Water Til It Weeps

Water better indoors... and out

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,

When they clink they need a drink,
when they clunk, they're drunk!

Then she'd water to "give them a good drink."

Here's why she did that, and how you can do as well.

Sylvia Graye, watering virtuoso for over 80 years in her business, Graye's Greehouse. She knew clay pots tapped with a stick would ring as they became dry, sound with a thud if moist.

Sylvia Graye, watering virtuoso for over 80 years in her business, Graye's Greehouse. She knew clay pots tapped with a stick would ring as they became dry, sound with a thud if moist.

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.

It can be almost fun to baby an aloe, for instance, just for the experience of learning a desert plant's ways.

It can be almost fun to baby an aloe, for instance, just for the experience of learning a desert plant's ways.

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.

Even roots suffer from downward spiral syndrome

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.

Roots grow wide but are forced to turn at the pot edge (A). Where competition becomes too great at the edge, roots next to moister lower levels have the advantage. Root growth descends. (B). The circling and competition happen again at the lower level and root growth is forced down (C).

Roots grow wide but are forced to turn at the pot edge (A). Where competition becomes too great at the edge, roots next to moister lower levels have the advantage. Root growth descends. (B). The circling and competition happen again at the lower level and root growth is forced down (C).

Eventually, all root tips converge at the bottom of the potted root ball. All new root growth and almost all absorption happens there because root tips are most capable of both actions.

Eventually, all root tips converge at the bottom of the potted root ball. All new root growth and almost all absorption happens there because root tips are most capable of both actions.

See the concentration of roots in the bottom half of this corn plant (Dracaena) root ball? That's normal for a potted plant.

See the concentration of roots in the bottom half of this corn plant (Dracaena) root ball? That's normal for a potted plant.

Outdoor plant or indoor, same bottom-heavy root mass.

Outdoor plant or indoor, same bottom-heavy root mass.

Even when the pot is large and the plant a short-term resident, roots follow this pattern. A single coleus grew for 3 months in this ceramic pot. We've depotted and upended the root ball so you can see how the roots filled the bottom of the container.

Even when the pot is large and the plant a short-term resident, roots follow this pattern. A single coleus grew for 3 months in this ceramic pot. We've depotted and upended the root ball so you can see how the roots filled the bottom of the container.

Wet the top, thrill the gnats!

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.

Adding a little water, not adding enough to weep out the bottom, can mean wetting only the top layer of soil (arrow). So few roots are there that only the fungi and pests in that layer can benefit.

Adding a little water, not adding enough to weep out the bottom, can mean wetting only the top layer of soil (arrow). So few roots are there that only the fungi and pests in that layer can benefit.

Moisture loving species need to weep, too

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.

Bigger, drier pot needs more water, sure!

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.

Understanding your houseplants' roots will help you with outdoor gardening, too. This annual flower grown in a cell-pack has the same bottom-heavy root system as a houseplant. It is better to water it thoroughly and watch for weeping rather than to sprinkle an unknown quantity over the top.

Understanding your houseplants' roots will help you with outdoor gardening, too. This annual flower grown in a cell-pack has the same bottom-heavy root system as a houseplant. It is better to water it thoroughly and watch for weeping rather than to sprinkle an unknown quantity over the top.

Shrubs, trees and perennials grown in containers also share the potted houseplant's rooting pattern. Here is a drawing of an actual root system of a shrub grown in a container.

Shrubs, trees and perennials grown in containers also share the potted houseplant's rooting pattern. Here is a drawing of an actual root system of a shrub grown in a container.

More about indoor watering

How to figure how much, how often for indoor plants in Growing Concerns 756: Simple recipe to water any plant perfectly.

 

Important note about that circling root:

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.

Root growth after transplant is faster if the congested bottom of the root mass is sliced off, and/or some circling roots are cut, so that new root tips can develop at more than one level. Of these four annuals, shown before planting and 30 days later, the one on the lower left was not treated to root pruning. Look how much more root growth occurred on those whose bottom and sides were trimmed.

Root growth after transplant is faster if the congested bottom of the root mass is sliced off, and/or some circling roots are cut, so that new root tips can develop at more than one level. Of these four annuals, shown before planting and 30 days later, the one on the lower left was not treated to root pruning. Look how much more root growth occurred on those whose bottom and sides were trimmed.

After transplant to open soil, root tips can grow out wide and the plant can gather water from a much bigger circle. Yet in the beginning, even with root pruning, the transplant is dependent on deep water since its roots are still concentrated at the bottom. It's still a potted plant but we cannot see the bottom to know we've watered until the drains weep. So it is essential to create a watering ring around a new plant, wide enough to encompass its original roots and some expansion. Scrape loose soil from far around the plant to build a levee 1- to 2 inches tall around the plant.

After transplant to open soil, root tips can grow out wide and the plant can gather water from a much bigger circle. Yet in the beginning, even with root pruning, the transplant is dependent on deep water since its roots are still concentrated at the bottom. It's still a potted plant but we cannot see the bottom to know we've watered until the drains weep. So it is essential to create a watering ring around a new plant, wide enough to encompass its original roots and some expansion. Scrape loose soil from far around the plant to build a levee 1- to 2 inches tall around the plant.

When you water, fill the levee. Water won't run away to moisten weeds nearby, and it forms a pool deep enough to have the weight to push down into the soil pores. That two inch depth of water will wet good garden soil 6- to 8 inches deep. Mulch over the levee but not against the stems of the plant, and the watering ring continues to work through the plant's critical establishment period.

When you water, fill the levee. Water won't run away to moisten weeds nearby, and it forms a pool deep enough to have the weight to push down into the soil pores. That two inch depth of water will wet good garden soil 6- to 8 inches deep. Mulch over the levee but not against the stems of the plant, and the watering ring continues to work through the plant's critical establishment period.

A watering ring can serve a group of plants, as for these small boxwoods planted as a hedge.

A watering ring can serve a group of plants, as for these small boxwoods planted as a hedge.