Hello, mainegard3. Too much nitrogen can do that but it can also result in small root systems, leaf burn and, at really high levels, can even kill some plants. The definition of high levels varies based on the plant that you are growing. Some can handle more than others.

There are soil kits sold at plant nurseries that will give you information on nitrogen levels if you mix some soil, a pill and water together. By reviewing the resulting color of the solution, you can determine if the nitrogen levels are high. Scotts can be 30% nitrogen, which is high compared to other regular fertilizers out there.

You can also make a real soil test by taking a soil sample to your Agriculture Extension Service. You can also indicate what plants you are growing so they can tell you if the nitrigen levels are fine or if they are close to being toxic to the plants. You will get a more accurate result.

I did not quite get why you are using Bayer Disease and Insect Plus Fertilizer but I would recommend using first some form of organic solution to the disease or insect problem as Bayer kills the bad insects that are causing you problems as well as the beneficial insects. With no or little beneficial insects to act as predators, the bad guys can easily get out of control even if you spray. But if the infestation is severe then spray; and after the insecticide has worn off, release beneficial insects ("after" so they will not be killed by the spray). I had a sudden and large infestation of bagworms about two years ago that required spraying some chemicals to get the darn thing under control.

I would suggest to try to keep things simple. To combat a disease, I would apply controls for that disease. If I have a type of insect causing problems, I would apply something that attacks those insects.

Hydrangeas do not need much in terms of fertilizers. When given lots of fertilizers, they do not react with lots of growth like roses do. A single fertilizer application in the northern half of the country will last a whole year. For a new hydrangea, you can apply 1/2 to 1 cup of compost, composted manure or cottonseed meal in June. You can also apply a general-purpose slow-release chemical fertilizer like Osmocote in June; but read the label to determine how much to apply.

During the rest of the growing season, you can add coffee grounds, liquid seaweed or liquid fish. Or nothing. All fertilizers should be discontinued around July-August so the plant goes dormant before early frosts arrive in the Fall and so new growth does not get zapped by winter.

Does that help you, mainegard3?
Luis