Although peace lily is best repotted in spring or summer while the plant is actively growing, knowing exactly when peace lily needs to be repotted is crucial and depends on paying close attention to the plant. Repotting is a traumatic experience for the peace lily and should only be done when absolutely necessary.
If normal growth has slowed dramatically, peace lily may need to be repotted. Although slow growth is normal while peace lily is dormant during the winter months, markedly decreased growth during spring and summer may indicate that the peace lily is pot bound, especially if the plant is fertilised regularly.
A pot-bound peace lily will often display roots growing on the top of the soil. When the pot is lifted, tiny white roots can be seen growing through the drainage hole in the bottom of the pot. Sometimes, it may seem as though the plant has a ball of tight roots and very little potting soil. When this happens, the roots are often in a hard clump that can easily be lifted from the pot. If the peace lily isn't repotted, the roots may eventually expand and crack the pot.
When water runs straight through the pot without dampening the potting soil, the peace lily is pot bound and ready to be repotted. Even if the soil is watered frequently, the potting soil remains dry. Often, the water will simply sit on top of the soil without absorbing into the soil As a result, the roots of the peace lily have no access to water.
Sometimes peace lily may be healthy, but the plant will look better and be healthier in a less crowded pot. This often occurs if the peace lily is planted in a container with other plants. Repotting may also be in order if the peace lily has grown so large that the pot looks out of proportion, or if the plant is top heavy and needs a broader, heavier pot to prevent it from tipping over.