Panicle hydrangeas are a garden favorite for a variety of reasons. Many home gardeners enjoy their ease of care, and heat tolerance. In this article, we take you through how to plant, grow, and care for Panicle Hydrangeas this season.
I. Appearance and Characteristics
Hydrangea paniculata, or panicled hydrangea, is a species of flowering plant in the family Hydrangeaceae native to southern and eastern China, Korea, Japan and Russia (Sakhalin). It was first formally described by Philipp Franz von Siebold in 1829.
Hydrangea is derived from Greek, meaning ‘water vessel’, in reference to the shape of the capsules.
Paniculata means ‘with branched-racemose or cymose inflorescences’, ‘tufted’, ‘paniculate’, or ‘with panicles’. This name is about the flowers of this species.
It is a deciduous shrub or small tree, 1–5 m (3.3–16.4 ft) tall by 2.5 m (8 ft) broad, growing in sparse forests or thickets in valleys or on mountain slopes.
The leaves are broadly oval, toothed and 7–15 cm (3–6 in) long. In late summer it bears large conical panicles of creamy white fertile flowers, together with pinkish-white sterile florets. Florets may open pale green, grading to white with age, thus creating a pleasing “two-tone” effect. In cultivation it is pruned in spring to obtain larger flower heads.
II. How to Grow and Care
Sunlight
Panicle hydrangeas are more tolerant of sun than most other types of hydrangeas. Plant in a location that receives at least four hours of sun a day for the most prolific flowering. A panicle hydrangea can grow in full sun, but may appreciate afternoon shade in hot climates.
Temperature and Humidity
Panicle hydrangeas can be grown throughout most of the country up to a Zone 8 climate. ‘Limelight’ is noted for its heat-tolerance and can be grown in Zone 9. But ‘Limelight’ is far from the only panicle hydrangea you can buy. After breeders saw how well it sold, they produced smaller versions, earlier-blooming ones, and selections whose white flowers turn rose and burgundy as they age. This latter feature got people all juiced up, but if you live in the South, temper your fervor. For the color change to happen, nighttime temperatures must drop into the 60s or below. Otherwise, flowers stay white and then gradually dry and turn brown. So don’t count on pink flowers in USDA Zones 7B, 8, or 9. In Zones 3 to 7A, enjoy the show.
Watering
Water regularly during the first year after planting to help your shrub get established. Panicle hydrangea is more tolerant of dry conditions than other hydrangeas, but continuing to water in subsequent years (especially during hot, dry spells) will encourage flowering. Too much water or poor drainage can lead to root rot.
Soil
Panicle hydrangeas are not fussy about soil, as long as it is well-drained. If there’s one thing that will cause your hydrangea to fail, it’s definitely wet or poorly drained soil. This is why we recommend that you do not add any kind of potting mix, topsoil, compost,…, when you plant a panicle hydrangea. As for pH, they can grow well in acidic to slightly alkaline soils.
Many people also wonder whether they can grow panicle hydrangeas in clay soils, and the answer is yes, provided that the clay is well-drained and doesn’t stay wet for prolonged periods. If you have clay soil, starting with the small quart plants that we offer is an easy way to minimize digging and get a plant off to a good start.
Fertilizing
These non-fuss plants don’t require fertilizer, but if you want your panicle hydrangea to grow faster, apply a granular fertilizer for shrubs in early spring. Too much fertilizer can lead to weak stems, so be wary of over fertilizing and of fertilizing other plants located around them.
Planting Instructions
Pruning
This plant can be trained to grow as a small tree by judicious pruning. But it achieves its best form when grown as a large shrub with multiple stems. Blooms occur on the current season’s growth (new wood), so prune as needed in the late winter to early spring. Untimely pruning can sacrifice some of the flowers for that growing season. When kept in its shrub form, the shrub will bear larger flower clusters if you thin it to five to 10 primary stems.
To train the plant to grow as a tree, choose one main stem to secure to a sturdy stake. Prune away competing ground stems. Remove any shoots that emerge from your main stem from the ground to about 3/4 of the way up that stem. Continuously check for shoots around the base of the plant, and remove them as they pop up. Your main stem will continue to grow with foliage at the top, taking on the look of a trunk. It can require two or more years before a true tree shape is accomplished.
Propagation
Hydrangeas can be propagated by taking cuttings and rooting them in soil. They are most easily propagated from new growth in late spring or early summer. Cut a 4 to 6 in. length of stem; the bottom should be cut right above a leaf node. Remove all leaves except for the top set. Moisten the bottom of the stem and dip in rooting hormone. Plant immediately in a container of well-moistened, high-quality potting soil about 2 inches deep. Then cover the plant to maintain moisture—a clear plastic bag does a good job of creating a mini-greenhouse for the plant. Keep in bright indirect sunlight, watering to keep soil moist. The cutting is ready to plant once it has rooted and does not come loose with a gentle tug.
You can also propagate this plant with ground layering. Remove the bottom leaves from a low hanging branch and bury it in a shallow trench in the soil. Place a rock or brick over top to hold it in place. After several weeks, the buried section of the branch should develop a strong root system. You can remove the branch and replant it in a pot or in a sheltered area of your garden.
Grow From Seed
Though it is possible to grow tree hydrangeas from seed, keep in mind that it is quite difficult. That’s why most gardeners go with propagating through cuttings.
If you do choose to propagate through seed, let several flowers fade on the plant. Harvest these flowers in a paper bag after a few months. This gives them time to dry out. Store the flower heads in the bag for another week to ensure they are dry. At that point, give the bag a good shake. This will loosen the tiny seeds from the flower heads. Keep in mind these seeds are about the size of a grain of salt or pepper, so they will be tough to find.
You can sow the seeds directly into the ground in the fall, or you can choose to hold onto them through the winter months and start them indoors in the early spring. Fill a container with potting soil, and sow the seeds on the surface; do not cover them with soil. Keep the soil lightly moist. Place the container in a sunny spot, and expect germination of the seeds within a matter of weeks.
Potting and Repotting
Panicle hydrangeas can be grown in a container for at least a couple of years (dwarf varieties may do well in a container indefinitely). Use a weather-proof container with drainage holes that is at least 16 inches wide. Fill with potting soil to the bottom of where the plant will sit. Place your hydrangea in the pot, fill in with soil around it, and water well. Add a thin layer of mulch to help preserve moisture.
Your hydrangea will need frequent watering in warm weather; check the container for moisture daily. In winter, check soil moisture every 10 to 14 days. If the plant’s leaves become stunted after a time, it’s time to move your hydrangea to a larger pot or transplant it into the garden.
Overwintering
To help your plants through the winter, keep the soil moist right up until the ground freezes. Cover the roots with 3 to 4 inches of mulch, taking care to remove it as soon as the temperatures warm up.
Pests and Diseases
Common Pests & Plant Diseases
Hydrangeas of all varieties can fall prey to aphids, rose chafers, and scale. Organic pesticides can help get rid of these pests. Slugs and snails will also be tempted to nibble on the plant. Remove the slugs and snails by hand, and deal with heavy infestations with natural methods, such as slug pellets.
Moreover, hydrangeas are prone to fungal diseases, such as powdery mildew, blight, and leaf spot, all of which can be treated with an appropriate fungicide. The plants might also fall victim to a variety of viruses, which can cause leaves to turn yellow and a plant to lose its flowers. The only real treatment is the removal of affected plants.
Common Problems
Tree hydrangeas are fairly easy to care for, as long as you get their growing conditions right. They’re somewhat susceptible to pests and diseases, but they’re also resistant to salt and pollution in their environment. The following are some common issues to watch out for.
Leaves Turning Black/Brown
Black or brown spots on foliage can often be a sign of a fungal disease. If the affected area is small, you might just want to prune it off. Or you can use a suitable fungicide.
Leaves Turning Yellow
Yellow foliage can often be a sign of unsuitable moisture conditions—both overwatering and underwatering. The soil should never be soggy or be allowed to dry out completely. Yellowing also can be a sign of too much fertilizer, as well as some diseases.
III. How to Get Panicle Hydrangea to Bloom
If your panicle hydrangea isn’t blooming, it could be that the plant isn’t well-established and needs a few seasons to settle in. But there are other reasons a hydrangea might not bloom:
- Pruning at the wrong time: make certain to prune when the plant is dormant or you may unintentionally remove flower buds.
- Deer: use repellant or netting if deer could be nipping off the flower buds.
- Too much shade: shade can affect flowering. Make certain the plant receives at least four hours of direct sun or filtered sun all day.
IV. Uses and Benefits
The height of many varieties of Hydrangea paniculata lends itself well to be used in your garden as a privacy screen, or grown in a hedge. These plants can be so large that they work very well as specimen plants throughout your yard.
The smaller varieties would make a really nice shorter hedge, or a nice addition to a foundation planting or border.
Don’t forget about container planting! The low maintenance aspect of panicle hydrangeas makes these plants great options for containers, just be sure that the container you have chosen is large enough to support the plant!
