That’s a question that has confused generations of owners of houseplants. Should you water from the top, that is, by pouring water on the surface of the potting mix and letting it percolate through the root ball, or is it better to water from the bottom, that is, by pouring water into the saucer and letting the plant “drink its fill?”
The answer is that both methods are perfectly acceptable and you can safely apply either method to almost any plant. There are only a few minor points to take note of … as explained below.
How to Water From the Top
When the plant’s potting mix is dry to the touch, hold the spout of the watering can just over the soil and slowly pour tepid water over the mix so it soaks in slowly. (If you pour too fast, the pot can overflow.) When you see water begin to flow through the drainage hole underneath, stop.
If there is still water in the saucer 30 minutes later (and that doesn’t usually happen very often), empty the saucer.
The advantage of this method is that it helps to leach the soil of mineral salts that otherwise tend to accumulate over time in any potting soil. Even though this method helps leach the mix, it’s still wise to repot plants into fresh, uncontaminated soil every year or so.
How to Water From the Bottom
In this method, pour tepid water into the saucer and let the plant soak it up. Often it does it so quite visibly: the water moves up in the potting mix almost as fast as you pour it into the saucer!
It is important not to underwater when you water from below! Pour enough to thoroughly soak the entire root ball. After a few minutes, go back and check things. If the saucer is completely drained, which means that the plant and the soil have absorbed all the water, that could still mean the plant didn’t get enough water. (Maybe it did, maybe it didn’t.) To be sure, pour in some more (probably less than the first time) and come back and check.
If there is still water in the saucer after 30 minutes, discard it.
The defect of this method is that it allows the mineral salts to migrate towards the top of the pot over time where, when they accumulate, they can harm the plant’s growth. On the other hand, unless your water is very hard, this effect is only going to be felt after a long time, probably several years. And the solution is simple enough: every now and then, water from the top to leach the potting soil.
Note that to be effective for any kind of watering, the saucer must be at least as wide as the top of the pot. For more information on this, read For a Green Thumb, Match Saucer Size to Pot Size.
Watering by Soaking
Soaking houseplants as a means of watering them rarely seems to be mentioned in books and web pages about houseplants, yet it’s a perfectly viable alternative to watering from above or below. And in some cases, it’s the best choice. It’s most often used for:
- Plants in a hanging basket whose saucer is ridiculously small and thus inefficient;
- Orchids and other plants growing in growing mixes so highly aerated that water runs right through without really moistening the particles and roots;
- Plants with such a mass of roots that the potting soil is compressed and unable to retain moisture;
- Plants that aren’t grown in pots (like those fixed to pieces of wood) such as air plants (Tillandsia).
That said, soaking can be used with any indoor plant.
In this method, fill the sink, a tray or a bucket with tepid water and set the pot into it, at least halfway to the plant’s rim (you can soak it fully, completely inundating the pot, but then the soil particles tend to float away.). Leave it to soak for 10 to 30 minutes so the plant and its potting mix will have time to absorb all the water they really need. Then, lift the pot, drain it well, then put the plant back in its usual place.
Exceptions Make the Rule
Some sources discourage watering from the top for certain plants, especially African violets (Saintpaulia) and cyclamens (Cyclamen persicum).
In the case of the African violet, the idea is to avoid staining the foliage, because any water inadvertently splashed onto the leaves during watering from the top may leave hard-to-remove white marks.
In the case of the cyclamen, the reasoning is different. It so happens this plant has a tuber that rises slightly above the potting mix and has a depression in the center. If you water from above, you risk filling this depression with water and that could lead to rot.
However, you can still water both these plants from the top if you want! Just be careful to direct the spout of the watering can onto the potting soil, near the rim of the pot, not on the foliage or the tuber. It’s as simple as that!
Watering: from the top, the bottom or by soaking: all are good choices. Just use the method that best suits your way of gardening.