What makes
wood ash different from coal ash is the amount of metals that can be found in coal ash. How do those metals get there? A tree, when it is growing, pulls what elements it needs from the soil, so unless it is on soil unusually rich in certain minerals, will not pull lots of metals up into the tissues. But coal is made from vegetation that fell into the swamp, got mixed with clay and other minerals, and the pores of the vegetation, while it was decomposing, were able to absorb metals in the soil.
Coal can be up to 10% "ash" which includes the clay minerals that were in the coal, while the ash left after burning wood is usually much less than 10%.
So what you need to do to fix your garden is to bind up those metals that are causing the veggies some growth irregularities. This is what is known as "chelation". Chelates are molecules that will bind with metals and in the case of needed metals, release them slowly as the plant absorbs them. One of the best chelating agents is urea, with its two ammonia groups. I would recommend using diluted
urine as fertilizer in your garden, say 1 part in 8 to 10 parts
water. Regular watering with this free and easy source of urea will bind up metals and metal oxides that were in the coal ash, and reduce their availability to the point that if the plant needs it, it can still get it, but is not swimming in it.
And next time, mix the ashes with some urine beforehand and you will likely avert this problem.