Category Archives: Horticultural Info

Notched Leaves on Rhododendrons

The Garden Artist Posted on by

NOTCHED LEAVES ARE CAUSED BY WEEVILS

Notched leaves on your rhododendrons are caused by a variety of species of weevils. The adult forms of the weevil tend to feed at night during the springtime when you’re resting after a hard day in the garden. The damage will not kill your plant, just cause unsightly notching on the leaves. Of course, the leaves being evergreen will be around awhile to annoy you.

rhododendron leaf damage
These notches on the Rhododendron leaf was caused by a weevil

• Hand pluck the critters.

One method of control is to go out to your garden in the evening with your flashlight and pluck the weevils from underneath the rhodi leaves and toss them into a bucket of water. This never appealed to me.

• Spray with systemic insecticide.

Another, more toxic method is to spray with a systemic insecticide, like Orthene. Make sure to follow the instructions on the label. Soak the leaves, both top and bottom as well as the soil underneath to get the best control.

• Accept imperfection.

The third method is to allow for a measure of acceptance of the notches and let nature take its course. Your neighbors will either respect your concern for the environment or talk about your lack of concern for aesthetics.

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Rhododendron and Azalea Cultural Information

The Garden Artist Posted on by

Generally speaking, cultural requirements are less “demanding” for lepidote (small-leaf) rhododendron and azaleas, both evergreen and deciduous. They tolerate, and to some extent require, more sun than elepidotes, and azaleas will also tolerate less well-drained soil. In all other respects, the general guidelines outlined above apply to all plants in this family.

Site Selection
Rhododendrons prefer a site that provides afternoon shade, some protection from wind, good drainage and air circulation. Sloping terrain is also a decided advantage.

Soil
Well-drained soil is a must. Use raised beds to plant on top of poorly drained soils. Ideally, soil should be acid (ph 4.5 – 6.0) and high in organic matter. Pine bark, coarse sphagnum peat moss, composted wood chips and other such materials can be worked into the soil to improve organic matter content and soil drainage. Incorporate a few handfuls of super phosphate (0-20-0) in the mix to stimulate root growth.

Planting
Container plant root balls must be sufficiently disturbed so that roots extend out from the ball. The planting hole should be wide but shallow. Loosen and amend soil only 8 – 10 ” deep so that the root ball sits on solid ground to prevent sinking. Plant only as deep as the top of the root ball with no soil on top of the ball. Do not pack soil tightly around the plant, as tender roots will be destroyed. Mulch 3″ deep and water thoroughly.

Rhododenron planting diagram
Rhododendron Planting Diagram

Mulching
Mulch with 3″ of pine bark, pine needles, oak leaves, composted wood chips or other loose airy material. Do not use maple leaves, grass clippings or other materials that pack down.

mulch
Loading mulch for placing under shrubs

Fertilizing
If plants hold good green color and grow well, no fertilizer is needed. Rhododendrons are not heavy “feeders”. A soil test can determine what elements are deficient if plants do not perform well. When necessary, apply a fertilizer formulated for acid loving plants in late winter or early spring. Don’t fertilize after June 1st.

Watering
Proper watering is an important after care practice, especially for the first several years as plants become established. Keep the soil moist but not wet. Water deeply, (apply 1″) in the absence of equivalent rainfall. Don’t water again until the soil starts to dry out. Afternoon wilting of new growth is normal. If leaves become turgid a few hours after sundown, no additional water is needed. Water requirements diminish in late summer and early fall as new growth hardens up for winter. Plants should, however, be watered going into winter following a dry fall.

Rhododendrons and Azaleas Classification & Differences

The Garden Artist Posted on by

This is part of an outline of a ten minute talk I gave to the Centerport Garden Club on November 9, 2010

HOW ARE RHODODENDRONS CLASSIFIED?

Rhododendrons are classified into two major groups, lepidote and elepidote?

  • Elepidotes are large leaved rhododendrons. They are the type of shrub that most individuals would associate as being a rhododendron. They do not have scales located on the underside of the leaves. Plants tend to be very large in their maturity.

    elipidote rhododendron

    Elipidote Rhododendrons have big leaves

  • Lepidote rhododendrons have smaller leaves and are usually low growing or dwarfs. They usually bloom earlier in the spring than the larger leaved elepidotes.

    lepidote rhododendron
    Lepidote Rhododendrons have small leaves

WHAT IS THE DIFFERENCE BETWEEN AZALEAS AND RHODODENDRONS?

rhododendron
Rhododendrons have 10 stamens, 2 per lobe

  • All azaleas are rhododendrons but not all rhododendrons are azaleas.
  • True rhododendrons have 10 or more stamens which is 2 per lobe. Azaleas usually have 5 stamens or 1 per lobe. Azaleas have 5 lobes in a flower
  • Azaleas tend to have appressed hairs which are hair parallel to the surface of the leaf. This is particularly true along the midrib on the underside of the leaf. It is easily seen in “evergreen” azaleas.
  • True rhododendrons instead of hair are often scaly or have small dots on the under side of the leaf.
  • Azalea leaves are never dotted with scales and are frequently pubescent.
  • Many azaleas are deciduous.
  • True rhodi’s are usually evergreen with the exceptions of R. mucronulatum and R. dauricum.
  • Azaleas have tubular funnel or funnel shaped flowers. Rhodi flowers tend to be bell-shaped.
    azalea
    Azaleas have 5 stamens, one per lobe

Rhododendrons and Azaleas- Classification

The Garden Artist Posted on by

This is an outline of a ten minute talk I gave to the Centerport Garden Club on November 9, 2010

Botanical Classification

Rhododendrons and azaleas belong to the genus Rhododendron of the heath family (Ericaceae).

  • The heath family includes the heaths and heathers, blueberries, mountain laurels and several other ornamental plant groups.  Most members of this family require acid soil and good drainage.

Rhododendron collectionThis is a selection of the Rhododendrons submitted to the judging of the Spring Flower Show at the NY Chapter of the American Rhododendron Society at Planting Fields Arboretum

Where are Rhododendron’s from?

Some are native to the US.

The British became the first explorers to seek out new additions.

Collecting has brought plants, seeds & cuttings from Japan, China & the Himalayas.

New species are still being collected in central China.

In the 1800’s they were so expensive & were considered a rich person’s plant. They appeared on estates and in arboretums.

Most of the Rhodi’s we know today are hybrids created from the parents of the plants collected by these plant explorers.

Azalea gardenAzaleas blooming in May in my garden in Northport NY

Common Types

  • Large leaf evergreen Rhodi’s: Great for screening and as a backdrop behind the flower garden, Catawbiense, English Roseum, Scintillation, Maximum
  • Small leaf evergreen Rhodi’s: some sport beautiful mahogany leaves during the winter months, Aglo, Dora Amateus, Mary Fleming, the PJM’s
  • Yakushimanum hybrids: usually 3’wx3’h with woolly indumentum on dark green leaves. Have wonderful winter interest, Crete, Fantastica, Ken Janek, Percy Wiseman, Prince & Princess
  • Species Rhododendrons, can present well in a mixed flower, shrub border. There is a species rhododendron garden in DC.
  • Azaleas-Evergreen: Michael Dirr begins his Azalea Cultivar & Hybrid Group section with:

“In some respects, it is paralyzingly frightening to attempt to present the cultivars of azaleas.”

There are so many but you can begin to study them realizing that some are named for their hybridizers: i.e. Girard Hybrids, Glen Dale Hybrids, Polly Hill’s North Tisbury Hybrids. Others by their location: i.e. Linwood Hybrids, Karume Hybrids of Japan.

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