Hydrangeas are often used as specimen plantings in landscape design. They are an old garden favorite known for their lovely, large, pink, blue, or white flowers. The pH of the soil determines the color of their blossoms, with some plants exhibiting pink and blue blooms. There are several varieties of hydrangea with mopheads being the most popular. Hydrangeas are easy to maintain. Their large blooms are a wonderful addition to any garden.
Mopheads, or Hydrangea macrophylla are also known as French hydrangeas. They are the most recognized of the hydrangeas. A mature mophead shrub can reach a height of up to 6 feet. Dwarf mopheads are also available. They reach a height of 2 feet. Mopheads and lacecaps are two French hydrangeas.
Hydrangea quercifolia or oakleaf hydrangea is native to the south east regions of the United States. Oakleaf hydrangea is a large deciduous shrub, which reaches a height of 6 to 8 feet. The blooms of the oakleaf hydrangea are white. It does well in southern climates because it can be grown in shade or partial shade, thriving on morning or late sun.
Hydrangeas are hardy in zones 2 through 8 depending on the variety you plant. They require a partially shaded area, with a northern or eastern exposure being ideal. It needs to be watered often during the summer season. To maintain moisture you should mulch the area around the hydrangea -- this will also help to keep the weeds down. The mulch should be approximately 4 inches deep. Hydrangeas should be planted in organically rich, well drained soil.
Blue Blooms or Pink Blooms
Acidic soil produces blue blooms. To create a more acidic soil apply 2 tablespoons of sulfur or aluminum sulfate to the soil, working it into the soil with your hand cultivator, and then water the area well. This should be done in early fall. If you prefer your hydrangea to have pink blooms, add lime to the soil in early fall. You should apply a cup of dolomitic lime to the soil surrounding the shrub, work it into the soil with your hand cultivator, and then water the plant well.
According to the United States National Arboretum, "Established bigleaf (mopheads), panicle, oakleaf and smooth hydrangea plants can often benefit from regular pruning. Removing about one-third of the oldest stems each year will result in a fuller, healthier plant." They suggest that this pruning should be done in the winter season. You may also need to prune away any dead, diseased, or damaged branches, which can be done at any time. Hydrangeas can also be deadheaded, which means that you can remove spent blooms at any time during the growing season.
Pruning to Control Height
Mopheads and oakleaf hydrangea flower on last year's growth, so if you need to prune them to control their height then you should do so after flowering is complete. Other varieties of hydrangea such as the panicle and smooth hydrangea blossom on new wood or the current year's growth -- they can be pruned at any time (late summer until early spring.) In spring you should prune before leaves appear.