How to Grow Sweet Pea Black Knight
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Sweet Pea Black Knight
Lathyrus odoratus 'Black Knight'
flowerBlack Knight is a heirloom variety of sweet pea known for its deep, dark maroon-black flowers with a rich, intoxicating fragrance. This climbing vine produces delicate, ruffled blooms ideal for cutting and attracts pollinators throughout the growing season. It's a cool-season annual that thrives in spring and fall conditions.
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Example Sweet Pea Black Knight timeline · Pittsburgh, PA (Zone 6b)
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Plant Sweet Pea Black Knight
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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First Sweet Pea Black Knight blooms
Around Jun 16≈ 60 days after planting
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Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 2-8; prefers cooler spring and fall seasons
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Seed Preparation
1 dayHard-coated seeds ready for planting
Scarify seeds lightly with sandpaper or soak in warm water for 24 hours to improve germination. Soak seeds the evening before planting for best results.
Seedling
2-3 weeksTender shoots emerge with first true leaves
Keep soil moist but not soggy. Thin seedlings to 4 inches apart. Provide support structures early; sweet peas are delicate climbers. Keep temperatures cool (55-65°F optimal).
Vegetative Growth
3-4 weeksVigorous vine development with leafy tendrils and climbing stems
Install sturdy trellises, twine, or netting for support as plants grow rapidly. Pinch off the top 2 inches of young plants to encourage bushiness and more flower stems. Keep well-watered and fertilize with balanced fertilizer every 2-3 weeks.
Flowering
6-10 weeksAbundant dark maroon-black ruffled blooms appear on long stems
Deadhead spent flowers regularly to encourage continuous blooming. Pick flowers frequently for arrangements; cutting stimulates more production. Apply mulch around base to keep roots cool. Water deeply during heat waves.
Seed Pod Development
4-6 weeksIf flowers are allowed to go unpicked, seed pods develop
Allow a few flowers to mature into seed pods if you wish to collect seeds for next year. Once heat arrives or plants decline, they'll stop producing flowers.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Spray with insecticidal soap or neem oil. Use strong water spray to dislodge. Introduce ladybugs or lacewings.
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Keep humidity high by misting plants. Spray with neem oil or sulfur dust. Ensure adequate water to prevent stress.
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Ensure good air circulation. Spray with sulfur or baking soda solution (1 tbsp baking soda per gallon water). Remove affected leaves.
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Hand-pick early morning or evening. Use copper tape around bases. Apply diatomaceous earth around plants.
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Use yellow sticky traps. Spray undersides of leaves with insecticidal soap. Introduce beneficial parasitic wasps.
Uses
Edible Flowers for Decoration
CulinarySweet pea flowers are non-toxic and can garnish salads, desserts, and beverages with their delicate, slightly sweet flavor and striking dark color. They add visual elegance to special occasion dishes. [source]
Cut Flowers and Floral Arrangements
CraftBlack Knight's long stems, deep color, and intoxicating fragrance make it ideal for fresh floral arrangements, bouquets, and wedding flowers. Flowers last 7-10 days in water, making them excellent for cutting gardens. [source]
Natural Fragrance
HouseholdThe intensely sweet and distinctive fragrance of Black Knight sweet pea flowers perfumes garden beds and cut arrangements naturally without any synthetic compounds. A handful of flowers can scent an entire room. [source]
Pollinator Attraction
WildlifeSweet peas are excellent nectar sources for bees, butterflies, and other beneficial insects. Planting Black Knight supports pollinators and beneficial garden insects throughout the flowering season. [source]
Victorian Garden Charm
HouseholdAs a classic heirloom variety, Black Knight sweet pea adds nostalgic, romantic appeal to cottage gardens and heritage plantings. This variety has been cultivated since the late 1800s. [source]
Harvest Tips
Begin harvesting when flowers are fully open but still fresh-looking, typically in early morning after dew dries. Cut stems 6-8 inches long using sharp scissors or pruners. Cut frequently and deadhead spent blooms to encourage more flowering throughout the season. Sweet peas typically produce best in spring (February-May in mild climates) and fall (August-October); production slows significantly during hot summers. Remove flowers before they fade to prevent seed pod formation, which redirects energy away from flower production.
Fun Facts
- 🌱 Sweet pea flowers exhibit a fascinating genetic phenomenon: the Black Knight variety's deep maroon color develops through anthocyanin pigments that intensify in cooler temperatures, producing even darker blooms in spring and fall.
- 🌱 Black Knight was developed in the 1880s by horticulturists during the Victorian era's height of interest in ornamental flowers, when sweet pea breeding competitions were major horticultural events.
- 🌱 Unlike most flowers that lose fragrance over time, sweet pea flowers actually increase their scent production as they age, making 2-3 day old cut flowers more fragrant than freshly picked blooms.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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