Aspen shavings would be fine as mulch. The impact on the nitrogen in your soil would be very minimal, but if you are concerned, spread a little composted manure before you lay down the wood chips. After the first year you will reach an equilibrium with the decaying mulch giving back what the newer mulch takes from the soil.
I avoid spraying mirical grow on your garden. It may give a quick boost but does nothing for the long term health of your plants nor which is a lot more important, your soil.
Linda C