Rather than dump chemicals all over your garden, you may want to explore the option of mycorrhizal fungi. This stuff has been around for ages. It was discovered by man in the 1800s, and well-documented by the 1930s.
This type of fungi develops a symbiotic relationship with plants, exchanging nutrients at fungal/membrane interfaces. They are considered to be the cornerstone of plant life on earth, as they help serve as a secondary root system, extending themselves far out in to the soil. They extract mineral elements and water from the soil, and exchange them for sugars in the host plant, thereby ensuring plant survival in even the most trying of conditions. They are believed to exist in 95% of the world’s plant root systems.
We poor fools often cringe at the concept of fungi. It is seen as bad, and unwanted, but by adding this humble fungi to your garden either before, or after mulching, you are doing your plants a world of good. Mycorrhizal fungi help different plants with different tasks. Some assist in water uptake, others with making fertilizer more accessible, some with gas exchange etc… They are adaptable and responsive to a plants needs, and will assist accordingly.
Adding it to your garden will also leave no room for nasty little brutes like phytophtera or botrytis.
You must feed and care for the precious little mycorhizii. However this is not hard, as they like the same things as plants…a little water and fertilizer will ensure they, and your garden flora, will flourish.