Monday, February 2, 2015

Featured Plant of the Day: 'Apple Blossom' Rhododendron

Rhododendron (subgenus Rhododendron) 'Apple Blossom' 

Type    Shrub, woody plant
Hardy range    5A to 8A
Height    7' to 8' / 2.20m to 2.40m
Spread    36" to 6' / 90cm to 1.80m
Growth rate    Slow
Form    Irregular or sprawling
Exposure    Partial shade or partial sun
Persistence    Deciduous

Bloom Color    Pink and white
Bloom Time    Spring

The flowers are fragrant and very showy.

This plant will grow in moist soil.
Suitable soil is well-drained/loamy, sandy or clay.
The pH preference is an acidic (less than 6.8) soil.

Leaf Color    Green
This plant has attractive fall colors.

Landscape Uses
-    Container plantings
-    Woodland garden
-    Border
-    Foundation planting
-    Massing
-    Specimen

Attributes and Features
-    Inconspicuous fruit

Propagation and Root Form
Propagation is from  cuttings and  seeds.This plant can be trained to a single trunk.

Best propagation time is in the  fall and  summer.
This plant's roots are  fibrous.

Culture Notes
Provide this plant with excellent drainage, organic soil and mulching.  Do not cultivate around it, since it has surface roots, and do not let the soil cover the stem.   It is not salt tolerant or drought tolerant and does not do well in sweeping winter winds.

Partially shaded locations give good growth, provided drainage is adequate. Roots rot in soil that drains poorly. I (Dr. Gilman) have had no trouble transplanting balled in burlap, although many are grown in containers. Pinch back the flowers after they have faded to eliminate the brown developing fruit if you wish. However, this is not essential for good flowering the following year. After all, these plants have flowered for millennia without our intervention. This plant is considered mostly allergy free and causes little or no allergy problems in most people.  Organic amendments in the backfill help establish plants quickly by encouraging roots to grow out of the container and into backfill soil.

Azaleas grow best in shade or partial shade.  A south or southwest exposure increases the chance of winter injury to evergreen types when grown in northern climates.  Plant in an acidic, moist, well-drained soil with a pH between 4.5 and 6.5.  Transplanting balled and burlapped or potted plants is most successful.  The shallow root systems are easily injured by deep cultivation but benefit from mulching.

Plants fail to absorb iron and have yellow leaves with green veins if the soil is not sufficiently acidic.  Finely ground sulphur can be added to the soil to increase acidity.  Have the soil tested before planting in order to determine the pH. Apply a 2:1:1 N:P:K ratio fertilizer two or three times each year before and after blooming and, perhaps, again as plants enter dormancy - timing is not as critical as previously believed.   Prevent winter burn in northern climates by avoiding exposed planting sites and by shading during winter.

'Apple Blossom' has white blossoms that are flushed pink, with deeper pink tips.  It blooms during the month of April.

Planting and establishing shrubs
The most common cause of young plant failure is planting too deep.  Plant the root ball no deeper than it was in the nursery.  In most instances, the root flare zone (point where the top-most root in the root ball originates from the trunk) should be located just above the landscape soil surface. Sometimes plants come from the nursery with soil over the root flare. If there is soil over this area, scrape it off.  The planting hole should be at least twice the width of the root ball, preferably wider.  In all but exceptional circumstances where the soil is very poor, there is no need to incorporate anything into the backfill soil except the loosened soil that came out of the planting hole.  Never place ANY soil over the root ball. If a row or grouping of plants is to be installed, excavating or loosening the soil in the entire bed and incorporating organic matter enhances root growth and establishment rate.

Weed suppression during establishment is essential.  Apply a 3-inch thick layer of mulch around the plant to help control weed growth.  Keep it at least 10 inches from the trunk.  If you apply it over the root ball, apply only a one or two inch layer.   This allows rainwater and air to easily enter the root ball and keeps the trunk dry.  Placing mulch against the trunk or applying too thick a layer above the root ball can kill the plant by oxygen starvation, death of bark, stem and root diseases, prevention of hardening off for winter, vole and other rodent damage to the trunk, keeping soil too wet, or repelling water.  Regular irrigation through the first growing season after planting encourages rapid root growth, which is essential for quick plant establishment.