Complex sentence: The root system of the bottom level of willows needs to develop large enough to support the willows on the above levels, so that the scaffold becomes obsolete and then it and the watering and fertilising baskets can be removed altogether.
Split into simpler sentences: The root system of the bottom level of willows needs to develop large enough to support the willows on the above levels. So that the scaffold becomes obsolete and then it and the watering and ferilising baskets can be removed altogether.