What You Need to Know About Hydrangeas
- Hydrangeas are typically easy to grow, even for a novice gardener.
- Hydrangeas are perennial shrubs, so they bloom yearly.
- Hydrangeas grow quickly. Some grow to a height of up to 10 feet and spread to cover a planting bed, so make sure you have enough space for them. Smaller varieties are suitable for compact plantings and even containers.
- Depending on the variety, hydrangeas bloom from mid-summer to early fall.
For this article, we’ll focus on bigleaf hydrangeas (Hydrangea macrophylla), which are the most common. If you’re picturing a mounding shrub with large, serrated leaves and showy, round or flat clusters of blooms, there’s a good chance it’s a bigleaf hydrangea.
Hydrangea Plant Care
Here are some general tips on caring for bigleaf hydrangeas. There are many types of hydrangeas, however, and many cultivars among bigleaf hydrangeas, each with specific care requirements. Keep your plant tag handy for requirements on soil, light, spacing, watering, etc. specific to your plant.
How to Plant a Hydrangea
Planting a hydrangea is a great project for a beginning gardener.
- Dig a hole twice the diameter or the root ball and deep enough that the top of the root ball rests at ground level. Break up the soil around the interior of hole a bit.
- Carefully remove the plant from the pot or cut the pot away and set the root ball in the hole. Fill the hole back in, sloping the soil slightly away from the plant.
- Add a 3- to 4-inch layer of mulch around the new plant to help keep the soil moist. Pull it back from the base of the plant to protect it from pests and disease.
- Water the area thoroughly and continue to water the hydrangea well throughout the first growing season.
Before beginning any excavation, call 811 to check for underground utilities.
When to Plant a Hydrangea
Plant hydrangeas in fall or early spring when the soil is warm but high heat isn’t a concern. Fall gives the shrub the most time to develop a strong root system for growth and blooming. Give the new shrub plenty of water, both before and after planting.
How Much Sun Do Hydrangeas Need?
Sunlight encourages blooms and color but be careful of heat. In northern parts of the country hydrangeas do well in full sun if you’re careful about providing supplemental water. For hydrangeas in the middle and southern parts of the county, partial sun — about 4 to 6 hours each day — is better. In these areas, plant a hydrangea where it gets plenty of sunlight early but has protection from the sun and heat later in the day. An area of dappled shade works but be careful that the hydrangea doesn’t compete with trees and other shrubs for water.
The Best Soil for Hydrangeas
Bigleaf hydrangeas grow in sandy, loamy and clay soils. While they need moisture, they do best in soil that drains well, minimizing the risk of root rot. Improve poor-draining soil by working in amendments. These amendments create pockets in the soil that encourage drainage while adding material to hold moisture the plants need. Blend in compost to provide organic material to nourish the plant. Hydrangeas can tolerate acidic, neutral and alkaline soils, but the pH level affects bloom color, as we discuss below.
Create your own organic soil amendments with a composter. We’ve got guides to help you choose a composter and show you how to compost.
Watering Hydrangeas
Hydrangeas need generous amounts of water. The large green leaves that create the perfect backdrop for blooms lose a lot of moisture through the day. Once a hydrangea is established, it needs about an inch of water a week. If the plant doesn’t get this amount from rainfall, supplement by watering it deeply at the base up to three times a week. Hydrangeas that receive lots of sun will need more than those in the shade. Again, make sure the soil drains well so the roots aren’t sitting in water.
Consider a soaker hose or drip irrigation system to deliver the right amount of water directly to the base of the plant. Our Drip Irrigation System Buying Guide gives you tips for finding the right system for your needs.
Pruning Hydrangeas
It’s usually not a good idea to prune bigleaf hydrangeas. In fact, if you’re wondering why a hydrangea isn’t blooming, pruning is often the reason. Most bigleaf hydrangeas bloom in mid-summer and create buds for future blooms in late summer on last year’s growth, known as old wood. Pruning either removes existing blooms or prevents blooms for next season. Even if you prune immediately after the blooms end, the plant might not have enough time to recover fully before cold weather causes damage. Some types of bigleaf hydrangeas bloom both on last year’s growth and new growth. While you can prune the old wood, you’ll be reducing the number of blooms for next year.
If you must cut back hydrangeas due to damage or overgrowth, do it in the spring and be aware that you can’t expect blooms that season. Cut away dead or diseased stems as necessary.
Fertilizing Hydrangeas
A balanced all-purpose fertilizer, such as a 10-10-10 is a good choice for feeding bigleaf hydrangeas, but one with twice the level of phosphorus — indicated by 10-20-10 — encourages blooming. Follow the package instructions and apply lightly a few times during the growing season. If you’re using a granular fertilizer, be sure to water it in thoroughly.
Confused about fertilizer numbers and nutrients? Read Everything You Need to Know About Fertilizer.
Hydrangea Flower Colors in Bigleaf Varieties
One characteristic of some bigleaf hydrangeas — those that start with blue, purple or pink blooms — is the effect soil acidity has on bloom color. Here’s how soil pH affects the color of these hydrangea blooms:
- Plants in acidic soils with a pH lower than 5.5, develop blue flowers.
- Soils with a pH of 6 or greater produce pink flowers.
- Variations in pH between these levels produce purple flowers or a mix of blue and pink blossoms on a single shrub.
Can You Adjust the Flower Color of Hydrangeas?
You can change the color of your bigleaf hydrangea blooms by altering the acidity of the soil with pH balancers. This is a gradual process that takes months, so don’t expect immediate results. Here are some tips:
- Start with a hydrangea that has blue, purple or pink blooms.
- Test your soil with a test kit to determine the current pH and monitor the changes.
- To raise the pH and produce pink flowers, add lime to the soil.
- To lower the pH and produce purple or blue flowers, add aluminum sulfate or garden sulfur, sometimes known as soil acidifier.
- If you’re not seeing the results you expect, check the pH of the water you’re using to irrigate the plants. Hard water is more alkaline, soft water is more acidic.
Follow the application instructions for the product you’re using.