Why is applying eggshells and tea residue harmful to flowers?

In daily life, some people like to place eggshells upside down in flower pots or use leftover tea to water flowers, thinking this will add nutrients to the flowers and promote rapid growth, but in fact it does just the opposite. When eggshells are placed upside down on flower pots, the residual egg white inside the shells flows into the surface layer of the potting soil and, after fermenting, generates heat that directly burns the plant roots. At the same time, after the egg white ferments it produces a foul odor that attracts flies to lay eggs and hatch maggots, which bite and feed on the roots, and this in turn easily triggers other pests and diseases, affecting the normal growth of the flowers. Residual tea contains theophylline, caffeine and other alkaloids, which have a relatively destructive effect on the organic nutrients in the soil and are not conducive to the growth of potted flowers. At the same time, when residual tea covers the surface of the pot, over time it will gradually ferment and rot, hindering air permeability of the potting soil and causing oxygen deficiency in the pot, which directly affects the respiration of the roots. However, eggshells that have been composted, with the clear liquid taken from them used as a top dressing, or eggshells that have been baked dry and crushed and applied into the potting soil, are beneficial to flower growth. Tea residue that has been composted and applied as a base fertilizer is also beneficial for improving the soil.