Understanding Sweet Peas for Cultivation
Growing sweet peas (Lathyrus odoratus) is an achievable pursuit for most gardeners, yielding an abundance of delicately scented, colourful flowers that are ideal for cutting. These annual climbers thrive in cooler conditions, making them a staple for spring and early summer displays. Understanding their basic needs – sunlight, well-drained soil, and support – is the foundation for success. Unlike some more robust climbing plants, sweet peas prefer a slightly less fertile soil to encourage flowering over leafy growth.
The allure of sweet peas lies not just in their visual appeal but their intoxicating fragrance, which varies by cultivar. From the ruffled, large-flowered Spencer types to the more compact ‘Cupani’ varieties, there's a sweet pea to suit most garden spaces, whether you're looking to adorn a trellis, a fence, or a hanging basket. They are true annuals, meaning they complete their life cycle in a single year, from seed to seed, making the annual ritual of sowing and growing them a cherished part of the gardening calendar.
Key Sweet Pea Varieties and Their Traits
When embarking on growing sweet peas, familiarising yourself with different types can help you choose what best fits your aesthetic and growing conditions. Spencer varieties are celebrated for their large, frilly blooms and long stems, making them excellent for cut flowers. They typically grow to about 1.8-2.5 metres (6-8 ft) tall.
The ‘Bicolour’ types often showcase striking combinations of colours, while the ‘Heirloom’ or ‘Old Fashioned’ varieties, such as ‘Cupani’, are prized for their intense fragrance and slightly smaller, more delicate flowers. These tend to be more compact, reaching around 1.2-1.5 metres (4-5 ft), and are well-suited for smaller gardens or containers. Ensure you select a variety suited to your climate and the support structure you intend to use.
The most crucial factor for success is sowing at the right time.
Planting Sweet Peas: Sowing Seeds and Establishing Plants
When to plant sweet peas can be approached in a couple of ways, both aiming to give them a head start. The most common method for growing sweet peas involves sowing seeds directly into the ground or into pots. For earlier blooms, particularly in cooler climates, it's beneficial to sow seeds indoors in modules or deep pots from late autumn through to early spring. Using deep pots (at least 15cm or 6 inches) is advisable because sweet peas develop a long tap root that requires space.
Soaking seeds overnight before sowing can improve germination rates, though this isn't always necessary for all varieties. Plant seeds about 2-3cm (1 inch) deep, spaced a few centimetres apart in trays or modules. Keep them in a cool, bright location, ideally a greenhouse or cold frame, to germinate. Once seedlings have developed a few sets of true leaves and the risk of hard frost has passed, they can be hardened off and transplanted into their final positions.
Direct Sowing Techniques
For gardeners in milder regions, or for a later flush of flowers, direct sowing sweet pea seeds outdoors in early spring (typically March or April) is perfectly viable. Prepare the soil well in advance, incorporating some well-rotted compost or manure for fertility, but avoid over-enriching it, as this can lead to excessive foliage at the expense of flowers. Sow seeds in a double row along a prepared support, such as netting or canes, spacing them around 10-15cm (4-6 inches) apart. This allows the young plants to establish and climb naturally.
Ensure seeds are sown with their ‘nose’ pointing upwards or sideways for optimal germination.
When planting out seedlings or sowing directly, consider the planting location carefully. Sweet peas require at least five to six hours of direct sunlight daily, preferably in a position with good air circulation. Protect young seedlings from slugs and snails, which are particularly fond of their tender shoots. You can use barriers, traps, or organic deterrents to keep these pests at bay.
Support Structures for Climbing
Sweet pea plants are natural climbers and require support to reach their full potential. This can be anything from simple netting stretched between canes to more elaborate trellis systems, obelisks, or even woven hazel or willow structures. The key is to provide ample climbing space and ensure the support is sturdy enough to hold the mature plants, especially in windy conditions. Erecting supports at the time of sowing or planting avoids disturbing the root systems later on.
Caring for Sweet Peas Throughout the Season
Once your sweet pea plants are established and starting to climb, consistent care is vital for a prolonged and abundant flowering period. Regular watering is paramount, especially during dry spells. Aim for deep watering rather than frequent, shallow sprinkles to encourage strong root development. Applying a mulch around the base of the plants can help retain soil moisture and suppress weeds, further aiding their growth.
Feeding is also important, but it should be done judiciously. While sweet peas benefit from nutrients, an excess of nitrogen can promote lush leaf growth at the expense of flowers. Once flowering begins, switch to a feed higher in potash, such as a liquid tomato feed, applied every two to three weeks. This encourages the plant to produce more blooms. Avoid feeding too early or too heavily.
Deadhead regularly, removing faded flowers before they set seed, to encourage the plant to produce more blooms throughout the summer. Seed formation diverts energy away from flower production.
Pruning and Training
While not strictly pruning, the ongoing training and encouragement of sweet peas are key to maintaining their appearance and productivity. As the tendrils develop, gently guide them towards the support structure. You can tie main stems loosely to canes or netting if they need extra help to adhere. Pinching out the growing tips of young plants when they are about 15-20cm (6-8 inches) tall encourages them to branch out, leading to a bushier plant with more flowering stems.
Healthy plants are less susceptible to pests and diseases.
Pest and Disease Management
Common issues when growing sweet peas include attacks from slugs and snails, particularly on young plants. As mentioned, prevention is key. Aphids can also be a nuisance, clustering on the young shoots and flower buds. A strong jet of water can dislodge them, or for more persistent infestations, an organic insecticidal soap can be used sparingly. Ensure good air circulation around the plants to minimise the risk of fungal diseases like powdery mildew, which can affect the foliage in damp conditions.
Companion Planting and Alternatives
Considering companion planting can enhance the health and appeal of your sweet pea displays. While sweet peas are not particularly fussy, planting them near certain flowers can offer mutual benefits or simply create a beautiful visual tapestry. For instance, sturdy plants like sunflowers can provide excellent support for climbing sweet peas, and their vibrant yellow tones complement the softer hues of many sweet pea varieties. Marigolds, often planted nearby, are reputed to deter nematodes in the soil.
When thinking about what to grow alongside sweet peas, consider their light and soil needs. Flowers that enjoy similar conditions, such as cosmos or certain varieties of petunias, can create a harmonious planting scheme. Nasturtiums, known for attracting aphids away from other plants, could also be a strategic companion, acting as a trap crop. Conversely, avoid planting sweet peas too close to vigorous plants like beans, which might outcompete them for resources and light.
Alternatives to Traditional Climbing
Not everyone has space for tall trellises, but that doesn't mean you can't enjoy growing sweet peas. For smaller gardens or patios, dwarf varieties are an excellent choice. These remain compact, typically reaching only 30-60cm (1-2 ft) in height, and can be grown in pots, containers, or window boxes. They often spill over the edges, creating a lovely waterfall of colour and scent without needing extensive support.
Another approach is to grow sweet peas in hanging baskets. Varieties like ‘Pendula’ or ‘Bijou’ are particularly well-suited for this, trailing elegantly over the sides. Ensure the basket is deep enough to accommodate their root system and that it’s placed where it will receive adequate sunlight. Remember that plants in hanging baskets tend to dry out more quickly, so regular watering and occasional feeding will be necessary.
Experimenting with different varieties and planting locations can lead to unique garden features.
Comparing Sweet Peas to Other Annual Climbers
While sweet peas are unique for their fragrance and delicate blooms, other annual climbers offer different aesthetics and growth habits. Nasturtiums, for example, are very easy to grow from seed sown directly outdoors and come in both climbing and bush forms, offering vibrant splashes of orange, yellow, and red. They prefer a sunnier spot and are more tolerant of drier conditions than sweet peas.
Morning glories (Ipomoea species) provide rapid growth and spectacular trumpet-shaped flowers that open in the morning. They are vigorous climbers and can reach significant heights quickly, making them ideal for covering unsightly fences or arbours. However, their flowers are generally not scented and last only a single day. Sweet peas offer a more refined elegance and the incomparable pleasure of their perfume.
The true magic of growing sweet peas lies in their dual capacity to enchant with fragrance and adorn with delicate, fleeting beauty.