A moss pole gives a climbing houseplant something to do what it does in the wild: grip a damp vertical surface with its aerial roots and haul itself upward. For aroids such as monstera, pothos and philodendron it often means bigger leaves and a stronger plant.
Why it helps
These plants are climbers. Given a damp, textured support, their aerial roots attach and feed, and the plant frequently responds by producing larger, more mature foliage than it would scrambling along the ground or flopping out of a pot. The pole also keeps a big plant upright and tidy.
Sphagnum or coir
This is the one moss-wall context where sphagnum is exactly right. A pole stuffed with damp sphagnum holds water and stays moist, which is what the roots want, and being upright and regularly watered it does not suffer the way sphagnum would on a dry vertical wall. Coir poles are tidier and longer-lasting but hold less water; sphagnum is messier but the roots love it.
Making and using one
Form a tube of plastic mesh, pack it firmly with pre-soaked sphagnum, and stand it in the pot behind the plant, anchored into the soil. Tie the stems in loosely to start, guiding the nodes against the moss. Then keep the pole damp: mist it daily or pour water down the top, and the aerial roots will grow into it and grip on their own. Extend the pole as the plant climbs.
Keeping it damp without the bother
The whole benefit rests on the pole staying moist, and a dry pole is the usual reason aerial roots refuse to attach. Daily misting works but is easily forgotten; growers with several plants tend to rig something steadier. A length of capillary wick run from a small reservoir at the top, a self-watering pole with a hollow core you simply top up, or a weekly thorough soak of the whole pole in the shower all keep the sphagnum damp with less fuss than hand-misting. Warm, humid air helps too, which is why these plants and their poles do well in a steamy bathroom.
Extending and the usual mistakes
Add to the pole before the plant overtops it rather than after, since a stem that has grown past its support flops and is awkward to retrain. Most problems come from two habits: letting the pole dry out, so roots never grip, and tying stems so tightly that they are throttled or snapped. Tie loosely, guide rather than force, and let the plant do the climbing itself. A pole that stays damp and is extended in good time turns a sprawling, leggy aroid into an upright specimen with markedly larger leaves.