After much research, I believe I killed my hydrangea (planted outdoors) by applying granular fertilizer and too much of it. The early growth from this season is all dead and I’ve cut the whole plant back. There are many insects congregating around the base. When I gently tug on the main stems, the plant remains in the ground. If it were dead, would it be easily pulled out of the ground? Should I throw in the towel at this point and replace it? Thank you.
Thank-you for contacting Toronto Master Gardeners with your question about your hydrangea.
Based on your description, it does sound as though you have inadvertently over-fertilized your shrub. Dried up leaves are a symptom for sure. If you applied the fertilizer at the base of the plant rather than along the drip line (the area below the branch tips), it may have damaged the tissue in that area as well. Granular fertilizer is fine for hydrangeas, but, as you probably found in your research, it should be applied sparingly and in the area of the drip line, so that the water coming off the leaves can moisten the granules and make the fertilizer available to the fine ends of the roots. Fertilizer should only be applied to plants at least 1 year old. Newly planted hydrangeas have often undergone fertilizing treatments at the grower and/or there may be slow-release fertilizer already in the potting soil used at the nursery. There is significant risk of over-fertilizing. As well, the new transplants are just establishing their root systems in the first season. The roots will not have extended out to the drip line yet.
Without a photo of the plant it is difficult to say whether it is dead. You mention that this season’s growth has died back, but I wonder if any of the older stems and leaves are still alive? If there isn’t any green growth on the plant, you might as well remove it and start again. The fact that the plant is secure in the ground may not mean it can be saved. A good root system will support the plant structurally, even as it dies off. If there are signs of green live growth, you could try to revive your plant by washing away or diluting the fertilizer as much as possible. To do this, you need to flood your garden area a few times over the next few days. Acting quickly will be key to inhibiting the uptake of the fertilizer by the plant.
This article on fertilizing hydrangeas will also give you some general pointers for future use.
Good luck with your hydrangea!