Written by davethetreecenters • March 20 Panicle Hydrangea – the hydrangea for colder zones
If you are new to gardening, hydrangeas can be confusing. Most people recognize the large round heads, usually in pink or blue, or the mophead hydrangea (Hydrangea macrophylla), so widely seen in summer-gardens in warm and hot zones. It can take a while, though, to discover that if you are in colder areas – zone 3, 4 and even 5 – trying to grow them can be frustrating. “How come I never get any flowers?”, or, “I planted one of those advertised as flowering twice in the season, but all I got were a few flowers at the end of summer!” – these are typical of the things we are asked.
For many years northern gardeners have grown a cousin of the mophead hydrangea, the panicle hydrangea, (Hydrangea paniculata). Big old plants of the original variety, the Pee Gee Hydrangea, still decorate public parks and cemeteries in many town, planted a century or more ago. For a long time this plant was the ‘poor cousin’ of the flamboyant mophead, but in recent years plant breeders have taken it and turned it into such a great plant that even southern gardeners have taken to growing it. So much easier to grow than mopheads, at least in most places, and a terrific late-blooming shrub that no garden should be without, these plants need different care, though (although not much of it) to get the best from them. They have pointed, conical flower-heads, not the round ones. Most begin white, although the popular Limelight variety, or the smaller Little Lime Hydrangea have fashionable lime-green flowers. Almost all of them gradually turn shades of pink as summer turns to fall, bringing some gorgeous fall colors to your garden.
So let’s take a look at these great plants, and learn how to grow them like a pro.
Panicle Hydrangeas Flower on New Stems
The simple reason mophead hydrangeas are so hard to grow in colder areas is the way they bloom. Flower buds form at the end of branches that grew the previous year, so if these are damaged – and they are sensitive to cold, especially late frosty weather in spring – you get no flowers. Simple to understand, even if frustrating. Sure you will get leaves, and yes, if you grow some of the newer varieties, like Endless Summer®, you will have flowers later in the season, because these can flower on new stems too. Trouble is, though, these ‘repeat-bloomers’ really do better in warmer, more humid zones anyway, and they never grow large in cold areas, while most gardeners want substantial shrubs that will fill their garden with bulk and impact.
So this is the first thing to understand. Since panicle hydrangeas flower on new stems, it doesn’t matter if some branches die in winter, or even if their new tips are damaged by a nasty late frost – you will get flowers anyway. We’ll come back to the impact of this fact on pruning a bit further down.
Panicle Hydrangeas Grow Fast
If you have a new garden then you want to see it full and blooming soon. Most mophead hydrangeas, even in good conditions, take maybe 5 years to reach 4 or 5 feet, and don’t become big, full bushes for several more. Contrast that with the panicle hydrangea, that can grow 3 feet in a single year, and within 5 years will be a full-sized shrub. These also come in several sizes, so you can have smaller, 3-4 foot varieties for smaller beds, and bigger 6 foot shrubs for larger spaces – all in a few years. Of course, like all plants, rapid growth isn’t a given, it depends on you planting in suitable conditions, so this is a good moment to say that these hydrangeas enjoy – and need – more sun than the mopheads, and will grow in drier soils too.
Best Conditions for Growing Panicle Hydrangeas
- Plant in full sun, or almost that, with some afternoon shade in hot zones
- Grow in ordinary well-drained soil, including clays and poor urban soil
- Add lots of organic matter, like compost, when planting, and as mulch
- Mulch again every fall – that way you won’t need fertilizers
- Water regularly when young, and don’t leave too dry through summer
Panicle Hydrangeas Need Pruning
When you grow bigleaf hydrangeas, they need very little pruning. Just a little tidying after their first blooming, and that’s it. With Panicle Hydrangeas you can leave them alone, but for the best results some simple annual pruning makes an enormous difference.
Two Basic Shapes
The first thing to consider is the basic form you want. The most common is as a bush sitting on the ground. For this you don’t need to do anything special – it’s the natural way they grow. The second is as a tree form – a bush raised on one central trunk, which could also be two or three tall trunks. How tall the trunks are is up to you, but the taller you make them, the longer it will take. Begin when your tree is new. Decide which of the strongest stems you want to keep, and remove everything else. This will stimulate those stems to send up long shoots. Take one, or more, of these and attach them to a strong stake, bending them carefully to the angle you want. Continue to remove shoots that sprout lower down, and keep training the stems to grow straight and tall, to the height you want. This might take a few years, but in the end you will have a plant that stands tall, and that you can put smaller plants underneath.
Three Basic Ways to Prune
Annual pruning should be done in early spring. If you haven’t done much pruning it is best to wait until you see a few buds swelling, so you know what is alive. Start by removing any dead branches and weak, skinny ones, and then you have a decision to make. Some gardeners like having panicle hydrangeas with really big flower clusters, which can easily be over a foot long. To have that you have to reduce the overall number of flower clusters. Other people want as many flowers as possible, even if they are smaller. Or, you might be in between, and want a good size, but nothing huge – the Goldilocks answer, “Not too big and not too small”. You get this choices by how you prune.
Hard Pruning – a smaller number of very large flowers
This might seem drastic, but don’t worry, it works. See the stems with shinier, light colored bark? Those are the ones that grew last year. Cut each one back hard, leaving just two pairs of buds on the part above the older stem it is growing from. This will stimulate long, vigorous stems that will grow very large stems. By the way, this is best done with a variety that has strong stems – perhaps the terrific Phantom Hydrangea, bred for stem strength.
Light Pruning – lots of flowers, but smaller ones
This is easy. Just cut off the old dead flowers, if you didn’t already do this in fall, back to the first pair of healthy-looking buds. The plant will produce lots of stems, with lots of flowers, but they will be smaller. This method is especially useful if you have a plant where you tried hard pruning, but a lot bent over and even snapped – not a great outcome.
Moderate Pruning – perhaps the best for most gardens
Most of us are going to go with this choice, with good-sized flower heads that aren’t so big they are likely to bend over, or break in a storm. Here, just cut back until you have 4 pairs of buds left on the stem. Always cut just a little way above the top pair, leaving them room to grow, but not a long piece of stem that will die-back.
One other thing about pruning. If you delay doing it, this delays flowering too. So in warmer zones, where the season is long, you can extend the flowering period for your panicle hydrangeas by leaving some until they are already sprouting well – they will bloom later than the ones you did when the buds were only just visible.
Lots of Great Plants to Choose From
Check out our collection of Panicle Hydrangeas on our Hydrangea Page. Modern varieties begin white, but many now turn pink very quickly, and you can have a great, ever-changing display, and lots of variety, by growing a selection of varieties.
