Grow Sweet Peas
Lathyrus in the garden
Lathyrus is like made for dividing the greenhouse into rooms.
Lathyrus needs lots of warmth and sun, so it should be placed in full sun. It will love your greenhouse. Lathyrus fully thrive when getting a lot of heat.
Photo: Grøn Kommunikation
Written by Lars Lund
Edited by Louise Curley
Sweet peas (Lathyrus odoratus) are a classic cottage garden flower, clambering over plant supports and filling the air with their heady fragrance. They’re hardy annuals and easy to grow from seed, and with hundreds of different cultivars you’re spoilt for choice.
Sweet peas can be sown in late autumn for an early crop of flowers or in late winter/early spring. Soak the seed overnight in a glass of water to help to soften the hard outer casing of the seed. Sweet peas develop long roots and don’t like to be constricted so it’s best to use tall pots or root trainers to sow into.
Clever sowing trays for the long roots are called Rootrainers.
Photo: Nielsons Garden
They don’t need extra heat to germinate but plenty of light is crucial to encourage stocky plants rather than thin, weedy seedlings. When the young plants have 4 or 5 sets of leaves pinch out the growing tip to encourage the plants to develop more shoots at the base – this will make bushier plants and mean lots more flowers.
Before they can be planted out into the garden, the plants need to be acclimatised to outdoor life. You do this by moving the pots outside during the day and then bring them back inside at night. Do this for 10 days or so, then plant out.
Sweet pea plants don’t like to dry out and they also need a rich soil, so incorporate plenty of well-rotted compost in the area where you plan to grow them. You can also add comfrey leaves or pellets to the planting holes, as this will provide plenty of potassium, a nutrient that encourages plants to produce flowers.
Sweet peas can grow to over 2 metres tall, so they’ll need some kind of support to scramble over. A tepee of bamboo canes or hazel beanpoles works well, or you can use a wooden trellis panel or train them to grow over an arbour to create a fragrant seating area.
Om Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.