Tuesday, February 10, 2015

Featured Plant of the Day: 'Trail Blazer' Rhododendron

Rhododendron (subgenus Rhododendron) 'Trail Blazer'

Type    Shrub, woody plant
Hardy range    5B to 6A
Height    4' to 5' / 1.20m to 1.60m
Spread    4' to 5' / 1.20m to 1.60m
Growth rate    Fast
Form    Rounded
Exposure    Partial shade or partial sun
Persistence    Evergreen

Bloom Color    Pink
Bloom Time    Spring and Summer

The flowers are very showy.

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

Leaf Color    Green
Fall Color    No change in fall color

 Landscape Uses
-    Woodland garden
-    Border
-    Massing

 Attributes and Features
-    Inconspicuous fruit

 Culture Notes
Partially shaded location gives good growth, provided drainage is adequate. Roots rot in soil that drains poorly. I (Dr. Gilman) have had no trouble transplanting these plants 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 been flowering quite nicely 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.

Rhododendrons are ornamental, ericaceous, broad-leaved evergreens.  Azaleas belong to this genus, but many are not evergreen.  They 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.

'Trail Blazer' has a vigorous growth pattern and sports light pink blossoms with deep red, center blotches.

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.