2008 Year in Review

Container Garden Planting-II

If you want your container garden plants to remain healthy be sure to consider the drainage potential of the container, said a University of Illinois Extension horticulture educator.

"Container drainage is critical to plant health," said Nancy Pollard. "A hole at the bottom of the container is a must. It allows the soil water to drain freely so adequate air is available for the roots.

"While various kinds of plants have different drainage needs, few can tolerate sitting in stagnant water. Healthy roots mean healthier plants."

Wet soils favor root rots because they leave little space for air to get to the roots. And plants rarely recover from root rots.

"If the pot does not come with a hole in it, figure out a way to make a hole," she said. "One way is to drill. Some decorative resin or plastic pots have pre-punched holes at the bottom for easy removal. Generally, very little soil falls through the hole.

"To keep soil from falling through large drainage holes, some folks use a coffee-filter paper over the hole. Small holes in the bottom of the pot allow the water to drain without losing significant soil."

Sometimes, she noted, a plant comes already planted in a pot with no drainage. The best solution is to take it to a sink, water it, then after a few minutes turn it on its side to allow the excess water to drain.

"Beware of pots with permanently attached saucers that make emptying the overflow difficult or impossible," she said. "I learned about this the hard way when my basil's leaves turned back because the roots were waterlogged--the result of a permanently attached saucer.

"Drainage of excess water is vital for the health of plant roots. It is much better to use a pot with a detachable saucer."

Slipping a container inside a slightly larger one is called double-potting. When double-potting, the plants grow in a pot liner. Often this is a plain plastic pot.

"This allows you to slip the pot liner in or out of the decorative container without disturbing the plant roots," she said. "Check to make sure the plants in the pot liner never stand in water--unless they are aquatic plants. If water accumulates in the bottom of the larger container, remove the inside pot and drain the water from the outside pot.

"Place gravel in the bottom of the outer pot if the decorative pot is deep enough. A little excess water can accumulate in the gravel without the plant roots having to stand in water."

Pollard said it is a myth that a layer of gravel under the soil inside the bottom of an individual pot will improve container drainage. Instead of draining right into the gravel, water "perches" or gathers in the soil just above the gravel.

"Water will not move across the boundary until all available air space in the soil fills up," she explained. "If soil at the bottom of the container becomes waterlogged, the roots have a greater depth with good aeration. So save the gravel for the outside pot. Placing damp gravel in a saucer underneath the pot may benefit the plant by increasing the humidity in the immediate area of the plants."

Self-watering pots use various methods to effectively draw water from a bottom reservoir into the soil without causing the soil to become too wet. Water may be drawn up into the soil by capillary action (wicking) through small soil columns, rope wicks, or the use of moisture sensors. Self-watering containers are especially useful for weekend cottages. People who do not have time to check plant-water needs daily may also benefit.

"Consistently available water is great for vegetables and tropical houseplants," she said. "Imagine a dozen stalks of sweet corn producing ears on your patio in a self-watering container. Plants that need to dry out like thick-leaved cactus do not usually warrant the extra cost of a self-watering container.

"For more information, use a web search engine using the keywords 'self-watering planter,' or 'self-watering container', or 'earth box.'"

Double-potting techniques may be used to achieve several goals such as overcoming the problem of no drainage holes in an attractive decorative pot, to quickly change seasonal displays, to combine plants with different environmental requirements, to minimize extreme soil temperature fluctuations, and to restrain desirable but invasive plants from spreading.

"Sometimes you fall in love with a wonderful container that has no drainage hole," she said. "This would be the perfect time to find a pot liner to fit inside so both you and the plants are happy."

In addition to decorative pots, decorative foil or plastic pot wraps are a form of double-potting. The wrap keeps water from leaking out. To avoid root rot from standing water, pierce a hole in the bottom of the wrapper or foil. Then place the container on a saucer.

"Alternatively, take the container to a sink, remove the wrapper, and then water," she said. "Let the water drain freely out of the holes in the bottom of the pot. After the pot finishes draining, replace the wrapper."

by  Editor, theCity1.com
March 14, 2008