How to Grow and Care for Pistachio Hydrangeas

Early blooms of the pistachio hydrangea

ISMODE / Getty Images

It's hard to beat a flowering hydrangea shrub when you're looking to make a showy statement in your garden. With large globes of brightly colored flowers, they are much-loved, hardy, ornamental plants with over 75 different hydrangea varieties to choose from.

The pistachio hydrangea is a compact, bushy cultivar of the bigleaf hydrangea (Hydrangea macrophylla). It stands out from the crowd because of the floral combination of chartreuse green centers and deep pink outer shades (similar to those of a pistachio nut). They bloom from early summer to fall, and the glossy dark green foliage looks great even when the flowers aren't on show.

Known for its versatility and fast growth rate, the pistachio hydrangea is a great choice as a striking flowering hedge, a border shrub, or for use in mass planting. It works well in small or large gardens, grows readily in patio containers, and the cut fresh or dried hydrangea flowers look lovely in a vase on your dining table.

As with other hydrangea species, this shrub is toxic to humans and animals, so it isn't one to have around pets that like to nibble on plants.

Common Name Pistachio Hydrangea
 Botanical Name Hydrangea macrophylla 'Horwack' Pistachio
 Family Hydrangeaceae
 Plant Type Deciduous
 Mature Size 2-3 ft. tall, 3-5 ft. wide
 Sun Exposure Partial sun
 Soil Type Any
 Soil pH Any, but pH can influence bloom color
 Bloom Time Summer, fall
 Flower Color Green and pink combination
 Hardiness Zones 5-9 (USDA)
 Native Area Asia
Toxicity Toxic people , toxic to pets

Pistachio Hydrangea Care

Pistachio hydrangeas are hardy shrubs that adapt to many growing conditions and are known for their heat tolerance and appreciation of morning sun. Plant them in the spring or fall in a sheltered spot out of harsh, cold winds. Space your pistachio hydrangeas 3 to 5 feet apart to encourage strong root development and allow the wide shrubs room to grow.

Light

These shrubs can grow in full sun and partial shade. They thrive when receiving morning sun and afternoon shade, so a position to the east of your house works well.

If you can only provide a full sun position, you'll need to keep the site consistently moist and be aware that your pistachio hydrangea might not produce as many blooms.

Soil

The key to producing good blooms is providing a moist, fertile, well-drained soil. Other than this, they are tolerant of a wide range of soils and pH levels (although the pH can impact the bloom colors). Adding organic matter will boost drainage and enrich the soil, promoting healthy abundant blooms.

Water

Be prepared to get the hose out regularly for your pistachio hydrangea. They need consistently moist soil and, during their growing season, will need watering at least once a week, especially during hot summers. Mulching in the spring helps the soil retain moisture.

Getting the balance right is important—you won't get abundant blooms if you overwater. When the top few inches of soil are dry, saturate but don't waterlog the soil.

Temperature and Humidity

There's a reason pistachio hydrangeas are popular in humid southern landscapes. These heat-tolerant plants love warm summer days, and, once established, they're also pretty drought-tolerant shrubs. But it's important to offer appropriate protection and shelter during harsh winter conditions.

Dry conditions aren't your pistachio hydrangea's friend. Watch out for browning leaves. This is a sign the humidity levels aren't high enough.

Fertilizer

Consider an all-purpose feed with a higher percentage of phosphorous to encourage impressive blooms. Select a bloom-boosting fertilizer with a 10-20-10 NPK on the label. Steer clear of too much nitrogen as this encourages foliage growth and fewer blooms.

Start feeding in spring every few months until the end of the growing season. Adding compost, manure tea, or other organic matter to your soil at the start of the growing season means you won't have to fertilize as often.

Pruning

Part of the plant's appeal is that this reliable bloomer has low-maintenance pruning requirements compared with some other hydrangea varieties. Because they bloom on new and old wood pruning mostly consists of removing weak, dead, diseased, and winter-damaged stems in early spring. Overpruning can result in a poor bloom show.

Propagating Pistachio Hydrangea

The pistachio hydrangea was awarded a plant patent in 2015. This means you could risk infringing copyright laws by propagating it. If you want to add additional hydrangea shrubs, buy mature plants or try propagating from a hydrangea species you already have in your yard that is not patent protected.

Potting and Repotting Pistachio Hydrangea

If you're keeping these compact hydrangeas on your patio in containers, select a loose soil that drains well and has excellent aeration. If you want to make your own, you could mix half all-purpose potting soil with perlite or peat moss (or coco coir, for a sustainable alternative).

These plants do well in terracotta pots that absorb water, and when repotting, choose one that is two sizes bigger than the existing one. They can be top-heavy with their large blooms, so select a wide pot that won't topple with the extra weight.

Repot in early spring once your plant has come out of dormancy and before the hot summer weather arrives. Roots growing out of the bottom of the pot are a good sign the plant needs repotting.

Overwintering

Protecting your shrub in harsh winters means it will be more likely to bloom consistently during the following summer, and there's less chance of dieback.

Some hydrangea winter care tips include:

  • Plant the shrub near a heat retaining wall or building, in bright morning sun and away from wind
  • Insulate the plant by circling with garden stakes and covering them in burlap or egg-crate foam
  • Inside the burlap circle, layer straw or oak leaves for additional protection
  • Mulch generously around the plant base

Common Pests and Plant Diseases

These plants aren't immune to the common pests that affect many bigleaf hydrangea cultivars. Look for things like aphids and red spider mites, especially on the underside of the foliage. If you take quick action, spraying with an organic insecticide like neem oil can be enough to rid the plant of these bugs.

The shrubs are also susceptible to bacterial wilt, blight, leaf spot, and powdery mildew. Keeping the plants spaced appropriately and minimizing overhead watering can help reduce problems with mildew.

How to Get Pistachio Hydrangea to Bloom

This stunning bigleaf hydrangea cultivar produces large globes of blooms. They look great on the plant and as cut flowers, although they aren't fragrant.

Like many hydrangea species, the soil's pH can impact the color. Adding lime to acidic soils in advance of flowering, encourages deeper color in the pink shades on the flower.

If your hydrangea isn't blooming successfully, it might be subject to sudden temperature fluctuations, harsh winters, or late frosts. However, pistachio hydrangeas do have better winter hardiness than some other Hydrangea macrophylla cultivars.

Deadhead spent flowers to encourage new blooms, and avoid overfertilizing as this can prevent flowering.

Common Problems With Pistachio Hydrangea

While these exotic-looking plants are relatively easy to care for, problems can still occur without the right care.

Curling Leaves

During very hot summers, you might see curling, wilting foliage. This isn't always a sign your plant needs water. Check again once the sun goes down and temperatures cool. If the foliage has perked up, this is the plant's built-in, energy-saving protection.

If the foliage remains curly, check if the top of the soil is dry; it might just need more regular watering.

Yellowing Leaves

A poor watering schedule can result in yellowing leaves. Don't let the soil get waterlogged or dried out, and steer clear of overfertilization. Keep in mind that hydrangeas grown in containers need more regular watering than those in the ground.

If you think irrigation is correct, consider the plant's location. Yellowing leaves are often the first sign your plant is getting too much direct afternoon sun.

Browning Leaves

Brown edges or tips on the foliage can be a sign you're using too much fertilizer or one that's too strong. Flushing the soil with water can help to resolve this issue.

FAQ
  • How long do pistachio hydrangeas live?

    These fast-growing hydrangeas can live for over 20 years with the right care and conditions.

  • What other Hydrangea macrophylla are similar to pistachio hydrangeas?

    If you can't get your hands on this cultivar, there are lots of other similar bigleaf cultivars. Why not look for an Endless Summer or BloomStruck hydrangea? They also have impressive mophead blooms and similar growing requirements.

  • Where should you plant pistachio hydrangea?

    Select a spot where your shrub won't be subject to strong gusts, and plant beside a wall if you want to promote warmth in colder winters.

Article Sources
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  1. Hydrangea (French Hydrangea, Mountain Hydrangea, Oak-Leaf Hydrangea, Peegee Hydrangea) | North Carolina Extension Gardener Plant Toolbox

  2. ‘Hydrangea’. ASPCA, https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/hydrangea