The quantity of water that the wick gives to the tree, depends on the hygroscopic attraction of the soil. This is the capillary principle: if the soil requires little, the wick gives little. If the soil requires more (e.g. when it is super dry sand or when it is salted) the wick gives more.

If the heat period is two to four months, then in general no refill is necessary. If the heat period is longer, we have on average one refill. That is why we have a cap in it. After the heat period a refill is not necessary anymore.