I simply use a shovel. A scoop shovel works and just start walking and lightly shaking the shovel so a little falls off. If it is just dumped on the ground, it is best to spread before rain! Also if it is just dumped on the ground, then a gravel shovel might be easier to use.
We buy semi-loads of wood ash to spread on the hay fields. You can put on up to 5-ton per acre without a lot of issue, but going above that rate you start to smother the hay crop. On a household scale, it is quite easy to over-apply on the sq ft scale in the garden, but pretty hard to do it on a larger scale.
