hydrangeas - Knowledgebase Question

Sayville, Ne
Question by JMKay76
May 3, 2009
I have received conflicting answers to whether or not to cut back my htdrangeas yearly or and when to do it. Also, pH of the soil deteermines the color of blooms, what pH level for what color? thanks joan

Answer from NGA
May 3, 2009


There are many different kinds of hydrangeas, but their cultural requirements are the same. Once you have selected your Hydrangea, growing it is relatively easy. Most Hydrangeas are natural woodland plants and like some shade. Morning or late afternoon sun is OK, but the flowers can burn if exposed to mid-day sun. If a Hydrangea has been planted in a poor location is usually easy to move; it has a relatively small compact root ball. Hydrangeas will grow in almost any soil, but will do better if the soil retains moisture. They should be watered frequently enough that the soil does not completely dry out. The flowers of many but not all H. macrophylla will range in color from pink to blue depending upon soil acidity. Acid soils produce blues and alkaline soils produce pinks. If you want to encourage one color, add lime to soil to make the soil more alkaline or iron sulfate to make it more acid. Hydrangeas do not demand a lot of special fertilizing. A good balanced fertilizer can be applied in the late winter or early spring. Mulching of your Hydrangeas is a good practice as it helps hold in water around the roots of the plant. The decaying of organic mulch will also add nutrients to the soil. Finally, a word about pruning. Hydrangeas do not require pruning except to remove dead wood. If you want to prune to encourage a particular shape, time the pruning based upon whether the Hydrangea blooms on the current or previous year's growth. If it blooms on the previous year's growth, prune right after it blooms. If it blooms on the current year's growth, prune in late winter or early spring, while it is dormant.

Soil pH does affect some hydrangeas. Macrophylla types will have blue flowers in acidic soils and pink flowers in alkaline soils. Some blues cannot be changed (Nikko, for instance) and all whites will remain white regardless of soil pH. Changing soil pH takes several months and you need to know your own soil's pH before you can determine just how much of what element to use to change the pH.

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