Use only natural untreated wood for your burning , no painted , creosoted ,tanalized or salt preserved stuff & don't use oils or firelihghter stick to get the wood burning use paper crackers & thin kindle sticks instead or a gas poker./ gas blowlamp .
The ash is high in potash , so if you sus which plants like a healthy dose go for it . A sprinkle of wood ash when sowing carrot sed in a fine furrow is said to deter carrot fly . It cetainly helps to have a teaspoon of the ash and mix in the carrot seeds , then sprinkle sow along the line because it helps you sow them thinly.
I was once told that laurel and yew are not the best of ashes to use but I've not read it in any decent reference books.