Here's why you should be more generous with water for anything grown in a pot. Learn why and how with your houseplants this winter, put it to good use watering new perennials, shrubs and trees this spring.
At right: Sylvia Graye of Graye's greenhouses in Plymouth, MI was "almost born in this greenhouse" and worked there into her 90's. She was a virtuoso with water. With wooden stick in one hand and hose in the other, she'd tap each clay pot and listen, saying,
Then she'd water to "give them a good drink."
Here's why she did that, and how you can do as well.
It's therapeutic to care for houseplants. For an outdoor gardener it's often a welcome change to water a pot rather than drag a hose, or to groom with scissors rather than a saw. It is equally fun to reach plants without climbing a ladder or going down on your knees.
Indoor gardening also allows a northerner to develop long term relationships with species from the tropics and other exotic regions.
However, we can become too close to our houseplants. We might have such fun fussing with them that we begin to water a little bit, often. That can be the death of some plants and cause chronic problems with others.
To do right by a plant in a pot, water to wet the entire root ball every time. That means adding water until you see some come out the drain holes into the saucer under the pot. Here's why.
Plants grown in containers develop bottom-heavy root balls. Roots grow wide at first, as in nature, but are forced to turn at the pot's edge. Once an edge gets crowded with questing root tips, roots in the most congested spots slow in growth and die back. The only root tips still able to grow are those at the bottom edge of that zone where the competition for water is less fierce. Those root tips extend themselves into moister soil below.
This cycle repeats in a downward spiral: Circling and competition, uppermost roots atrophying and lower being able to continue. In time, all the growing tips of the roots are at the bottom of the pot. New growth happens only there, and most water and nutrients are taken up there because root tips do both those things far better than older root segments.
If you water just a little, you wet only the top inch or two inches of the root ball. That may make the surface of the potting mix moist enough to support fungus gnats or stem-rotting fungi but it doesn't do any good for the roots 'way below. Roots cannot sniff out and retrieve water. They cannot grow through a dry layer of soil. With stingy watering, growth slows. The plant becomes weak and susceptible to problems like a proliferation of scale insects.
You might be growing a peace lily (Spathiphyllum) that loves to stay moist. You're right in that case to add water every time the top couple inches of the pot feel dry. So you may say, "There's no need to see water come out the bottom." However, even there it's better to add water until the pot weeps, so that you know the whole pot's moist. We've seen many cases of plants dying from dehydration even though the pot surface is moist, because the important lower level just got drier and drier over time. Drips and drabs of water never reach those roots.
When you water a moisture-loving plant frequently you almost certainly need to add less than when you water something like a jade or a cactus that prefers to dry all the way down between wettings. Yet in both cases, do water until the pot weeps through its drains. Then wait 20 minutes before dumping that overflow, to give root tips and the wall of the pot a chance take up the excess.
Never leave water in the drain dish more than an hour or so. Root tips rot when they are deprived of oxygen and standing water does displace oxygen in that critical bottom layer of the root ball.
How to figure how much, how often for indoor plants in Growing Concerns 756: Simple recipe to water any plant perfectly.
If you are planting a tree, shrub or even a large perennial such as hardy hibiscus (H. moscheutos) beware girdling roots that hook back around the plant's main canes or trunk, such as the uppermost main root in the previous drawing. Identify, then remove or spread that root or it will one day stop the trunk's growth and may kill the plant.
More about girdling roots in What's Coming Up 49.