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Ultimate guide to panicle hydrangeas (Hydrangea paniculata)

Panicle hydrangeas – also known as peegee hydrangeas, hardy hydrangeas, and Limelight hydrangeas, are the easiest to grow, most adaptable of all hydrangeas. We like to call them the “black thumb hydrangea” because they are so easy and reliable, they make even people who have no experience (or claim to have a black thumb, which we don’t believe even exists, frankly) look like garden rock stars. So don’t be intimidated by this guide – we created it just to address the myriad questions we get on these popular plants.

 

Contributors: Stacey Hirvela

 

Where can you grow panicle hydrangeas?The foliage in my panicle hydrangeas is yellowing. What's wrong?Therer are so many panicle hydrangeas on the market! How do I pick the right plant for me?
Picking a perfect spot for panicle hydrangeasMy panicle hydrangeas isn't blooming at all. You said these were easy! What gives?What's a pee gee hydrangea?
Can you grow panicle hydrangeas in a container?Why aren't my flowers turning from white to pink/red?Do panicle hydrangeas make good cut flowers?
Can you keep a panicle hydrangea smaller through pruning? What about hydrangeas trees?I need to transplant a panicle hydrangea. When should I do that and how?
Which is better for pruning panicle hydrangeas - fall or spring?The stems of my panicle hydrangea are on the gound and/or don't hold the flowers up. What's wrong and what can I do about it?My hydrangea is wilting, even though I keep watering it. what's going on?

Where can you grow panicle hydrangeas?

One of the things that makes them so popular – besides their undeniable good looks – is that they grow over so much of North America, from chilly USDA zone 3 through balmy USDA zone 8 (even USDA zone 9 in the case of ‘Limelight’). That means they can be planted everywhere from Manitoba to Mobile, and in every area, you can count on big, beautiful blooms in summer. Panicle hydrangeas offer the best cold and heat tolerance of all the types of hydrangeas.

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Picking a perfect spot for panicle hydrangeas

Light

Panicle hydrangeas are the most sun-tolerant of all hydrangeas, and in colder climates (say, USDA zone 3-6), we recommend at least four hours of bright sun each day; six or more is preferable, as it encourages the strongest stems and the most flowers. In hotter climates (USDA zone 7 and warmer), afternoon shade is beneficial, but the plants should get at least some sun each day.

Soil

Overall, panicle hydrangeas aren’t finicky about soil, but good drainage is a must. Soils that are too wet lead to root rot, so avoid planting them in any area that stays wet for any length of time. Aside from that, any average soil in your landscape will do. They can even grow in clay soil, provided it is well-drained. They are tolerant of a range of pH levels, from acidic to alkaline, so unless you live in an area of extreme soil pH, you should not need to make any changes to successfully grow panicle hydrangeas.

Planting

Do not amend the soil when you plant panicle hydrangeas. Do not add any kind of compost, potting mix, top soil, etc. to the hole when you plant in the ground. This leads to something called the “bathtub effect”, wherein water infiltrates very rapidly into the amendment you added, but as it drains and hits your natural soil surrounding the hole, it slows to a halt. During this time, it sits around the roots, leaving them susceptible to rot. This is our recommendation for planting all of our shrubs, however, it bears repeating here, as this is the number one reason we’ve seen that recently planted panicle hydrangeas might struggle. Make your life – and your new plant’s life – easy: plant directly into your natural soil only, water after planting, and apply a 2-3”/5-7 cm layer of shredded bark mulch.

Water

Like any newly planted shrub or tree, panicle hydrangeas need regular water during their first year or two. Once they are established, they can survive dry conditions, however, too much hot, dry weather can compromise blooming, so regular watering is recommended for the most and best looking flowers.

Fertilizing

In most areas, it is not necessary to fertilize panicle hydrangeas regularly. If you want them to grow more quickly, an application of a granular fertilizer formulated for shrubs (like a rose fertilizer) in early spring is sufficient. Avoid fertilizing panicle hydrangeas excessively, as this can lead to weak stems. Be particularly aware of incidental fertilizing, such as that applied to a nearby lawn or flower bed, as these tend to be high in nitrogen and more likely to push soft, rapid growth that causes weak stems.

Flowering

“Panicle” describes the shape and arrangement of the blooms of the plant, but it’s easiest to think of them as essentially football-shaped (and sized!). They bloom in summer (mid-late spring in zone 8/9). The flowers start out white, but as summer stretches on and days start to get shorter and nights cooler, they start to take on pink to red tones. Exact color depends on the variety, and some varieties turn a new color entirely, while some will do so gradually, producing a multi-color shaded effect. If the color the flowers turn is muddy, that typically indicates the plant is in too much shade and/or that temperatures, and particularly night time temperatures, have been too high.

The color the blooms turn is a genetic trait that develops with the natural aging of the cells in the florets, and is not influenced by any condition in the soil, like pH level. You can’t change panicle hydrangeas’ color by treating with aluminum sulfate or planting in acidic soil – they will always stay in the pink/red range.

Winter

Because panicle hydrangeas are so tolerant of cold climates, they need little to no special treatment for winter. As long as a good 2-3”/5-7cm layer of mulch is over the roots, it’s prepared to soldier through the impending cold, ice, snow, and wind.

Pruning

Panicle hydrangeas bloom on new wood – in other words, they create their flower buds for the year only after they’ve begun to leaf out in spring. This means that they can be pruned without negatively impacting their bloom. Though pruning is not strictly necessary, it encourages stronger stems, better blooming, and an overall more attractive shape. If you are starting with a very small plant such as one purchased online, keep pruning to minimum until it has had the chance to develop some good body.

When to prune: panicle hydrangeas can be pruned in late fall, once the plant has gone completely dormant (i.e., has lost all of its leaves and has been bare for at least two weeks), or in early spring, just as the new growth begins to emerge. Aim to cut the plant back by about one-third its total height; in other words, if it is 6’ tall, cut off about 2’. You should also cut off any thin, spindly stems and side branches. If you have a panicle hydrangea tree (also known as a standard or tree-form hydrangea), see our article on their care and pruning for additional tips

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Panicle hydrangea FAQ

Can you grow panicle hydrangea in containers?

Yes! They do great in containers. The general guideline is that a plant should be two zones hardier than yours for the best chance at winter survival, but thanks to their hardiness and toughness, they can be grown in a container even in zone 4. Be sure to choose weatherproof containers, made of a material that can stay outdoors all winter without breaking, cracking, or flaking, for your panicle hydrangea, and of course, the container must have large, open drain holes in the bottom. Other than this, all of the care instructions given above apply to container-grown plants as well. When winter comes, check the soil for water every 10-14 days. If it is dry, apply a bit of water – nothing like you’d do in summer, just a bit to moisten the top layer. Depending on the size and the growing conditions, you should be able to grow a panicle hydrangea in a container for at least three years before it needs to be transplanted in the landscape. You’ll know it’s time to transplant if the flowers and leaves appear smaller and stunted, and/or it becomes very difficult to keep watered in normal conditions.

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Can you keep a panicle hydrangea smaller through pruning?

No, this is not a practical strategy. If you need a small panicle hydrangea, you should select one of the dwarf varieties like Little Lime, Little Quick Fire, or Bobo, as these will naturally stay on the smaller side. Even though it seems like you could cut a full-sized panicle hydrangea back really severely and that would cause it to grow little that season, the opposite usually happens, and it grows a lot. Think of it this way: the bigger a plant gets, the bigger its root system is. A large, well-established root system can function as a sort of “engine” fueling growth, so that if you cut it back to the ground, it fires on all cylinders and quickly pushes out a ton of new growth. Because it was formed so quickly, that growth is typically soft and weak, and it winds up laying on the ground for the season.

Fun fact: you can use this to your advantage if you’d like – cutting an established panicle hydrangea back severely results in weak stems but ludicrously gigantic flowers, which can be harvested to use as fresh or dried cut flowers. The plant can then go back to regular maintenance pruning to get back into shape.

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Which is better for pruning panicle hydrangeas - fall or spring?

From the plant’s standpoint, either one is more or less fine. The advantages to pruning in fall are that you can minimize the risk of stems breaking from heavy ice or snow and that typically, there’s less going on in terms of yardwork in late autumn, so it’s easier to fit the task into your schedule. The advantages to pruning in spring are that it preserves the dried flower skeletons all winter, which are much more interesting to look at than a pruned plant, you can easily repair any snow or ice damage in spring, and finally, by waiting until the new growth starts to emerge on the plant, that essentially lets it tell you where to cut. Just make your cuts above where large, healthy buds are emerging, roughly half to one-third down the stem.

My personal preference is spring pruning, but you can choose whichever time works better with your schedule, provided you follow the guidelines given above in the pruning section.

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The foliage on my panicle hydrangea is yellowing. What’s wrong?

Provided that the yellowing leaves are confined to the center part of the plant, this isn’t a cause for concern. It’s not an uncommon occurrence, particularly for those that were planted the same year. Basically, what happens is that as the plant has grown through the season, the upper portions began to shade the center, make those inner leaves less effective energy-producers. As a result, the plant takes the energy in the chlorophyll, causing the leaf to yellow, and then drops it.

If the yellowing is seen on new growth and/or leaves toward the ends of the branches, it may indicate overwatering/poor drainage. If you’re concerned about what you’re seeing, you can always contact us with a photo for our thoughts.

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My panicle hydrangea isn’t blooming at all. You said these were easy! What gives?

Being extremely cold tolerant and blooming on new wood makes panicle hydrangeas exceptionally reliable bloomers. However, there are a few possible explanations for why one may not be blooming:

  1. Too much shade. In shady areas, blooming may be sparse or perhaps not occur at all in extreme conditions. Plant in at least four hours of sun or filtered light all day for best bloom.
  2. Too young. Most panicle hydrangeas bloom well from an early age, but sometimes, they need to be established before they will devote energy to blooming well. Follow all of the care instructions above to get your plant off to a good start, and keep it growing healthy and vigorously. Remember that a good root system must be in place for flowering to occur. If you’re starting with a small plant that you ordered online, it can take several seasons for it to become large enough to bloom.
  3. Flowers eaten by deer. Deer are particularly fond of the flowers of hydrangeas and are amazingly capable of eating just the developing flower bud, leaving few other signs of their presence. If deer are an issue in your area, protect your plants with a repellent, fence, or netting.
  4. Improper pruning. Panicle hydrangeas can be pruned in early spring and still bloom that year. However, if you pruned very late in spring, it can remove the buds that were developing. This more typically results in a delay of bloom rather than eliminating it, but depending on how late it was pruned and the growing season, no flowers that year is a possibility. Be on the safe side and prune in early spring, before or just as the plant starts to leaf out.

A final possibility is that the plant simply hasn’t bloomed yet that season. We often hear from gardeners who bought a panicle hydrangea in bloom the previous year in, say, May or June, and planted it in their landscape. That leaves them wondering why the plant isn’t in bloom the following year at that same time. What actually happened in this case is that the grower who was growing the plant prior to purchase kept it in a protected greenhouse and probably turned the heat on early so that they could ship a nice blooming plant to the garden center in time for the prime shopping season. However, once the hydrangea is planted outdoors, it will take on a more natural, seasonal cycle, blooming later in the season. This is totally normal and no cause for concern – just be patient. Depending on your climate, some later-blooming varieties like Pinky Winky and ‘Limelight’ may not show buds until well into July, even early August in cool areas.

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Why aren’t my flowers turning from white to pink/red?

As stated above, the only color that panicle hydrangea flowers can develop is pink or red. If this doesn’t happen, it’s due to one of two reasons:

  1. The plants experienced water stress. This can be due to too much or too little water, but in either case, it causes the plant to conserve its resources, resulting in flowers that simply go brown instead of aging to pink. Because panicle hydrangeas bloom during what is the hottest, driest part of the year in many areas, they may need supplemental water now and then during their bloom time, especially if rainfall is scarce or they aren’t on irrigation. Mulch helps this a lot too.
  2. High temperatures. If temperatures, and particularly night time temperatures, are high, the color change many be muddy or not occur at all.

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What about hydrangea trees?

Hydrangea trees, also known as standards or tree-form, are specially trained by growers to take on that unique form. It takes a few seasons of careful pruning and training to create them, so they cost quite a bit more than a regular shrub-form panicle hydrangea. Hydrangea trees are not grafted like some roses or trees are, where the “trunk” and the “canopy” are different, so you needn’t worry about the bottom overtaking the top. However, some special care is required to keep them looking their best, which you can read about in our standard care article

Due to their higher cost, garden centers may not bring in a lot of panicle hydrangeas, and they often sell out fast. If you are looking for one, contact your garden center about ordering them for you; autumn is the best time to do that for spring of the following year. Most of our full-sized panicle hydrangea varieties are available as standards.

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The stems of my panicle hydrangea are on the ground and/or don’t hold the flowers up. What’s wrong and what can I do about it?

Strong, sturdy stems that hold the blooms upright all season is one of our top considerations in evaluating panicle hydrangeas for introduction. However, these three cultural/environmental factors that can prevent them from achieving their full potential:

  1. Too much shade. Panicle hydrangeas need at least four hours of bright sun, or filtered light all day, for the strongest stems. In shaded conditions, they will stretch toward the light, which leads to weak, spindly growth.
  2. It’s best if you prune panicle hydrangeas back by about one-third their total height each year, as described in the pruning section. At this time, you should also remove any thin side branches as well. This gives you the strongest, sturdiest framework. If you cut back more than that, it can push a lot of weak, soft growth – however, this should only last a season, and if you prune properly the following year, those weak stems will be just a memory.
  3. If you want to fertilize your hydrangea, once a year in early spring is sufficient. If the plant gets a lot of fertilizer, and particularly high nitrogen fertilizer, that can push soft, weak growth. If you often fertilize a lawn or flower bed nearby, this can inadvertently reach the hydrangea.

One last consideration: sometimes, recently planted hydrangeas can flop. This can be due to multiple factors, including all of the reasons above, as well as the limitation of the root system to the container, or plants being closely spaced at the nursery or garden center. This is a temporary condition that should not recur – just plan to prune the plant according to instructions above that autumn or the following spring. If you wish, you can cut the flowers off to enjoy in a vase indoors, which will un-weight the branches.

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There are so many panicle hydrangeas on the market! How do I pick the right plant for me?

We hear you – it can be difficult to decide! Here’s a quick look at the different varieties we offer and what makes each one unique:

Bobo® - the smallest on the market (3’ tall and wide), lacy white flowers turn pink, best color and blooming in cooler climates

Fire Light® - full-sized (6-8’ tall and wide), full mophead flowers turn red.


‘Limelight’ – full-sized, green flowers turn burgundy-pink, fairly late to bloom.


Little Lime®
– dwarf (3-5’ tall and wide) version of Limelight; blooms earlier and has better fall color.

Little Quick Fire® - dwarf (3-5’ tall and wide) version of Quick Fire, early blooming.

Pinky Winky® - Very robust lacecap, flowers shade from deep pink to white.

Quick Fire® - earliest to bloom; lacecap flowers turn red early in summer. Very nice foliage.

Zinfin Doll® - the most colorful; medium size and early-mid season bloom time.
 

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What’s a pee gee hydrangea?

Some people refer to panicle hydrangeas as “pee gee” (or “peegee,” or “pg”) hydrangeas. However, this term refers to a specific variety – a very old one known as Hydrangea paniculataGrandiflora’, which was shortened to simply the p in paniculata and the g in Grandiflora. As such, we prefer the more general term for our hydrangeas. The true peegee hydrangea is an interesting plant for those who love garden history, but modern introductions offer significant improvements over it in terms of stem strength, flower quality, bloom time, and color.

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Do panicle hydrangeas make good cut flowers?

Yes! In fact, they’re outstanding as cut flowers, both fresh and dried. Depending on how you like to use them, you may find the dwarf varieties more suitable, as the very large ones, like Pinky Winky, require a very large base to look in-scale. Don’t cut the flowers when they are freshly opened: wait until the last florets at the tip of the flower are starting to open to reduce the risk of wilting. Strip off as much foliage as you can before arranging, which also minimizes wilting. If you want to dry the flowers, simply place in a vase with just an inch or so of water, let the plants take it up naturally, and do not replace the water. They will dry straight and fluffy.

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Whether you are going for fresh or dried cut flowers, know that the color that they are when you cut them is the color they will keep. In other words, if you want flowers with the pink/red tones, cut them after that has developed. They will not naturally progress to that color in the vase.

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I need to transplant a panicle hydrangea. When should I do that and how?

Hydrangeas in general transplant pretty easily, thanks to their shallow root systems. The very best time to transplant them is in early spring, before the new growth begins, but they can be transplanted later in spring or in fall, when the weather has cooled off, if necessary. Avoid transplanting when it’s hot and sunny, unless it is absolutely necessary (i.e., construction, moving, etc.).

When transplanting, it’s always a good idea to prepare the new spot as much as possible before digging the plant out of its current location. Once you see the size of the root ball, you may need to adjust the new hole a bit, but overall, you should aim to minimize the time the plant spends out of the ground. Plant in the new spot using only your natural soil, water well after planting, and mulch. The plant may struggle a bit that first season, but keep it watered and cared for – it will rebound and be just fine in the long run as long as you provide the TLC to get it through the first several months after transplanting.

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My hydrangea is wilting, even though I keep watering it. What’s going on?

This is one of the most common questions we hear about panicle hydrangeas. It’s usually tricky to answer, however, because both too much water and too little water cause panicle hydrangeas to wilt. To determine which is the cause of your plant wilting, think about its growing conditions: how often do you water it? Is it watered by hand or with a sprinkler system? Has it been hot and dry, or has there been reasonably good rainfall? While panicle hydrangeas perform best with regular water, they can suffer severely in situations where the soil is poorly drained/stays wet for long periods, so your perspective on how much water it has been getting, and how often, is a key part of determining the issue.

There are a few visual cues you may be able to pick up on as well. The drooping foliage on overwatered plants tends to feel kind of soft and flabby. It may take on dark brown or even black tones. Often, in these cases, the flowers wilt dramatically as well. If the plant is getting too little water, the drooping leaves often feel dry and crispy, have light brown spots (especially around the edge) and take on kind of a dusty look. Unless the lack of water is extreme, the flowers usually won’t wilt when the plant is under-watered. If you’re not sure, contact us and attach a photo.

If the plant is being overwatered/has poor drainage, cut back the water if you can. Water less frequently, or adjust irrigation heads to deliver less water to the plant. Overwatering on panicle hydrangeas is frequently caused by amending the soil at planting time with compost, potting mix, or something like that (even though we explicitly recommend against this in our planting instructions). If this is the case, the plant should be removed, the soil amendment thoroughly incorporated with the natural soil, and then the plant replanted. It may drop its leaves, but it will recover provided that conditions improve.

If the plant is getting too little water, usually some extra water during hot periods should be sufficient. You should also put down 2-3”/5-7cm of shredded bark mulch, which keeps roots cool and conserves moisture. If you find that these measures are still not sufficient, that may indicate the plant is getting a bit too much sun for your climate. In that case, consider transplanting it when the weather cooperates.

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Still have questions? We’re here to help! You can contact us with your gardening questions and one of our horticulturist will get back to you. Please include your zip/postal code and a photo if possible.

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