I have raised vegetable garden beds and a few weeks ago experienced a large wildfire where the vegatation and homes on all sides of us burned as did the structural aspects of three of my beds. Needless to say there is a lot of ash in the air as well as visibly on the soil in my garden. My question is should I dispose of all the soil in my beds prior to planting new vegetables? Is my soil toxic? Should I throw away the vegetables currently growing in those beds?

I think that the ash will be very valuable when worked into the soil properly. Just turn your soil and mix it in.

I don't have any advice regarding your beds, I just wanted to say how deeply sorry I am for you and all the others suffering from these massive fires that have destroyed so much.

@BigBill if the ash came from burning vegetation i would agree with you, but i think we are talking people's homes and the contents there in. After 9/11 for example i believe the ash was quite toxic. I am not disagreeing with you. I don't know enough and wonder if the ash should be analyzed? These are vegetable beds after all. I think the answer to @NikkiMcRory very good question may be more complex and i wish i had an answer i was more confident to give.

Welcome to the forums Nikki. There are really no words to describe how devastated we are for our California friends who suffered and are suffering these fires. Many blessings in your journey to recovery.

That's true but 9/11 was concrete, steel, desks, ceiling tiles etc. very little wood percentage wise.
I just figured wildfires, trees, shrubs, houses etc. would be more likely to produce an ash not quite so toxic as that of the twin towers.

Let me start again...

The ash could be toxic. And, if you mix large amounts of ash with water and soil, it turns into a cement-like sludgey mess. The ash, if it was just wood ash, and in small amounts, probably would be good for your soil because, I think your area has pretty alkaline soil.

But in large amounts, not so much.

Wow! Had no idea.

Thank you everyone for taking the time to answer my questions. I also appreciate your well wishes, as it certainly has been a trying time. My concern too was related to potential toxins from things burning in nearby houses, sheds and cars. I'm leaning towards pulling everything out, including soil and starting again. I'm only a bit reluctant due to the worms, bugs, etc. that are living in and enrich my soil.

NikiMcRory- I think it would help if you could describe if you are in a tightly knit subdivision, or a more rural area, etc. My first thought when I read your post, was that it would be good for your garden because I pictured rural and brush and Bill mentioned. How close were the homes to you?

DaisyI said:Some of the ash from CA wildfires has been very toxic. Not only that but, when you add water to ash, you essentially make concrete.

Water + ash = lye after leaching (potassium/sodium hydroxide in solution) (will raise pH of surrounding soil) (probably flushed well over time with rainfall)

Water + lime (a major component of some ash) = slaked lime, aka non-hydraulic cement (which is different from concrete, the end product usually made with hydraulic, eg. Portland cement, plus aggregate mixed in)

Our home backs up to the Santa Monica Mountain Reserve, so there is some ash coming strictly from trees, grass and brush. However we have neighbors on both sides of us that lost their homes and when you look at the flames as there houses were burning they were very much blowing on our direction. From where my garden is, I would guess that one house is approximately 500 feet or less away.

Baja_Costero said:

Water + ash = lye after leaching (potassium/sodium hydroxide in solution) (will raise pH of surrounding soil) (probably flushed well over time with rainfall)

Water + lime (a major component of some ash) = slaked lime, aka non-hydraulic cement (which is different from concrete, the end product usually made with hydraulic, eg. Portland cement, plus aggregate mixed in)

And if we add grease, we will have soap.

I wouldn't worry too much about tossing ash away and losing worms, lady bugs, and other beneficial garden bugs. If the soil is not too toxic, they will reappear in no time at all. I dealt with 4 years of volcanic ash and Daisy is right. It doesn't wash away, it turns to concrete and causes all sorts of problems, like poor drainage if it is worked into the soil and plugged up pipes.
During the active volcanic years we were told by Civil Protection not to try to wash away the ash.

Volcanic ash is a totally different thing from fire ash. Volcanic ash is basically exploded bits of rock and glass distributed in fine particles by the wind. Fire ash, aka wood ash, is the products of combustion, namely the oxidation of carboniferous (mostly plant) material, plus human products like plastics. Volcanic ash has a lot of silicates in it (some forms more than others)... again, think rock, but finer. Wood ash has metal salts in a relative abundance that reflects their occurrence in plant matter. The number one component in wood ash is usually calcium carbonate or calcium oxide (which turns into calcium carbonate over time), followed by salts/oxides of other metals like potassium. There's not much silicon in the ash that's left over after plant material and wood has burned, compared to volcanic ash.

Not to be overly sciencey about this stuff but I think that difference does matter.

As for the original question of what to do after everything burns down, I don't see a great need to remove everything. 500 feet is pretty far for toxic burn products to travel in any great quantity unless there was a wind driving them that direction. A friend of mine swears by the use of ash from campfires in his garden, and his plants are pretty great. Wood ash will tend to raise the pH of the soil, which could be an issue. This effect will be both immediate (potassium hydroxide is very water soluble and will leach out in heavy rain) and longer term (calcium carbonate is not very water soluble, but the carbonate will tend to end up as bicarbonate in solution over time, as it does in groundwater for example).

If this were my mess to clean up, I would try to remove the ash where it is obviously piled up after something big and woody burnt down, and just mix the rest of it into the soil, maybe along with some fresh compost to help reduce the soil pH some. On the plus side, charcoal is a pretty good soil additive and has the potential to actually improve the soil if it's mixed in right.

I would first ask...
What were the garden beds framed with?
Cedar? Redwood?
Poison "pressure treated" lumber?

How much ash from the houses actually is covering the garden?

And most importantly...
How alkaline was the soil before the fire?

I've been watching the damage on the nightly news too, and recognizing areas where I've visited, even known people...

Climate change is a thing, whether the super wealthy care to acknowledge it or not... And.." a stitch in time"..

I feel bad for everyone affected, and... Worry for the future of the planet...

Having said the above, I would probably scoop off the ash but keep the soil.

You are on site, was the garden contaminated with household ash?
I don't mean ash drifting in on the wind, I mean piles of Chinese drywall, and pleather furniture, chipped wood cabinets and toxic wall to wall carpet...

I could probably provide garden space for a few refugees...

NikkiMcRory said:Our home backs up to the Santa Monica Mountain Reserve, so there is some ash coming strictly from trees, grass and brush.

However we have neighbors on both sides of us that lost their homes and when you look at the flames as there houses were burning they were very much blowing on our direction.
From where my garden is, I would guess that one house is approximately 500 feet or less away.

Ok... Just read this....

I wouldn't worry too much about flames from 500 feet away... And... Ash and embers from the trees shouldn't be an issue either.

It still comes down to what the beds were constructed from, and... What the ph was before the fire.

They sell ph testers online and in some garden supply centers.

Should be a simple thing to determine whether the ph is safe for the veggies.

A my house... I pile brush in the new garden areas, and shovel dig the soil after burning the brush pile(s). But... I'm in acidic sand.

I read an article this afternoon that said the ash from one of the Southern California fires in 2007 had a pH of 12.7! I take back what I said. Don't mix any of the ash with your native soil. Get rid of it.

Fascinating topic. I went through a phase where I wanted to grow Protea. In Florida. I know. Dumb idea. And no it didn't work. They all succumbed to fungus from humidity. But I was successful in germinating several flats of seeds of different species before I killed the plants. And the one ingredient necessary to germinate Protea and Banksia seeds? FIREWATER. Literally. Water that has soaked through the ash and embers of burnt plant material from wildfires. That is how the seeds are germinated in Australia and South Africa in the wild. The seeds are so hard and so tough, evolution has decided that they have go through the fire themselves to weaken the outside, then the firewater leaches in and provides certain chemicals that trigger germination. Each packet of seeds I got from South Africa gave specific directions for making the firewater, and scarifying the seed in absence of a wildfire at your location. It was one of my more memorable adventures in gardening. But I was warned during master gardner lectures years ago not to use ash in the garden here, because the soil is already acidic from leaf mold from mainly oak and pine detritus. And never under any circumstance should anyone anywhere use ash from their charcoal grill from briquets.

Ash is actually alkaline. In areas with high alkaline content in the soil (like Nevada), adding wood ash would be detrimental. In Northern California, the soil is acidic so adding some wood ash would be helpful. In Southern California, the soil is already alkaline so adding wood ash would be a problem.

Like California, Florida soil is acidic or alkaline, depending upon where you are. The pine woods have acidic soil but the southern coastal areas are build on limestone. You've never shared where in Florida you live and its a big state but, if you were told not to add wood ash, I suspect you live in an alkaline soil part of the state.

Here is the article I read a couple days ago:
http://articles.latimes.com/20...

From that article:

Some ash collected in residential areas after the October fires registered a pH of 12.7, a level more caustic than ammonia and nearly as caustic as lye.

To clarify: there is no way to measure the pH of something except as it exists in aqueous solution, and by definition the aqueous solution of wood ash, given time to leach, is basically lye. All wood ash is highly alkaline. Historically this feature was a driving force for the production of potassium hydroxide, before the onset of industrial production techniques. There is nothing particularly different about the ash from California wildfires compared to any other wood ash.

I have explained how and why wood ash is alkaline, given one of its most common water-soluble ingredients is potassium hydroxide. The effects on garden soil would be completely dependent on the quantity and amount of time it has to wash out. A little ash mixed into the soil is no big deal; a lot of ash will tend to have more dramatic, longer-lasting effects. Compost mixed in with the ash will tend to attenuate its alkalinity as compost is somewhat acidic. There's no need to panic about wood ash having a high pH. We knew that before we heard the latest measurements.