A quick guide to growing sweet peas | How to to plant Lathyrus odoratus

A quick guide to growing sweet peas

Lathyrus odoratus is beloved for its sweet, honey-like flowers. They can be grown as annuals or herbaceous or evergreen perennials with pinnate leaves and showy pea-like flowers.

The Basics

  • USDA Zones: 3-8, can tolerate frost and temperatures down to -7C
  • Height at maturity: 40-300 cm (depending on the variety)
  • Width at maturity: 30-60 cm (depending on the variety)
  • Light needs: Semi-shade/indirect sun
  • Type of soil: Well-drained with manure
  • Soil pH: Slightly alkaline (7.0 to 7.5)
  • Features: Fragrant
  • Position: Compact varieties are good in pots but most like to be in borders
  • Pruning: Trim off spent and faded blooms
  • Best time to sow seeds: September-April
  • Flowering period: Late winter to late spring
  • Warnings: Unlike edible garden peas, sweet peas are poisonous

Starting your seeds

The optimum time to sow sweet peas is in autumn. A spring sowing also works, although the flowers will appear later.

In USDA Zones 7-10 with mild winters, you can sow your sweet pea seeds in fall around October. For colder climates (Zones 3-5), you can start seeds in November so long as temperatures can stay above freezing all winter. You will likely need to keep them in a greenhouse during the coldest parts of the winter.

Sweet peas don't like to be transplanted so it's best to plant them where you want them to flower. Sow the seeds about 3-5 cm deep and 15 cm apart. 

Germination takes about 2-3 weeks. Stake your plants in advance so as not to disrupt the roots.

Only start watering your sweet peas after they have germinated. Keep temperatures at a steady 5°C (40°F). 

Store trays in a cold greenhouse or cold frame, but don't provide them with heating pads as this can cause the seeds to rot.


As the weather warms, sweet peas will wake up and begin blooming right until the first heatwave of the summer.

Day length, temperature and light intensity determine when your sweet peas will flower. In the UK flower can be expected from early March under glass, in California or Georgia for example, cut flower can easily be produced in time for the Christmas market.

You can fertilize your sweet peas with a potash-rich feed twice per month.