The color of the blue or pink flowers on bigleaf and mountain hydrangeas is determined by the soil in which they are planted. It’s a common belief that pH, which is the measure of soil acidity, is the main factor that turns flowers blue. While pH plays an important role, it is the aluminum, which is present in most soils, that makes the flowers blue.

How pH effects hydrangea flower color

Think of pH as a faucet in the ground that allows aluminum to flow. A pH of 5.5 or lower (more acidic) opens the faucet, and the aluminum becomes available to the hydrangea root system. The plant moves the aluminum from the roots to the flowers, which turns them blue. As the pH rises (becomes more alkaline), the faucet starts to close and eventually shuts off, making the flowers pink. The aluminum is still in the soil, but it becomes unavailable to the plant because of soil chemistry.

What makes hydrangeas pink?

Many container-grown hydrangeas have little or no aluminum in their soil, which is why you see many red and pink flowers in your garden centers.

In my experience:

• Most red-flowering potted hydrangeas will be dark blue to purple once they are planted in ground with a lower pH.
• Hydrangeas that have lighter pink flowers in pots usually turn light to medium blue once planted in ground with a lower pH.
• White flowers do not change color regardless of soil chemistry.

How to use amendments to change hydrangea flower color

1. Consider getting a soil test before applying these products to know what pH and mineral content you are working with.
2. There are many products available at your garden center that can help you get the color you want.
3. To turn pink flowers blue, look for soil acidifiers that will lower the pH, and add aluminum.
4. To turn blue flowers pink, add lime to raise the soil pH.
5. Keep in mind that application rates of these products can be misleading and are often used to increase sales; less is often more.
6. Whatever your goal, add amendments in fall or spring; while it might take a year to kick in, the effects should last for a few years after that.

Bob Aube is the founder and co-owner of Morningstar Nurseries, a wholesale nursery in West Kingston, Rhode Island.

Fine Gardening Recommended Products

Ashman Garden Cultivator (1Pack)

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

Solid Build—The Ashman Garden Cultivator/Tiller is strong in construction so that it can withstand heavy work in the garden. The blade and the shaft are coupled well for deep digging and uprooting the soil from the depths. It serves the purpose of cultivation very well. Create a blooming crop and watch it blossom and reap the benefits. Sharpened Fine piercing Blade—The blades are razor sharp and are made to pierce into any kind of soil and to serve digging, loosening soil, and weeding. The blades are rust-proof and have chip-resistant coating enhancing durability. Use it to control weeds, bury crop residue in the soil, and for preparing a proper seed bed. High-Quality Design—The thoughtful design incorporated to shape the blades in L shape helps dig deep into the soil and rip it from beneath for cultivation. This helps a lot when weeding. Dig well and plant well. The handle is made to fit in the hand well and can be held tightly to apply push and pull forces effectively. Practical Utility—The garden cultivator is made with “practical utility” as the core of its purpose. It serves all the necessary purposes when gardening. Helps mix soil, which will loosen it up, providing more nutrients for the crops.

Buy at Amazon

Spearhead Shade Gardening Shovel with Steel-Reinforced Fiberglass Handle

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

Reduce Digging Effort - The Spear Head Spade is the first hybrid shovel/spade, guaranteed to make your toughest digging up to 80% easier than regular shovels and spades, even in the toughest soil conditions. Ideal for landscaping and gardening. Multi-Purpose Shovel - Spear Head Spade is a versatile tool that can be used for digging, planting, weeding, cutting, and edging. It is designed to handle tough soil and clay conditions, and can cut through roots and tough vegetation with ease. Innovative Design - Has a unique blade design that makes it more efficient and easier to use than traditional spades. The blade is shaped like a spearhead, with a pointed tip and a curved edge that allows it to penetrate the soil more easily. Ergonomic D-Handle - The large, cushioned D-grip offers comfort and better leverage for gloved and ungloved hands alike, reducing strain on the hands and wrists. Lightweight & Strong - Durable handle is made of special steel-reinforced, pultruded fiberglass to withstand heavy use. 60% stronger than EN-3388 shovel/spade standards, 33% thicker and 25% harder than normal shovels. Sharpened from tip to tail at a 35 degree angle for an effective and durable edge.

Buy at Amazon

Gardzen 3-Pack 72 Gallons Garden Bag

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

High Quality Fabric - Gardzen Garden Waste Bags are made from 4.4oz/yd2 (150g/㎡) durable polypropylene fabric that can withstand heavy loads and rough handling. Please note that they should not be left out in the sun for long periods. Environmentally Friendly - These reusable yard waste bags are an environmentally friendly choice as they can be used over and over again, unlike disposable bags. The strong handles make it easy to carry the bags, even when they are full. These garden bags for debris allow you to complete your gardening tasks efficiently and effectively, while minimising waste and promoting sustainability. Large Capacity - With a height of 30 inches and a diameter of 26 inches, there is plenty of room for a large amount of garden waste. Whether it's leaves, branches or grass clippings, these yard waste containers can handle it all. A Must-Have For Gardeners - these leaf bags are an essential tool for managing garden waste and can make your gardening tasks much more efficient. The large capacity and durable construction make them ideal for storing and transporting various items. The yard bags can also be folded and stored compactly when not needed, saving valuable space. Package Included - A great value set of 3pcs heavy duty lawn and leaf bags. 3pcs white plastic hoops. There are 2pcs double stitched webbing handles in the top and 1pc strong webbing corner handles in the bottom.

Buy at Amazon