What's the most difficult thing to get right in gardening? Learning how to water plants in pots. Whether the pot contains a fence post cactus or a beautiful Iceland poppy, the process is exactly the same, and so are the problems.
Look at the soil mass in any one of your pots. I'd bet there's a gap between the outside edge of the soil and the inside wall of the pot. This is natural shrinkage of the potting soil when it dries out. Shrinkage is even more profound where potting soil contains large amounts of peat, as is the case with hot house azaleas.
Naturally you want to rehydrate the plant, so you pour on the water. It drains down the gap around the edges and out the bottom. Little to none soaks into the soil mass. This trains the plant to root only on the outside of the soil mass, which is where it finds moisture on a regular basis. If you remove the root ball from the pot and slice it into two identical halves, you'll see that no roots exist within unused soil in the middle. It's probably dry as a bone, too.
If you could rewet the entire soil mass, the roots have incentive to abandon the edges and venture into the center of the rootball to find additional moisture. Problem is that once the root ball shrinks and dries, the water moves through too fast to be absorbed at all.
To really make plants thrive, there is a method of watering potted plants that's sure to turn lackluster to brilliant in just a few days. It's also excellent for rehydrating peat based potting soils after a long, hot summer or houseplants from a furnace heated winter.
Shallow under-bed plastic storage boxes are helpful for watering any plant in a pot, particularly in the summer when stressed by heat. Fill the box with the garden hose till the water is about three inches deep. Then pack the box with potted plants; let them sit in the water for about an hour.
The potting soil will act like a wick to gradually draw water up through the drain holes into the root ball. With unglazed red clay pots, the water may even seep in through the outer walls by osmosis. Moisture moves upward inch by inch until the entire soil mass is wringing wet. You'll know when it reaches saturation because the surface of the soil becomes darker and wet to the touch.
This tells you it's saturated all the way through. Remove your pots to set aside on gravel or in a sink to drain away excess water before they go back to their regular spot. In the meantime I refill the plastic box with another batch of plants and repeat.
You can do this method one pot at a time in a bowl on the kitchen counter. Consider adding a pinch of Miracle Gro crystals to the water so fertilizer is taken up into the center soil as well. Fertilizers require water to make nutrients available to plants, so this is a perfect way to water and feed at the same time.
This method is ideal for vegetable plant seedlings. Getting water to saturate the peat rich seed seed starting soils without damage to tender seedlings can be a challenge Even a modest flow rate on top can scour the light soil out of place without saturating, dislodge seed and expose roots. It also discourages the dreaded damping-off disease.
Watering from the bottom up is most essential with seedlings and succulents because both groups suffer from overwatering and rot. You also know the entire root zone has been adequately moistened, not just the top inch or so. But when you see how well bottom-up watering works for all your potted plants, you'll never water from the top-down again.