The sweet pea, with flowers reminiscent of a butterfly’s flitting wings, has proven irresistible to gardeners ever since the 17th century when Franciscus Cupani, a Sicilian monk, recorded the original wild sweet pea, Lathyrus odoratus, in 1695.
Cupani’s Original is a rare variety: the original cultivated sweet pea grown by a schoolmaster in England from seed sent to him in 1699 by Father Cupani. The enticingly fragrant flower, with its mauve and maroon bi-colour blossoms, continues to be listed as one of the top 10 best-selling sweet pea varieties.
Today, seed starters have their pick of prized sweet pea strains from the descendants of the earliest introductions to the traditional Grandiflora and premium Spencer types to more recent varieties including dwarf sweet peas that can be grown in containers and hanging baskets.
While sweet pea enthusiasts are known to scour seed catalogues, online sources and local seed swaps for the most intensely perfumed and exclusive varieties, there are also those who grumble that sweet peas are difficult to grow.
The tall flowering stems of Chatsworth, a Spencer sweet pea variety, flourished in Lenore Linton’s St. Vital garden late last fall, with each of the lavender flowers producing five to six ruffled petals. Linton picked her last long-stemmed sweet pea bouquet of the season on Nov. 5. What’s her secret?
Linton starts her sweet pea seeds in mid-April. The hard, outer coat of the sweet pea seed (which is about the size of most pea-like seeds) does not easily absorb water.
To improve the rate of germination, Linton makes a small, shallow nick in the outer coat of each seed using a file, taking care to not damage the hilum (the small scar on the seed where the root was formed). This method is called scarification.
Next, Linton soaks her sweet pea seeds in water for 12 to 24 hours until they swell in size, an indication that moisture has permeated the outside skin.
The seeds are then sown into small, 7.5-centimetre pots filled with a good-quality soilless potting mix, watered and placed in a warm, bright location (18 to 20 C is ideal). The soil must be kept evenly moist and not allowed to dry out. Once the seeds sprout — about two weeks later — Linton plants them in her garden into a well-prepared site at the base of a trellis made from stucco wire.
Let’s stop to consider what is meant by a well-prepared site. Graham Rice is a renowned transatlantic plantsman who lives and gardens on both sides of the pond in Pennsylvania and Northamptonshire, England. I contacted Rice — who is the author of The Sweet Pea Book (Timber Press, 2003), a definitive resource for sweet pea growers — and asked him to share with Free Press readers his most important tip for growing sweet peas successfully.
"Look after the roots," he replies by email.
"Never allow the roots to become constricted in their seed pods and prepare the site so there is plenty of rich soil into which the roots can grow easily."
In his book, Rice explains that the roots of sweet peas grow deeply into the soil.
Planting seeds at the proper depth into rich, well-drained, friable or loamy soil is key to success. The message is clear to gardeners whose soil is heavy clay: amend your soil with organic matter as a shallow layer of good soil on top of a compacted layer of soil is not sufficient.
Rice recommends the process of digging a trench about 30 cm across and as deep as your digging spade.
"Then, fork over the bottom of the trench to the depth of your digging fork until the soil is loose and spread a layer of about 7.5 cm of organic matter on the top," he writes.
Linton is a proponent of this practice, and each fall replenishes the top layer of her seed bed with well-rotted compost so that it is ready for planting the following spring. Since sweet peas are heavy feeders, Linton sprinkles All Natural Tomato & Vegetable Fertilizer onto the soil at the time of planting and then again in mid-summer. High in calcium but low in nitrogen, this added nutrition promotes the growth of flowers while encouraging strong stems, root production and healthy microbial life in the soil.
Sweet peas like cool temperatures. A light touch of frost will not harm them, however, protection in the event of a hard, late spring frost will need to be provided. Maintaining even, consistent moisture is essential throughout the growing season. In addition, similar to the ideal conditions favoured by clematis vines, the sweet pea likes to have its head in the sun and its feet in the shade.
In the quest for favourite, scented varieties, sweet pea collectors often cast their net widely. Linton, for example, obtained the seeds for her Chatsworth sweet peas through her daughter who lives in the United Kingdom and who sourced them from Thompson and Morgan.
In Manitoba, heirloom sweet peas are available through a variety of sources including Heritage Harvest Seeds in Carman, which carries a highly sought-after variety — America. Introduced in 1896, its petals are red and white striped.
Mary Brittain, co-owner of The Cottage Gardener Heirloom Seedhouse & Nursery in Newtonville, Ont., reports that she h as already sold out her supply of Lathyrus odoratus King Edward VII, a highly scented sweet pea. A grandiflora type, it was introduced by sweet pea breeder Henry Eckford in 1903. King Edward VII’s vivid deep-crimson colour is another attribute, Brittain says, that makes it highly desirable.
One of my favourites, Black Knight, is also an introduction by Henry Eckford (1898) and has riveting deep purplish-maroon blossoms. On the lighter side, Butterfly, an Old Spice type introduced in 1878 by Suttons of England, has white blooms with lavender edges. Both of these varieties are available through Baker Creek Heirloom Seeds (rareseeds.com).
High Scent, a Grandiflora type, is sought after for its intense fragrance and is excellent for cut-flower bouquets. Available from West Coast Seeds in Delta, B.C., the flowers of High Scent are white with bluish edging.
Erin Benzakein, a farmer florist who owns Floret Flowers, a specialty-cut flower farm in Washington State that ships seeds across North America, says that Nimbus (a waved Spencer type) with its inky grey, eggplant-streaked blooms is one of her favourite sweet pea cultivars.
"I’ve learned that one of the secrets to getting longer sweet pea stems," Benzakein says, "is a technique that can be counterintuitive to beginning gardeners — pinch them."
When her sweet peas are 10 to 15 cm tall, Benzakein cuts out the central growing tip just above a leaf node, leaving just two or three leaf nodes. "This encourages the plant to branch vigorously from the base and produce long, strong stems," she says.
To prolong blooming, Benzakein stresses the importance of harvesting and deadheading the flowers frequently so that plants do not set seed. By following this practice, you too could be harvesting and enjoying scented bouquets as late into the season as November, weather permitting.