• Sandi Manna

What's wrong with my hydrangeas?


Black spots on hydrangea leaves could be indicative of fungal disease

Summer is in full swing and that should be the perfect season for your hydrangeas, but lack of blooms, spots and other issues can drive you crazy trying to figure out what's wrong and how to fix it.

Let's talk about the big one first, lack of blooms. That is the number one question we get asked about hydrangeas every year. If your hydrangeas aren't blooming, here are some possible solutions.

Don't prune your hydrangeas. They don't need it. They shouldn't ever be cut back to the ground in the fall. If you're pruning your hydrangeas, you could be pruning the blooms right off of them before they even form. Some hydrangeas bloom on old wood, or branches that are at least a year old. Some hydrangeas bloom on new wood, or wood that has grown the current season. Many of the new hydrangeas that are currently on the market take the guesswork out of it. They bloom on both old and new wood. If your hydrangea isn't blooming, it could be because it's been pruned, or pruned incorrectly. Sometimes a hydrangea needs a little rejuvenative pruning. After a few years, the mophead hydrangeas may produce less blooms. Prune out no more than 1/3 of the oldest branches early in the spring, and clean out the dead wood. This will rejuvenate your hydrangeas. The branches you prune out will not bloom this year. Next year, those branches will be full of beautiful leaves and more lustrous than before, but the third year they will bloom profusely! Be selective when you prune the branches, you don't want to prune out all the branches in the same area or you'll have a section of hydrangeas with no blooms! If you're looking to control the size of the plant, you can trim the tips of the branches immediately after flowering, but don't cut beyond two leaves or you'll find your hydrangea won't bloom again. If the hydrangea is too large for it's space, it's best to get a newer, smaller variety.

It's also possible a late frost killed the flower buds or drying winter winds. Plants are much more in tune with subtle temperature changes and micro-climates than we ourselves are. Hydrangea buds are very susceptible to winter. Although hydrangeas are certainly hardy in our zone, it's the roots that are hardy while the buds are more susceptible to winter damage. For most of our clients, we wrap their hydrangeas (and other winter sensitive shrubs) in burlap. If you think about it, it's really not much different than you and I putting on a jacket. The burlap allows the shrub to breathe, but protects it from cold, drying winter winds. Simply wrap it before the first frost, and unwrap it after the last frost (late April). To protect your shrubs, drive some tall wooden stakes into the ground creating a frame. Wrap the burlap around the frame and secure it either with staples or tying it. Leave the top open. If we have snow, it will collapse the top if you close it over, and snow is insulating so it will help protect your hydrageas.

So now we've discussed pruning and wrapping your hydrangeas in burlap. Maybe you've tried all this and they still aren't blooming. Should you add fertilizer? Compost? Some other type of soil ammendment? You could, but what they really need is just a complete rejuvenative pruning. Start over from scratch so to speak. In the fall, after their branches are bare, prune them hard, all the way back to the ground. But wait, didn't I say earlier NOT to prune them back in the fall? Aren't I contradicting myself? I did say that, but only if you've been cutting them back regularly. At any time really. I find for hydrangeas in particular, rejuvenative pruning is best done in the fall, or early spring, while the shrub is dormant. This minimizes the shock to the plants system. You won't have blooms this year, next year you still won't have blooms – but your hydrangea will come back much thicker. It's the 3rdyear that you'll get an explosion of blooms.

What about spots you say? Your hydrangea leaves have small, brown spots – or even worse...they've got large brown patches and chunks of leaves missing! These are pictures I borrowed (with permission) from the Guilford Facebook page. It was started as “Does anyone know whats wrong with my hydrangeas?”, and turned into a lengthy thread about all the different problems people had with their hydrangeas, which led me to writing this article.

Fungus is the culprit here. You may all have forgotten, but I, as a landscaper, have not forgotten how horribly wet this spring was! Just beyond ridiculous! All that moisture stays trapped in the soil and fungal spores develop. Fungus can show up as a simple spot or spots as in this photo, or it can really take hold and start to decompose individual leaves. The cure is a relatively simple one. Clean up any fallen leaves (this is true of roses too, as well as any other plants that are exhibiting signs of fungus). Fallen leaves left on the ground allow the fungal spores to keep reproducing. Avoid evening watering. If you must water in the evening, water as soon as you get home, allowing plenty of time for your plants to dry off before dark. The best time to water any plant is in the morning. That's when the ground is naturally wet from dew. Mother Nature may have a temper sometimes, but she's never wrong! Avoid overhead watering. Overhead watering gets the leaves wet. During times of high heat and high humidity, it's difficult for leaves to dry off and that can lead to development of fungal spores. It's always best to water plants at the base. You'll also want to pick up a fungicide. There are many good fungicides located at any local garden center.

So we've covered blooms, spots. What else? Oh, insects.

Insects come in two basic groups. The first group is piercing/sucking. These types of insects are small insects that pierce the plant leaves and suck the liquid, or sap, out of the plant. This can cause yellowing and distortion or puckering of the leaves. The leaves affected by sucking insects can curl, distort, yellow and then turn brown and drop.

Your second group of insects is the biting/chewing variety. They think your garden is their all night salad buffet and happily munch away leaving your leaves with holes, or even worse – skeletonized.

The hydrangea tier moth will tie two leaves together with silk and create a small leaf fort where they hide. They will then feed on both the leaves and the flowers of your hydrangeas. These “forts” almost look like a dead leaf that has fallen onto your hydrangea. Brown in nature, if you see any type of these forts, it's best to open them up and you'll see the caterpillars hiding inside. You can go ahead and squish them together, or just cut off the damaged leaves and throw them in the trash.

In most cases, an insecticide soap is a good tool for eliminating insects.

Keep in mind there is a threshold for insect disease.

How unsightly is it?

How damaging to the plant is it?

What is the insects ability to reproduce and cause further damage?

If the insect damage is obvious from a distance, it's definitely above a tolerable threshold and should be managed.

If you're strolling through your garden and happen to notice it, perhaps it should be monitored closely before treatment. A few holes in your plant leaves aren't dreadful and it's most likely not going to be a severe enough infestation to cause permanent damage.

If you don't see it unless you're really working with that particular plant, or you're really looking, then it's probably fine, but you should still always monitor your garden for disease and insect activity as well as any changes in plant health.

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