JARS v51n3 - Containers Are Murder!

Containers Are Murder!
Richard Murcott
East Norwich, New York

Reprinted from the Winter 1995 New York Chapter newsletter, The Rhodora

During the last 15 to 20 years, the nursery industry has changed the way they grow and ship rhododendrons. Instead of in-ground growing, they have switched to growing the plants in containers with an artificial mix as a growing medium. This technique allows them to produce a salable plant quickly, efficiently and economically. There is only one problem: the typical casual gardeners who purchase the plant in the spring have a terrible time keeping it alive after they have planted it in their garden. It is my guess that fully 75 percent of all containerized rhododendrons purchased in the spring by casual gardeners do not live three years.

Why? Because the mix in which the roots are growing in the container is so different from natural soil that water will not move into the root zone of the plant after it has been planted.

Soil can be looked at as what a chemist would call a colloid. Water moves through soil by capillary action. The water moves laterally (horizontally) and can actually move vertically. We have all seen soil dry out during the day from sunlight, but the next morning it is damp again. This dampness is water that has moved up from below by capillary action. When the gardener plants a containerized plant, he creates three different soils: the mix in which the plant is growing; the back fill which should be made up of a mixture of top soil and organic matter, and the great mass of existing soil in the garden. The combination of the back fill and the potting mix will not allow capillary action to carry water from the mass of garden soil to the root ball of the newly planted rhododendron. Water that falls outside of the root ball has no way to move to the roots. Rain and sprinkles do not do the job because of the umbrella effects of the leaf canopy of the plant.

Spring planted containerized plants must be hand watered weekly for six months! There are no casual gardeners willing to do that, even if they knew that was the only way to insure success with the plant. They have never been told that because they probably would not have purchased the plant in the first place if they had been so informed.

Let me explain how to plant a containerized rhododendron no matter when it was purchased:

FIRST - Dig a hole twice the diameter of the container and just as deep, no deeper.

SECOND - Remove the plant from the pot and examine the roots, if they are visible. The extreme root ends should be white, not brown. (If they are brown return it to the nursery and get another with white root tips.) Gently, gently remove some of the outer layer of mix to expose some of the roots, being sure the roots stay moist, especially the newly exposed root tips.

THIRD - Place in center of the hole and back fill with a mixture of half peat moss (or organic matter - remember, no lime should have been added to the compost if that is what you use). The back fill should be tamped down using your hands or gently with your foot. It is not a contest to see how hard you can tamp it down, but it still should not be loose as that will really stop the capillary action of the water moving to the plant. The top of the root ball should be at ground height or ½ inch above, never deeper. Soil should never be placed on top of the root ball.

FOURTH - A 6-inch thick layer of leaves, pine needles or wood ships should be placed on the root area extending out a foot beyond the back fill area, If this is before May 15, ½ cup of 5-10-5 fertilizer can be broadcast on top of the mulch. Never put fertilizer in with the back fill. The plant and backfill area should be watered directly from a hose. This watering must be duplicated weekly until October 15.

Of course, if you plant it in August or September, your watering schedule is greatly shortened. The winter is the great equalizer. It brings all three soils back to one colloid and thus allows lateral transport of water to the plant.

Let's take a quick look at what typically happens to our casual home gardener who has just spent a lot of money to purchase a magnificent rhododendron in April or May. Let's say the gardener plants it perfectly as directed above. It is spring and he/she is really turned on to gardening and diligently waters the plant weekly for the next few weeks. The plant blooms and the gardener is ecstatic at the display! It is now the end of May and the plant puts out enormous leaf growth, virtually doubling the amount of leaf area. Unknown to the gardener, but very apparent to the plant, the soil is still cool and the roots haven't even thought about growing out of the magnificent potting mix in which it has been growing. Why should it? The mix is moist and loaded with fertilizer from the nursery. The back fill area doesn't compare, and also the cool soil temperature is not conducive to root growth.

It starts to turn hot. The gardener now starts to lose interest in gardening. There are many other joys calling him/her away from the garden and the gardener begins to forget the plant. (It has been watered consistently for six to eight weeks already. That surely should be enough, the gardener thinks.) The plant with its double canopy of leaves loses water rapidly in the hot, sunny weather, and since water is not being supplied to the root area because the capillary action has been blocked, the plant wilts. Our friendly gardener notices the wilted plant and is surprised because other plants right next to this one are perfectly okay. The gardener waters the plant and to his/her joy, within a few hours it again looks perfectly healthy. The gardener has just learned a lesson. One can skip watering until the plant wilts and then water and the plant will respond immediately. That is a deadly lesson - to the plant .

Even though the plant looks as if it has bounced back, it hasn't. Great damage has been done to the root system by the desiccation shock, and repeating it increases the damage. Invariably the watering done is enough to bounce leaves back, but the root ball never gets fully wet. Many roots are still deadly dry and will abort. By the middle of August when it is really hot, the plant begins to look quite bad. Many leaves have dropped and the "recovery watering" does not have the remarkable effect it did in June. Going into winter, the plant is sparsely leafed, with no flower buds and is a good candidate to die over the winter from "winter kill." If the gardener had a one-year guarantee on the plant, and has saved the receipt, he/she will be able to replace it next spring for free, but sadly, that is usually not the case. The chances are good that the gardener will not try rhododendrons again. Another lost prospect.

Just talk to any casual gardeners and ask them what they think of rhododendrons and they will look wistfully at you and say they are truly magnificent, but, "I can't grow them." We must get the word out on proper planting and care!