When the soil (actually, it's potting mix) in your houseplants go beyond the usual "slightly dry" to a nearly crispy "desert dry" a curious phenomenon occurs — the potting mix repels water. Any water you pour on a really dry plant does little more than moisten the soil's surface. That's because extremely dry potting mixes pull away from the sides of a pot, leaving a gap between the pot and the root ball. When you water these ultra-dry plants from above, the water runs off the top of the mix, down the gap, and out of the pot.

When a plant reaches a state of extreme dryness from either neglect or long-term dormancy, watering from the top is almost pointless. The plant needs a real soaking so that it can recover. Fill a sink or bucket with tepid water and plunge the pot into it, using a weight (a rock or brick) placed carefully near the edge of the pot to keep the plant from floating around. Then, add a few drops (no more than that) of liquid dishwashing detergent to the water to help the water counteract the soil's repellent action.

After about an hour, remove the plant and let any excess water drain through the pot. If the plant is still alive (not all plants recover from severe drought), it should soon plump up noticeably. Even after the root ball expands to its original size, an open space may remain between it and the edge of the pot. Fill in the gap with potting mix so that the moisture can soak into the root ball instead of flowing around it.