Many folks grow hydrangeas for their abundant long-lasting blossoms and their dramatic beauty in a landscape. Hydrangea plants are easy to care for, and unlike most other blooming plants, the color of some hydrangea blossoms can be controlled or changed. Changing hydrangea bloom color is accomplished by regulating the acidity of the soil.
Nikko Blue Hydrangea
Not all hydrangea varieties can change color. Those that are naturally white will remain white no matter how or where they are grown. Most hydrangea blooms tend to subtly change color as they mature, but only those that are naturally pink or blue can be made to completely change color. This would include the colored Big Leaf and Pee Gee varieties. Big Leaf hydrangeas are also known as mopheads or lace caps.
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If your hydrangea has blue blooms, amending the soil to make it more alkaline will change the blooms to pink. Likewise, a pink hydrangea's blooms will become blue by increasing the acidity of the soil.
It is much easier to change pink hydrangeas to blue than it is to change blue hydrangeas to pink. It is also much easier to control the color of hydrangeas grown in pots instead of in the ground. The presence or lack of aluminum in the soil is key to changing hydrangea bloom color.
Garden centers offer aluminum sulfate which can be added to the soil around hydrangeas to make the soil more acidic for blue hydrangea blooms. Apply aluminum sulfate around plants that are at least two years old, watering the plants well before applying. Mix one tablespoon of aluminum sulfate per gallon of water and apply throughout the growing season to retain the blue blooms.
If your soil is naturally acidic but you want pink hydrangeas, the plants cannot be given the opportunity to use the aluminum present in the soil. Raising the soil pH to between 6.0 and 6.2 will prevent the plant from taking up aluminum from the soil. Using a fertilizer high in phosphorus will also prevent the plant from taking up aluminum and will encourage pink blooms.
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There are four categories of hydrangeas, and you must know what type of hydrangea you have when determining how to properly care for your plant. These hydrangea categories are Hydrangea macrophylla, Hydrangea arborescence, Hydrangea quercifolia and Hydrangea paniculata. Most hydrangeas are hardy to growing zones 4 or 5 on up through zone 8.
Hydrangea macrophylla are commonly called Big Leaf, Mophead and Lacecap hydrangeas. Big Leaf hydrangeas are some of the most popular hydrangeas. Most of these bloom in July to August and have blue or pink blooms, although a few varieties have white flowers. Except for the white varieties, any of the Big Leaf hydrangeas can be forced to change color. If a Big Leaf hydrangea needs to be pruned, this should be done in early summer, before the next season's flower buds are formed.
These hydrangeas bloom on old wood that was formed during the previous growing season. The flower buds are formed in August through October, so do any necessary pruning in midsummer, prior to August. If the plant has any dead wood, it may be pruned off at any time. After a Big Leaf hydrangea has reached five years old, about a third of the stems can be pruned back to the ground each summer to help revitalize the plant.
When planting a Big Leaf hydrangea, give them a spot where they can grow as large as they'd like. They can be cut back in midsummer if they're getting too large for their space, but they'll soon grow back to their large size. Give a Big Leaf hydrangea plenty of room right from the start and it will be much easier to care for.
Nikko Blue Hydrangea
Hydrangea arborescence includes the Annabelle hydrangea and its relatives. Annabelle hydrangeas have large white blooms which often reach up to ten inches in diameter. Annabelle hydrangeas are a native plant of the Eastern United States and they prefer to grow where they can have morning sun and afternoon shade, or dappled shade all day. Hot afternoon sun will make Annabelle's heavy blooms fade more quickly. Annabell hydrangeas bloom from early summer through August or September.
Annabelle hydrangeas are a popular landscape shrub because they will bloom reliably even after a severe winter or a heavy pruning. In the far north, Annabelle hydrangeas will die back to the ground each autumn, then send up new growth in the spring and still bloom profusely during the summer. The blooms tend to be quite heavy, sometimes bending the stems to the ground. The stems can either be staked for support, or kept pruned to about 24 inches to help promote stronger stems that are better able to support the blooms.
Annabelle hydrangeas bloom on new wood formed during the current growing season, and they should not be pruned in the spring while they are preparing to bloom. They can be pruned any other time of year, but in general it isn't necessary to prune Annabelle each year except for removing dead wood or any branches that don't contribute to a nicely shaped plant. Annabelle hydrangea is a lovely plant that is very easy to care for.
Hydrangea quercifolia is more commonly known as Oakleaf hydrangea. Oakleaf hydrangeas are also native to the United States, and as their name suggests, they have large, deeply lobed leaves. The white blooms of Oakleaf hydrangeas are beautiful in early to midsummer, and the blooms tend to turn a lovely shade of pink as they age. Oakleaf hydrangeas also add a splash of color to the landscape in the fall as their large leaves turn brilliant red, burgundy, orange or yellow, especially if they receive some sunlight.
These hydrangeas are more tolerant of sun and dry conditions than other types of hydrangeas, but they will not tolerate wet feet. Plant Oakleaf hydrangeas in well draining soil, or provide them with a raised bed if your soil has poor drainage. Oakleaf hydrangeas should be pruned at the same time and in the same manner as the Big Leaf hydrangeas.
Hydrangea paniculata are commonly called PeeGee hydrangeas. PeeGee hydrangeas are popular because they will grow in a variety of climates and are hardy up to zone 3. Like the Oakleaf hydrangeas, PeeGee's white blooms tend to turn pink as they age. PeeGees often grow very large, up to 8 to 10 feet tall and just as wide, so allow plenty of room when choosing a spot to plant a new PeeGee. They do appreciate some shade in very hot climates and PeeGees are tolerant of sun if they receive enough moisture. PeeGee may be pruned at any time except in midsummer when they are preparing to bloom, and this is a hydrangea that can also be pruned to a tree shape.
A hydrangea doesn't require much special care. You may want to give your hydrangea a balanced, slow-release granular fertilizer once a year in late spring to keep it happy. Spread the fertilizer under the plant, but not right next to the trunk, and keep in mind that not enough fertilizer is always better than too much.
All hydrangeas will grow and bloom well with morning sun and afternoon shade. But they will not be happy in heavy shade and won't grow well if planted directly beneath a shade tree. In cool northern regions, a hydrangea may grow well with more than a half day of full sun, but if your landscape is hot and mostly sunny, you may want to limit your hydrangeas to the PeeGee varieties. Unfortunately, it may be difficult to grow hydrangeas in far southern areas that rarely see frost.
Hydrangeas are quite easy to propagate, so much so that they almost seem eager to produce roots. Softwood propagation and layering are the recommended methods for propagating a hydrangea.