Geraniums, with their vibrant blooms, are popular flowering plants used in seasonal gardening. While many gardeners purchase pre-grown plants or rooted cuttings, starting these annuals from tiny seeds is a specific propagation method. This approach, known as growing seed geraniums, provides a cost-effective way to cultivate a large number of plants. The process requires a longer lead time than purchasing established plants, but it offers access to unique varieties.
Defining Seed Geraniums
Seed geraniums are cultivated sexually from a seed, rather than vegetatively through a stem cutting. These plants are botanically members of the genus Pelargonium, not the true perennial geraniums (cranesbills). The common name “geranium” is applied to these annual bedding plants due to a historical classification error. Pelargonium species propagated from seed typically exhibit a more compact and uniform growth habit compared to their cutting-grown relatives.
They are often slightly smaller, usually growing 12 to 15 inches tall, making them suitable for mass plantings in beds and borders. While their flower heads may not be as massive as some high-end cutting varieties, seed geraniums produce numerous blooms, ensuring dense coverage of color. The most popular are the zonal geranium types, recognizable by the distinct horseshoe-shaped markings on their leaves.
Key Differences from Cutting-Grown Varieties
Seed geraniums are substantially cheaper than those grown from cuttings, making them ideal for gardeners needing large quantities. A single packet of seeds can yield dozens of plants for less than the price of a few nursery-grown individuals. This cost-effectiveness makes them the preferred choice for large-scale landscaping and municipal plantings.
In terms of appearance, cutting-grown varieties, often called zonal geraniums, are typically genetically advanced to produce larger flowers and a more vigorous, uniform size. Seed geraniums, while uniform within a specific seed series, generally have smaller flowers and a less intense vigor than the highest-performing cutting varieties. However, modern breeding has significantly reduced the performance gap between the two types over recent decades.
Starting from a commercially packaged seed provides a high degree of assurance that the plant is free from viruses and diseases. Vegetative propagation relies on mother stock, which can sometimes harbor unseen systemic pathogens that are passed directly to the cuttings. The process of sexual reproduction helps to cleanse the plant line, resulting in inherently healthier young plants.
A major consideration is the time required for a seed geranium to reach maturity and bloom, which is significantly longer than for a cutting. They require a long indoor growing period, often 12 to 16 weeks from sowing until they are ready to be transplanted outside after the last frost. Seeds must be started indoors in mid-to-late winter (January or February) to ensure blooms by the warm weather planting season.
Successful Cultivation from Seed
Cultivation begins by sowing seeds indoors approximately 10 to 12 weeks before the last expected spring frost date. Use a fine, sterile, and well-draining seed-starting mix, ensuring it is moistened before placing the seeds. Seeds should be sown lightly, covering them with only about 1/8 inch of the starting mix or vermiculite.
Geranium seeds require specific conditions for successful germination, primarily high heat. The soil temperature must be consistently maintained between 70°F and 75°F, often necessitating the use of a bottom heat mat. Temperatures exceeding 78°F, however, can inhibit germination.
While some varieties may benefit from a chilling pre-treatment to soften the seed coat, the most important factor is maintaining consistent warmth and moisture. Germination can occur quickly, sometimes in a few days, but it may take up to four weeks. Once the seedlings emerge, remove any plastic dome covers to allow for air circulation and prevent damping-off disease.
Seedlings need 12 to 16 hours of bright light daily, best achieved using supplemental grow lights positioned close to the plants to prevent them from becoming spindly. When the seedlings have developed two sets of true leaves, they should be transplanted into slightly larger containers. Before planting outdoors, the seedlings must undergo “hardening off,” slowly acclimating them to outdoor conditions like wind and direct sunlight over seven to ten days.