Offsetting carbon should be about reducing emissions, not soaking up cabon. Planting trees does absorb carbon, but it is hard to argue what the land being planted was used for previously. Does a small forest absorb more CO2 than grassland? How quickly?
The correct method is to give money to developing countries to pay for them to use technologies that really do make a difference. This is the technique being used by most 'genuine' green companies. Planting trees needs to be clarified.
Why are we planting trees while still chopping down forests in the Amazon?