The easiest way to plant geranium is from transplants, which are easy to find at nearly every garden center in spring. You’ll find cultivars propagated by seed, which are largely varieties with the single flower form. Since these plants must be protected from cold, wait until the threat of frost has passed before planting.
Space plants about 8 to 12 inches (20-30 cm) apart, and around the same depth as their original planting pots. Mulching the plants is also recommended to help retain moisture.

Pot Size : 6 Inch Black Plastic Basic Nursery Pot.
Botanical name – Pelargonium x hortorum
Height – 1 to 3 feet (30.5 to 91.4 cm)
Spread – 1 to 3 feet (30.5 to 91.4 cm)
Sun exposure – Full sun to partial shade
Soil requirements – Rich, well-drained
Hardiness zones – 10 to 11 (as perennials)
When to plant – Spring, after last frost