No-dig-vegetablegarden.com has a great idea for keeping potted plants hydrated.

For potted plants, recycle old kitchen or bath sponges by cutting them into small pieces and mix with the potting mix. The sponges will absorb excess water but keep the soil moist for longer. It’s a great alternative to peat moss or soil moisture aids for smaller projects.

You’ll want to, of course, make sure the sponges are completely clean and free of chemicals that could harm your houseplants.