You can use vinegar to lower the pH of your soil, but be aware that in order to achieve blue blooms, you will need both an acidic environment and aluminum ions. The acidic environment will also need to be a sustained over a period of time, which could be hard if rainwater is washing the vinegar away.
To start "blueing," most hydrangeas need a pH level of 5.5 or lower. To make your soil more acidic, dilute 1 cup of apple cider vinegar into about 1 gallon of water. If you're fresh out of apple cider vinegar, you can also use white vinegar, but be aware that white vinegar tends to be much stronger.
A pH of 7 is neutral, and household vinegar has a pH of around 2.4 (which is quite acidic). The theory is, applying diluted vinegar to the soil will lower the pH enough to change the color of your hydrangea blooms. This strategy will make the soil more acidic, but not for long!
Mix one cup of apple cider vinegar with 10 litres of water (an average watering can's worth) and direct the solution at the base of the hydrangea, avoiding the leaves. Do this every couple of weeks and the colour will gradually change.
Many gardeners add vinegar to their watering can to change the acidity of their soil and turn their hydrangeas blue.
Use vinegar diluted with water in a ratio of 20 parts water to one part apple cider vinegar. Water the plants along their base. Try not to get the vinegar-and-water solution onto the leaves, because it can burn the foliage.
If you're growing hydrangeas, use coffee grounds to affect their color. Coffee grounds add extra acidity to the soil around hydrangeas. On a chemical level, this increased acidity makes it easier for the plant to absorb naturally occurring aluminum in the dirt. The effect is pretty blue clusters of flowers.
Soil can be made more acidic by adding Soil Acidifier, ammonium sulfate or aluminum sulfate. Follow application rates on the packaging. You can also lower pH levels by incorporating naturally acidic organic materials such as conifer needles, sawdust, peat moss and oak leaves. Coffee grounds are also slightly acidic.
Espoma Organic Traditions 6 lb. Garden Sulfur Soil Acidifier is an all-natural mineral that can be used to lower the pH of your soil. It can also provide plants with sulfur, a nutrient that promotes growth and dark greening. It will turn hydrangeas from pink to blue.
Place the hydrangeas on the cutting board and use the sharp knife to cut the end of the hydrangea at a 45 degree angle. Then cut a small slit vertically up the middle of the newly trimmed stem. Place the hydrangea(s) in the vase filled with hot water. Let sit for a minimum of one hour and voila!
Best Fertilizer For Hydrangeas
Organic, slow-release fertilizers for roses (such as a 15-10-10, or 10-5-5 formula) work well on hydrangeas, giving the plants the nutrients they need to increase the size and quantity of their blooms.
Adjust the Soil pH
Most garden soils tend to be neutral so you'll need to amp up the acidity to go blue. You can do that in a variety of ways. Organic acidifiers include sulfur and sulfate. There are also easy-to-use soil additives made specifically for hydrangeas.
Hydrangeas produce a “sap” that clogs their stems and blocks water from traveling up it to those gorgeous blooms. The boiling water helps to do away with the sap.
Keep good air space between the plants; don't crowd them together or against other plants. Don't give bigleaf hydrangeas too much love; if they're too comfortable (water, fertilizer, etc.), they may devote all their foliage to leaves instead of blooms.
Hydrangeas that bloom on new wood can be safely pruned in late fall once the plants have gone dormant or in early spring. Next year's flower buds won't be formed until late spring the same year they bloom, so there is no risk of removing the buds if you prune in fall or spring.
If you want to grow blue hydrangeas but you live in an area where your soil is alkaline, you will need to reduce the pH of your soil, and ensure it contains aluminum ions. What is this? There are home remedies such as coffee grounds, pine needles and apple cider vinegar which can help to make your soil acidic.
However, many times it's easy to turn those pink imposters back to blue, should one so desire. Simply squeezing a few lemons or limes over the plant somewhat raises the acidity level of the soil, consequently turning the blooms from pink to blue.
Coffee grounds and tea bags can be used as a mulch around hydrangeas. It changes the pH of the soil and makes the pink ones turn to blue.
Hydrangea Care Tips
Water at a rate of 1 inch per week throughout the growing season. Deeply water 3 times a week to encourage root growth. Bigleaf and smooth hydrangeas require more water, but all varieties benefit from consistent moisture.