Should You Use Lime on Hydrangeas? What You Need to Know

With their large, colorful blooms, hydrangeas are a much-loved garden shrub One of the tricks to growing gorgeous hydrangeas is understanding how soil pH affects bloom color. This often leads to questions about using lime, which raises pH, on hydrangeas Below, we’ll explore if applying lime to hydrangeas is recommended and how it impacts color.

How Lime Affects Hydrangea Bloom Color

Most hydrangeas change color based on the pH of the soil they are grown in. Acidic soils with a pH below 6 cause hydrangeas to produce blue flowers. Alkaline soils over pH 7 result in pink or red blooms. The reason involves the availability of aluminum in the soil, which causes the blue pigment.

Lime, or calcium carbonate, is an alkaline substance. Adding lime raises the pH, making the soil more basic. Therefore, applying lime to hydrangeas in acidic soil will make the blooms turn pink or red.

The typical recommended soil pH range for growing hydrangeas is slightly acidic, between 5.2 and 6.2. This encourages beautiful, vivid blue or purple blooms.

Should You Add Lime to Your Hydrangeas?

Whether or not to add lime depends on your goal for bloom color Here are some considerations

• If you want blue hydrangea flowers, avoid using lime. Stick to an acidic soil pH instead.

• If your soil naturally stays at an ideal pH range, there is no need to add lime to change the color.

• To induce pink blooms, mix in lime around the roots. How much to add depends on your current soil pH.

• Never add lime without testing your soil first. Too much can negatively impact hydrangeas.

• It’s easier to make soil more alkaline than to lower pH. Go cautiously with lime.

• Once added, it can be difficult to reverse the effects of lime over multiple seasons.

How to Safely Add Lime to Hydrangeas

If your desired bloom color is pink or red, follow these tips for safely using lime on hydrangeas:

• Always test soil pH first before adding amendments like lime. Kits are inexpensive and take the guesswork out.

• Determine how much lime is needed to raise the pH just slightly based on soil test results. A little goes a long way.

• Mix in lime deeply in the planting hole when first planting. Afterward, sprinkle lightly on top around the root zone of established plants.

• Add powdered dolomitic limestone as it contains calcium and magnesium, both beneficial to hydrangeas.

• Recheck soil pH 2-4 weeks after initial application to assess if more is needed.

• Add lime just once or twice per year early in the season. Overapplying can burn roots and leaves.

• Consider bulb fertilizers tailored for bluing or reddening hydrangeas instead of lime if unsure.

Hydrangea Blooming Problems From Too Much Lime

While a little lime can gently nudge blooms to pink, overdoing it has consequences. Adding too much lime to hydrangeas can result in:

• Burnt leaf margins from highly alkaline soil burning the roots

• Stunted growth and wilting from damaged roots unable to take up water

• Nutrient deficiencies as overly alkaline soil makes minerals unavailable

• Few or no flowers because the shrub is stressed and struggling

• Eventual death if soil nutrients are completely out of balance

The impact depends on how much excess lime was applied and how quickly you can try to remedy the situation. Lightly sprinkling in some sulfur can help lower pH if caught soon enough.

Achieving Blue Hydrangea Blooms Without Lime

You don’t have to mess with soil amendments to enjoy vivid blue hydrangea flowers. Some options include:

• Choose naturally acidic soil when planting like under pine trees. Avoid spots where lime was recently used.

• Incorporate peat moss or compost into the soil to help acidify it. Coffee grounds also lower pH.

• Use an acidic fertilizer made for hydrangeas. Options like Holly-Tone and Espoma Holly-Tone include iron, sulfur and aluminum.

• Try a fertilizer with aluminum sulfate, which is very effective at creating blue blooms.

• Grow hydrangea varieties specifically bred to bloom blue regardless of soil pH. Many panicle and smooth hydrangeas have this trait.

The Bottom Line on Lime and Hydrangeas

So should you put lime on your hydrangeas? It’s not inherently harmful if applied minimally and carefully based on soil testing. But it’s also unnecessary if your goal is the coveted blue flowers most hydrangea fans desire.

Sticking to a slightly acidic soil pH avoids the guesswork of using lime. Select naturally acidic planting spots, use acidic compost and fertilizers, and grow dedicated blue-blooming varieties. With a little planning, you can easily enjoy gorgeous blue hydrangea blossoms summer after summer.