How to Grow Sweet Peas: A Guide for Winter Gardens

Imagine stepping into your winter garden and being greeted by cascades of delicate, butterfly-like blooms releasing clouds of honey-sweet fragrance into the crisp air. That’s the magic of sweet peas-one of the few flowering plants that actually thrives when temperatures drop. While most gardeners are putting their beds to rest for winter, you could be nurturing a spectacular display of Lathyrus odoratus, transforming your garden into a fragrant paradise during the coldest months.

Sweet peas have been beloved by gardeners since the Victorian era, prized for their incredible range of colors-from pearly whites through soft pastels to deep magentas and inky purples. But what truly sets them apart is their intoxicating scent, described as a blend of honey and orange blossom. Unlike their modern cousins bred for size and form, many heirloom varieties maintain that powerful fragrance that made them famous. Best of all, these climbing annuals are surprisingly easy to grow if you understand their preferences.

Understanding sweet pea’s cool-season nature 🔗

Sweet peas possess a unique characteristic that makes them perfect for winter gardens: they genuinely prefer cooler weather. While most flowering plants sulk or go dormant in winter, sweet peas produce their most vibrant blooms and strongest fragrance when temperatures drop. This cool-season preference is so strong that excessive heat above 30°C can cause bud drop and reduced flowering.

This temperature preference affects when and how you plant them. In regions that experience regular frosts, you’ll want to sow seeds in very late winter or early spring as soon as the soil becomes workable-don’t wait until your last frost date, as that’s often too late. However, if you garden in mild winter climates, plant sweet peas in late fall so they can develop strong root systems through winter and bloom spectacularly in late winter and early spring.

Regional planting strategies 🔗

Your planting strategy should match your climate. In colder zones where winter temperatures regularly drop below freezing, starting seeds indoors about six to seven weeks before your last frost date gives you a head start. The seedlings can handle light frosts, so you can plant them out earlier than most annuals. In warm winter areas, autumn planting takes advantage of cooler temperatures for root development, setting up the plant for maximum flowering when spring arrives.

Preparing the perfect soil foundation 🔗

Sweet peas are what gardeners call “greedy” plants-they need nutrient-rich soil to produce those abundant flowers. The ideal foundation is rich, deep, loamy soil that’s moist but well-drained. Think of it like a sponge that holds water but never stays soggy. Waterlogged soil is sweet pea’s enemy, quickly leading to root rot and plant death.

Soil pH matters significantly for these plants. Sweet peas perform best in neutral to slightly alkaline soil, with a pH range between 6.0 and 7.5. At this range, nutrients remain readily available and the beneficial nitrogen-fixing bacteria on their roots can thrive. Testing your soil is simple with inexpensive kits available at garden centers. If your soil tests too acidic, incorporate agricultural lime several weeks before planting. For alkaline soils above 7.5, adding sulfur or organic matter like pine needles can help lower the pH.

Building nutrient reserves 🔗

About six weeks before sowing, dig a trench where you plan to grow your sweet peas and fill it with well-rotted manure or compost. This advance preparation gives the organic matter time to integrate with the soil, creating a nutrient reservoir the plants can tap throughout their growing season. Sweet peas fix their own nitrogen through root nodules, so focus your fertilization efforts on phosphorus and potassium to promote flowering rather than excessive leafy growth.

Starting from seed successfully 🔗

Sweet pea seeds have notably hard coats that can slow or prevent germination. Professional growers recommend pre-treating seeds to improve germination rates. The simplest method involves soaking seeds in lukewarm water for 12 to 24 hours before planting. You’ll notice some seeds swell-these are ready to plant. For stubborn seeds that don’t swell, gently nick the seed coat with a knife or sandpaper, being careful to avoid the small round scar called the “eye.”

When sowing, plant seeds about one-quarter to one-half inch deep, as darkness is required for germination. If starting indoors, use deep containers or root trainers since sweet peas develop extensive root systems relative to their size. Standard seed trays work, but deeper containers encourage stronger growth. Germination typically takes 14 to 21 days at temperatures between 55-65°F.

Direct sowing versus transplanting 🔗

While you can direct sow sweet peas into prepared garden beds, starting them in containers offers more control. You can protect young seedlings from harsh weather, monitor them closely for pests, and time their planting more precisely. However, sweet peas don’t appreciate root disturbance, so handle them gently during transplanting. Space plants 20 to 30 centimeters apart to allow adequate air circulation and room for growth.

Mastering the art of pinching 🔗

Here’s where many gardeners hesitate, but pinching is crucial for developing bushy, productive sweet pea plants. When your seedlings reach about four to six inches tall, use your thumb and finger to pinch out the growing tip just above a pair of leaves. This simple action redirects the plant’s energy from single-stem growth to developing multiple side shoots.

It might seem counterintuitive to remove growth from a plant you want to flourish, but pinching encourages strong side-branching that produces far more flowers than a single stem ever could. Think of it as pruning a fruit tree-short-term sacrifice for long-term abundance. Those side shoots will become the flowering stems that fill your garden with color and fragrance for months rather than weeks.

The cordon method for show-quality blooms 🔗

For gardeners wanting maximum-sized blooms for cutting or showing, there’s an alternative approach called cordon training. Select the strongest shoot and continuously pinch out all tendrils and side shoots as they develop. This forces the plant to concentrate all its energy into producing larger, more dramatic flowers on a single stem. Cordon-grown plants require regular tying to tall stakes and can grow much taller than the typical six-and-a-half feet, but they produce spectacular exhibition-quality blooms.

Providing essential support structures 🔗

Sweet peas are natural climbers that can reach six to eight feet tall-sometimes even taller with proper care. Installing support structures at planting time is critical, as trying to add them later risks damaging established roots and tangled vines. The support needs to be sturdy enough to handle wind and the weight of mature, flower-laden plants.

Simple options include bamboo canes arranged in wigwam shapes, wooden stakes with horizontal strings, or purpose-made netting. Traditional pea sticks-twiggy branches pushed into the ground around plants-offer a rustic, natural-looking option that eventually becomes invisible as vines grow. Whatever support you choose, position it close to the plants so their tendrils can easily grasp onto it. Tie in wayward shoots gently with garden twine or specialized sweet pea rings to guide growth in the desired direction.

Watering and feeding for continuous blooms 🔗

Sweet peas are thirsty plants, especially once flowering begins. Water deeply whenever the top few inches of soil feel dry, ensuring moisture reaches the entire root zone. In dry weather, plants in the ground may need checking every three to four days, while container-grown sweet peas often require daily watering. Applying a thick layer of mulch helps retain soil moisture and keeps roots cool, extending the flowering period.

While sweet peas fix their own nitrogen, they still benefit from supplemental feeding during the growing season. Apply a balanced liquid fertilizer monthly, or switch to a high-potassium formula like tomato feed once flowering begins. The extra potassium promotes flower production without encouraging excessive leafy growth. On light or nutrient-poor soils, feeding once or twice weekly maintains vigorous flowering.

The importance of deadheading 🔗

Perhaps the single most important maintenance task for sweet peas is removing spent flowers before they set seed. This practice, called deadheading, is absolutely critical because sweet peas will stop flowering if seedpods are allowed to develop. The plant interprets seed production as the completion of its life cycle and redirects energy away from creating new blooms.

Check plants every few days and snip off faded flowers with scissors or pinch them off with your fingers. Bonus benefit: cutting flowers for indoor arrangements essentially performs deadheading while providing you with fragrant bouquets. The more you cut, the more flowers the plant produces-it’s a wonderfully rewarding cycle.

Troubleshooting common challenges 🔗

Sweet peas face several potential problems, though most are preventable with proper care. Fungal diseases like powdery mildew and root rot typically arise from poor air circulation or waterlogged soil. Space plants adequately, avoid overhead watering, and ensure excellent drainage to minimize these issues. If powdery mildew does appear as a grey leaf coating, it’s often worsened by drought stress, so maintain consistent soil moisture.

Aphids commonly attack tender new growth, sucking plant sap and potentially transmitting viral diseases. Inspect plants regularly and address infestations early with insecticidal soap or by encouraging beneficial insects like ladybugs. Slugs and snails can devastate young seedlings, so protect plants when first transplanting them into the garden.

Environmental stress signals 🔗

Yellow leaves often indicate nutrient deficiencies or watering problems. While sweet peas produce their own nitrogen, they need adequate phosphorus, potassium, and micronutrients. Pale, yellowing foliage might signal iron deficiency in alkaline soils, while purple-tinged leaves could indicate phosphorus deficiency. Regular soil testing and balanced fertilization prevent most nutrient issues. If problems arise, foliar feeding with liquid fertilizer provides quick correction while you address underlying soil conditions.

Harvesting for maximum enjoyment 🔗

One of sweet pea’s greatest joys is cutting them for indoor arrangements. The best time to harvest is early morning when stems are fully hydrated and flowers are just opening. Cut stems with sharp, clean scissors just above a leaf node where new growth can emerge. Place cut stems immediately into cool water to maximize vase life, which typically ranges from four to seven days.

Regular harvesting actually encourages more flower production, making it a win-win situation. Don’t be shy about cutting generously-you’re not depleting the plant, you’re stimulating it to produce even more blooms. For the longest possible flowering season, consider succession planting by sowing new seeds every two to three weeks during the appropriate planting window. This ensures continuous blooms rather than one massive flush followed by decline.

Choosing varieties for your garden 🔗

The range of available sweet pea varieties is truly remarkable. Heirloom varieties like ‘Cupani’ offer the most intense fragrance and historical charm, with smaller flowers in classic bicolors. Modern hybrids like ‘April in Paris’ provide larger blooms and unusual colors like creamy yellow, though some sacrifice fragrance for size and form. For containers or small spaces, dwarf varieties like ‘Bijou Mixed’ grow just two to three feet tall and require no support.

When selecting varieties, consider whether fragrance or appearance is your priority. If scent is paramount, stick with heirloom varieties or modern cultivars specifically bred for fragrance. If you want dramatic blooms for cutting or showing, modern hybrids with larger flowers may suit your needs better. Most seed companies clearly indicate which varieties are particularly fragrant, making selection easier.

What do you think? Have you tried growing sweet peas in your winter garden? What challenges or successes have you experienced with these fragrant climbers?

References

1. https://www.almanac.com/plant/sweet-peas
2. https://www.rhs.org.uk/plants/lathyrus/growing-guide
3. https://www.johnnyseeds.com/growers-library/flowers/sweet-peas/sweet-peas-key-growing-information.html