The most immediate and visually striking difference lies in the flower's form. Heirloom or Grandiflora-type sweet peas produce smaller, simpler flowers. These blossoms typically consist of a single row of petals, giving them a delicate, graceful, and classic appearance. Their form is closer to that of the original wild species from which all sweet peas were bred. In contrast, Spencer-type sweet peas are celebrated for their large, dramatically ruffled, and frilled flowers. They possess a much fuller form, often with multiple layers of petals, creating a lavish and opulent bloom that is the hallmark of modern floral competitions and cutting gardens.
The architecture of the plant's flowering stems further distinguishes the two types. Heirloom varieties are renowned for their exceptional floriferousness, meaning they produce a very high quantity of flowers per plant. It is common for a single stem of an heirloom sweet pea to carry four, five, or even more individual blooms. This creates a profuse display of color but can sometimes come at the cost of individual flower size and stem length. Spencer varieties, bred primarily for their use as cut flowers, focus energy on producing stronger, longer stems. These stems typically carry three or four, but sometimes only two, of their massive blooms. This structural adaptation makes them far superior for floral arrangements, as the sturdier stem can better support the weight of the large, heavy flower.
From a sensory perspective, fragrance is a critical differentiator. This is an area where heirloom sweet peas almost universally excel. They have been selected over generations for their intensely sweet and powerful perfume, which can easily fill a garden or a room. The scent is often described as the quintessential "sweet pea" fragrance—honeyed, orange-blossom-like, and incredibly potent. While many Spencer varieties are also fragrant, the intensity and consistency of their scent can be more variable. The breeding focus for Spencers was primarily on visual characteristics like flower size and form, so fragrance was sometimes inadvertently diminished. Some modern Spencer strains may have a lighter scent or, in rare cases, be nearly scentless.
Both types are climbing annuals, but their overall growth vigor can differ. Heirloom sweet peas are generally considered tougher and more tolerant of a wider range of conditions, including poorer soil and less-than-ideal weather. They are often earlier to flower and can be more resilient in the heat. Spencer sweet peas, being more highly bred, can sometimes be slightly more particular in their requirements, needing consistent moisture and fertile soil to produce their best and largest flowers. They were specifically selected for their ability to produce those spectacular blooms on long stems, a trait that demands more energy from the plant.
