Flowers & bulbs

How to Grow Sweet Peas: Fall Sowing, Care & Bloom

Quick answer

Penn State lists sweet peas as hardy annuals: sow outdoors in fall about six weeks before first frost. Bedding plants can go out in early spring. Seeds are poisonous — do not plant next to edible peas (NC State). Watch for slugs, snails, and aphids.

Sweet peas at a glance

PlantDirect sow: 6 wk before last frost
SunNC State: full sun (at least 6 hours); some shade is OK; rich, fertile, well-drained soil; even moisture; mulch; add organic matter.
SpacingNC State: height about 3–8 ft (bush vs climber); width about 2–3 ft; allow about 3–6 ft of space.
Days to bloomBloom season June–July (Purdue HO-80)
-7-6-5-4-3-2-1LF+1+2+3
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Updated

Sweet pea (Lathyrus odoratus) is an ornamental cool-season annual — not the edible garden pea (Pisum sativum). NC State: seeds are poisonous (low severity). Keep plantings away from edible peas.

Sweet pea flower (Lathyrus odoratus)
Sweet pea flower (Lathyrus odoratus). Photo: Ermell, Wikimedia Commons, CC BY-SA 4.0 (resized).

Sourced from university extension guides. For dates where you live, use the ZIP planting planner.

Planting timing

Penn State How Hardy Are Your Annuals?: sweet peas are hardy annuals. “Hardy annual seeds are best planted outdoors in fall, about six weeks before the first frost.” Bedding plants can be set outdoors in early spring. If you start hardy annuals indoors in spring, start about four to six weeks before the last frost. (Penn State Extension).

NC State: plant in early spring in cool climates; flowering drops if seed pods develop; plants struggle in hot humid summers. (NC State)

Depth, height and support

NC State: height about 3–8 ft (bush vs climber); width about 2–3 ft; allow about 3–6 ft of space. Climbers need a trellis or other support for twining tendrils. Avoid the same bed in consecutive years. Seed-depth inches are not stated on the NC State or Penn State pages used here — follow the packet when it gives a depth.

Sun, soil and water

NC State: full sun (at least 6 hours); some shade is OK; rich, fertile, well-drained soil; even moisture; mulch; add organic matter. Hardy annuals tolerate some frost.

Care and safety

Deadhead to prolong bloom; remove pods (NC State). Provide a trellis for climbers. Prefer compost-rich soil over printed fertilizer product rates. Safety: seeds are inedible/poisonous — NC State lists low-severity symptoms; do not sow beside edible peas. See also how to grow garden peas.

Bloom

NC State: bloom May–July. Purdue HO-80 (in plants.json): bloom season June–July — both labeled by source.

Pests and diseases (organic)

NC State: “No known insect or disease problems. Watch for slugs, snails and aphids.” Slugs/snails: handpick at night; iron phosphate bait as the label directs (UC IPM). Aphids: strong water spray; insecticidal soap with thorough coverage per label (UC IPM aphids).

Related: how to grow garden peas · organic pest control · ZIP planner · what flowers to plant in fall

Frequently asked questions

When do I sow sweet peas?

Fall: about 6 weeks before first frost (Penn State). Spring: early spring bedding plants (Penn State; NC State), or indoor start about 4–6 weeks before last frost if you follow Penn State’s general hardy-annual indoor guidance.

Are sweet peas edible?

No. Seeds are poisonous; keep them away from edible peas (NC State).

How do I stop slugs organically?

Handpick at night; iron phosphate bait as labeled (UC IPM).

Sources