Repotting your peace lily is a great idea, especially if you've noticed roots coming out of the drainage holes and the foliage losing some of its vibrancy. Peace lilies can outgrow their pots quite quickly, especially if they're thriving, so your assessment sounds spot on.
When it comes to timing, repotting is best done in the spring when the plant's growth naturally accelerates. However, if your peace lily looks like it really needs more space now, you can repot it outside of this period. Just make sure to do it carefully and avoid repotting if the plant is flowering, as this can stress it further.
For the pot, aim for one that's about 1-2 inches larger in diameter than the current pot. Ensure it has good drainage holes to prevent water from pooling at the bottom, which can lead to root rot.
As for soil, peace lilies prefer a potting mix that retains moisture but drains well. A good indoor potting mix augmented with a little perlite or bark to boost drainage can be ideal. Look for mixtures tailored for tropical plants or use a general potting mix and adjust it accordingly.
When repotting, gently remove the plant from its current pot, teasing out the roots a bit, especially if they're tightly bound. Place it in the new pot at the same depth it was growing before, fill in with the potting mix, and water it thoroughly to settle the soil.
To minimize stress, keep the plant in a similar environment as it was before—away from direct sunlight and drafts. You might also consider misting the leaves to maintain humidity levels. Once repotted, leave it undisturbed for a week or so to let it recover from the move.
For more information on caring for peace lilies, checking resources like the Royal Horticultural Society or local botanical gardens can be really helpful. These organizations often offer detailed care sheets and advice for indoor plant enthusiasts. Good luck with your peace lily!