How To Grow Sweet Peas

Sweet peas are one of the garden’s most cherished flowers, offering beautiful blooms and an intoxicating fragrance that can transform any outdoor space. As a climbing annual, these delightful flowers provide vertical interest and a profusion of color from spring through early summer. With over a decade of growing experience, I’ve found that sweet peas reward even modest efforts with spectacular results. This guide will walk you through everything you need to know to successfully grow these beloved flowers in your garden.

Understanding Sweet Peas

Sweet peas (Lathyrus odoratus) are annual climbing plants that complete their lifecycle in one growing season. They produce delicate, butterfly-like blooms in a range of colors from white and cream to pink, purple, blue, and red.

Most varieties grow 6-8 feet tall and need support to climb. Their tendrils naturally wrap around trellises, fences, or other structures. Sweet peas prefer cool conditions and will stop flowering once temperatures consistently rise above 70°F (21°C).

When to Plant Sweet Peas

Timing is crucial for sweet pea success. These plants prefer cool weather and will stop flowering in hot summer temperatures.

In mild climates (USDA zones 8-10), fall planting is ideal. Sow seeds between September and November for spring blooms. In colder regions (zones 3-7), start seeds indoors 4-6 weeks before your last expected frost, or direct sow outdoors as soon as soil can be worked in early spring.

For continuous blooms, consider succession planting every 2-3 weeks during the appropriate planting window for your region.

Choosing the Right Location

Sweet peas thrive in full sun to partial shade. In cooler climates, they appreciate full sun (6+ hours daily). In warmer regions, afternoon shade helps extend the blooming period.

Select a spot with good air circulation to prevent fungal diseases. The location should accommodate a support structure like a trellis, fence, or obelisk that’s at least 6 feet tall.

Sweet peas prefer well-draining soil that retains some moisture. They won’t tolerate waterlogged conditions or completely dry soil.

Preparing the Soil

Sweet peas are heavy feeders that thrive in rich, fertile soil. Prepare your planting area by digging to a depth of 12-18 inches (30-45 cm), removing any weeds or rocks.

Incorporate plenty of organic matter like compost or well-rotted manure. This improves both drainage and fertility. Sweet peas prefer a neutral to slightly alkaline pH (6.5-7.5), so consider adding lime if your soil is acidic.

A week before planting, work in a balanced fertilizer or bone meal to provide phosphorus for strong root development.

Starting Sweet Peas from Seed

Sweet pea seeds have hard coats that benefit from scarification before planting. Nick each seed with a nail file or soak them in water for 24 hours to speed germination.

For direct sowing, dig a trench about 2 inches (5 cm) deep. Space seeds 3-4 inches (7-10 cm) apart, then cover with 1 inch (2.5 cm) of soil. As seedlings grow, gradually fill in the trench to encourage deep root development.

For indoor starts, use biodegradable pots to minimize root disturbance during transplanting. Maintain temperatures around 55-65°F (13-18°C) for best germination. Expect seedlings to emerge in 7-14 days.

Transplanting Seedlings

Transplant seedlings when they’re 3-4 inches (7-10 cm) tall and have at least two sets of true leaves. Harden them off by gradually exposing them to outdoor conditions over 7-10 days.

Space plants 6-12 inches (15-30 cm) apart, depending on variety. Water thoroughly after transplanting and provide immediate support for climbing.

Supporting Your Sweet Peas

Install support structures before or at planting time to avoid disturbing roots later. Sweet peas climb using tendrils that wrap around supports.

Effective support options include:

Bamboo teepees or obelisks
Trellises or netting
Chicken wire attached to posts
Branches or twiggy sticks

Ensure supports are sturdy enough to handle mature plants, especially in windy locations. Initially, you may need to gently guide young plants onto their supports.

Watering and Feeding Sweet Peas

Consistent moisture is essential for sweet peas. Water deeply once or twice weekly rather than frequent shallow watering. Aim to keep soil evenly moist but never waterlogged.

Apply a 2-inch (5 cm) layer of mulch around plants to retain moisture and suppress weeds. Keep mulch away from stems to prevent rot.

Feed plants every 2-3 weeks with a balanced liquid fertilizer. Once flowering begins, switch to a high-potassium fertilizer (like tomato feed) to encourage more blooms.

Encouraging More Flowers

The secret to abundant sweet pea blooms is regular harvesting. Cut flowers frequently—ideally every 2-3 days—to prevent seed pod formation, which signals the plant to stop flowering.

Pinch out growing tips when plants reach 4-6 inches (10-15 cm) tall to encourage branching and more flowering stems. Remove any side shoots that form in the leaf axils below the fourth or fifth set of leaves.

Deadhead diligently, removing any spent blooms or developing seed pods unless you’re specifically saving seeds.

Common Sweet Pea Varieties

Sweet peas come in numerous varieties with different growth habits, colors, and fragrance levels:

Spencer Types

These have large, wavy flowers on long stems, making them excellent for cutting. Popular varieties include ‘King Edward VII’ (crimson), ‘Royal Wedding’ (white), and ‘Blue Ripple’ (lavender-blue).

Grandiflora Types

These older varieties typically have stronger fragrance but smaller flowers than Spencers. ‘Cupani’ (purple and deep blue) is an heirloom variety dating back to 1699.

Dwarf and Container Varieties

‘Knee High’ and ‘Bijou’ varieties grow only 2-3 feet tall, making them perfect for containers or front borders.

Managing Pests and Diseases

Sweet peas can face several challenges during their growing season. Stay vigilant and act quickly if you notice problems.

Common Pests

Aphids – Control with a strong spray of water or insecticidal soap
Slugs and snails – Use barriers like copper tape or beer traps
Thrips – Introduce beneficial insects or use neem oil

Disease Prevention

Powdery mildew – Improve air circulation and avoid overhead watering
Root rot – Ensure good drainage and avoid overwatering
Fusarium wilt – Use disease-resistant varieties and practice crop rotation

Remove and destroy (don’t compost) any severely affected plants to prevent spread to healthy specimens.

Harvesting and Using Sweet Peas

Sweet peas make exceptional cut flowers. Harvest in the morning when stems are turgid and flowers are just opening. Cut stems as long as possible and place immediately in water.

For longest vase life, change water daily and keep arrangements out of direct sunlight. A typical bouquet will last 4-7 days indoors.

Note that unlike the edible garden pea, sweet pea plants are toxic if ingested. Keep cut flowers away from pets and children who might chew on them.

Saving Seeds for Next Year

Allow a few flowers to develop seed pods if you wish to collect seeds. Wait until pods turn brown and begin to split before harvesting.

Dry pods completely in a paper bag, then remove seeds and store in a cool, dry place in labeled paper envelopes. Sweet pea seeds remain viable for 2-3 years when properly stored.

Be aware that hybrid varieties won’t grow true from saved seed, so stick to heirloom or open-pollinated varieties if seed-saving is important to you.

Troubleshooting Common Problems

If your sweet peas aren’t thriving, consider these common issues and solutions:

Poor germination – Seeds may be too old or soil too cold; try pre-soaking seeds
Leggy seedlings – Provide more light and cooler temperatures
Few or no flowers – Check for excessive nitrogen, insufficient sun, or heat stress
Yellowing leaves – May indicate overwatering, nutrient deficiency, or pest issues
Dropping buds – Often caused by heat stress or inconsistent watering

Companion Planting with Sweet Peas

Sweet peas grow well alongside many garden plants. Consider these companions:

Low-growing flowers like alyssum or pansies to shade roots
Spring bulbs that will bloom before sweet peas reach full size
Herbs such as borage that attract pollinators

Avoid planting sweet peas in the same spot year after year to prevent soil-borne diseases. Practice a 3-4 year rotation for best results.

Growing Sweet Peas in Containers

Sweet peas adapt well to container growing if given adequate space and support. Choose pots at least 12 inches (30 cm) deep and wide.

Use high-quality potting mix enriched with compost. Containers will need more frequent watering and feeding than garden-grown plants.

Dwarf varieties are ideal for containers, but standard climbers can also thrive with proper support. Consider placing pots near seating areas to enjoy their fragrance.

Conclusion

Growing sweet peas rewards gardeners with beautiful, fragrant blooms that brighten any garden space. With proper timing, rich soil, consistent moisture, and regular harvesting, you can enjoy these delightful flowers from spring through early summer.

If you’re uncertain about specific growing conditions in your area, consult with your local extension office or garden center for regionally-appropriate advice. Sweet peas have been garden favorites for generations—with good reason—and now you have all the knowledge needed to grow them successfully in your own garden.