jane4874May 20, 2009

I'm wondering, is it recommended to plant my azalea in a semi-shadey place under a walnut tree?- this tree will get so thick that you can't see through it. The area will get decent light in the early half of the day, but by 1 or so it will begin to get shaded out. The tree is healthy - my ferns do very well. jane

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morz8(Washington Coast Z8b)

Shade issue aside, rhododendrons and azaleas are often not compatible with English or black walnut. Both produce juglone in roots, bark, leaves that is injurious to plants in the rhododendron family, others.

Here is a link that might be useful: Walnut and azaleas

    Bookmark   May 21, 2009 at 11:37AM
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rhodyman(SE PA, USDA Z6)

I agree 100%. One section of my rhododendron garden started dying. Looking around I found a couple black walnut seedlings in the woods nearby. The roots of these black walnuts were invading the rhododendron bed, killing the rhododendrons. I cut down the walnut trees and dug a trench around the rhododendron beds, cutting any roots that were growing into the beds. The remaining rhododendrons recovered.

The roots of Black Walnut (Juglans nigra L.) and Butternut (Juglans cinerea L.) produce a substance known as juglone (5-hydroxy-alphanapthaquinone). Persian (English or Carpathian) walnut trees are sometimes grafted onto black walnut rootstocks. Many plants such as tomato, potato, blackberry, blueberry, azalea, mountain laurel, rhododendron, red pine and apple may be injured or killed within one to two months of growth within the root zone of these trees. The toxic zone from a mature tree occurs on average in a 50 to 60 foot radius from the trunk, but can be up to 80 feet. The area affected extends outward each year as a tree enlarges. Young trees two to eight feet high can have a root diameter twice the height of the top of the tree, with susceptible plants dead within the root zone and dying at the margins. The juglone toxin occurs in the leaves, bark and wood of walnut, but these contain lower concentrations than in the roots. Juglone is poorly soluble in water and does not move very far in the soil.

    Bookmark   May 23, 2009 at 12:20PM
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