When it comes to adding ash to your garden, there are two questions to answer: how much and when. Ash is very versatile in the garden, as it’s used for mulch, compost, soil conditioner, fertilizer, pest deterrent and more. You can add ash to any of these uses and still keep your garden healthy and beautiful.
It's not good for plants to have lots of nitrogen (ammonia) in the soil. Ammonia is toxic to many plants, and also has a bad odor, so it doesn't really help them grow either. If you're going to put wood ash in your garden, you'll want to avoid using high-nitrogen fertilizers like ammonium sulfate or urea.
The amount of wood ash you use depends on the size of your property. You want to apply enough ash to give your plants the nutrients they need, but not so much that you overload them with ash.