The blue color, it’s a color many homeowners want to have in their landscape. One plant we see in the garden to bring on the color blue comes from the plant Hydrangea.
Hydrangeas are native to many countries in Asia: Mainland China, Japan, Korea, Himalayas and Indonesia.
The color blue, it’s a color many homeowners want to have in their landscape. One plant we see in the garden to bring on the color blue comes from the plant Hydrangea.
What makes hydrangea turn blue or any shade of pink? The primary contributor is soil pH.
Hydrangeas are an unusual sort of plant because, for some varieties, the color of the blossoms depends upon the pH balance of the soil. This is true of blue hydrangeas, which may also bloom pink or lavender depending upon soil acidity.
In this article, we will explain this phenomenon and provide some tips to help you give your hydrangeas just the right kind of soil conditions to produce blue blooms.
Know The pH Level Of Your Soil
Acidic soil produces blue blooms and alkaline soil produces pink blooms, so the first thing you should do is determine what kind of soil you have. There are a number of ways to test your soil.
1. Perform an informal test: You can determine whether your soil is alkaline or acidic using simple white vinegar. Just put a cup of your soil into a plastic or glass container and pour white vinegar over it.
If the soil bubbles up, you know that it is alkaline. The more vigorous the bubbling, the more alkaline the soil. If no bubbles appear, you know that your soil is acidic. [More Here]
2. Perform a scientific test. To be more precise, you will want to know the exact pH of your soil. This will help you determine what color of flowers you can expect from your hydrangeas. Generally speaking, you can expect:
- 5.5-6.5 pH = Lavender Blooms
- 6.5+ pH = Pink Blooms
- 5.5- pH = Blue Blooms
You can test your soil using a soil pH testing kit [amazon] which you can purchase online or at your local garden center. Alternately, you can take a sample of your well-drained soil to the garden center or to your local government county extension office for testing.
Take Steps To Amend Your Soil
Once you know the pH level of your soil, there are a number of things you can do to adjust it to provide just the right environment to produce blue hydrangea blossoms.
Adding elemental sulfur to the soil is a very simple method if you already have hydrangeas established. To use this method, you would simply sprinkle the sulfur around the plants on the surface of the soil.
If your soil is loamy or silty, you should us about three-quarters of a pound of sulfur to treat an area of 25 square feet. If it is sandy or a combination of sand and loam, you should use one-quarter of a pound of sulfur to treat 25 square feet.
Don’t put the sulfur too close to the bushes. Your treatment should begin about half a foot away from the trunk of each plant and extend to a couple of feet outside the drip line (farthest edge of the foliage).
Mix the sulfur into the surface soil with a rake or spade and water the area generously to help it soak in and reach the roots. Reapply in the fall and the spring to maintain vibrant blue flowers.
Acidic Compost & Aluminum Sulfate
Another method you can use to make your soil more acidic is to add aluminum sulfate powder along with acidic compost (aka ericaceous compost). Both of these can be purchased at your local garden center.
To apply you would sprinkle the compost around your plants in much the same way as elemental sulfur. Follow up by watering with a solution of aluminum sulfate and water.
This should be a very mild solution consisting of no more than a tablespoon of aluminum sulfate per gallon of water. A stronger solution will burn your hydrangeas’ roots.
High Potassium Fertilizer
Selecting the right fertilizer will help keep your hydrangeas’ blossoms blue. Be sure to choose a fertilizer that has a high level of potassium and a low level of phosphorus.
Avoid fertilizers that contain bone meal as this is very alkaline. Look for fertilizer mixes that are labeled as being formulated for rhododendrons, camellias, and azaleas.
Use Naturally Acidic Organic Compost
You can create your own acidic compost by choosing the components of your compost pile carefully. A combination of coffee grounds, grass clippings, fruit, veggie scraps and other organic matter makes a very nice top dressing around your hydrangeas.
Be sure to let the materials compost completely and then work them into the soil just as you would elemental sulfur. The nice thing about using organic compost is that you don’t have to worry about it damaging roots or contaminating the soil (or groundwater).
Be advised that this method does take more time and patience than the other methods described.
Use Rain Water To Care For Hydrangeas
Tap water tends to be more alkaline. This is especially true of hard water. Rainwater is generally more acidic. Set up a rainwater catchment system to keep an ample supply of water for your hydrangeas.
Collecting rainwater for all of your outdoor watering needs is a thrifty and earth-friendly choice.
Avoid The Negatives
If you have not yet planted your hydrangeas, be aware of what you should avoid. If you have chalky soil or soil that is filled with flint rock, don’t bother to plant hydrangeas unless you are going to be content with pink or lavender blooms.
Furthermore, don’t plant your hydrangeas next to a concrete foundation or other structure because concrete tends to alter soil pH toward the alkaline.
Grow Container Hydrangeas
If you do not have hydrangeas already established, you may wish to simply start them and keep them in containers. This will give you complete control of soil conditions at all times.
For details on pH and Blue Hydrangeas, watch the video below…
Be Patient & Flexible!
Understand that amending the soil and changing the hydrangea color is not a magic trick. Even if you use commercial, chemical soil amendments it is likely to take several blooming seasons to make a change.
Additionally, other environmental factors will influence the color of your hydrangea blooms.
Even if you apply just the right amendments and keep after it doggedly, the humidity, the temperature, rainfall and other factors may affect your results.
For this reason, you may be better off simply feeding your hydrangeas to be healthy and hardy and accepting and cherishing the color of their blooms, come what may!