweet peas usually grow without too much trouble if they are in full sun and given regular water and fertiliser. Plants in too much shade may fail to grow and flower well and can develop powdery mildew, which are white spores that coat the leaves. Remove affected leaves and bin immediately, do not add to the compost.  Powdery mildew on sweet peas may also be treated with a fungicide spray such as EarthCare Rose Black Spot & insect spray. When spraying the foliage follow the directions on the back of the pack and spray both sides of the foliage. Repeat applications may be needed for further control. Remember not to spray when beneficial insects and bees are around.