Perennial sweet pea

Sun

Full sun for the best flowering; tolerates partial shade.

Water

Water regularly during establishment. Established plants tolerate some drought, but flower better with deep watering during prolonged dry spells.

Soil

Well-drained soil with moderate fertility; tolerates clay if drainage is adequate. Neutral to alkaline soil suits it well.

Height

6-9 ft (1.8-2.7 m) with support

Spread

3-6 ft (0.9-1.8 m), potentially wider as established clumps spread

Flowers

Summer into early autumn; usually rose-pink, with white and deeper pink forms also available. Flowers are unscented.

Foliage

Blue-green leaves with paired, broad leaflets and branching tendrils, carried on flattened, winged stems. Top growth dies back for winter.

Growth

Fast once established

Care needed

Medium

• Pollinators
• Drought tolerant
• Cold hardy
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Very tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   2 ft (0.6 m)

2. After 1 year

   3 ft (1.1 m)

3. After 2 years

   5 ft (1.5 m)

4. After 3 years

   6 ft (1.8 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Invasive in

the US and Australia

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Install a sturdy trellis, wire mesh or other support before spring shoots lengthen.
• Water deeply during the first growing season and during extended summer drought.
• Apply a thin layer of compost in spring; avoid heavy nitrogen feeding, which encourages leaves rather than flowers.
• Mulch around the root zone, keeping mulch away from the crown.
• Remove spent flower clusters before pods mature to prolong flowering and reduce self-seeding.
• Pull unwanted seedlings promptly and remove spreading shoots before they become established.

Pruning. Cut dead stems back to ground level in late autumn or late winter, before new shoots emerge. During growth, guide stems onto their support and shorten or remove shoots that smother neighbouring plants.

Late winter

Cut away remaining dead stems and repair supports before new growth starts.

Spring

Plant container-grown plants, water them in thoroughly and mulch around the root zone.

Late spring

Guide young stems onto the support and remove unwanted seedlings.

Summer

Water during prolonged dry weather and remove faded flower clusters before seed pods develop.

Early autumn

Remove remaining pods where self-seeding is unwanted and check for shoots spreading beyond the planting area.

Late autumn

Cut down collapsed top growth if it is untidy, or leave it until late winter.

• Train over a sturdy fence or trellis to provide summer flowers and seasonal screening.
• Use on a large obelisk toward the back of a cottage border, with catmint or hardy geraniums below.
• Combine with a robust climbing rose for overlapping summer colour, keeping the pea from covering the rose.
• Let it scramble over a low wall or sunny bank where its spread can be contained and seedlings removed.

Garden styles it suits: Cottage garden, English country, Romantic rose garden, Traditional, Farmhouse and Pollinator garden.

Plant it with: Climbing roses, Catmint, Hardy geraniums, Yarrow, Hollyhocks and Lavender.

Wildlife: Flowers provide nectar and pollen for bees, particularly larger bees able to work the pea-shaped blooms. Dense summer growth offers temporary shelter for insects.

• Aphids cluster on soft shoots: wash them off with water and encourage ladybirds and other predators; use insecticidal soap only if needed.
• Powdery mildew produces a white coating on leaves: improve airflow, water the soil during drought and remove badly affected growth.
• Slugs and snails damage emerging shoots: inspect young growth, remove pests and use barriers or labelled slug controls where necessary.
• Poor flowering often follows deep shade or excessive nitrogen: move to a sunnier position if practical and stop high-nitrogen feeding.

Toxic to people, cats, dogs and horses if eaten; all parts should be treated as poisonous, especially the seeds. Substantial or repeated ingestion can cause lathyrism, with serious weakness and neurological damage. Do not confuse it with edible garden peas, and keep pods away from children and animals.

Where it spreads. Spreads by seed and an expanding rootstock, and can be difficult to eradicate. It is invasive in parts of the western United States, including California and the Pacific Northwest, and is an environmental weed in parts of southern Australia, including Victoria and Tasmania. Avoid planting near natural areas in these regions and check local guidance.

• Annual sweet pea (Lathyrus odoratus)

  Usually has fragrant flowers in a much wider range of colours and dies after one growing season; perennial sweet pea is unscented and regrows from its rootstock.

• Narrow-leaved everlasting pea (Lathyrus sylvestris)

  Has much narrower, lance-shaped leaflets and generally smaller, duller pink flowers; perennial sweet pea has conspicuously broader leaflets and larger flower clusters.

The epithet latifolius means broad-leaved, while everlasting pea refers to its perennial habit rather than the annual life cycle of ordinary sweet peas.

Propagation. Grow from seed sown in spring or autumn. Lightly nick the hard seed coat away from the small seed scar, or soak seeds overnight before sowing. Flower colour may vary in seedlings; established plants have deep roots and are difficult to divide or move.

Accepted botanical name

Lathyrus latifolius

In the US and Canada

Introduced in Canada, Hawaii and the lower 48 states.

Native range

Albania, Algeria, Austria, Baleares, Bulgaria, Corse, Czechoslovakia, France, Greece, Hungary, Italy and Krym.

Measured

Soil pH 5.8 to 7.5. Average height 56 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.