- Zone: 4-9. - Bloom- Summer-Fall. - Light: Sun- Part Shade. - Heat Tolerant. - Hydrangeas are attractive flowering shrubs that are easy to grow from seed in home landscapes. Several species of hydrangea seeds are readily available from home and garden stores as well as seed catalogs. Hydrangeas are commonly planted as specimen plants or used to create colorful shrub borders. The shrubs develop numerous long-lasting flowers that bloom from summer through fall. Hydrangeas are hardy plants that are easy to grow and care for indoors before you transplant them in your landscape. - Step 1 - Fill a planting flat for seeds two-thirds full with vermiculite or perlite potting soil. - Step 2 - Water the potting soil to increase the soil moisture. - Step 3 - Sprinkle four hydrangea seeds in each section of the flat and cover with plastic wrap to maintain soil moisture and humidity. - Step 4 - Place the planting flat with the hydrangea seeds in a bright location. Hydrangea seeds require ample sunlight to germinate, but you should avoid placing the flat in direct sunlight to maintain a stable temperature. Hydrangea seeds germinate in 10 to 14 days. - Step 5 - Fill 1-gallon potting containers with a mixture of peat soil and organic compost. - Step 6 - Transplant the hydrangea seedlings to 1-gallon potting containers once the plants develop three to four healthy leaves. - Step 7 - Place the individual potting containers in a sunny location and maintain soil moisture until you are ready to plant the hydrangeas in your landscape. Late spring -- after the risk of frost has passed -- is the best time to plant hydrangeas in your landscape.