Multiple customer Question/Questions: (This set of questions is often asked and asked by many customers ~ so here is my best advice/suggestions)How should I prune my hydrangea? Is there something that could be added to my hydrangea that would turn the pink flowers blue? Is this a good idea?

Answer: (To the best of my ability) The hydrangea, macrophylla, is widely used in different zones of our state. It comes from Japan, is deciduous, has a symmetrically rounded growth habit, and grows 4-6 feet high and as wide. It does well as a landscape shrub or in a container. The blue and pink colors of the hydrangeas depend on the amount of aluminum in the soil that is absorbed by the roots.
The blue flowers appear on the hydrangea that has a soil pH of 5.5 or less.
In alkaline soil, it is difficult achieve a pH of 5.5 or less.

This normally means we have pink flowers since the aluminum is tied up in an insoluble form that cannot be absorb by the roots.

White cultivars are generally white and are not affected by the soil's pH.

Flowers grown for the florist trade have lime or superphosphate added to the soil mixture, which will tie up the absorption of aluminum resulting in pink to red flowers.

For blue flowers, they add aluminum sulfate (51.0%) to lower the pH in the soil. You can purchase this at your nursery. Depending on the size of the plant, add 1 tablespoon to cup per plant in late fall. Make 2 to 3 more applications in the early spring and again in late spring depending on your existing soil pH. This treatment must be done now and again next spring to change the flower color. A simple test kit for pH is available at your nursery.

The eastern side of the house is the best location in very warm areas or plant in partial shade, to avoid the hot afternoon sun. This plant likes a well-drained, porous soil. The flower buds are formed at the terminal of the stem (apical dominance) of last year's growth. If this flower bud is damaged, other flower buds down the stem will develop. If you cut the tips of the branches before the flowering season you will have more branches and flowers. This could cause too many flowers that are crowded together and will not fully develop on the shady side
The first 1-3 years the plant will not need to be pruned, except for cross or unsightly branches which should be cut to the ground. For the life of the plant, you must keep the center open to the light and air for a healthy bush. To cut flowers for the house or removing dying flowers, cut between the bottom of the flower head and above the first set of leaves. Cutting lower than the first set of leaves could stimulate unwanted growth from the lower buds at the leaf nodes.

Maintenance pruning can be done now by removing the dead, weak, diseased and broken stems on both the new and old wood by cutting to the ground as close as possible. Do not remove more than one-third of the old wood at a time. I like to leave some of the inside wood longer than some of the outside to keep the bush from becoming a "roundy-moundy." Keep the inside open to light. By pruning now, it should give the plant sufficient time for the new growth to harden before freezing weather.

The plant can be pruned just above a node, remembering that next year's flowers will grow on the new growth of the old stems. To get the biggest flower clusters, reduce the number of stems per plant; for numerous medium and smaller clusters, keep more stems.

If you have an overgrown or neglected shrub, I would cut it back to within 12 inches of the ground. Then cut back week or diseased stems followed by old wood stems near the center to the ground. If done now, you may still have a few blossoms next year and many more the following year. Continue the maintenance program next year.

Hydrangeas like soils high in organic matter. Compost worked into the soil before planting and adding peat moss will help to make the soil acid. Wood chips or other mulch material will help the plant throughout the year. A balanced fertilizer, such as 15.15.15 or a slow release fertilizer (Osmocote, Nutricote or Polygon) 4 ounces of 10.10.10 should be placed at the base of the plant and deep watered before the leaves appear. Here is a picture of my fall compost, it's free and you can find it everywhere in New England ;)

Again, white cultivars are not affected by soil pH. However, availability of aluminum may result in a pink or blue eye in the flower, depending on its presence or absence in the soil.

Hydrangeas do very nicely in containers as you can control the soil pH as well as the location of the pot for best blooms.

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