How to Plant and Care for Colorful Bigleaf Hydrangeas
Bigleaf hydrangeas are widely planted and wildly loved by gardeners because of their lush floral displays in shades of lavender, pink, and blue. They have a wide-spreading form and loads of thick stems that can grow up to 6 feet tall. Their large, deep green, broad-oval leaves are stunning as well.
The flowers of the bigleaf hydrangea (Hydrangea macrophylla) can change colors depending on the pH of the soil in which they are planted. The flower color of all bigleaf hydrangea plants is affected by the degree of acidity or alkalinity in the soil. Pink- or red-flowered kinds tend to develop purple or blue flowers when grown in acid or neutral mixtures, and the ones that are normally blue turn pink or a reddish-purple color in alkaline potting soil.
In the summertime, gardeners tend to become pretty love-struck over the hundreds of varieties of the bigleaf hydrangeas available to them. There are more than 400 known cultivars between two species: lacecaps and Hortensia.
Lacecap hydrangeas: This hydrangea produces flowers that resemble flat caps with frilly edges. The flower is a round disk of smaller flowers, edged with larger flowers that are quite showy.
Hortensia hydrangeas: This is a low-growing shrub and the most common form of hydrangeas that are grown in pots. Each of the plants has a short, woody stem and several branches with opposite pairs of pointed oval leaves that are quite shiny. The leaves have stalks that are about an inch long and the main stem and branches can each terminate with a round flower head that can be up to about 7–8 inches wide, made up of many four-petaled flowers from 1–2 inches wide. Sometimes you may find smaller specimens available that have only the unbranched main stem topped by a single flower head. The flowers have greenish buds that will open up to be blue, pink, red, or purple.
Blue Hydrangeas Like Acidity
For true blue hydrangeas, the soil needs to be acidic (pH of 5.5 or lower). If your existing soil is more alkaline, you will need to increase the acidity, which can be done by adding organic acidifiers like sulfur or sulfate soil additives.
When, Where, and How to Plant Bigleaf Hydrangeas
When: Plant bigleaf hydrangeas in the spring or the fall.
Where: They are hardy in USDA zones 5 through 9 and will do best in sun to partial shade depending on your location. You can grow bigleaf hydrangeas in shady areas all across the United States, but too much shade often results in really pretty leaves but no flowers. If you have high shade in your yard that is created by deciduous trees or evergreen, you might find that it's the perfect place to plant these flowers (if you live in the East, Northwest, or Midwest part of the country). If you live in California, just about any shady area will work for you if it is not too dense. In the northern part of the country, they require no shade at all. They prefer moist, well-drained soil, but if they're grown in highly alkaline soils they can develop yellow leaves, which is a symptom of chlorosis.
How: Start by digging a hole as deep as the root ball, but two to three times as wide. Set your plant in the hole, and fill it about half full with soil and water thoroughly. When the water has completely drained, fill the remainder of the hole with soil and water again. Space hydrangeas from 3 to 10 feet apart, depending on your location.
Pink Flowers Like Alkalinity
Although genetics plays a part in the coloring of hydrangeas, it is possible to change the bloom color by adjusting the pH of the soil. Soil with a pH below 5.5 (strongly acidic) produces blue flowers, while a higher pH tends to favor pink flowers.
Planting From Cuttings
If you have access to healthy cuttings, bigleaf hydrangeas are easy to grow using this method because of their readiness to root. Here's how it's done:
- You want to start with a cutting from a branch that has new growth and also has not yet flowered. The new growth has a lighter color than old growth with a stem that is not as rigid.
- About 4 to 5 inches from the tip of the branch, make a horizontal cut making sure there are at least three pairs of leaves on the cutting.
- Trim off the lowest pair of leaves flush to the stem, but leave at least a couple of pairs of the leaves at the tip of the cutting.
- If the leaves that are left at the tip are large, cut them in half and remove the outer half. Cutting them will keep the leaves from scraping the sides of a plastic bag that you will place over your cutting later to keep the humidity up.
- I suggest you dust the bottom of the stem with a rooting hormone to encourage rooting. You might also dust the stem with an anti-fungal powder to discourage rot.
- Fill a pot with moistened potting soil and place the cutting in the soil, pushing it in until the first pair of leaves. To get rid of air gaps that might have formed around the stem, water the cutting lightly.
- Loosely cover the entire pot with a plastic bag, making sure that the bag doesn't touch the leaves of the cutting, which could cause them to rot.
- Place your pot in a warm area sheltered from wind or direct sunlight.
- You should check on your cutting every few days to be sure there's no rotting.
- Only water again when the top layer of the soil is dry. Cutting should root in only a few weeks. You can gently pull on the cutting to see if roots have formed. If there is any resistance, the roots have formed.
Some of Our Favorite Bigleaf Hydrangeas
This section is filled with information on some of our favorite varieties of hydrangeas.
Nikko Blue (hortensia): This plant grows to be about 6 feet tall with large clusters of blue or lavender flowers. The flowers bloom on old wood. Pruning is required just after the flowers die out in order to maintain the size and shape of the plant and to remove weak, damaged, or old branches and leaves.
Variegata tricolor (lacecap): The gorgeous green leaves of this fast-growing plant are edged with a creamy white color. The flowers are blue or lavender, and this deciduous plant is an excellent choice for a shrub border. It will grow from 4–6 feet tall and wide.
Alpen Glow (hortensia): Words alone cannot describe the beauty of the red, snowball-shaped clusters that are the crowning glory of this exquisite plant. A deciduous shrub, it produces mophead clusters of flowers in the summer that can grow as large as a cantaloupe. The glossy, green leaves only add to the beauty of its extraordinary blooms. If soil pH is highly acidic, the coral-red flowers will become more purplish.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2018 Mike and Dorothy McKenney