You may hear us refer to "sun" and "shade" hydrangeas around the Farm, and while the meaning of this distinction may be apparent, these classifications tip you off to more differences in plant husbandry than you might think!
Most of the hydrangeas you will commonly encounter in gardens are derived from one of two species: The Bigleaf Hydrangea (Hydrangea macrophylla) or the Panicle Hydrangea (Hydrangea paniculata). The former is what most people probably picture when they think of a hydrangea — domed "mopheads" of blue, purple, pink, or white flowers — and these are what we typically refer to when talking about shade hyndrangeas. But while these beauties are queens of the shade garden, they simply can't stand the hot summer sun without a bit of cover.
That's where Hydrangea paniculata comes in! This easy, reliable shrub can take full sun in our Pacific Northwest climate, and in the heat of summer, it's hard to beat its floral show. While you won't find baby blue blooms in these sun hydrangeas, the classic conical clusters of white blooms found on varieties like 'Limelight' or the updated 'Limelight Prime' are stunning in their own right. And plant breeders have even extended the color range of sun hydrangeas into the pink realm with varieties like 'Diamond Rouge' and 'Pinky Winky.' Plus, many newer varieties boast flowers that reliably age to a stunning, deep red-pink as temperatures begin to cool in the fall. (That touches on one of the many reasons we love them: Their blooms persist for months!) They make great cut flowers at virtually all stages in their bloom and are even beautiful dried. And although their blooms will change color as they age, it's important to note that you can't alter the bloom color by adding fertilizer or other amendments like you can with shade hydrangeas.
Planting a Paniculata
Panicle hydrangeas are tolerant of most soils, although they will perform best in those same "Goldilocks" soil conditions that all gardeners covet: moist and well-draining. They are also great candidates for container culture, so long as you have a pot that is large enough for your shrub's ultimate size! When planting a sun hydrangea in the ground, it's best not to amend your soil with compost, but rather to use 100% native soil in order to help prevent excess water from collecting around your plant's root ball.
Once you've found the perfect spot for your sun hydrangea and dug a hole, water everything separately before planting — both the hole and the plant — then water everything again after you've finished planting. Your hydrangea will benefit from an application of a couple inches of mulch after going in the ground, which will help it to retain moisture. Like most plants, you will need to water it deeply for the first year or two until it gets established, but after that panicle hydrangeas are fairly drought tolerant.
As hydrangeas go, panicle hydrangeas are low-maintenance, in part because they don’t need a lot of fertilizer. In fact, too much of a good thing can actually be a problem! Over-fertilization can lead to weakened stems that have a tendency to flop when loaded with heavy blooms. A single spring application of an organic, slow-release fertlizer like E.B. Stone's All Purpose Plant Food should be plenty. If you are seeing weak stems and decreased bloom, your plant is likely over-fertilized, and the culprit might even be runoff from your lawn! (A lack of water combined with excess heat can also affect your plant's bloom.)
If you spot yellowing leaves towards the center of your plant, this isn’t a cause for concern. As sun hydrangeas grow through the season, it is normal for the upper portions of a plant to begin shading the center. However, if the yellowing is seen on new growth or leaves toward the ends of the branches, this may indicate overwatering or poor drainage. Overwatered plants can droop similar to underwatered plants, but if the leaves are dry and crispy, it's probably the latter.
Pruning Sun Hydrangeas
Panicle hydrangeas bloom on new wood, meaning they don't set flower buds until after they’ve begun to leaf out in spring. This makes them much more forgiving than their shade counterparts when it comes to the timing of any pruning you might want to do. (They also successfully avoid damage from untimely spring freezes, which can be a problem for shade hydrangeas.) Although pruning isn't strictly necessary, it encourages stronger stems, enhanced bloom, and an overall better shape. If you are starting with a very small plant, it's best to keep pruning to minimum until your specimen is larger, but once it has filled out, you can cut back up to a third of the plant's height per year. Sun hydrangeas can be pruned in late fall once they have gone completely dormant (you'll want to wait until two weeks after the plant has dropped all of its leaves) or in early spring just as the new growth begins to emerge.
With their ease of care and beautiful, long-lasting blooms, sun hydrangeas are a welcome addition to a sunny spot in any garden. We carry many varieties at the Farm, and our team is always happy to help you out with selecting the best one to fit your space.