I have been struggling to grow sweet peas (Lathyrus) here in TO over the last 10 years ? because of our summer heat.
Is it hopeless to keep on trying? If not please advise me on what varieties to grow and how best to plant. Any guidance will be appreciated.
Thank you for contacting the Toronto Master Gardeners. This is the perfect time of the year to start thinking about annual seeds as many Ontario seed companies will be starting to re-stock and mail seeds. And no, there is always hope when gardening!
As you mentioned, heat waves can be detrimental to growing these beauties which require full sun (six hours of sun) but prefer cooler temperatures (Eastern exposure is preferable). Maintaining the roots ‘cool’ and moist with compost, mulch and other plantings in front could be one way to keep them thriving. However, ensure good drainage as otherwise they can rot easily.
In terms of varieties, the New York Botanical garden found that some of the Lathyrus odoratus cultivars from breeder Keith Hammett are fairly heat tolerant. They suggest trying: ‘April in Paris’, ‘North Shore’ and ‘Blue Celeste’. Other sources indicate that ‘Matucana’, a very old cultivar from Sicily and ‘Cupani’ are heat-tolerant cultivars. When going through seed companies catalogues, try searching local ones as they probably will be carrying the most successful cultivars for our climate and generally indicate in the description which are the most heat-tolerant varieties.
Also please refer to Ask a Master Gardener’s when-to-plant-sweet-pea for planting details. Although this question related to planting sweet peas in London, Ontario the last frost date in Toronto is around the same time – May 11-20, so the advice provided in this post is relevant to your garden.
Good luck in growing these fragrant beauties.