[Caltona]

I saw Monty on Gardners World mention that you can't plant a walnut near other fruit trees, but he didn't say why and how far apart. What is their effect on other fruit trees as I wish to plant a walnut about 50m away from apple/pear trees. Would this be OK?

[crosseyedsheep]

I've seen some mention before that a black wallnut tree shouldn't be planted near a vegetable garden, it's a companion planting issue, if you want more info google "companion planting" and "black wallnut" together. If you're planning on planting the walnut 50 Metres from the fruit trees I wouldn't imagine it will effect them.
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Xeyedsheep

[GPI]

50 metres should surely be ok.
The roots of most Walnut trees and to a greater degree Black Walnut (Juglans nigra ) produce a plant harming substance known as juglone which can be found in their leaves and roots.
These leaves and roots have an allelopathic effect, which prevents other plants (including apple trees) growing in its root zone through the production of poisons.
This plant harming zone usually extends about a ft outside of the roots, but much farther if fallen walnut leaves are allowed to drop,blow, lie, and decompose at the base of other plants.

In fairness Caltona, you swould be safe enough just leaving 30 metres from the apple tree, as long as you rake up the leaves of the walnut when they fall.
PS. don't compost them as this can still be harmful if spread at the base of plants in the future.
Good luck with your walnut.

[Caltona]

[Caltona]