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Gardening Answers Knowledgebase

Search Results for ' Juglans'

PAL Questions: 4 - Garden Tools: 1

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Keywords: Zelkova, Xylosma, Thujopsis, Taxodium, Tamarix, Poa, Pennisetum, Casuarina, Baccharis, Festuca, Juglans, Alnus, Palms, Allergies

PAL Question:

What could cause sinus allergy symptoms every December?

View Answer:

According to Thomas Ogren's book, Allergy Free Gardening , the genera Alnus, Baccharis, Casuarina, Festuca, Pennisetum, Juglans, Poa, Tamarix, Taxodium, Thujopsis, Xylosma, Zelkova, and palm trees all produce pollen during December.

(Source: Ogren, T.L., Allergy-Free Gardening: The revolutionary guide to healthy landscaping , 2000, pp.262-265)

Also check out Allergy Free Gardening website.

This article on Low-Allergy Gardens has some tips on allergy-friendly landscapes.

Season Winter
Date 2007-04-02
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Keywords: Grafting, Woody plant propagation, Juglans

PAL Question:

Is it possible to graft a walnut scion onto a maple tree?

View Answer:

The book, Plant Propagation edited by Alan Toogood (American Horticultural Society/DK Publishing 1999) says that Juglans regia and Juglans nigra, grown for their edible nuts, are usually whip-and-tongue grafted. You would "use a slightly narrower scion than the stock so the thinner scion bark will align with the stock's cambium more easily."

I was not able to find any information on grafting a walnut scion onto a maple, but here is an article (pdf) on propagating Eastern black walnut trees by William Reid, which has detailed information.

This publication (a very large PDF!) from the University of Georgia College of Agricultural & Environmental Sciences, entitled "Propagating deciduous fruit plants common to Georgia" (1999) indicates that whip grafting or ring budding will work best for walnuts.

Season All Season
Date 2007-04-03
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Keywords: Juglans, Compost, Allelopathy

PAL Question:

Will black walnut leaves cause compost to be allelopathic? Should they be kept out of compost? Or is this folklore? The specific compost is made with chicken manure (fresh), grass clippings and walnut leaves. Are there plants that tolerate the toxin in black walnut?

View Answer:

It seems that the main source of toxicity is the roots of the walnut tree, rather than the leaves or shells. However, there are still those who believe that there is enough juglone in the leaves that they should be fully composted before use in the garden. Below are excerpts from information published online in various university extension websites, by various authors, and now unavailable:

"This toxic affect on surrounding plants appears to be related to root contact, as walnut hulls and leaves used as mulch have not shown toxic effects on plant growth. [Warning- Frank Robinson disagrees.] Because Walnut roots do not occupy the surface layers in most soil, many shallow rooted plants growing under walnut trees don't come in contact with the roots and are not affected by them." [Michigan State University]

"You've probably always heard that you should never add black walnut sawdust [or wood chips] to the compost pile because the juglone will kill everything that grows in the compost. Abraham says that's not necessarily true; that juglone is not found in walnut saw dust or wood chips. Nor do dead walnut trees exude juglone. Juglone is harmless to humans so you can go right ahead and safely eat fruit and vegetables grown near walnuts."[Katy Abraham]

"Robinson doesn't agree on the use of walnut residue in composting. He has this to say about black walnut saw dust, husks and leaves affecting plants. 'Tomatoes growing in clean soil in pots were severely stunted when leaves and nuts fell into the pots while we were on vacation. I know what juglone can do. I have seen a 15-year-old rhododendron killed a few weeks after its owner mulched it with black-walnut husks, and roses injured by an application of compost containing black-walnut sawdust.'" [Robinson]

"The juglone toxin occurs in the leaves, bark, and wood of the walnut but these contain lower concentrations than the roots. Juglone is poorly soluble in water and does not move very far in the soil. Walnut leaves can be composted because the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks. In soil, breakdown may take up to two months. Black walnut leaves may be composted separately, and the finished compost tested for toxicity by planting tomato seedlings in it. Sawdust mulch, fresh sawdust or chips from street trees prunings are not suggested for plants sensitive to juglone, such as blueberry. However, composting of bark for a minimum of six months provides a safe mulch even for plants sensitive to juglone." [Ohio State University]

"To be on the safe side, composted material containing juglone should be allowed to breakdown over a period of time before use. This composted material can be used with plants that are not susceptible to juglone damage. If it is important to use it for general composting purposes, testing it first with a few tomato plants for a few weeks should reveal its level of toxicity." [Abraham]

This may also be of interest: The Walnut Tree: Allelopathic Effects and Tolerant Plants from the Virginia Cooperative Extension.

Frank Robinson's article "Under the Black Walnut Tree," Horticulture magazine, October 1986, pp. 30-33 concludes that many plants are indeed able to tolerate juglone's toxicity. Some of the juglone-tolerant plants listed in the article and in other sources are included on Viette's Beautiful Gardens website.

Season All Season
Date 2008-03-27
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Keywords: Juglans, Allelopathy

PAL Question:

I would like a plant list of plants that are resistant to the juglone toxin.

View Answer:

Juglone, a toxin produced by walnuts (Juglans spp.), can be a problem for many plants. Luckily, some don't mind it.

Here is a list of juglone-tolerant plants, from University of Wisconsin Urban Horticulture.

Virginia Cooperative Extension also has a list.

Ontario's Ministry of Agriculture has similar information.

Season All Season
Date 2008-06-04
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Keywords: Prunus, Pruning, Juglans, Gleditsia, Cornus, Birch

Garden Tool: A common question gardeners have is when to prune. "When the shears are sharp!" is the often-heard answer. In reality there are a few timing guidelines that do matter.

First of all, certain trees are known to "bleed" when pruned while the sap is rising in late winter and early spring. Maples, dogwoods, birch, elm, walnut and honey locust are the most common.
Bleeding usually won't hurt the tree, but the pruning cuts are slower to heal which may leave susceptible trees vulnerable to infection. These trees should be pruned right after leaves fall off in autumn.

Cherry trees are at risk from the destructive cherry bark tortrix. The tortrix is attracted to fresh pruning cuts, so cherry trees should not be pruned between May and August when the tortrix is active.

Spring flowering shrubs should be pruned immediately after flowering so that the new growth has time to form next year's flower buds. Summer flowering shrubs may be pruned in winter because flowers are formed on this season's growth.

Pruning resources online:

Season: All Season
Date: 2007-05-17
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June 24 2013 12:55:25