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Rhododendron catawbiense


 

Rhododendron catawbiense
Catawba rhododendron

Culture: Like other members of this genus and family, this species requires acidic well-drained soils with a pH of 4.5 - 6.0. If these conditions cannot be provided, then rhododendrons should not be planted, for they will surely fail. They should also be located where they receive partial shade, such as on the north or east side of buildings or under limbed-up pine or oak trees. Exposure to too much sun in the winter or summer will increase the amount of winter or dessication injury. Placement in heavy shade is tolerable but produces loose or open canopies and reduced flowering. In the Midwest, soils typically have to be acidified by addition of powdered sulfur and acidic peat moss incorporated throughout the growing area of the shrub.

The heavy soils commonly found in the Midwest require that some accommodation to drainage must be made. Consider planting on slopes, raised beds or planting high with generous amounts of organic mulch. Regardless of site, the use of organic mulches greatly helps cultivation of these plants. Acidic pine needles are great where you can get them. Otherwise, almost any organic mulch will do. Occasional addition of powdered sulfur may be needed to keep the pH low. The root zone should be disturbed as little as possible and the soil should be kept uniformly moist. Supplemental water will need to be provided in dry weather and soils must be moist but not wet going into the winter. Protection from strong winter winds is also essential to good culture in the Midwest. Planting next to buildings, or using evergreen windbreaks or fences will help to slow winds. Grouping closely with similar or other plants will help keep winter humidity higher, reducing dessication injury. Typically pruning is only needed to remove dead branches. Fertilization should be kept light and acid-forming fertilizers are recommended to control soil pH. Nursery-grown plants are usually obtained as B&B specimens or in containers. Container-grown plants should have their root systems sliced vertically in several places with a knife along the outer surface to encourage roots to grow out into the new soil. The fibrous roots of this genus are shallow but easy to establish.

As part of the Ericaceae family, rhododendrons and azaleas are very choosy about their environment. If they are unhappy, plants are short-lived. Properly cultured, they can last many decades.

The secret to minimizing problems on rhododendrons is to provide appropriate environmental conditions as described above. A common problem in the Midwest is Phytophthora Wilt, which results from growing the plants in wet, heavy, poorly drained soils or from planting too deep. Unfortunately symptoms of the wilt include a curling of the leaves that resembles drought symptoms, prompting gardeners to apply even more water. Winter injury, although lessened by proper culture, may still occur in some of our more harsh winters. The most common winter injury is browning of the flower buds that may include death of the flowers if severe enough. Avoid placing plants on exposed sites. Inadequate cultural conditions predispose plants to a host of problems.

Insect problems include lacewing flies, weevils, borers and Japanese beetles. Possible disease problems include Phytophthora root rot, botrytis, leaf spots, leaf hoppers and leaf miners.

Usage: Rhododendrons are the number one garden plant in the US and much of the rest of the world. This species makes excellent specimens and is useful in the back of large shrub borders and for naturalizing purposes, under the light to moderate shade of large limbed-up trees. This genus typically doesn't fare well in containers because of sensitivity to drought and cold injury.

 
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