Big Leaf Hydrangeas: A Beginner's Guide to Planting, Growing, Pruning, and Changing Flower Color

Hydrangeas were first introduced by Sir Joseph Banks from a Chinese garden in 1739. They're the birth flower of June, and almost always bloom then. Big Leaf Hydrangea (Hydrangea macrophylla) are the most common kind, with the largest blooms.

Hydrangeas are hardy to -20 degrees Celsius, although winds at -15 degrees Celsius will kill tender wood to the ground. In colder areas, damage to the buds may occur in winter and late spring, so cover the plant with an old sheet, blanket or cardboard container when temperatures drop below freezing. If you live in an area with winters below -20 C, a cylinder of chicken wire placed around the plant and filled with leaves provides excellent cold protection.

Planting Hydrangeas

Big leaf hydrangeas prefer partial shade. Morning sun and afternoon shade is perfect in inland areas; on the coast, no shade is required. Give them moist, well-drained soil and avoid planting on hot, dry, exposed sites.

Incorporate compost, well-rotted manure or mushroom manure thoroughly into the top 8 to 12 inches of soil with a shovel. Organic matter holds nutrients and water in the soil and helps prevent stress from fluctuations in soil moisture levels. As with any other shrub, plant the root ball level with the soil surface, and water thoroughly immediately after transplanting.

Fertilization and Watering

Don't fertilize hydrangeas at all until they are established, 4 to 8 weeks after transplanting. Once established, feed with an all-purpose fertilizer. Hydrangeas are water-demanding, so water whenever the plant begins to wilt in the absence of rainfall. Avoiding this wilt is particularly important during the spring months when the flower heads are forming. Be sure to monitor the soil moisture around your hydrangeas during dry weather.

Changing the Color of Hydrangea Flowers

Aluminum changes the color of the flowers - lots of aluminum makes blue, while no aluminum makes pink. Most gardeners change the pH of their soil to achieve the desired color. It may take a year to see a noticeable change in flower color from this treatment.

• To make flowers pink, add 1 cup of dolomite lime per 10 square feet and water into the soil. Areas with naturally alkaline soils will have naturally pink Hydrangeas.
• To make flowers blue, add wettable sulphur to the soil; 1/2 cup of wettable sulfur per 10 square feet. Water in. Areas with naturally acid soil will have naturally blue Hydrangeas.