There about 70 species of Hydrangeas and over 500 cultivars, which are split into many different groups, the two groups gardeners are most familiar with are Mopheads Hydrangea shrubs and Lacecaps Hydrangea shrubs. The Mophead Hydrangea flowers are what we are more familiar with when we think of Hydrangea shrubs.
The Mophead Hydrangea flowers are the big showy snowballs of flowers, whereas, the Lacecap Hydrangeas are much less showy, usually flat in appearance. Both are apart of the bigleaf hydrangea variety (Hydrangea macrophylla), which can reach a height of 8 feet tall. Mophead Hydrangea flowers can vary in color depending on the soil pH.
Hydrangeas are going to perform best in locations that get early morning sun and dapples of light throughout the day. Avoid garden locations that are hot and dry will be beneficial for optimum growth and health. If these conditions are unavoidable add plenty of compost and mulch to help retain moisture and keep the soil cool.
To prevent bud damage to your hydrangea, watch for spring frosts and cover plants if frost does occur. Early fall frost can also cause damage to your hydrangea, so keep an out as late fall approach.
Hydrangea flower color change
If you have hydrangeas blooming pink or red every-year and you want to add some big bursts of indigo blue it might be simpler than you think. Many hydrangea flowers will change from blue to red or from red to blue depending on the soil’s pH.
Soil pH changes the availability of aluminum to the hydrangea shrub. Depending on the soil’s pH range there are different nutrients either more or less available to the hydrangea. this is true of most nutrients and when it comes to aluminum the more acidic the soil the more available aluminum is to the Bigleaf Hydrangea shrubs.
For Bigleaf snowball hydrangeas, the availability of aluminum results in cellular processes that changes flower color from either blue to red or visa vera. That change could come as a shock to anyone purchasing a hydrangea of one color to find in future years flower color is different.
If the pH of the hydrangea is opposite to your landscape or garden’s pH there can be a color change once the roots start to grow into their new environment. You could plant hydrangea bushes all around the yard and garden, and by controlling the soil acidity in the different locations your blooms would vary from blue to red.
The science behind the change
This color change happens from the presence of the anthocyanin pigments in the petals of hydrangea. Other places we see these pigments are in blueberries and raspberries, and it's what makes red cabbage red, as well as responsible for some of the fall color change.
Anthocyanin pigments will vary the color of hydrangea petals depending on soil acidity. If soil acidity is high, meaning the pH is around 5.5 or lower the flower colors will develop into a deep blue. When pH is above 7.0 the flowers change to a red color.
Studies have shown that the mechanism that affects petal color in hydrangea is the availability of aluminum in the soil. In the same manner that other nutrients are either available at certain levels or unavailable completely to plants, so too is aluminum. These aluminum ions are what directly affect the color of hydrangea flowers.
When the garden soil has a high pH(more acidic) there is more aluminum available to the plants. When the soil pH becomes sweet(more alkaline), the aluminum in the soil becomes less available to the plant.
Depending on which color you prefer adjustments can be made to your soil to be more acidic for blue or more alkaline for red blooms. You can gradually change the pH of your soil by the addition of dolomitic lime or sulfur, one to raise the pH and the other to lower it.
Tips to change Hydrangea flower color
Soil pH indirectly affects the flower color of many hydrangea flowers by affecting the availability of aluminum in the soil. When the soil pH is acidic (pH 5.5 or lower), aluminum is generally more available to the roots. When soil pH is neutral or alkaline (pH 7.0 or higher), the availability of aluminum in the soil decreases.
To change flower color from pink to blue, broadcast 1/2 cup of wettable sulfur per 10 square feet. Finish by working the amendment into the top few inches of soil and irrigate.
To change flowers from blue to pink, broadcast one cup of dolomitic lime per 10 square feet. Finish by working the amendment into the top few inches of soil and irrigate.
It may take a year to see a noticeable change in flower color from this treatment. A quicker way to achieve a change in flower color is through liquid soil drenches.
To intensify or develop a bluer hydrangea flower, dissolve one tablespoon of alum (aluminum sulfate) in 1 gallon of water and drench the soil around the plant in March, April, and May.
To intensify or develop a pinker flower, dissolve one tablespoon of hydrated lime in 1 gallon of water and drench the soil around the plant in March, April, and May. Avoid getting the solution on the leaves because foliar damage may result.