Can I Make My Hydrangea Stems Stronger?

April 8, 2024 | C.L. Fornari | Hydrangeas

We got a great email from a customer last week, who asked how he might make the stems on his Hydrangea shrub stronger. I loved this question, because it is not only something that many of our customers wonder about, but the answers aren’t always what they expect.

I responded that I assumed he was asking because some of his plants were flopping over with the weight of their large flowers. One of reasons that we love all types of Hydrangeas is because of their large, showy flowers, but those flowers can be heavy, especially after a rain. How to hold the hydrangea flowers up?

When I read the customer’s question, I immediately thought about putting weights into the Hydrangeas, so they might work out and get stronger. In some ways this isn’t too kooky, in that with plants it’s “use it or lose it” as well. The wind that blows plant stems back and forth, for example, helps to strengthen them.

Whether you are wondering about your drooping, blue Endless Summer blooms, falling Annabelle flowers, or the bending branches of your Lime Light, here is what you need to know about the stem strength of Hydrangeas.

Weaker stems are usually a genetic thing. For example, Annabelle Hydrangeas tend to fall over when flowering or after a heavy rain, while Incrediball, a similar arborescens which has been selected for sturdier stems, does not. In the panicle group, the PG (Hydrangea paniculata ‘Grandiflora”) has weaker stems while Fire Light stems stay upright, even with heavy flowers. One reason that Limelight Prime was selected and brought to market is because it was more stem-sturdy than the original Limelight. Endless Summer stems fall over sooner than some other blue hydrangeas. Stem sturdiness is something that breeders focus on when trialing new Hydrangea varieties that they introduce, so you’ll see that most of the newer varieties are more stem-sturdy than older types.

This is a tree form of Hydrangea paniculata ‘Grandiflora.” It was one of the first named paniculata varieties and the name ‘Grandiflora’ says it all: the flowers are huge. So huge, in fact, that they bend the stems down, almost creating a weeping form of tree. ‘Grandiflora’ isn’t very popular anymore, because of the lack of stem sturdiness, but if the gardener accepts it as a weeping tree, it’s really quite lovely.

Endless Summer is probably the most popular large, blue Hydrangea on Cape Cod, and with good reason. It’s fairly bud-hardy, the flowers are a rich, medium blue, and it’s the remontant type that flowers prolifically on buds formed in the previous August, and has some fresh flowers on new stems in the fall. The stems are not particularly sturdy, however, especially if the plant has been well fertilized so that the flowers grow larger. No matter, think of your Endless Summer as a blue waterfall and treasure every flower.

Incrediball Hydrangeas are in the same species as Annabelle: arborescens. These native Hydrangeas are also called “smooth Hydrangeas.” Incrediball was selected because although it has the same large, white flowers that Annabelle does, they are held up on sturdier stems and are less likely to fall over after a heavy rain. Photo courtesy of Spring Meadow Nursery.

2. Fertilizer makes it worse! Many people assume that fertilizer will make a plant stronger, but actually the opposite is true. Fertilizer promotes larger blooms and faster growth, and that fast growth is weaker. So the more you feed a Hydrangea, the more likely it is to bend over.

Sometimes people think that fertilizing a plant will make it stronger, but the opposite is true. Fertilizer will make the plant have larger, heavier flowers and weaker stems. So if you have a plant that’s already prone to flopping, don’t fertilize unless a soil test shows that you need to add nutrients. You could keep the soil healthy and the plant happy by top-dressing all around your Hydrangeas with composted manure, however. An inch of compost in the spring or fall, spread from the stem to past the dripline and covered by an inch of bark mulch, would be good for all Hydrangeas.

3. Hard pruning will create weaker stems. Pruning always stimulates growth, because the plant wants to replace what it’s lost. But that new growth is naturally weaker. If you prune a large Hydrangea such as a Limelight or PG back hard, it will respond with fast, upright growth that isn’t as strong. Older stems are sturdier. For the strongest paniculata stems, only remove crossed branches, and those heading into the center of the plant, aiming for removing less than 1/4 of the plant’s total size.

If you cut a panicle or smooth Hydrangea back hard, you’ll see the plant will respond with straight, upright growth and huge flowers. That new growth will be weaker, and the large flowers will be likely to pull the stems over, especially if they are wet. And of course, a hard pruning of the blue macrophylla Hydrangeas will result in fewer flowers.

So how can you strengthen your Hydrangea stems? Go easy on the pruning and fertilizing, and know that some varieties will always be prone to bending, especially when the flowers are large and wet from rainfall. If your plants need supporting, see the link to an invisible method of staking below.

Limelight Prime is a newer version of Limelight. It was selected for earlier blooming, sturdier stems, and a brighter, pleasing pink color as the flowers age. Thanks to Proven Winners and Spring Meadow Nursery for supplying this photograph.

Look for the newer, more stem-sturdy varieties of Hydrangeas at Hyannis Country Garden this season. We also carry Hydrangeas that have always been less prone to flopping, including Invincibelle Spirit II, Little Quick Fire, Pinky Winky and others. From short, to medium and tall, there is a Hydrangea for every garden.

Invincibelle Spirit II is one of the pink arborescens. They are quite stem-sturdy, and grow to about 4 feet tall and 5 feet wide.

Some paniculata types have flowers that are a bit more lacy, and these aren’t as heavy. The blooms have both fertile and infertile flowers in them, making them attractive to pollinators as well. This one is Little Quick Fire.

Pinky Winky is a paniculata that has large, pointed flowers held upright on sturdy stems. It will grow tall, however, so place this Hydrangea where it can grow to six feet or more.

BTW, if you have flopping Hydrangeas (or peonies!) and want to stake them so they have a natural form, there’s a description of how to do it on this blog: https://gardenlady.com/how-to-stake-flopping-peonies-and-hydrangeas/

Posted in Hydrangeas

1 Comment

Linda Lord on April 11, 2024 at 12:09 pm

The history of falling hydrangeas and how and what to do was great. I’m always learning about my hydrangeas and so happy CL that you give us great advise.

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