Container Gardening Watering, pests and common problems from Gardening Wisdom


There is a very simple rule when it comes to watering container plants.  Always water so that at least 15-20 per cent of the water poured in the top comes out the bottom.  Having done this, do not water again until the surface of the soil is just dry to the touch. 

Until your finger comes away dry from touching the soil, the plant does not require watering.  This system of watering ensures that the entire soil ball is wet so tender young roots do not go begging for moisture.  If the soil ball is wet right to the bottom of the pot, the roots too will grow to the bottom of the pot. 

Deeply rooted plants are invariably healthier and better able to resist stress than are the more shallowly rooted ones.  A thorough watering also ensures that all excess fertilizer salts are always being moved to the bottom and right out of the pot so as not to damage the tender young feeder roots.

"Another reason why plants kept in rooms are generally unhealthy, is, that they are watered in a very irregular manner."

Ladies Companion to the Flower Garden 

when your container goes bone dry

Should the artificial soil mix dry right out, it will pull away from the sides of the pot as it shrinks.  This will allow the water to run quickly and easily down between the pot wall and the soil ball, not doing any good to the plant in the process. 

The remedy with these types of shrinking soils is to sit the pot in a tub or pail of water for at least an hour to allow the soil ball to absorb all the water it can handle and expand again.  If the container is too large to move into a tub, then very slow and often-repeated waterings will accomplish the same thing. 

I have often had to trickle water over some of the larger containers three or four times, with a half-hour between waterings, to convince them to rehydrate and soak up moisture.

learn restraint

The secret to this container watering, whether it be inside or outside potted plants, is to learn restraint. 

If you touch the soil and your finger comes away damp, then do not add more water.  Too much water will kill a plant almost as fast as will too little. 

Mr. Heinrich did not mean to be particularly sexist when he refers to the ladies killing their plants by "extreme kindness"; the fact is that at the time of writing, maintaining the container gardens was very much a proper ladies form of gardening. 

Women, at least those who would purchase and read a book on container gardening, did not work out in the fields but rather gardened on a more refined scale.

"A great many ladies kill their plants by extreme kindness; that is, they keep on feeding them until the plants get too much water, when the roots rot and the plants die."

Heinrich  The Window Flower Garden p30

container garden pests

Most outdoor pest problems come under the heading of either aphids or spider mites.  Throw in the odd caterpillar, mealybug or scale and the cast of common pests is fully assembled.  

"Washing with a syringe, and abundance of water, is however, probably a better mode; as it has been often observed that neither the green fly nor the red spider will ever infest a plant that is frequently syringed."

Ladies Companion to the Flower Garden

 While Mrs. Loudon has often been accused of spreading inaccurate gardening practices, in this she had a good point.  Frequent misting does indeed knock back both aphids and spider mites.  If aphids are hosed off  a plant with a sharp spray,  these same aphids do not climb back onto the plant.  More may, and likely will,  hatch from survivors but repeated and forceful sprayings will easily keep the aphid population under control.

Spider mites do not seem to be as easily affected by a sharp spray of water but they do not like repeated mistings as their foraging and breeding seem affected by the water. 

In my experience, this is more of a preventative type of insect control than a remedy for a mite infestation. 

soap spray recipe

To knock back mite problems, I fall back on insecticidal soap sprays.  Soap, mixed at 1part soap to 40 parts water does an admirable job of killing mites and other soft-bodied insects such as aphids.

"The mealy bug is easily seen and found by the white flowery or mealy appearance this insect presents when fully developed.  Picking out the bugs with a small pointed piece of stick is about the best and safest method of keeping down these white, but objectionable and undesirable pests."

Canadian Horticulturalist

mealy bugs and scale

Mealy bugs and Scale are a bit harder to kill with soap as they have protective outer coats that repel the soap sprays. 

Some gardeners add 1 part of rubbing alcohol to the soap spray to help the soap penetrate the waxy surface.  Others take a simpler approach and simply rub the offending insect with a toothbrush dipped in the soap solution. 

A sharp pointed stick is as simple a solution as can be found for mealy bugs and works quite nicely if time is of no concern.  While the Canadian Horticulturalist may have recommended whale oil soap - a product that is in short supply today - their advice on the moving of scale before spraying is quite good and effective.

"The best remedy is to wash off the scale with a weak solution of whale oil soap and water.  It used to be a common saying amongst gardeners in my apprenticeship days that "to move the scale was to kill it," so that friction sufficient to move the scale is desirable, as well as the application of the solution as mentioned."

Canadian Horticulturalist

Whatever the easy solution to common garden pests, whether it be water sprays, soaping or even hand -picking of the odd caterpillar, Mr. Linus Woolverton, editor of the Canadian Horticulturalist in 1901 said it best when he wrote, "Too often the application of preventatives and remedies is neglected until the plants are infested with insects, when severe measures have to be taken, and strong solutions used, that will perhaps kill the plant before it removes the pest." 

This at least remains true to this day.  It is far better to control pests when they are newly established rather than when they are firmly entrenched on the plant. For that, we need the discerning and constant attention of the gardener.  Some things never change.

"The usual modes of entrapping snails, slugs and wood-lice, are laying down slices of raw potatoes or cabbage leaves at night, and examining them before the dew is off the plants in the morning."

Ladies Companion to the Flower Garden

diseases of container garden plants

Most diseases of container plants fall into the root rot, mildew or leaf spot fungus problem categories.  Root rots are primarily caused by overwatering;  and when combined with cool temperatures, overwatering is an invitation to a variety of rot type problems. 

garlic fungicide recipe

The simplest solution is to water as recommended above and to move container plants indoors for any short periods of cool temperatures. 

Other environmentally sound controls include the use of a garlic drench if the problem has already occurred.  Crush a clove or two of garlic into an inch of water in a saucepan.  Simmer gently for a few minutes to spread the oils through the water.  Allow the water to cool and then pour this over the pot.  Make enough of the mix to thoroughly soak the pot.  Garlic is a potent bacteria killer and we have used this mix successfully on a variety of problems from damping off to stem rots.

"It is of course impossible to lay down any code of rules which would be equally applicable to every garden."  

The English Flower Garden. 

lime sulphur mixes

Mildews and leaf spot fungus problems are easily treated with lime sulfur mixes, available at garden centers or a mix of 2 tablespoons of baking soda in a gallon of warm water. 

The baking soda might burn tender leaves such as impatiens, so it is important to test a few leaves first and dilute the concentration of baking soda in the mix by adding extra water if burning occurs. 

The classic method is to spray the test leaves and wait 24 hours to assess any damage.  Both of these, the lime-sulfur spray and baking soda will need to be repeated weekly or after rains have washed the leaves. 

As with pests, constant and immediate attention is needed to stop disease problems before they become established.

Author Note: This is an ongoing project to publish the entire Gardening Wisdom (award winning book) online.  I usually publish one part of a chapter a week and you can be notified of new additions by signing up for the newsletter from the navigation bar

Gardening Wisdom Table of Contents

The Introduction

Chapter One

Container Gardening Basics     Container Garden Watering

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