Rhododendrons: Walnut-Rhododendron compatabilty

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by James Arthurs, May 16, 2004.

  1. James Arthurs

    James Arthurs Member

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    Since mid-summer last year, there have been 2 rhodos and 2 pieris sitting in the shaded area under my walnut. This was to have been a temporary (two or three week) situation, but they wound up passing the winter there. The walnut is out in full leaf (and has flowered);so far, my ericacea seem really happy. This is my concern: can I expect much more bliss in this corner ?
    (It would be difficult to move them right now.) The walnut is about thirteen years old, 23 +/- feet tall,and 23 feet +/- across. The ericacea are 3 to 5 feet tall & 10 to 15 years old. I'm surprised at the current (early) lack of juglone damage, but maybe it's too early in the season. Any advice/relevant experience?
  2. HortLine

    HortLine Active Member 10 Years

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    Vancouver, BC
    Rhodo-Walnut Compatibility

    The tolerance to juglone is not known for all plants. Rhododendron is listed as NOT tolerant to the chemical. Pieris is not listed as tolerant or intolerant.

    Since small amounts of juglone are released by live roots, particularly juglone-sensitive plants may show toxicity symptoms anywhere within the area of root growth of a black walnut tree. However, greater quantities of juglone are generally present in the area immediately under the canopy of a black walnut tree, due to greater root density and the accumulation of juglone from decaying leaves and nut hulls. This distribution of juglone means that some sensitive plants may tolerate the amount of juglone present in the soil near a black walnut tree, but may not survive directly under its canopy.

    Species survival near or under black walnut trees is further complicated by the fact that the amount of juglone present in the soil depends on soil type, drainage, and soil micro-organisms.
  3. mr.shep

    mr.shep Well-Known Member 10 Years

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    San Joaquin Valley, California
    Hi James:

    It has been my experience that Rhododendrons can withstand the juglone
    coming from the buds and the nut hulls. The problem that I've had, also
    with Camellias is that the roots of the Walnut, either a Black Walnut, an
    English Walnut grafted on Black Walnut rootstock and even English
    Walnut seedlings have extensive, invading root systems. It was not the
    juglone that caused me the most trouble, it was the root system of the
    Walnut that became so intermingled with the roots of the Rhododendrons
    and Camellias and almost choked those plants to death. When I dug up
    the plants to transplant them elsewhere I found that their root systems
    were almost completely encapsulated by the Walnut roots. For the short
    term your Rhododendrons can withstand the onslaught of the Walnut but
    for the long term you had better move them to another location if you want
    them to live.

    Below is a very good URL on juglone.


  4. Jacky

    Jacky Member

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    Vancouver, Canada
    If the root system is the problem, how can other plants - like acer palmatum, do quite well (also our buddleia). Apparently Rhodo. perclymenoides and Exbury (Gibraltar and Balzac) do quite well - these are azaleas ...

    Does anyone know of a large rhodo. that can survive the juglone? I have a perfect spot for it - just needs to be large, and preferably pink or white!

    Thanks in advance,


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