Spreading is a hedging technique that uses stock options in the hedging of stock option risks. Unlike delta neutral or contract neutral
hedging strategies which uses also the underlying stock sometimes in the hedging of directional risks.
In essence, what spreading as a hedging technique really does is to simply sell as much of the option greeks as those that you want to hedge. Period.
If you are holding long call options, hedging the time decay risk would require you to sell to open options with as much total theta value as
you are already holding such that the overall theta value of your position becomes zero or very near zero. The effect of this hedging would be
such that as your long positions decay, your short positions
would also decay as much, putting the same amount of money back into your pocket.