• Skip to main content
  • Skip to secondary menu
  • Skip to footer

Garden Making

Inspiring ideas and information for great home gardens

  • Design
  • Containers
  • Food
  • Gardens to visit
    • British Columbia
    • Alberta
    • Manitoba
    • Ontario
    • Quebec
    • New Brunswick
    • Nova Scotia
    • Newfoundland
    • England
    • U.S.
  • Events Calendar
    • By organizing group
    • By location of events
    • British Columbia
    • Alberta
    • Saskatchewan
    • Manitoba
    • Ontario
    • Quebec
    • New Brunswick
    • Nova Scotia
    • Prince Edward Island
    • Newfoundland & Labrador
    • Form to list your event
  • Reader photos
    • Reader images of gardens
    • Container gardening images
    • Reader images of plants in 2019
    • Reader images of plants in 2018
    • Reader images of plants in 2017
    • Reader images of plants in 2016
    • Submit photo to Garden Making
  • Shop
You are here: Home / Making a Garden / PJM rhododendrons make gorgeous display

PJM rhododendrons make gorgeous display

By Judith Adam Filed Under: Making a Garden

 

Two PJM rhododendrons blooming in the front garden are making a gorgeous display, with hundreds of lavender-pink flowers stopping traffic on my road. Each spring, people ask what these shrubs are, and I’m pleased to say almost every garden can have some. The small-leaved lepidote rhododendrons in the PJM group are the easiest rhodos to grow. (For a list of cultivars, see my “Making a Garden” blog entry on March 30, 2011.) The secret to their success is their ability to grow in the alkaline soil found in southern Ontario.

Rhododendrons are ericaceous plants and require acid soil, usually found where granite forms the underlying bedrock. The bedrock in southern Ontario is limestone, and that causes our soil to be alkaline, quite the opposite to what rhododendrons need. Soil acidity or alkalinity is measured on a scale of one to 14, with neutral at seven. Soil registering below seven is acidic, and soil above seven is alkaline. The measurements are referred to as pH (parts hydrogen), and the measurement for my garden soil is pH 7.3, or slightly alkaline. Getting my head around the fine points of pH science would require a degree in soil chemistry, but it’s not hard to understand in simple terms. As a demonstration, distilled water measures neutral (pH 7), baking soda is strongly alkaline (pH 9), and bleach is drastically alkaline (pH 13). Going the other way (below neutral pH 7), black coffee is strongly acidic (pH 5), tomato juice is very acidic (pH 4), and lemon juice is extremely acidic (pH 2).

As it happens, rhododendrons grow best in soil with acidity in the range of black coffee (pH 5 to pH 6). Acidic soil amendments (like sulphur in pellet or powder form) can be dug into alkaline soil, but their acidity is short-lived and quickly overwhelmed by the surrounding alkaline environment. Consequently, I often see declining rhododendrons— particularly  large leaf elepidote cultivars—with sparse, yellowed foliage and few flowers. They just can’t cope with alkaline soil. Fertilizer might perk them up for a few weeks, but then they return to their sickly state.

Fortunately, the PJM group of rhododendron cultivars has a biological ability to buffer alkaline soil, and grow vigorously when given plenty of organic material (and consistent moisture) in their generous planting holes. I add lots of peat moss, composted manure and leaves when planting. I also place a three-inch (8-cm) layer of leaves over the root zone in autumn. In spring, they get a drink of water-soluble fertilizer (using a nearly balanced analysis) after they finish flowering to help them grow new twigs and buds for next year’s blooms.

The PJM shrubs have been in full bloom for almost two weeks, and now two shrubs of ‘Olga Mezitt’ are about to open. These will have vibrant pink flowers, and likely add another two weeks to the display. The shiny foliage continues to be attractive after the flowers are finished, and takes on a deep burgundy colour in cold weather. The two PJM shrubs grow in light shade, and have become leggy (four feet/1.2 m) as they reach for light. This has been an advantage, as one climbs into a long-needled pine, and the other reaches up to window height, allowing the flowers to be visible from indoors. The ‘Olga Mezitt’ shrubs are in direct sunlight and are more compact, with deeper colour in their winter foliage.

 

Other posts by Judith:

  • Making sense of fertilizers  
  • ‘Pink Charm’ narcissus
  • Primrose time
  • Fertilizing lawns
  • Lady’s mantle: a survivor

Published: April 25, 2012 | Updated: February 6, 2019

Sign up for Garden Making updates

We do not share emails. Your information will be used as outlined in our Privacy Policy.

Please look for our email. You must click on the link in the email to confirm. Check your inbox or spam folder.

About Judith Adam

Judith Adam is a horticulturist, landscape designer and author of several best-selling gardening books, including Landscape Planning. She lives in Toronto.

Reader Interactions

Comments

  1. gerald keleher says

    September 19, 2017 at 3:32 pm

    do PJM rhododendrons lose their leaves in winter?

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Footer

Search

Reader submissions

  • Enter draw to win a prize
  • Form to list your event
  • Submit photo to Garden Making

When you’re looking for

  • Books for gardeners
  • Containers in your garden
  • Design
  • Food to grow
  • Gardens to visit
  • Growing from seed
  • How to
  • Plant ideas
  • Tips for gardeners

Garden Making magazine

  • Buy magazine issues
  • Garden Making list of magazine issues
  • Garden Making index of magazine articles

Copyright © 2021 Inspiring Media Inc. | GARDEN MAKING is a registered trademark | About | Service | Terms of use | Privacy policy | Account