How to Keep a White Hydrangea White
Hydrangeas are beautiful, large-leafed flowers that come in a wide variety of colors such as vibrant blues, purples, pinks and whites. These flowers originated in the Japan, but do well in most parts of the world. The color of hydrangeas can be altered by adjusting the pH levels of the soil surrounding the hydrangeas. Anybody can change the color of hydrangeas and all it takes is a little effort to have your white hydrangeas looking their best.
Test the pH level in the soil surrounding the hydrangea. The higher the level, the more acidic it is. Keep the pH level between 6.0 and 6.2.
Add a well-balanced, slow release fertilizer containing equal parts of nitrogen, phosphorous and potassium. Choose a good fertilizer such as 10-10-10 from the store.
Test the pH level again to make sure it is not too high. The pH level should not be above 7.0.
Fertilize the ground surrounding the hydrangea once in late winter. Apply 1 lb. of fertilizer per 100 square feet of soil.
Water regularly with a garden hose, but make sure you don't overdo it or that the water does not stand on the soil. Excess water could cause the plant to wilt and rot. Place 3 to 5 inches of mulch around the base of the plant to protect it. Use shredded wood bark or compost mulch around hydrangeas.
Generally white hydrangeas do not contain pigment and usually do not change color. However, when white hydrangeas get older they can turn blue or pink at the tips. You can try to prevent it by using a well-balanced fertilizer that is low in phosphorous and keeps the acidic levels down. You may need to fertilize in the spring or summer if the soil pH levels need adjusting. Do not try to alter the pH level too much at one time or it could dry out the plant and kill it.
Make sure the hydrangea is in a place where there is morning sun and cool afternoon shade. If it gets too hot and dry the flowers can wilt and turn brown in color.
Do not place a hydrangea under a tree for shade, because the tree will most likely absorb the nutrients and harm the hydrangea.