I grew up with a proper fire pit in the backyard, but it wasn’t until much later that I learned how the leftover blacken bits of wood ash could be used as fertilizer. If you still enjoy a classic bonfire every now and then, here is how you can recycle the remnants and help your garden grow!
Wood ash contains nutrient rich potash and raises the soil pH level, otherwise known as "Sweetening the Soil." It makes a wonderful fertilizer for plants that would suffer in more acidic soil such as Lavender, Lilac, and Rosemary, and veggies like Cauliflower, Beets, and Spinach. Simply search "alkaline-loving plants" to see what else makes the list.
In terms of application every 2nd Fall is sufficient. Sprinkle a 1/4 cup around established plants, or rake lightly into the top layer of fresh soil before planting (about 1 lb per 50 square feet). You can also add the ashes directly to your compost bin; just make sure to keep the ratios low—about 5 percent of the overall mix.
(Image: MaryAnne Petrella)
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But don't leave your extra ash lying around in open buckets where it gets rain. Water and ash make a nasty caustic skin-burning stew....
Please don't put wood ash on your garden without doing a little research first. Being too heavy-handed can easily kill your green friends in a flash. Here is some information on using wood ash wisely.
http://www.gardensalive.com/article.asp?ai=749
Also, there's this product called Soil Reef that I used in my veggie garden for the first time this year and i love it. We had our best year yet. It's made of some sort of incinerated trees, kind of like wood ash.
http://soilbiochar.com/
I'll definitely be using it again in my other gardens.
Ash is great if you have acidic soil, common in places with sufficient rain to raise a lawn.
If you live in an area with alkaline soil (low rainfall / arid areas,) DON'T add ash or eggshells or lime to your soil. Use acidic additives such as coffee grounds, pine needles, sulfur or sawdust.
If you live in Central Texas skip this. We're on a limestone bed and have plenty of alkaline.
Best to do your research on your particular local soil type. Most veggies like slightly acidic soil.