yes, but don't use too many as they are hi pH.

Here is a link that might be useful: mrtexas

You can "fertilize" with lots of things, including peeing on your citrus; the three main issues with wood ash are first, not all ash is the same; second, ash is typically about 0-1-3 NPK, so it is missing the most important ingredient, Nitrogen; and third, wood ash will raise the pH of your soil, which is commonly a bad thing for lemons, unless your soil has a very low pH. Lemons... and Meyers are really what I know most about, like pH between 5.5 and 7; but will grow in soil up to 8 and still produce fruit; you may have to add extra nutrients at the higher pH, as the tree will not absorb them as well.
Obviously all of this depends on where you live, what kind of soil you have, etc.; and if you are growing your trees in containers, that is another matter altogether. Bottom line, if they were my citrus, I would probably skip the wood ash in favor of a good balanced fertilizer and supplements of Calcium, Sulfur, Magnesium, Iron, and maybe Zinc.

You need to know that wood ash contains, as its primary component, CaCO3 (calcium carbonate). Not only can it quickly raise the pH, but it will affect (in a bad way) the uptake of other essential elements. It is considered a VERY alkaline substance. Certain hardwoods, like oak, contain the most CaCO3. Oak is a favorite choice for wood fires.

I should add that wood ash CAN be used to amend outdoor soils, as long as you know for certain that your native pH is very low. It should never, ever be added to a container medium.

I regularly add woodash to my outdoor beds and plantings throughout the winter.
I've also added woodash to container mixes without a problem. Now, however,
I prefer to know exactly what goes into my mix - so I skip the ashes in favor of
Dolomitic Garden Lime and a complete fertilizer.

Ash will also clog up a good mix, so it's best to avoid on that count as well.

Josh

woow! thanks guys for all your messages. Looks like it would be better to buy some sort of fertilizer and add it to my trees. Thanks!

I try to use as much natural fertilizer as possible. I am a retired chemist not a greenie wienie. Most of the "organic" fertilizers are low in potassium. Therefore wood ashes tend to help reach a balanced plant food if used correctly (sparingly), in concert with another fertilizer. The calcium in oak ash is mainly from the bark or leaves. Same for most all hardwoods.

I use hi dollar 6-2-2 organic + cheaper cottonseed meal + a little potassium nitrate + epsom salts in my mix. If I had a good supply of ash I would skip the potassium nitrate.